Geochemistry, Environmental Conditions and Human ...people.rses.anu.edu.au/doc/Long2012.pdf‘An Ear...

‘An Ear to the Ground’: Fish Otolith

Geochemistry, Environmental

Conditions and Human Occupation

at Lake Mungo

Kelsie Elizabeth Long

Honours thesis submitted as part of the B.A. (Hons) degree

completed in the School of Archaeology and Anthropology, in

conjunction with the Research School of Earth Sciences, Australian

National University, Canberra

29th

October 2012

Statement of Authorship

I certify that all work in this thesis is my own and that no other person’s work

has been used, in part or whole, unless otherwise acknowledged in the text.

Name: Kelsie Elizabeth Long

Date: 29th

Oct 2012

Signature:

i

Abstract

Fish otoliths are calcium carbonate structures that form within the inner ear of

teleost fish. They are usually employed in archaeological studies as indicators

of human diet and resource use. Recently, however, they have been

investigated for their geochemical properties and how these can be used for

dating and as palaeoenvironmental indicators. This study analyses the

geochemical composition of otoliths collected from a series of hearth sites at

Lake Mungo in the Willandra Lakes World Heritage Area of New South

Wales. Radiocarbon and amino acid racemisation were tested as methods of

dating the otoliths. Oxygen isotope, strontium isotope and elemental abundance

ratios were measured across the banded growth lines of fish otoliths in order to

assess their use as high resolution recorders of past environmental conditions

and to identify fish migration. Fish otoliths from the same hearth site are

assumed to have been killed and eaten at the same time, a theory which is

backed up by radiocarbon dating and the similarities of geochemical assays.

Difficulties in identifying age lines and associating the sampled areas to these

caused slight offsets in the dataset. Nevertheless it is demonstrated here that

evaporative trends experienced by fish are able to be identified as are potential

points of migration. This thesis concludes that these otoliths are an ideal tool

for multidisciplinary research providing links between their internal

geochemical records, the archaeology of the hearth sites and the geology of the

surrounding sediment layer.

ii

Acknowledgements

This thesis would not have made it to print without the support, supervision

and encouragement of a large number of people. My biggest thanks go to my

supervisor Rainer Grün for his encouragement and guidance over the past year.

His enthusiasm and sense of humour were the main reasons I took on this

project and I regret nothing!

My thanks to the staff and students of the Research School of Earth Sciences

for their interest, support and acceptance, even though I came from the other

side of campus. A massive thankyou goes to Rachel Wood for showing me

how to prepare my samples for radiocarbon dating and for explaining the

quirks of OxCal to me. I’d also like to thank Harri Kokkonen for his assistance

in the tricky and time consuming tasks of cutting, polishing and recutting the

otoliths for analysis. To Ian Williams my eternal gratitude for supervising my

use of the SHRIMP-SI, we had many late nights dealing with this new machine

but the results made it all worthwhile. To Les Kinsley, thank you so much for

supervising my use of the LA-ICP-MS and LA-MC-ICP-MS and for having

the patience to answer my many questions about their inner workings. A big

thankyou also to Mark Jekabson, from conservation, planning and research in

the ACT, for his assistance in aging the otoliths.

The research reported in this thesis was undertaken with permission from the

Elders’ Council of the Two Traditional Tribal Groups from the Willandra

Lakes Region World Heritage Area (WLRWHA) and the Technical and

Scientific Advisory and Community Management Committee of the

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WLRWHA. I would like to thank the Elders for their interest in, and support

of, this work.

This research was undertaken under the auspices of an Australian Research

Council Discovery Project, Human Responses to Long term Landscape and

Climate Change, awarded to Dr Nicola Stern, Professor Colin Murray-Wallace

and Dr Kathryn Fitzsimmons. The otoliths studied for this project were

collected by Nicola Stern and Daryl Pappin, the project’s Cultural Heritage

Officer, under an Aboriginal Heritage Impact Permit (No. 1131516) issued to

Nicola Stern by the New South Wales Department of Environment and

Heritage. I would like to thank Nicola Stern for making unpublished project

data available for use in this thesis, for showing us the haunting beauty of the

Willandra Lakes and for generally being very helpful and brilliant.

This past year would not have been as wonderful or as productive as it was

without the interest and support of my family and friends and I would like to

thank them for being a part of it. Finally, in lieu of a boyfriend I would like to

thank my good friend and housemate Lauren Harvey for providing me with

encouragement, support and endless cups of tea throughout this year even

whilst working on her own honours thesis. We did it!

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Contents

Abstract ______________________________________________________ i

Acknowledgements ____________________________________________ ii

Contents ____________________________________________________ iv

List of Figures _______________________________________________ vii

List of Tables_________________________________________________ ix

Chapter 1: Introduction ________________________________________ 10

1.1 Aims ______________________________________________________ 13

1.2 Site description ______________________________________________ 13

1.3 Thesis Overview _____________________________________________ 17

Chapter 2: Background ________________________________________ 19

2.1 Archaeological Research at Lake Mungo __________________________ 19

2.2 Description of the Willandra Lakes System ________________________ 24

2.2.1 Lake system hydrology ___________________________________________ 24

2.2.2 Lake Mungo ___________________________________________________ 26

2.3 Fish Otolith Geochemistry _____________________________________ 31

2.3.1 Overview ______________________________________________________ 31

2.3.2 Identification of Otolith Age Lines __________________________________ 32

2.3.3 Golden Perch (Macquaria ambigua) ________________________________ 33

2.3.4 Elements and isotopes ____________________________________________ 35

2.3.3.1 Oxygen isotopes ________________________________________ 35

2.3.3.2 Strontium Isotopes ______________________________________ 39

2.3.3.3 Elemental abundances ___________________________________ 41

2.3.5 Fish Otolith Geochemistry and Archaeological Sites ____________________ 44

2.4 Geochemical dating techniques __________________________________ 45

2.4.1 Radiocarbon ___________________________________________________ 46

2.4.2 Amino acid Racemisation _________________________________________ 49

2.5 Summary ___________________________________________________ 51

Chapter 3: Methodology ________________________________________ 53

3.1 Sampling Strategy ____________________________________________ 53

v

3.2 Sample Preparation and Analysis ________________________________ 54

3.2.1 Aging the Otoliths _______________________________________________ 55

3.2.2 Radiocarbon Dating _____________________________________________ 57

3.2.2.1 Sample Pre-treatment ___________________________________ 57

3.2.2.2 Graphitisation of CO2 ___________________________________ 57

3.2.2.3 Calibration and modelling ________________________________ 59

3.2.3 Amino Acid Racemisation ________________________________________ 59

3.2.3.1 Pre-treatment procedures ________________________________ 59

3.2.4 Elemental and Isotopic measurements _______________________________ 60

3.2.4.1 HelEx laser system ______________________________________ 60

3.2.4.2 Varian 820 Inductively Coupled Plasma Mass Spectrometer (ICP-

MS) for elemental concentration measurements _____________________ 61

3.2.4.3 The Neptune Multi-Collector Inductively Coupled Plasma Mass

Spectrometer (MC-ICP-MS) for strontium isotope measurements _______ 63

3.2.5 Sensitive High Resolution Ion Micro Probe - Stable Isotope (SHRIMP - SI)

Oxygen isotopes _____________________________________________________ 64

3.2.5.1 SHRIMP sample preparation______________________________ 65

3.2.5.2 Analysis of Oxygen isotope ratios __________________________ 66

Chapter 4: Results _____________________________________________ 68

4.1 Otolith Aging________________________________________________ 68

4.2 Radiocarbon Dating ___________________________________________ 59

4.3 Amino Acid Racemisation (AAR) _______________________________ 70

4.4 Results from SHRIMP-SI, LA-ICP-MS and LA-MC-ICP-MS _________ 72

4.4.1 Oxygen Isotope Ratios ___________________________________________ 83

4.4.2 Elemental Abundances ___________________________________________ 83

4.4.3 Strontium Isotope Ratios __________________________________________ 84

4.4.4 Summary of Results _____________________________________________ 85

Chapter 5: Discussion __________________________________________ 86

5.1 Sampling Strategy ____________________________________________ 87

5.2 The Site Chronology __________________________________________ 88

5.2.1 Radiocarbon Dating _____________________________________________ 89

5.2.2 AAR _________________________________________________________ 90

5.3 Otolith Geochemistry, Environmental conditions and Fish Migration ____ 92

5.3.1 Hearth #926 ____________________________________________________ 92

5.3.2 Hearth #952 ____________________________________________________ 96

vi

5.3.3 Individual Otoliths ______________________________________________ 98

5.4 Temperature Assessment ______________________________________ 105

5.5 Strontium isotopes ___________________________________________ 106

5.6 Discussion Summary _________________________________________ 109

Chapter 6: Conclusions and Recommendations ___________________ 111

References __________________________________________________ 115

Appendices __________________________________________________ 124

Images of sampled areas of otoliths in relation to age lines (in blue): __________ 124

Radiocarbon modelling script _________________________________________ 126

vii

List of Figures

Figure 1.1: Map of the tributary and distributary streams of the Lachlan River

_____________________________________________________________ 14

Figure 1.2: The Willandra Lakes system and Lake Mungo survey areas ____ 15

Figure 1.3: Satellite map of fish bone hearth sites _____________________ 16

Figure 2.1: Diagram of lunette formation ____________________________ 25

Figure 2.2: Diagrammatic representation of Bowler’s stairway analogy ____ 26

Figure 2.3: Diagrammatic representation of Bowler’s stratigraphic units ___ 27

Figure 2.4: Current geological map of a section of the Lake Mungo lunettes 29

Figure 2.5: Diagrammatic representation of position of otoliths in fish _____ 32

Figure 2.6: Image of Adult Golden Perch ____________________________ 34

Figure 2.7: Diagram of δ18

O values of vapour and precipitation moving inland

_____________________________________________________________ 37

Figure 2.8: Calibration curve for conventional radiocarbon ages __________ 48

Figure 2.9: The two chiral forms of amino acids ______________________ 49

Figure 2.10: Age and temperature dependency of D/L ratios _____________ 50

Figure 2.11: Error calculation of amino acid age estimation _____________ 51

Figure 3.1: Transverse thin section of (M. ambigua) sagittal otolith _______ 56

Figure 3.2: Diagram of graphitisation line at RSES, ANU _______________ 58

Figure 3.3: Otoliths mounted in laser ablation sample holder ____________ 61

Figure 3.4: Schematic diagram of a Quadrupole ICP-MS _______________ 62

Figure 3.5: Schematic diagram of a Neptune MC-ICP-MS ______________ 63

Figure 3.6: Schematic diagram of the SHRIMP-SI ____________________ 65

Figure 3.7: SHRIMP-SI spots taken across otolith #926-1 _______________ 66

Figure 4.1: Overlayed thin section and SHRIMP-SI spot images of otolith

#926-3 _______________________________________________________ 69

Figure 4.2: Otolith #926-1, oxygen isotope, strontium isotope , Sr/Ca and

Ba/Ca results and associated images _______________________________ 73

Figure 4.3: Otolith #926-2, strontium isotope , Sr/Ca and Ba/Ca results and

associated images ______________________________________________ 74


viii

Ba/Ca results and associated images ________________________________ 75















Figure 5.1: Otolith #926-4 overlayed laser track, SHRIMP-SI spots and age

lines _________________________________________________________ 88

Figure 5.2: Modelling of radiocarbon results _________________________ 90

Figure 5.3: AAR results plotted against mean radiocarbon ages __________ 91

Figure 5.4: Valine D/L ratios plotted against mean radiocarbon ages ______ 91

Figure 5.5: Otoliths of hearth #926, oxygen isotope, Sr/Ca and Ba/Ca ratios 93

Figure 5.6: Otoliths of hearth #952, oxygen isotope Sr/Ca and Ba/Ca ratios _ 97

Figure 5.7: Otolith from hearth #953, oxygen isotope, Sr/Ca and Ba/Ca ratios

_____________________________________________________________ 99

Figure 5.8: Otolith from hearth #982, oxygen isotope, Sr/Ca and Ba/Ca ratios

____________________________________________________________ 100

Figure 5.9: Otolith out of context, #953-5, oxygen isotope, Sr/Ca. Ba/Ca ratios

and mean Sr-isotope values _____________________________________ 102

Figure 5.10: Otolith from hearth #1168, Sr/Ca and Ba/Ca ratios and mean Sr-

isotope values ________________________________________________ 104

Figure 5.11: The mean strontium isotope values of each otolith _________ 108

ix

List of Tables

Table 2.1: Summary of the current Lake Mungo stratigraphy and OSL dating

results _______________________________________________________ 30

Table 4.1 Radiocarbon dating results, calibrated and uncalibrated ________ 70

Table 4.2 AAR D/L values and mean radicarbon dates _________________ 71

10

Chapter 1

Introduction

Fish otoliths are carbonate accretions within the ears of teleost fish that are

often found preserved in middens or hearths at archaeological sites. They have

generally been utilised by archaeologists for studying past human diets and

resource use, however recently their geochemical properties have been

employed to study palaeoenvironments in association with human occupation

(Wurster and Patterson 2001, Wang et al. 2011). Preliminary applications of

measurements of stable isotope analysis and elemental abundance ratios of fish

otoliths from the Willandra Lakes have shown promising results for

environmental reconstruction, however these were not relatable to human

occupation (Boljkovac 2009). By examining in situ otoliths this thesis attempts

to relate geochemical records of past environmental conditions to human

occupation.

The Willandra Lakes World Heritage Area is of great archaeological, cultural

and geological significance. It features some of the oldest evidence for human

occupation in Australia and a detailed geological record of lake level

fluctuations throughout the Pleistocene (Bowler et al. 2003). It has been

suggested that new avenues for research and interpretation need to be explored

at Lake Mungo in order to better associate human occupation with ambient

environmental conditions and to assess how the two interacted over time

(Bowler 1998, Hiscock 2008, Allen and Holdaway 2009, Bowler et al. 2012,

11

Stern et al. in press). Previously studies have relied on the position of

archaeological remains within the lakeshore lunettes as proxies for

environmental conditions but these associations are too broad and a more

precise, detailed record is required.

This thesis will explore the potential applications of fish otoliths for dating

human occupation events and associating them with palaeoenvironmental

conditions at Lake Mungo. This is with a view to using the geochemical

records contained within otoliths from throughout the Willandra Lakes to

create a more detailed record of environmental fluctuations in association with

human occupation. This will be achieved through the sampling of a number of

otoliths from a recently uncovered section of hearth sites in the Lake Mungo

shoreline lunettes. These large crescent shaped aeolian dunes were formed on

the shoreline during periods of alternating stable and unstable lake conditions

(Bowler et al. 2012) . Measurements of oxygen isotope ratios and elemental

abundance ratios will be made across otolith age lines and these will be

assessed within each hearth site for similar fluctuations or trends potentially

related to ambient environmental conditions. Strontium isotopes have shown

promise as indicators of fish migration and will be employed here to see if fish

movement between the lakes can be assessed (Boljkovac 2009). The

application of radiocarbon dating to fish otoliths as well as amino acid

racemisation will be assessed to provide chronological information about

human occupation.

Evidence for human occupation at Lake Mungo has been found in geological

layers indicative of times when lake levels were fluctuating (Bowler 1998,

12

Bowler et al. 2012, Stern et al. in press). A current theory as to why humans

were attracted to the lakeshore at these times is that large quantities of fish,

mainly golden perch (Macquaria ambigua), were trapped in the lake by

evaporative conditions (Bowler 1998, Bowler et al. 2012). It is thought that

humans then came to the lakeshore and took advantage of the supine, oxygen-

starved state of the fish to easily ‘scoop [them] up in shallow waters’ (Bowler

1998: 146). This will be referred to as the ‘easy prey’ hypothesis. Recent

studies of the geochemical composition of golden perch (Macquaria ambigua)

otoliths from the Willandra Lakes have generated some interesting results in

relation to Bowler’s easy prey hypothesis. In 2009, honours student Katarina

Boljkovac became the first person to analyse stable isotope and elemental

abundance ratios in otoliths collected from the Willandra Lakes World

Heritage Area. Otoliths were surface collected from the lunettes bordering

Lake Mungo. Results from measurements of oxygen isotopes, strontium

isotopes and elemental abundances across the otolith rings showed that one of

the fish had experienced a trend of increased evaporation in the years leading

up to its death. This was interpreted as supporting evidence for Bowler’s

(1998) ‘easy prey’ hypothesis. Unfortunately a direct link was not able to be

established between human occupation and these otoliths because the otoliths

were not found in situ. This study will broadly assess how geochemical

analyses of in situ fish otoliths can be associated with human occupation, to tell

us something about past environments and determine if fish were being

collected after an evaporative trend.

1.1 Aims

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The primary aim of this study is to assess the usefulness of geochemical

analyses of fish otoliths for determining chronology and past

human/environment interactions at Lake Mungo.

Within, and relating to this primary aim, are a number of secondary aims.

These include:

- To test the theory that fish were being collected from an

evaporating lake.

- To test the suitability and reproducibility of geochemical

methods for dating (14

C and amino acid racemisation),

temperature assessment (δ18

O, Sr/Ca, Ba/Ca) and migration (Sr

isotopes).

Overall, this study seeks to demonstrate the applicability of geochemical

techniques to fish otoliths, within the archaeological setting of Lake Mungo, as

tools for providing temporal links between human occupation and

environmental conditions. By applying earth science technologies and

geochemical techniques to archaeological remains this thesis also seeks to

demonstrate the potential benefits of a cross-disciplinary approach to research.

1.2 Site description

The otoliths used in this study were obtained from lunettes bordering the site of

Lake Mungo, which forms part of the Willandra Lakes system. This system is

made up of seven large dry lake basins that once formed a major overflow area

for seasonal floodwaters coming down the Lachlan River (see Figure 1.1)

14

Figure 1.1: The tributary and distributary streams of the Lachlan River Basin in the central Murray Darling basin, south

eastern Australia (Kemp and Rhodes 2010).

15

Lake Mungo is indirectly connected to the other lakes in the system via an

overflow outlet with Lake Leaghur (see Figure 1.2 A). One of its main

characteristics is the presence of eastern lakeshore lunettes which act as a

record of past lake fluctuations. The largest of the Lake Mungo lunettes is

called the Walls of China (see Figure 1.2 B).

Erosion of the Walls of China by wind and water has over the years uncovered

a large number of archaeological remains. In 2011 field work at Lake Mungo

conducted by Nicola Stern and colleagues from La Trobe University recorded a

large number of fish bone hearths situated on the Walls of China lunettes in an

area of rapidly deflating sands. The location of this site in the lunettes can be

seen in Figure 1.2 B and a satellite photo of the hearths in association with each

other can be seen in Figure 1.3.

Figure 1.2: The Willandra Lakes system (A) and Lake Mungo foot

survey study areas (B). Images are courtesy of Nicola Stern and the

Lake Mungo Archaeology Project.

16

Initial recording of these hearths noted that they were associated with a period

of fluctuating lake conditions as indicated by laminar sands containing patches

of alternating clean white quartz and pelletal clay (Stern et al. in press). They

also contained a large number of in situ otoliths. Bracketing optically

stimulated luminescence (OSL) ages place this layer between 14,500 - 20,000

years ago, a period covering the last glacial maximum (LGM) (Stern et al. in

press). Ten otoliths were obtained from five of these hearth sites spreading

Figure 1.3: Satellite map of fish bone hearth sites, Lake Mungo

lunettes. Red dots represent archaeological finds. Image is courtesy of

Nicola Stern and the Lake Mungo Archaeology Project.

17

from the bottom (hearth #926) to the top of the sediment accumulation

sequence (hearth #982).

The otoliths showed no signs of scarring or chipping from any post-

depositional repositioning and were considered to be found in situ. This is with

the exception of one otolith collected from hearth #953 which is suspected to

be out of context. These otoliths will be used as a case study for assessing how

the use of geochemical techniques for dating, recording ambient environmental

conditions and tracking fish migration can be used in a wider study of human

occupation events and their temporal association with lake conditions.

1.3 Thesis Overview

In providing an introduction and background to this topic this chapter has

described the main aims of this thesis in terms of the need to find new tools for

assessing the occurrence of human occupation and the associated

environmental conditions. The following chapter presents an overview of

archaeological and geochemical research at Lake Mungo, as well as providing

background information concerning the principles, techniques and application

of isotope and elemental analysis of fish otoliths as methods for determining

environmental conditions, migration and chronology. Chapter 3 will describe

the methodology employed in this study to assess how fish otolith

geochemistry can be used to investigate past human climate. This will include

the analytical processes and machines used for gaining isotopic ratios,

elemental abundance measurements and dating information as well as

identifying otolith age lines. The results from these analytical techniques are

18

presented in Chapter 4 and a discussion of the data gained in relation to the

interaction of human occupation, past environment conditions, and chronology

at Lake Mungo can be found in Chapter 5. The final chapter of this thesis

summarises the information gained from this study, presents the main

conclusions, and offers recommendations for improvements to the techniques

used here to enable their future application to this and other archaeological

sites.

19

Chapter 2

Background

This chapter firstly provides a review of past work at Lake Mungo and how the

theories generated from this have suffered from a lack of multidisciplinary

research. This is followed by a description of the hydrological setting of the

lake, its associated stratigraphy and current understanding of the region’s

geology and relationship with lake level changes. A brief overview is then

provided for the geochemical and biological properties of otoliths and some of

the relevant geochemical techniques that have been applied to them, followed

by a brief description of the fish species, golden perch (Macquaria ambigua),

whose otoliths are used in this study. Archaeological studies that have

benefited from otolith geochemical techniques are then illustrated with

examples from Australia and overseas. Lastly, there is an introduction to the

fundamentals of the dating techniques radiocarbon dating and amino acid

racemisation (AAR) and how these can be applied to fish otoliths in order to

date human occupation events.

2.1 Archaeological Research at Lake Mungo

This section provides an overview of past archaeological studies undertaken at

Lake Mungo and some of the theories that have developed from these,

concerning human occupation and environmental conditions.

20

In 1969, the erosion of the lowest southern area of the Lake Mungo lunettes

revealed something unexpected: cremated human remains (WLH 1). The

archaeological investigations that followed this discovery revealed a second set

of human remains, this time a fully articulated skeleton with evidence of ritual

burial (WLH3). Numerical dating of these remains pushed human presence at

Lake Mungo back as early as 40-50 ka (Bowler et al. 2003).

Early interpretations of the archaeological records of Lake Mungo were that

humans had been continually occupying the site for the past 20,000 years. The

1969 discovery of human remains were originally dated to this time frame and

their spatial association with artefacts similar to those observed to be used by

historic aboriginal occupants of the Murray Darling Basin led to a theory of

occupational and cultural continuity. This theory discounted evidence for

dramatic environmental changes having occurred throughout this period as

simply demonstrating the extreme adaptability of the Aboriginal population

(Bowler et al. 1970: 47).

Recent reviews of these interpretations, and the evidence they were based on,

has identified a common trend of drawing upon ethnographic information to

validate interpretations. Sparse archaeological evidence was being

supplemented with historic observations to support the theory of ‘cultural

continuity’ and continuous occupation at Lake Mungo (Hiscock 2008). Allen

and Holdaway (2009) argued that when an ethnographic model was applied to

the archaeology it had the effect of reducing temporal relationships and placing

more emphasis on spatial association as a proxy for temporal association. Thus

artefacts that were in close spatial proximity may have actually been thousands

21

of years apart. They also argued that the presence of favourable conditions in

the past should not be taken as meaning that people were in a position to take

advantage of them (Allen and Holdaway 2009). The occurrence of human

populations at Lake Mungo was more sporadic and opportunistic than

previously thought and the interplay between human behaviour and

environmental conditions was of greater significance.

The size and occurrence of human populations at Lake Mungo has fluctuated

over time and this has been connected to lake level changes. Maximum

occupational density at the Lake Mungo site has been placed at between 45,000

and 43,000 years ago during a period of high freshwater conditions (Bowler et

al. 2003). The gradual decline of occupational evidence following this was

originally interpreted as indicating human response to increasing lake level

fluctuations and aridity. Human remains found in sediments related to high

water phases at Lake Mungo and large numbers of aquatic remains in hearth

sites nearby, supported this interpretation (Bowler et al. 1970: 44). The theory

was that humans were only attracted to the lakeshore at times when the lakes

were experiencing full freshwater conditions and aquatic life was abundant

(Barbetti and Allen 1972).

Excavations and surveys since that time have generated large amounts of

archaeological material, including a number of fish bone hearth sites, at periods

when lake levels were fluctuating. One particular hearth site was reported by

Bowler (1998: 147-148) at the Lake Mungo Tourist Site. This hearth was

found sandwiched between two layers of pelletal clay and radiocarbon dating

placed associated charcoal at 34,000 BP (ANU-2964). Pelletal clay is produced

22

during low lake level conditions and high winds (Bowler 1973: 316). Over 500

otoliths were uncovered and it was interpreted as being ‘the opportunistic

response of humans to changing landscape components’ (Bowler 1998: 146).

Bowler argued that partial lake drying, as suggested by the pelletal clay, would

have affected the fish within the lake leaving them slow and easy to scoop up

from the shallow waters. Human populations are theorized to have taken

advantage of this (Bowler 1998). This became the ‘easy prey’ hypothesis and

demonstrated how a geological assessment of lake hydrology could be applied

to the archaeology for a broad association of ambient conditions.

The need for a more detailed assessment of human occupation in association

with environmental conditions has also been expressed by Allen and Holdaway

(2009). They agreed with much of Bowler’s (1998) assessment of lake

conditions and the chronology they were associated with but argued that there

were not the tools available to fully understand the density and extent of human

occupation at these times. They argued that there was no way of making an

assessment of whether or not the lake represented ‘easy pickings for Aboriginal

Hunter gatherers [during the Pleistocene]’(Allen and Holdaway 2009:100).

They also noted that Gillespie (1998:180) had argued for an opposing theory

that people were exploiting terrestrial produce more than aquatic during phases

of fluctuating lake conditions, though there is little recent evidence to back this

up. The final conclusion reached by Allen and Holdoway (2009:102) was that

Bowler’s assessment of the relationships between strata, human occupation and

lake conditions spanning 15,000 to 50,000 years BP was so far the most

successful approach. The main concerns with Bowler’s lake lunettes are that

23

they occur sporadically along the lakeshore and it is not always easy to date

their occurrence. This is particularly true for dating the timing of lake

conditions in association with human occupation. A more detailed method that

can be directly dated and provide environmental information in connection

with the sites archaeology is needed.

Recently, a large number of radiocarbon ages have been taken from surface

collected fish otoliths and shells in areas relating to each of the Willandra

Lakes basins (Bowler et al. 2012). At Lake Mungo the otolith ages clustered

between 19,400 and 20,400 cal BP and between 37,000 to 45,000 cal BP. The

most recent of these, coincident with the LGM, is also closely associated with

ages for fluctuating lake levels as indicated by pelletal clay dune (PCD)

development and dated by OSL of sediments and radiocarbon in charcoal

(Bowler et al. 2012). There is a similar clustering of otolith ages and low lake

levels at many of the other lakes in the system but with different timings for

their occurrence. Bowler et al. (2012) interpreted this as further evidence for a

connection between detrimental environmental conditions, such as increased

salinity and evaporation, and an immediate focus on these times for human

harvesting of fish. Of course the lack of in situ finds used in this assessment,

means that these fish and the dates obtained cannot be directly associated with

human occupation. The studies presented here have demonstrated that by

integrating the occurrence of human occupation with the lunette geological

makeup a broad association between these events and lake level changes can be

made. A more detailed assessment that can not only be directly associated to

24

human occupation but is also able to date these events in association with

ambient environmental conditions is needed.

2.2 Description of the Willandra Lakes System

The flow of water through the Willandra Lakes system is related to periods of

flooding and drying which is dictated by conditions at the main water source.

This section describes what is currently known about the flow of water through

these basins and what Lake Mungo’s position is in relation to this.

2.2.1 Lake system hydrology

The Willandra Lakes are a series of interconnected basins that once formed the

terminal overflow outlets for the Lachlan River sourced in the Great Dividing

Range. Since around 15,000 years ago these lakes have experienced mostly

dry, stable conditions. During the Pleistocene floodwaters regularly filled these

lakes and were maintained for long time periods. The main control effecting

the absence or presence of water in the Willandra lakes would have been the

amount of melt-water at the source which in turn was controlled by changes in

regional and global climate (Bowler 1971, Bowler et al. 2012).

Current understanding of how water availability upstream affected the

occurrence of water in the Willandra Lakes is based on analyses of lakeshore

lunettes. Clay dunes develop in the presence of a shallow saline water body

with strong unidirectional winds coincident with a hot dry season (Bowler

1973) whilst quartz sand dunes (QSDs) are associated with lake full conditions

(Bowler 1998). The occurrence of high winds would have led to the deposition

25

of these different sand types on the lake shorelines, a visual representation of

this process can be found in Figure 2.1.

Once each lake reached overflow level the excess water would flow into the

next lake in the sequence. When the evaporation cycle took hold and

floodwaters receded, the lakes furthest from the source dried out first leading to

a staggering in the timing of low lake levels in the geological record. A

stairway analogy is used by Bowler et al (2012) to describe this relationship

(Figure 2.2). Within a single wetting and drying cycle Outer Arumpo exhibited

in its dunes a relatively short lake full stage followed by two phases of lake

floor exposure, whilst Lake Mungo exhibited a longer period of permanent

Figure 2.1: Lunette formation A = typical QSD and B = typical PCD.

Figure is adapted from Bowler (1986).

26

water and only one phase of lake floor exposure (Bowler et al. 2012). It is

important to consider the lunettes of each lake rather than assuming the same

chronology of lake full and dry events across the entire system. The next

section will deal with the specific geological and hydrological setting of Lake

Mungo within the wider Willandra Lakes system.

2.2.2 Lake Mungo

Lake Mungo is connected indirectly to the rest of the Willandra Lakes system

via an overflow passage to Lake Leaghur. This makes it a unique location for

studying the evaporation of lake levels and their connection with human

occupation because once water arrived in Lake Mungo the only way it could be

removed was through evaporation (Bowler 1998: 121). Once water levels fell

below the overflow connection Lake Mungo became more sensitive to

fluctuations in local climate rather than those of the upstream area. This unique

Figure 2.2: Diagrammatic representation of Bowler’s stairway analogy.

Numbers are the spot heights taken from digital elevation and local

surveys in metres above the Australian Height Datum taken from

Bowler et al (2012:274).

27

hydrologic setting and subsequent lake level fluctuations at Lake Mungo have

created one of the most detailed lunette sedimentary records in the whole

Willandra area. The discovery of numerous archaeological remains within this

sedimentary record has allowed for the broad association of lake level

fluctuations with evidence of past human occupation and the tentative

assigning of time frames for these events.

Current understanding of the Lake Mungo stratigraphy comes mainly from the

work of Bowler who provided a detailed description of lakeshore sediment

layers and their relationship to lake level changes (Bowler et al. 1970, Bowler

1998, Bowler et al. 2012). These phases from oldest to youngest were named

Golgol, Mungo (separated into lower and upper sections), Arumpo and Zanci.

Their association as described by Bowler (1998) can be seen in Figure 2.3.

The environment surrounding Lake Mungo is highly variable with large

amounts of rainfall and wind causing erosion of artefacts and the sediments

they lie in. Bowler’s stratigraphy is mainly based on a few key sections of the

Figure 2.3: Diagrammatic representation of the ideal presentation of

Bowler’s stratigraphic layers within the Lake Mungo lunettes, taken

from Bowler (1998: 124)

28

lunette, some of which are no longer visible (Bowler 1998). A recent

geological map of the site, marking past layers and recent reactivations, is in

the process of being drawn up for the entire lakeshore lunettes, see Figure 2.4.

Nicola Stern and colleagues at the La Trobe University have also produced a

revised stratigraphy for the site (see Table 2.1). This stratigraphy was

developed based on observations of the lakeshore lunettes and was then related

back to Bowler’s units. The unit of interest to this study is the Arumpo/Zanci

(unit E) section within which a large number of hearth sites have been

uncovered. This is roughly coincident with LGM and is characterised by

rapidly fluctuating lake levels interspersed with periods of complete drying

(Stern et al. in press).

29

Figure 2.4: Current geological map of part of the Lake Mungo lunettes,

the fishbone hearth sites considered in this thesis are circled in black and

are associated with the Arumpo/Unit E layer. Red = Unit A

(Golgol), Cream = Unit B (Lower Mungo), Yellow = Unit C (Upper

Mungo), Red cross-hatch = Unit D (‘Red Lunette’), Brown = Unit E

(‘Arumpo’), Reddish Brown = Unit F (Reactivated Arumpo), Khaki

green on the vegetated bits = unit I = Holocene alluvial fans, Bright

green = unit J (modern alluvium), Tan = unit H = (modern aeolian).

Image courtesy of Kathryn Fitzsimmons, Nicola Stern, and Paul

Kajewski, the Lake Mungo Archaeology Project.

30

Table 2.1: Summary of the stratigraphy and OSL dating of the central

Mungo lunette prepared by Kathryn Fitzsimmons and Nicola Stern for

MAP project members, May 2012

31

2.3 Fish Otolith Geochemistry

This section describes the main properties of fish otoliths that have made them

valuable tools in fishery science for making age assessments, tracking stock

migration, and recording ambient environmental conditions. There will also be

an overview of the main geochemical techniques that have been applied to fish

otoliths for dating, environment assessment and tracking migration.

2.3.1 Overview

Fish otoliths are structures composed of 99% calcium carbonate (CaCO3) in the

aragonite form which is deposited incrementally on an organic matrix within

the inner ear epithelium of teleost fish (Degens et al. 1969, Casteel 1976,

Campana 1999). This mineralization process is different to most other

calcifying structures such as bones and enamel, in that it occurs within an

acellular medium in the epithelium called the endolymph (Payan et al. 2004:

535-536). The crystal structure of the otolith once deposited is metabolically

inert. Unlike bones, which are continuously resorbed and remineralized, otolith

growth is continual and occurs even when somatic growth has ceased (Maillet

and Checkley 1990, Campana 1999, Campana and Thorrold 2001). There are

three main otolith types in the inner ear of teleost fish, the lappilus, astericus

and sagittae (Panfili et al. 2002). The locations of which can be seen in Figure

2.5. Of these the most often used in studies is the sagittal otolith due its size

and greater likelihood of preservation.

32

2.3.2 Identification of Otolith Age Lines

The deposition of calcium carbonate onto the otolith surface forms periodic

rings similar to those of trees. These appear as grouped dark and light bands

when examined in thin section under a light microscope. Studies have shown

that there is a link between the number of pairs of light and dark rings and the

number of years a fish lived for (Campana 1999, Morales-Nin 2000, Woydack

and Morales-Nin 2001).

Morales-Nin (2000) found that although the link between age and rhythmic

growth mark formation is well established, the mechanism that relates the

growth marks in the otoliths with the age of the fish is not known. These bands

may be related to seasonal variations in the availability of food, or temperature

with faster growth in warmer months leading to the light bands (translucent

bands) and slower growth in colder months leading to the darker bands (opaque

Figure 2.5: Diagrammatic representations of the position of otoliths

within the head (A) and inner ear of teleost fish (B). Figure adapted

from Pantili et al. (2002).

33

bands) but further study into these different processes are required (Wheeler

and Jones 1989). Daily otolith growth increments have been identified in some

fish groups but not within golden perch (Macquaria ambigua) (Pannella 1971).

Diurnal rhythms and their links to otolith pH and age ring development have

also been studied but there is still some debate as to whether this applies to all

fish species and how other factors such as metabolic rate, season and

photoperiod affect this (Tohse et al. 2006). It is generally accepted that fish

otoliths form periodic light and dark rings that represent one year of growth but

this is best validated for each fish species.

The use of this aging technique for golden perch (Macquaria ambigua) otoliths

has been validated for up to 22 years of age (Anderson et al. 1992, Stuart

2006). The majority of studies have successfully employed banding

identification for the determination of seasonal fluctuations in geochemical

measurements across the otoliths of a range of fish (Wurster and Patterson

2001) and for identifying season of death (Higham and Horn 2000, Disspain

2009, Disspain et al. 2011).

2.3.3 Golden Perch (Macquaria ambigua)

Golden perch are one of the main species of fish whose remains are often

found associated with human occupation at Lake Mungo. This study utilises

golden perch otoliths for geochemical analysis and as such a brief overview of

their modern habitat preferences and reproductive strategies is provided.

The golden perch or yellow belly (see Figure 2.6) is a carnivorous,

potamodromous fish that is commonly found in the Murray-Darling river

34

system of NSW and in the Lake Eyre and Bulloo internal drainage systems of

Queensland, NSW and South Australia (Allen et al. 2002).

Golden perch inhabit a wide range of environments including lakes, rivers and

impoundments but are commonly associated with lowland, turbid slow flowing

rivers. Males tend to mature at 2-3 years and females at 4 years. Previous

studies indicated that spawning of golden perch was induced by a rise in water

level and water temperature (Cadwallader and Backhouse 1983). More recently

this ‘flood pulse concept’ has been replaced with evidence of a more flexible

breeding strategy with spawning and recruitment occurring both during full

flood conditions and when waters rise only to the river banks. There are a wide

range of temperatures at which golden perch have been known to spawn

(Mallen-Cooper and Stuart 2003). Studies of golden perch have indicated that

these fish can tolerate a wide range of salinities and temperatures but this has

only been tested on juvenile (6 month old) fish which were exposed to

Figure 2.6: Adult Golden Perch (Macquaria ambigua), by Gunther

Schmida sourced from the Murray Darling Basin Commission:

http://www.vic.waterwatch.org.au/file/inform/Golden%20Perch.pdf

http://www.vic.waterwatch.org.au/file/inform/Golden%20Perch.pdf

35

increased salinity for less than a month (Langdon 1987). Overall the golden

perch is a fish well adapted to survive in a wide range of conditions and this

has allowed it to persist in modern river systems even with man-made stream

diversion and regional environmental changes (Mallen-Cooper and Stuart

2003).

2.3.4 Elements and isotopes

As layers of calcium carbonate are laid down on the otoliths surface so too are

elements and isotopes from the ambient water incorporated into its matrix

(Campana 1999). Some of these elements and isotopes are formed in

equilibrium with the ambient water and have been found to vary according to

ambient concentration (Gillanders and Munro 2012) and temperature (Kalish

1991) as well as having different levels in different salinities. These traits have

recently been employed in environmental reconstruction (Radtke et al. 1996,

Knudson 2009) and tracing fish migration (Outridge et al. 2002, Mc Culloch

et al. 2005).

2.3.3.1 Oxygen isotopes

Studies in laboratory controlled conditions have shown that oxygen isotopes

are deposited within otolith calcium carbonate layers in or near equilibrium

with the ambient water with a slight fractionation effect caused by changing

water temperatures (Kalish 1991, Radtke et al. 1996, Thorrold et al. 1997,

Patterson 1999).

Oxygen has three isotope of varying natural abundances: 16

O (99.762%), 17

O

(0.038%), 18

O (0.200%). In fractionation processes the lighter isotopes of

36

oxygen tend to react at a faster rate than the heavier isotope, for example when

water evaporates the vapour becomes enriched in the lighter isotope (16

O) and

the water left behind becomes more concentrated with the heavier isotope (18

O)

(Mook 2006: 6).

The fractionation of oxygen isotopes between water and calcium carbonate is

temperature sensitive a phenomenon which has led to their main use as

palaeothermometers. Provided that a) the oxygen isotope composition of past

water bodies can be established, b) that the oxygen isotopic composition of

carbonates have not been altered by post deposition effects and c) that oxygen

isotopes are deposited at or near equilibrium with the surrounding waters, then

a formula can be used to establish past temperatures (Faure and Mensing

2005). In marine foraminifera the application of palaeothermometry

calculations have established that an 18

O increase of 0.26‰ in carbonate

represents a 1ºC temperature decrease (Hoefs 2004: 168).

Otoliths in general show very good preservation and records of oxygen isotope

ratios have been gained from otoliths dating as far back as the Jurassic period

(Patterson 1999). Andrus and Crowe (2002) studied the effect of various

cooking processes on otoliths elemental and isotopic compositions and found

that only burned otoliths showed any major changes in oxygen isotope ratios

but elemental fluctuations were more variable between the different treatments.

The isotopic composition of the oceans has changed not only over time but

over space due to the incorporation of different quantities of freshwater from

different regions (Hoefs 2004: 170). This effect is more pronounced in river

37

systems where precipitation, flood waters and the linking up of different water

source areas cause dramatic changes in isotopic composition over space and

time. In order to calculate temperature from the oxygen isotope ratios of past

carbonates the composition of the water needs to be established.

Summer precipitation is enriched relative to winter precipitation at high

latitudes, at low latitudes the amount of precipitation has a greater impact with

increased rainfall leading to lower δ18

O values. In general colder environments

are also likely to have lower δ18

O values. The δ18

O values of marine carbonates

are close to zero whereas lacustrine carbonate samples have negative values

due to depletion of 18

O in meteoric water relative to seawater, see Figure 2.7

(Faure and Mensing 2005: 705).

Figure 2.7: Diagram of the changing δ18

O values of water vapour as it

travels inland from the ocean as well as the change in the δ18

O values of

precipitation and how this is reflected in continental rivers and lakes.

From: http://suvratk.blogspot.com.au/2009_11_01_archive.html

http://suvratk.blogspot.com.au/2009_11_01_archive.html

38

Changes of oxygen isotope ratios in water are related to salinity, temperature

and the occurrence of evaporation or precipitation (Campana 1999, Campana

and Thorrold 2001). A recent paper by Gillanders and Munro (2012) collected

water samples and fish from ten sites of varying salinities along the Coorong

lagoon in South Australia. They measured oxygen isotopes of the water and the

otoliths and found a positive linear relationship between δ18

O and salinity

(Gillanders and Munro 2012: 1142).

Questions have also been raised about the possible effects of somatic growth

rate and otolith calcification rates on the stable isotope composition of otoliths.

Høie et al (2003) studied these effects on cod by rearing larvae and juvenile

fish in two different temperatures and generating different growth rates by

varying the amount of prey. Results suggested that oxygen isotopes were not

affected by the changes in somatic or otolith growth rates. Oxygen isotopes

were shown to be deposited independently of kinetic and metabolic effects.

The relationship between temperature and δ18

O values in a study of the otoliths

of lab reared Australian salmon has shown that, when ambient conditions were

taken into account, a 1‰ change in δ18

O was equivalent to ~4.8ºC change in

temperature (Kalish 1991). A study by Elsdon and Gillanders (2002) examined

the interactive effects of temperature and salinity on otolith chemistry by

rearing juvenile black bream in controlled laboratory conditions. They found a

general trend of decreasing δ18

O values with increasing temperature, an affect

also found by Thorrold et al. (1997) and Kalish (1991). The δ18

O values

showed a strong relationship with salinity with increasing concentration of the

water leading to increasing δ18

O values of the otoliths. An association between

39

oxygen isotope composition of fish otoliths and those of the ambient water can

be made. A relationship between fish otolith oxygen isotopes and temperature

has also been established but the effect of ambient composition is more

significant.

2.3.3.2 Strontium Isotopes

In terms of fish studies, strontium isotope ratios are mainly used for tracking

migration or identifying natal populations (Mc Culloch et al. 2005, Walther

and Thorrold 2009). They have also been employed in archaeology to track

human migration by using the ratios of 86

Sr/87

Sr in tooth enamel and comparing

it to 86

Sr/87

Sr ratios of soil and water samples taken from areas surrounding

their assumed occupational areas (Grupe et al. 1997, Bentley et al. 2002).

There are four naturally occurring stable isotopes of strontium: 84

Sr (0.56%),

86Sr (9.86%),

87Sr (7.0%) and

88Sr (82.58%).

87Sr is produced by the

radioactive decay of 87

Rb. Variations in 87

Sr/86

Sr are a function of the age and

original Rb and Sr composition of the source (Outridge et al. 2002).

The concentration of Sr in streams and lakes depends on the mineral

composition of the bedrock and on climatic factors (Palmer and Edmond

1992). In the south-western states of America elevations in Sr concentrations

are attributed to the effects of evaporative concentration cause by the semiarid

to arid climatic conditions experienced in the region (Faure and Mensing 2005:

413). The Sr isotope composition of streams changes continually with the

inflow of water from tributaries, groundwater and surface runoff.

40

To use strontium isotope ratios (87

Sr/86

Sr) of fish otoliths as migratory

indicators they need to be deposited in equilibrium with the strontium isotopes

of the water and not be affected by growth rates of metabolic process. Also, the

strontium isotope ratio of the water needs to vary between the possible

migration areas otherwise a measure might show no variations or ‘spikes’ even

if the fish has moved.

Strontium isotope ratios are not affected by climatic, physiological or dietary

processes and occur in higher concentrations within carbonate materials than

elements with similar radiogenically derived properties (Kennedy et al. 2000,

Campana and Thorrold 2001). The 86

Sr/87

Sr in fish otoliths is a direct reflection

of external water 86

Sr/87

Sr. In the ocean the 86

Sr/87

Sr is constant but in

freshwater systems the 86

Sr/87

Sr of stream and river flows is based on the

isotopic composition of dissolved products derived from the catchment

watershed (Mc Culloch et al. 2005: 638).

High resolution measurements of strontium isotopes can be obtained using

laser ablation multicollector inductively coupled plasma mass spectrometry

(LA-MC-ICP-MS). The application of this process to otoliths has been

demonstrated in a number of papers including Barnett-Johnson et al. (2005) for

tracking the natal origins of salmon; Woodhead et al. (2005) for tracking the

movement of a diadromous fish species from marine to freshwater; Outridge et

al. (2002) for looking at the movement of the anadromous Dolly Vardenn char

(Salvelinus malma) and McCulloch et al. (2005) for tracking the life history of

Australian Barramundi.

41

Strontium isotopes are most useful for tracking migration or identifying natal

areas in highly variable environments with known 87

Sr/86

Sr ratios for the

underlying geology but they can still provide an indication of migration if for

example the early years of a fish’s life show one signature (87

Sr/86

Sr) and the

later years show another.

2.3.3.3 Elemental abundances

The main assumption for micro-chemical analyses of fish otoliths is that a

relationship exists between the concentration of trace elements in the

environment and those within the otolith (Collingsworth et al. 2010).This has

proven to be true for a number of trace elements including strontium, barium

and magnesium in a variety of fish species (Wurster and Patterson 2001,

Elsdon and Gillanders 2004). The chemical composition of the endolymph

fluid, from which otoliths are formed, controls the rate of calcium carbonate

deposition on the otoliths surface and is affected by environmental and

biological variables such as temperature, spawning and food availability

(Payan et al. 2002, Elsdon and Gillanders 2004, Payan et al. 2004, Tohse et al.

2006).

Otoliths are, in general, characterised by lower levels of Mg/Ca, Mn/Ca and

Ba/Ca than is found in corals, animal bones or fish scales but they also

preserve a better chronological record within which to place these trace

element variations (Campana and Thorrold 2001). There are well documented

differences observed in the elemental ratios of otoliths of fish moving through

freshwater, estuarine and marine waters with higher concentrations of Sr/Ca

42

found in marine and higher Ba/Ca found in freshwater (Gillanders 2005). This

has been the main use of elemental abundances, tracing migration of

diadromous and anadromous fish (Albuquerque et al. 2010, Arai 2010,

Macdonald and Crook 2010, Gillanders and Munro 2012)

One of the few experimental studies on the effect of temperature versus

ambient concentrations on the elemental composition of freshwater fish

otoliths is by Collingsworth et al. (2010). In their study juvenile yellow perch

(Perca flavescens) were raised in tanks of three different temperatures with

three different water concentrations at each temperature. Otoliths were then

analysed using LA-ICP-MS to see if the four elemental ratios Sr/Ca, Ba.Ca,

Mg/Ca and Mn/Ca revealed any trends. Little or no effect was found for

Mn/Ca and Mg/Ca which varied both across and within the treatments. This

supported findings that Mg/Ca may be physiologically regulated (Woodcock et

al. 2012). Sr/Ca ratios increased with increasing elemental concentration of

water as well as temperature as did Ba/Ca ratios except at low temperatures

(below 10°C). These results are in line with those found in similar studies of

marine and estuarine fish. For example, Walther and Thorrold (2006) found

that for the estuarine fish Fundulus heteroclitus the majority of strontium and

barium in the otoliths came from the water (83% of Sr and 98% Ba) and not

food (17% of Sr and 2% Ba). A similar study of Elsdon and Gillanders (2004)

showed that temperature and ambient chemistry contributed most to the trends

observed in otolith Sr/Ca and Ba/Ca for black bream (Acanthopagrus

butcheri). Other studies have shown a positive linear correlation between

otolith and water Ba/Ca as well as otolith and water Mg/Ca (Gillanders and

43

Munro 2012). A recent experiment by Woodcock et al. (2012) determined that

water is the primary source of magnesium in otoliths but that the ratios of

Mg/Ca did not vary with changes to water composition or diet and it is

therefore unlikely to be of use in environmental studies.

Studies of different fish species have shown varied results for the incorporation

of Sr and Ba in association with ambient conditions. Some of these contrast

with the studies described in the section above such as Limburg (1995) and

Kennedy et al. (2000) who both found significant effects of changed diet on

freshwater fish otolith Sr/Ca ratios and Sr isotopes. The suggestion has also

been made that there is a threshold for Ba incorporation into otoliths at very

high ambient values (De Vries et al. 2005, Miller et al. 2010). Others have

suggested that higher levels of strontium in otoliths facilitate the uptake of

barium from the water. These opposing studies suggest that there may be

species specific effects influencing elemental deposition in otoliths. Elemental

data has also shown to be affected by different cooking and trash disposal

treatments on otoliths and so caution is suggested when interpreting

geochemical fluctuations of otoliths from hearth or midden sites (Andrus and

Crowe 2002).

There have been a wide range of studies conducted on the otoliths of many

marine and estuarine species of fish. Freshwater fish have only recently been

studied for environmental effects on elemental uptake and as such results are

still being coalesced. The one thing that can be taken from the experiments

described above is that the main influence on the elemental composition of fish

44

otoliths, in particular Ba/Ca and Sr/Ca, are ambient water concentration and

temperature but that species specific effects on elemental uptake should not be

discounted.

2.3.5 Fish Otolith Geochemistry and Archaeological Sites

Recent applications of elemental abundance and isotopic studies of fish otoliths

to assist with archaeological site interpretations in terms of

palaeoenvironmental conditions have shown promising results.

This honours thesis is based on the earlier study by Katarina Boljkovac (2009)

who identified an increasing trend of evaporation within surface collected

golden perch otoliths from the Lake Mungo site. She also identified what may

be seasonal trends in oxygen isotopes in the early lives of the fish. The

techniques she utilized involved collecting oxygen isotopes via the SHRIMP II,

LA-ICP-MS for Sr/Ca ratios and LA-MC-ICP-MS for strontium isotope

measurements. The relative value of these analytical techniques for fish

otoliths geochemical analysis will be expanded on in Chapter 3 (Methodology).

There is only one other example of the application of geochemical analyses of

fish otoliths to an archaeological site in Australia and that is the work

completed by Disspain et al. (2009, 2011). This study expanded on the use of

otolith characteristics, for determining past fishing practices by applying

elemental abundance analysis to gain further information about fish life

history, migration and environmental conditions.

Internationally there have been a number of cases where otolith geochemistry

has been applied at archaeological sites. These usually investigate climate

45

during a specific period of time to see how this ties in with associated

archaeological evidence. For example Wurster and Patterson (2001) micro-

milled freshwater drum (Aplodinotus grunniens) otoliths from the site of

Eastman rock shelter in northeast Tennessee, USA, to gain high resolution δ18

O

values. Freshwater drum form annual bands due to a cessation of growth at

10°C and Wurster and Patterson (2001) used this to find the start of the

growing season in the otolith age lines and to then calculate water δ18

O values.

Fish otolith δ18

O values were used in a similar way by Wang et al. (2011) and

Walker and Surge (2006) for examining climatic events affecting local

inhabitants during the Late Holocene at the Pine Island archaeological sites in

Florida, USA.

In summary, the application of fish otolith research to archaeological sites is no

longer confined to age, weight and length analyses. Geochemical analyses of

fish otoliths have provided new avenues of research not only in fisheries

science but in studies of archaeological sites in Australia and overseas. The

above studies have demonstrated the applicability of fish otolith geochemistry

for assessing past temperatures and seasonality of fishing practices at a number

of archaeological sites. Fish otoliths have also shown close associations with

human occupation due to their occurrence in hearth sites and shell middens. By

dating these in situ finds dates for human occurrence can also be gained.

2.4 Geochemical dating techniques

A wide range of dating techniques have proved useful for determining relative

and absolute ages for in situ materials and for constructing chronologies at

46

archaeological sites. At Lake Mungo OSL, radiocarbon and AAR dating

methods have provided ages for some of the oldest evidence for human

occupation in Australia (Bowler et al. 2003). Correct dating was integral for

determining the timing of alternating lake full and dry conditions observed in

the lunette sedimentary sequence and as a tried and tested absolute dating

technique radiocarbon is the best method for this (Bowler 1998, Bowler et al.

2012). Amino acid racemisation is a numerical dating technique that has

proved useful in constructing relative stratigraphies from shells (Murray-

Wallace 1995) and emu eggshells (Magee et al. 2009) in Australia. An

assessment for the viability of AAR results from fish otoliths has yet to be

established but may prove to be quite a useful technique for differentiating the

age ranges for large numbers of samples at a low cost. This section provides an

overview of the fundamentals, methods and calibrations of radiocarbon dating

and amino acid racemisation.

2.4.1 Radiocarbon

The principles and methods behind radiocarbon dating are described in this

section including the production of radiocarbon in the atmosphere, its

incorporation into living organisms, its decay and how these are analysed and

calibrated to produce an absolute date.

Carbon occurs naturally in the form of three isotopes at different levels of

abundance: 12

C (98.9%), 13

C (1.1%) and 14

C (radiocarbon; 1 atom in around

1012

atoms of 12

C). 12

C and 13

C are stable isotopes whereas 14

C is radioactive

(Hoskin and Wysoczanski 1998). Radiocarbon is continually produced in the

47

upper atmosphere when cosmic rays from the sun interact with nitrogen in the

following reaction: 14

N + n (neutron) → 14

C + p (proton) (Grün 2006).

The resulting 14

C atoms oxidise to form 14

CO2 which is rapidly spread

throughout the atmosphere and is then taken up by plants via photosynthesis

and by animals through the food chain. The atmosphere and hydrosphere have

constant 14

C levels due to the equal production of 14

C and its decay. The 14

C

activity within plants and animals remains equal to that in the atmosphere for

as long as the organism is alive. This is due to the continuous absorption of 14

C

and its subsequent decay. Once a plant or animal dies no new 14

C is being

taken up and so the level of 14

C diminishes via radioactive decay. 14

C decays

with a half-life of 5730 ± 40 years. Thus the radiocarbon left in the sample

compared to a modern standard yields the radiocarbon age. Early studies

assuming that the activity of radiocarbon in the atmosphere was constant over

time were not correct. Radiocarbon ages need to be calibrated to take into

account past fluctuations of 14

C in the atmosphere. This is done by radiocarbon

dating samples of known age and using them to create a calibration curve

(Grün 2006), see Figure 2.8.

48

Calibrated ages are labelled as cal BP and uncalibrated ages as BP or ka BP.

Pre-treatment of samples removes contaminates and isolates the carbon. The

better the pre-treatment procedure and the more concentrated the carbon, the

lower the errors of the systematic radiocarbon date (Grün 2006, Ramsey 2009).

The pre-treatment processes and calibration programs used in this study to gain

the most accurate and precise dates possible will be described in Chapter 3

(Methodology).

Figure 2.8: Calibration of conventional radiocarbon ages. Depending

on the shape of the calibration curve, the calibrated ages may have

smaller or larger errors that the conventional radiocarbon age (A), or

may result in two separate age ranges (B) from Grün (2008).

49

2.4.2 Amino acid Racemisation

Amino acid racemisation is a relatively new technique for building up relative

chronologies from biogenic materials such as shells. The principles and

problems associated with this technique are described in this section. Amino

acids are the building blocks of proteins. A total of 20 different amino acids

occur in nature with each containing a carboxylic group (COOH), an amino

group (NH2), a hydrogen atom and a radical group. There are two chiral forms

of amino acids and these are the L (lævorotatory – turning a plane of polarised

light to the left) form and the D (dextrorotatory – turning a plane of polarised

light to the right) form (Miller and Clarke 2007), refer to Figure 2.9.

Living organisms contain only L-amino acids and so the ratio of D/L is zero.

After death L-amino acids begin to change in D-amino acids in a process called

racemisation. Racemisation occurs until equilibrium is reached when the ratio

of D/L is one. The rate at which racemisation occurs varies between the

different amino acids and is temperature dependent. See Figure 2.10 for

Figure 2.9: The two chiral forms of amino acids are mirror images of

each other from Grün (2008).

50

relationship between racemisation, temperature and age (Miller and Clarke

2007).

If racemisation occurs at a constant temperature then the ratio of D/L is a

function of time and an approximate age for that sample can be obtained. If

temperature was not constant then the age obtained from AAR will be less

reliable (see Figure 2.11). D/L ratios also change more rapidly in younger

samples compared to older samples and as such precision of AAR diminishes

with the age of the sample (Grün 2008).

AAR has been successfully employed on emu eggshells and has proven useful

for constructing relative chronologies in a number of coastal sites in southern

Figure 2.10: Principles of age and temperature dependency of the D/L

ratio (after Wehmiller and Miller 2000). At a constant temperature the

D/L ratio is a function of time, on the other hand, if the age of the sample

is known, the D/L ratio can be used for estimating the average storage

temperatures Grün (2008).

51

Australia (Murray-Wallace 1995) and so the validity of its application to fish

otoliths at Lake Mungo is a potential next step for constructing relative

chronologies.

2.5 Summary

In summary there is a need for further work at the Willandra Lakes site to gain

more detailed information about the palaeoenvironmental conditions within

which human occupation was contextualised. The ratios of oxygen isotopes

and elements such as Sr/Ca and Ba/Ca within otolith age rings are deposited in

Figure 2.11: Principles of error calculation of an amino acid age

estimation. Additional random errors would arise from any

uncertainty in the measurement of the calibration point, systematic

errors from the application of alternative kinetic functions from Grün

(2008).

52

association with ambient water composition and temperature. Otoliths have

been used for radiocarbon dating at sites but the precision and accuracy of the

dates gained have not been assessed for their use in dating human occupation at

Lake Mungo. AAR racemisation has shown promising results with shells and

egg shells but has not yet been applied to otoliths. Strontium isotope ratios in

otoliths have been employed for tracking the movement of fish through

different water bodies and may be useful in determining the timing of fish

entry into Lake Mungo when applied to the otoliths in this study. Overall the

potential for fish otoliths as tools for assessing human interactions with

ambient environmental conditions on similar time scales is phenomenal. The

methods used to measure isotopic and elemental ratios in fish otoliths and

assess their ability, in this study, for developing palaeoenvironmental records

associated with human occupation on a temporal scale are described in the

following chapter (Chapter 3 Methodology).

53

Chapter 3

Methodology

The previous chapter presented an overview of current studies into the

deposition of isotopic and elemental ratios in fish otoliths and how they vary in

relation to ambient environmental conditions. The methods and machines

employed in this study for measuring such ratios are described in this chapter.

Firstly there will be an explanation of the sampling strategy used to assess the

suitability and reproducibility of techniques used for dating, recording

environmental trends and identification of the occurrence and timing of

migration.

3.1 Sampling Strategy

Firstly the otoliths in this study were collected from hearths in order to

associate them with human occupation. These hearth sites were all situated

within the Arumpo unit (Unit E) and seem to be spatially associated events;

they are however situated on different stratigraphic horizons within this layer.

Given the large OSL dated range for this unit, between 14,500 and 25,500 ya

(Stern et al. in press), these hearth sites could represent occupation events

which occurred thousands of years apart. The hearths are spread between #926

at the bottom of the sequence and #982 at the top. The sampling strategy

employed in this study was to obtain at least one otolith from each of these

bracketing hearth sites in order to establish the limiting ages for this

54

sedimentary unit. Fish within each hearth site should have been killed and

eaten at the same time and thus have very similar radiocarbon ages. Thus by

also dating multiple otoliths from three of the hearths the suitability and

reproducibility of the results would be assessable. This sampling strategy,

taking at least one otolith from the top and bottom of the sequence and taking

multiple from a few of them, also allowed for the comparison of the

geochemical histories of otoliths taken from the same hearth site. Again

because they should have been killed and eaten at the same time, fish otoliths

from the same hearth should have similar geochemical fluctuations reflecting

ambient conditions whilst they were both in the same water body. This should

also allow for a determination of the likelihood of each fish being in the same

body of water for their whole lives or if migration was occurring.

Otoliths were collected by Dr Nicola Stern during the 2011 field survey of the

Walls of China lunettes. A total of ten otoliths were obtained from within five

hearths sites with three from hearth #926, two from #953 and #952 and one

from each of the others, #982 and #1168. Otoliths from troughs and gullies

were avoided in order to minimise the possibility of secondary depositional

events due to recent high winds and rain. Some concerns were raised about

otolith #953-5 which may have been collected out of context and this should be

reflected in its radiocarbon results.

3.2 Sample Preparation and Analysis

I conducted the preparation and analysis of samples under the supervision of

Rainer Grun, Harri Kokkonen, Les Kinsley, Ian Williams and Rachel Wood at

55

the Research School of Earth Sciences (RSES). Amino acid racemisation

(AAR) samples were prepared and analysed by students at the University of

Wollongong under the supervision of Colin Murray-Wallace.

3.2.1 Aging the Otoliths

For this project one of the main goals was to obtain high resolution

geochemical data from across the otolith age rings in order to reconstruct water

conditions experienced over the course of each fish’s life. It was therefore vital

to be able to recognise and record otolith age lines and to relate isotopic and

elemental abundance measurements to these. The most common and well

established method for aging otoliths described in the literature involved

embedding otoliths in epoxy resin and then cutting 0.5mm thick slices from the

centre section. These were then examined under a microscope and those closest

to the nucleus were mounted onto microscope slides. For aging the thin

sections were viewed under a transverse light microscope and annual marks in

the form of coupled light and dark bands were counted (Anderson et al. 1992:

116).

A main concern when preparing otoliths for this study was that if thin sections

were taken straight away they would not provide enough otolith for sampling

for geochemical analyses. Instead, otoliths were cut transversely though the

nucleus using a diamond edged saw and again at 5mm towards the ventral axis.

This centre section was then embedded in epoxy resin and the side closest to

the nucleus was polished. The left over otolith parts were packaged separately

for radiocarbon dating and AAR. High resolution photographs of the transverse

56

faces were taken and an initial age assessment made. After all other analyses

were completed the thin sections of these faces were developed and placed on

microscope slides. These thin sections were then aged under the supervision of

Mark Jekabson, an ecologist with the ACT Parks, Conservation and Land,

following the method of Anderson et al. (1992) and Stuart (2006). Younger

fish bands were easily counted along the dorsal-ventral axis but for older fish,

the bands across the proximal face on either side of the medial groove were

most visible. A band was counted as an annual mark if it could be seen on both

sides of the medial groove (Figure 3.1).

Sources of error in the first aging from photographs were due to difficulty in

identifying the nucleus and the last full year of growth which was remedied

when thin sections were obtained. The main concern with the thin section

Figure 3.1: Transverse thin section through the nucleus of the left

sagittal otolith of an M. ambigua individual aged to ≈16 years. Dots are

representative of annual bands and triangles are false bands.

(da=dorsal apex; df=distal face; mg=medial groove (sulcus); n=nucleus;

o =opaque material along dorsal-ventral axis; pf=proximal face;

t=translucent band; va=ventral apex, from Anderson et al (1992).

57

aging was loss of otolith layers during the preparation procedures for laser

ablation and SHRIMP-SI spot sampling not to mention the preparation of the

thin sections themselves these and other sources of concern are further

discussed in Chapter 5 (Discussion).

3.2.2 Radiocarbon Dating

The fundamentals of radiocarbon dating have been described in Chapter 2. The

amount of radiocarbon in the otoliths was measured using the accelerator mass

spectrometer (AMS) at the RSES. The preparation of otoliths was conducted

by myself and Rachel Wood. We followed the procedures outlined in the ANU

radiocarbon lab protocols for the pre-treatment and graphitization of carbonate

samples.

3.2.2.1 Sample Pre-treatment

Firstly all samples were weighed. Then the outer coating of samples was

removed using a handheld tungsten carbide drill followed by an acid leach to

ensure any surface contaminants were removed. The procedure for the acid

leach involved submerging each sample within 2ml of 0.01N HCl to remove

10% of the sample surface. Samples were flushed with MilliQ water before

being dried and re-weighed. Orthphosphoric acid was then used to acidify the

carbonate samples to produce CO2 gas.

3.2.2.2 Graphitisation of CO2

For AMS analysis the CO2 generated from the samples needed to be converted

into graphite. At ANU a graphitisation line with the ability to load multiple

58

samples of CO2 into separate reactors was used. The graphitisation line is a

vacuum line constructed from stainless steel valves and ultratorr fittings (see

Figure 3.2).

The vacuum on the line is achieved by connection to a rough pump and a turbo

pump. The line was preconditioned following the ANU radiocarbon lab

procedures. Before any samples were loaded the line was flushed with H2.

Then samples were added with a syringe needle. Opening the valve to a water

trap, and then to the vacuum enabled the evacuation of the adaptor and the

needle. The CO2 was then dried using a dry ice trap and transferred along the

line using a glass dewar containing liquid nitrogen which froze down the CO2.

Each CO2 sample was then transferred to a graphitization reactor containing

Mg(ClO4)2. Hydrogen was then added to twice the concentration of the CO2

and heaters set at 570°C were placed on the iron containing portion of the

reactors. This drove the reaction: CO2+2H2 →C+2H2O. Any H2O formed

during this reaction was taken up by the Mg(ClO4)2, thus preventing its

interference in graphite formation.

Figure 3.2: A diagram of the graphitisation line used at the RSES

radiocarbon labs taken from ANU Protocol handbook.

59

3.2.2.3 Calibration and modelling

Radiocarbon dates were calibrated using the online Oxcal program (Bronk

Ramsey 2008, Bronk Ramsey 2009a, Bronk Ramsey 2009b) and the Intcal09

calibration curve (Reimer et al. 2009). This program also enables the building

of chronological models which involve both absolute dates and knowledge of

the site stratigraphy. A Bayesian model was applied to the calibrated samples

in order to further constrain the dating of the sites by taking into account the

single phase of sediment accumulation. The hearths were observed to have

been covered by a single phase of sediment accumulation with hearth #926 at

the bottom and hearth #982 at the top. These were entered into the model as the

start and end boundaries of occupation at the site. An outlier model was then

applied to identify any samples which did not fit due to being substantially

older or younger than the maximum age range. All modelling data can be

found in the Appendices.

3.2.3 Amino Acid Racemisation

Samples of each otolith were sent to the AAR laboratory at the University of

Wollongong and were prepared and analysed under the supervision of

Professor Colin Murray-Wallace. Preparation for analysis followed the

procedures of the ‘University of Wollongong Amino acid Geochronology

Laboratory Sample Preparation and Laboratory Procedures guidelines’.

3.2.3.1 Pre-treatment procedures

Due to the small size of the otolith samples and their pure appearance it was

deemed unnecessary to do an initial ultrasonic clean but an acid etch was

60

conducted to remove any adhering cements or grains. Approximately 33% of

the carbonate mass was digested, as per the lab guidelines. Specimens were

then hydrolysed for 22h at 110°C in c. 7 M HCl. Then the samples were

rehydrated using a solution containing 0.01M L-homoarginine. The L-

homoarginine acted as an internal standard for calculation of the amino acid

concentrations of the samples. AAR measurements were undertaken using an

Agilent 1100 reverse phase, high-performance liquid chromotograph (RP-

HPLC) with a Hypersil C-18 column and auto injector, following the analytical

methods set out in Kaufman and Manley (1998). D/L values were determined

based on peak area calculations and analytical precision was typically better

than 3%.

3.2.4 Elemental and Isotopic measurements

3.2.4.1 HelEx laser system

The HelEx laser system is used for ablating in situ materials for the measuring

of elemental abundances by the Varian 820 MS Quadropole ICP MS, and of

isotopic ratios by the Neptune MC-ICP-MS. The laser cell was designed and

developed in house at the ANU RSES and consists of an argon fluoride

excimer laser that can be pulsed rapidly across a sample to gain high resolution

measurements of elements. It operates at a wavelength of 193 nm and has an

energy density of approximately 5 Joules per square centimetre for each pulse.

Otoliths were placed within the sample holder as seen in Figure 3.3.

61

Two laser tracks with a spot size of 50μm were run at 0.01mm per second on

each of the otoliths from the centre out to both of the ‘wings’ for collecting

elemental abundance ratios. For strontium isotope measurements an initial spot

size of 140μm was employed but this did not provide a high enough resolution

and so a spot size of approximately 85μm was run, more slowly, across one

side of each otolith face, from the centre to the ‘wing’. A description of the

ANU laser system can be found in the paper by Eggins et al. (1998).

3.2.4.2 Varian 820 Inductively Coupled Plasma Mass Spectrometer

(ICP-MS) for elemental concentration measurements

Secondary atomized and ionized particles from the laser are moved through the

Inductively Coupled Plasma (ICP) using argon as a carrier gas. These ions are

Figure 3.3: Otoliths mounted in sample holder for laser ablation. The

standards can also be seen with Davies reef coral in the top left and Nist

612 synthetic glass in the top right. Image courtesy of Les Kinsley.

62

accelerated, by a pumped vacuum system, through a cone orifice into an

expansion chamber. Ions are extracted through a skimmer cone and shaped and

focused by a series of ion lenses. The Varian-820 is a quadropole mass

spectrometer which means that the ion stream is filtered through four parallel

metal rods. The voltage of these rods can be changed to allow only ions of

certain mass to charge ratio through and into the detector (see Figure 3.4).

Measurements of the standards NIST 612 and a Davies Reef coral were taken

before and after each run. The elemental concentration of the pressed Davies

Reef coral standard can be found in Alibert et al. (2003). Analysis of the

elemental data obtained from the Varian involved making a background

subtraction, determining the ratios of different elements to calcium, making a

drift correction and calibrating results against the standards. The majority of

this was done using Excel, Kaleidograph and a MATLAB program, which also

smoothed out peaks in the data caused by large particles entering the gas lines.

Figure 3.4: Schematic diagram of the components of a Quadrupole

ICP-MS. Taken from: http://icpms.ucdavis.edu/)

http://icpms.ucdavis.edu/

63

3.2.4.3 The Neptune Multi-Collector Inductively Coupled Plasma

Mass Spectrometer (MC-ICP-MS) for strontium isotope measurements

In order to gain high resolution strontium isotope ratios this study made use of

the Neptune MC-ICP-MS. The Neptune operates in similar manner to the

Varian 820 ICP-MS and is hooked up to the same HelEx laser but uses a

different method to separate and count ions. As a magnetic sector mass

spectrometer the Neptune separates ions according to their mass to charge ratio

by dispersing them through a magnetic field. These ions are then sent through

the double focusing section where they are collected and counted in a number

of Faraday cups each tuned to a specific ionic mass (Figure 3.5).

Figure 3.5: Schematic diagram of the Neptune MC-ICP-MS

Taken from: http://www.textronica.com/msline/neptune_scheme.jpg)

http://www.textronica.com/msline/neptune_scheme.jpg

64

Faraday cups were set to collect masses: 83(Kr), 83.5, 84(Sr+Kr), 85 (Rb), 86

(Sr+Kr), 86.469, 87 (Sr+Rb) and 88 (Sr). The half masses were set to monitor

for rare earth elements but none were identified and so corrections for these

were not necessary. The main potential interfering factor was Kr and so this

was monitored, measured and corrected for. A tridacna shell was used as a

standard and was measured ten times at the beginning and end of the analyses.

An initial gas blank was also taken to gain a background subtraction

measurement for 86

Sr/88

Sr. Excel was again employed as the main graphing

program.

3.2.5 Sensitive High Resolution Ion Micro Probe - Stable Isotope

(SHRIMP - SI) Oxygen isotopes

In the preliminary study of fish otolith oxygen isotopes by Katarina Boljkovac

(2009) the SHRIMP II was utilised. The SHRIMP-SI is the next generation of

SHRIMP II dedicated solely to the measurement of stable isotopes of low

mass. SHRIMP analysis begins by bombarding the target surface with high

energy primary ions, leading to the ejection of secondary ions. The ion beam

extracts around 2ng of sample at a time leaving a small pit on the surface 40

μm in diameter. Ionized secondary particles fly into the high resolution mass

spectrometer where they are separated according to their mass to charge ratio.

The energy analyser separates the ions according to their energies and then a

large magnet separates them according to mass. The ions to be measured (18

O

and 16

O) are directed into the Faraday cups in the Collector (see Figure 3.6).

65

3.2.5.1 SHRIMP sample preparation

After laser ablation the otoliths were wet-polished to remove laser cuts and

then dried in a 60 ºC oven overnight. They were then cut out and remounted

into the smaller mould sizes required for use in the SHRIMP SI along with the

two standards (NBS18 calcium carbonate and NBS19 Limestone 8544). The

polished surface was then covered by a thin layer of aluminium and placed in

the metal fittings needed for mounting in the SHRIMP-SI. Eight of the ten

otoliths were chosen for oxygen isotope measurements based on their hearth

locations and the elemental abundance information gathered. Three from hearth

#926, two from #952, two from #953 and one from the top hearth of the

Figure 3.6: Schematic diagram of the components of the SHRIMP-SI

taken from the RSES website:

http://shrimp.anu.edu.au/shrimp/instruments_shrimpsi.php

http://shrimp.anu.edu.au/shrimp/instruments_shrimpsi.php

66

sequence #982. A printed visual reference of each otolith as they appeared

under the SHRIMP-SI camera was used to create a map of spots taken.

Between 30 and 65 spots were taken 40μm apart towards either the dorsal or

ventral axis starting from the outer edge and moving in towards the nucleus

(Figure 3.7). This was done to ensure all later years of growth were sampled.

Spots were taken and dark areas on samples were avoided as sources of

possible contamination.

3.2.5.2 Analysis of Oxygen isotope ratios

Final analysis of oxygen isotope results involved graphing isotopic ratios

against otolith age lines using Excel and then comparing these graphs for

otoliths in the same hearth going back from time of death. The oxygen isotope

Figure 3.7: SHRIMP-SI spots taken from the dorsal edge of otolith

#926-1 and into the nucleus.

3mm

67

ratios measured by the SHRIMP SI are presented as delta values (δ) given in

parts per mill (‰). δ18

O values were determined by the international accepted

formula (Hoefs 2004: 24).

Where Rspl = 18

O/16

O ratio of the sample and Rstd= 18

O/16

O ratio of the

standard.

68

Chapter 4

Results

This chapter presents the results from otolith aging and geochemical analyses

including radiocarbon dating, AAR, measurements of oxygen and strontium

isotopes and of Sr/Ca and Ba/Ca ratios. Error bars have been removed from the

graphs presented here as they obscured the presentation of track lines. Any

points of excessive deviation were not plotted in the graphs. Otoliths #926-2

and #1168-9 were excluded from oxygen isotope analysis due to time

constraints.

4.1 Otolith Aging

According to the results of otolith aging in this study, the majority of fish have

been identified to be between 10 and 12 years of age at death. The age lines

relating to later years of fish growth are much thinner than the earlier years,

particularly in the older otoliths, and as such were difficult to identify and

easily damaged. In all the otoliths, growth layers showed different levels of

preservation around the otolith surface which made aging of some areas easier

than others. In this study thin sections were made after analyses were

completed. This meant that due to preparation procedures such as polishing and

cutting, small sections of the otoliths’ outer layers were chipped away (see

Figure 4.1).

69

The outer ring of each otolith was incomplete, meaning that each fish died part

of the way through their last year of growth. An attempt was made to

determine season of capture but due to the thin size of outer otolith layers and

slight loss of material during thin section preparation this was not possible (see

Figure 4.1). Recommendations for avoiding these inconsistencies between

aging and analysis will be presented in Chapter 6 (Conclusions and Future

Recommendations).

4.2 Radiocarbon Dating

Radiocarbon results from the AMS were calibrated using the online Oxcal

program (Bronk Ramsey 2008, Bronk Ramsey 2009a, Bronk Ramsey

2009b)and Intcal09 curve (Reimer et al. 2009). The calibrated radiocarbon

dates are all very closely associated as can be seen in Table 4.1. Dating of

Figure 4.1: The overlayed images of otolith #926-3, thin section and

SHRIMP SI spots, showing the loss of outer layers between when

samples were taken and when otoliths were aged.

70

otolith #953-5 found it to be quite a lot younger than the others in the sample

and so was removed from modelling as an outlier.

4.3 Amino Acid Racemisation (AAR)

The AAR results are presented in Table 4.2 as D/L ratios for each amino acid

compared to the mean radiocarbon ages (cal BP) obtained for each otolith. The

D/L ratios for the younger otolith #953-5 were indistinguishable from those of

the other otoliths. The close association of these otoliths found by radiocarbon

dating was not observable in the D/L ratios which showed a much broader

scatter. The amino acids measured were aspartic acid (ASP), glutamic acid

(GLU), serine (SER), alanine (ALA), valine (VAL), phenylalonine (PHE),

isoleuceine (ILE) and leucine (LEU).

Table 4.1: The results from radiocarbon dating of the ten otoliths from

hearths #926, # 952, # 953, #982 and #1168

71

Table 4.2 AAR D/L values, their means and standard deviations alongside the mean radiocarbon dates

ASP GLU SER ALA VAL PHE ILE LEU

sample no. Area Area Area Area Area Area Area Area Radiocarbon (mean cal BP)

926-1 0.618 0.277 0.618 0.389 0.2 0.698 0.269 0.291 19257

926-2 0.519 0.227 0.506 0.424 0.147 0.433 0.226 0.17 19186

926-3 0.508 0.205 0.488 0.382 0.196 0.402 0.192 0.229 19161

926-4 0.503 0.206 0.532 0.39 0.202 0.421 0.213 0.232 19263

953-5 0.532 0.215 0.588 0.383 0.232 0.504 0.235 0.267 13656

953-6 0.536 0.222 0.451 0.36 0.162 0.478 0.234 0.145 19236

952-7 0.513 0.207 0.503 0.384 0.132 0.386 0.2 0.189 19177

952-8 0.592 0.272 0.54 0.544 0.171 0.528 0.276 0.268 19181

1168-9 0.463 0.187 0.417 0.34 0.115 0.319 0.172 0.127 19180

982-11 0.507 0.241 0.505 0.426 0.183 0.457 0.229 0.222 19254

mean (not including #953-5) 0.5291 0.2259 0.5148 0.4022 0.174 0.4626 0.2246 0.214

std dev (not including #953-5) 0.042733 0.027934 0.056219 0.053132 0.033935 0.09718 0.03066 0.052113

72

4.4 Results from SHRIMP-SI, LA-ICP-MS and LA-MC-ICP-

MS

The results from SHRIMP-SI spot sampling, LA-ICP-MS and LA-MC-ICP-

MS tracks are presented in the following section. As there were only ten

otoliths analysed in this study all graphed results are presented here instead of

in the appendices. Results for each analytical method are shown above an

image of the associated tracks or spots on the otolith surface (see Figure 4.2-

4.11). Following this will be a brief written description of the key features of

the results from each type of analysis and a summary of the main trends

overall.

73

0.0

4.0

8.0

12.0

16.0

20.0

0

0.02

0.04

0.06

0.08

0.1

01234567891011

Elemental abundances

Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mol)

Ba/C

a (mm

ol.m

ol)

Age (years)

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800

#926-1

87S

r/8

6S

r

Figure 4.2: Otolith #926-1 results for oxygen isotope

analysis and associated SHRIMP spots (A, B),

Strontium isotopes and associated track (C, D), Sr/Ca

and Ba/Ca ratios and associated track (E, F)

A

B

C

D

E

F

74

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1,0501,1001,1501,2001,2501,300

Elemental Abundances

Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mo

l)

Ba/C

a (mm

ol.m

ol)

Time (seconds)

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800

#926-2

87S

r/8

6S

r8

7S

r/8

6S

r

Figure 4.3: Otolith #926-2 results for measurements of Sr/Ca and Ba/Ca ratios (A) track line on otolith (B) and strontium isotope ratios

(C) measured on the same track

A

B

C

75

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0

0.05

0.1

0.15

0.2

0.25

0.3

01234567891011


Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mol)

Ba/C

a (mm

ol.m

ol)

Age (years)

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800

#926-3

87S

r/8

6S

r

Figure 4.4: Otolith #926-3 oxygen isotope ratios and

associated SHRIMP spots (A, B), Strontium isotopes

and associated track (C, D), Sr/Ca and Ba/Ca ratios

and associated track (E, F).

A

B

C

D

E

F

76

0.0

5.0

10.0

15.0

20.0

0

0.05

0.1

0.15

0.2

0123456789


Sr/Ca

Ba/Ca

Sr/

Ca (

mm

ol.

mol)

Ba/C

a (m

mol.m

ol)

Age (years)


measurements and associated SHRIMP spots (A, B), Sr/Ca and

Ba/Ca ratios and associated track (C, D) Strontium isotopes (E)

and same track as elemental.

A

B

C

D

E

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0123456789Ages (years)

#926-4

87S

r/8

6S

r

77

0.0

5.0

10.0

15.0

20.0

25.0

0

0.08

0.16

0.24

0.32

0.4

012345678910

Elemental AbundancesSr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mo

l)

Ba/C

a (mm

ol.m

ol)

Age (years)

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

012345678910Age (years)

#953-5

87S

r/8

6S

r

A

B

C

D

E Figure 4.6: Otolith #953-5 results for oxygen isotope

measurements and associated SHRIMP spots (A, B),

Sr/Ca and Ba/Ca ratios and associated track (C, D)

strontium isotopes (E) for the same track.

78

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700

#952-6

87S

r/8

6S

r

0.0

1.7

3.3

5.0

6.7

8.3

10.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0123456789


Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mo

l) Ba/C

a (mm

ol.m

ol)

Age (years)


measurements and associated SHRIMP spots (A, B), strontium

isotopes and associated track (C, D), Sr/Ca and Ba/Ca ratios and

associated track (E, F).

A

B

C

D

E

F

79

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700

Time (seconds)

#953-7

87S

r/8

6S

r

0.0

3.2

6.4

9.6

12.8

16.0

0

0.05

0.1

0.15

0.2

0.25

0.3

012345678910


Sr/Ca

Ba/Ca

Sr/

Ca (

mm

ol.

mol) B

a/C

a (m

mol.m

ol)

Age (years)


measurements and associated SHRIMP spots (A, B),

strontium isotopes and associated track (C, D), Sr/Ca and

Ba/Ca ratios and associated track (E, F).

A

B

C

D

E

F

80

0.0

2.0

4.0

6.0

8.0

10.0

0

0.04

0.08

0.12

0.16

0.2

01234567


Sr/Ca

Ba/Ca

Sr/

Ca (

mm

ol.

mol) B

a/C

a (m

mol.m

ol)

Age (years)


measurements and associated SHRIMP spots (A, B), Sr/Ca

and Ba/Ca ratios and associated track (C, D), Strontium

isotopes (E) for the same track.

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

01234567

Age (years)

#953-8

87S

r/8

6S

r

A

B

C

D

E

81

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

2,2502,3002,3502,4002,4502,500


Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mol)

Ba/C

a (mm

ol.m

ol)

Time (seconds)

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800900

#1168-9

87S

r/8

6S

r

Figure 4.10: Otolith #1168-9 results for Sr/Ca and Ba/Ca ratios (A), otolith surface before all analysis with a broken line

showing approximate position of laser track (B) and strontium isotopes (C) taken along the same track.

A

B

C

82

0.0

3.3

6.7

10.0

13.3

16.7

20.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0123456789101112


Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mol)

Ba/C

a (mm

ol.m

ol)

Age (years)

Figure 4.11: Otolith #982-11 results from oxygen isotope

measurements and associated SHRIMP spots (A, B), Sr/Ca and

Ba/Ca ratios and associated track (C, D) and Strontium isotopes

(E) from along the same track

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0123456789101112Age (years)

#982-11

A

B

C

D

E

83

4.4.1 Oxygen Isotope Ratios

The results from SHRIMP-SI oxygen isotope measurements showed errors of

less than 0.3‰ for each sample spot. More spots were able to be taken from the

earlier years of otolith growth compared to the later smaller age rings. Thus

when looking at the graphs of oxygen isotope ratios it is necessary to be

mindful that the later ratios are an average of those years and each spot may be

related to different seasonal growth periods. The lack of fluctuations in later

years compared to early ones is more likely the result of technological

limitations for sampling, than the absence of such variations. It is interesting to

note that the majority of otoliths show a marked increase in oxygen isotope

ratios towards their final years of life.

4.4.2 Elemental Abundances

Fluctuations in Sr/Ca and Ba/Ca ratios have shown in past and recent otolith

studies (Elsdon and Gillanders 2004, Collingsworth et al. 2010, Gillanders and

Munro 2012) to vary with environmental conditions and ambient

concentrations and as such are the main focus of this study. Sr/Ca and Ba/Ca

measurements are reported as ‘mmol.mol’ and are all plotted against years of

otolith growth except in the case of otoliths #926-2 (Figure 4.3 A) and #1168-

9 (Figure 4.10 A) which are graphed against measurement time (seconds) due

to the difficulty in associating tracks with age lines. When Sr/Ca and Ba/Ca

ratios were graphed together different scales were used to take into account the

much lower amount of Ba/Ca. The y-axes are scaled to best show trends and

deviations between the Ba/Ca and Sr/Ca.

84

As with the oxygen isotope ratios, a higher resolution of elemental ratios were

able to be measured within the larger ringed early years of otoliths compared to

the thinner later ones. The LA-ICP-MS was able to take a higher number of

samples from within each age ring compared to the SHRIMP-SI and therefore

achieved a higher resolution of sampling overall. In addition, each elemental

ratio was measured at the same time and so fluctuations between Sr/Ca and

Ba/Ca ratios on the same track are closely associated and not affected by

difficulties in matching age lines to analysis. All the otoliths showed

differences in the Sr/Ca and Ba/Ca ratios of their early years compared to their

later years with the majority showing a marked increase in ratios in later years.

4.4.3 Strontium Isotope Ratios

An eleven point running mean was taken for the 87

Sr/86

Sr ratios and these were

graphed against measurement time due to difficulty in associating them with

otolith age lines. The exceptions to this were otoliths #926-4 (Figure 4.5 E),

#953-5 (Figure 4.6 E), #952-8 (Figure 4.9 E) and #982-11 (Figure 4.11 E)

where 87

Sr/86

Sr ratios could be related to age lines and were graphed

accordingly. All 87

Sr/86

Sr ratios drop to a value of 0.7126 not long before the

edge of each otolith except for otolith #1168-9 (Figure 4.10 C) which rises

from 0.7126 at the beginning of the track and never drops back down. Otoliths

#926-1 (Figure 4.2 C), #926-3 (Figure 4.4 C) and #926-4 (Figure 4.5 E) also

show a rise from 0.7126 in the early section of the track before flattening out

and then returning to this value later on. Slight rises after this are most likely

due to the laser cutting into the resin.

85

Four of the eight otoliths, #926-4 (Figure 4.5 E), #953-5 (Figure 4.6 E), #952-8

Figure 4.7 E) and #982-11 (Figure 4.11 E) had LA-MC-ICP-MS tracks taken

on the same side as SHRIMP-SI spots and LA-ICP-MS tracks and so are more

closely relatable to these. No interference was noted for Krypton and no rare

earth elements were found, so no correction for this was needed. Any effect of

machine drift was corrected internally.

4.4.4 Summary of Results

The results from geochemical analyses of the individual otoliths showed a

number of interesting trends. Oxygen isotope ratios of the majority of otoliths

increased in the later years as did Sr/Ca and Ba/Ca ratios. Slight dips in the

strontium isotopes concurrently with rises in oxygen and/or elemental ratios in

a number of the otoliths seem to indicate a change in location and/or water

composition. These results will be placed within the context of each hearth site

and discussed in relation to what information they provide about the

occurrence of evaporative conditions at Lake Mungo, possible temperature

fluctuations and fish migration in the following chapter (Chapter 5 Discussion).

86

Chapter 5

Discussion

This chapter begins with a re-evaluation of the sampling strategy employed in

this study. The main concerns are how successful it was for associating fish

otolith geochemical records with human occupation and allowing for an

assessment of dating and geochemical techniques. The main area for potential

error in this study is the association of otolith age lines with the analytical data.

This will be discussed in terms of how small age offsets affect the dataset.

After investigating the potential sources of error, an assessment of the

chronological information obtained from the otoliths will be made with respect

to the chronology of the site. The results of AAR D/L ratios will be compared

to the radiocarbon dates. Then the geochemical assays taken across the age

lines of the otoliths will be discussed in terms of the environmental conditions,

temperatures and migration events they record. Special attention will be given

to the multiple otoliths from hearth sites #926 and #952 as these fish are likely

to have died at the same time and should therefore have comparable isotopic

and elemental histories since they entered Lake Mungo. These will also be

used for identifying inconsistencies within elemental and isotopic ratios and

radiocarbon dating results. This will be followed by discussions of the results

from the individual otoliths, mainly concerning whether or not they show

similar trends to those of hearths #926 and #953 and how this relates to the

palaeoenvironmental conditions associated with human occupation of the area.

87

5.1 Sampling Strategy

The main aim of this study was to assess the usefulness of geochemical

analyses of fish otoliths for determining environmental conditions surrounding

human occupation and for placing these within the chronology of the site. The

sampling strategy described in Chapter 3 (Methodology) was based on similar

dating and geochemical information being obtained from otoliths in the same

hearth. The radiocarbon dating was able to be assessed using this strategy of

comparing the results of otoliths from the same hearth which showed close

relationships. In order to compare the Sr/Ca, Ba/Ca and oxygen isotope ratios

across the age lines of the otoliths, there needed to be the identification and

sampling of the last year of growth which is indicative of time of death.

This proved to be more difficult than expected and sources of error in

identifying the final layers of growth could throw off comparisons of

geochemical assays within and between otoliths of the same hearth site. The

ability to identify the last year of growth is hindered by loss of layers during

preparation for geochemical assays and original preservation at the site. When

both SHRIMP-SI spots and LA-ICP-MS tracks were obtained they were taken

across the same side of each otolith but covered slightly different areas as, for

example, seen in Figure 5.1 for otolith #926-4 (images of these for the other

otoliths can be found in the Appendices). The Sr/Ca and Ba/Ca measurements

were taken at the same time, so there is no offset between these data sets. The

strontium isotopes are also closely associated with the elemental abundances in

otoliths #926-4, #953-5, #952-8 and #982-11 because they were taken along, or

right next to, the same track. Because it is necessary when using the SHRIMP

88

SI to have a level sample surface it was necessary to polish otoliths after laser

ablation. Therefore, this may have affected the association of oxygen isotope

ratios with elemental and strontium isotope due to erosion of age-lines.

Oxygen isotope ratios were measured on the same side of the otolith as

elemental and strontium ratios but along a different transect with a different

machine. This means that the oxygen isotopes and elemental abundances may

have been measured across different age lines particularly in the later growth

years.

5.2 The Site Chronology

The archaeological evidence for human occupation across the Lake Mungo

lunettes is sporadic and although it occurs within sedimentary units that have

been assigned broad approximate ages, dating of the human occupation events

themselves could assist in building up more detailed chronological record.

Figure 5.1 Otolith #926-4, showing laser tracks, marked with black

dashes, SHRIMP-SI, black spots, and the otolith age lines for #926-4,

marked in blue.

89

5.2.1 Radiocarbon Dating

The results from radiocarbon dating and calibration show that nine of the ten

otoliths are closely related to within a 500 year time span from 19405-18913

cal BP. Those from within the same hearth site showed very close ages except

for hearth #953 where otolith #953-5 was found to be around 6,000 years

younger confirming the suspicion that it was out of context. This suggests that

the otolith dates are also those of the hearths except for #953-5. The close

associations of the hearths are best presented in the modelled image as shown

in Figure 5.2. A t-type outlier model was used, and all dates are assumed to

have a prior outlier probability of 5% (Bronk-Ramsey 2009b). With the

exception of the anonymously young date otolith 953-5 (ANU-27810), all

dates were found to have a <5% chance of being an outlier by the model.

Otolith 953-5 was excluded from the modelled image. A weighted average of

the two dates from 926-3 was used for this model. These dates place the

hearths in association with a later phase of sediment accumulation within the

bracketing OSL dates (14,500 and 25,500 years) for this unit. Humans were

occupying the shorelines of, and taking fish from the water of, Lake Mungo

near the end of the LGM (21-17ka), a time when the lakes were previously

thought to have dried out completely (Bowler 1998, Stern et al. in press). This

also coincides with the recent high concentration of radiocarbon dates from

surface collected otoliths placing them at 21-17ka (Bowler et al. 2012). The

lack of in situ otoliths being dated previously has led to difficulties in

associating human occupation with this time period but the otoliths from this

study now provide a link between them and the occurrence of water in the lake.

90

5.2.2 AAR

The AAR D/L ratios obtained from the otoliths were calibrated against the

radiocarbon dates. Figure 5.3 shows the AAR D/L ratios plotted against the

radiocarbon ages for the older otolith samples. The AAR results scatter widely

amongst these closely associated dates.The valine (VAL) D/L ratios are the

only ones to show a distinction between the very young otolith (953-5) and the

older otoliths but this is in the opposite direction than expected; D/L ratios for a

younger sample should be smaller (see Figure 5.4). These results indicate that

Figure 5.2: Radiocarbon dates have been calibrated against IntCal09

(Reimer et al 2009) and modelled as a single phase using Oxcal v4.2

(Bronk-Ramsey 2009b).

91

the application of AAR to fish otoliths is not a useful technique for gaining

detailed information about the chronology of human occupation in this

sedimentary sequence.

Figure 5.3: AAR results plotted against mean radiocarbon ages

excluding the youngest samples (#953-5).

0.1

0.2

0.3

0.4

0.5

0.6

0.7

19,160 19,180 19,200 19,220 19,240 19,260

AAR vs Radiocarbon

ASP

GLU

SER

ALA

VAL

PHE

ILE

LEU

D/L

rat

ios

Radiocarbon (Cal BP)

Figure 5.4: AAR results for Valine plotted against mean radiocarbon

ages for each otolith

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

13,000 14,000 15,000 16,000 17,000 18,000 19,000 20,000

VAL vs Radiocarbon

VAL

D/L

rat

ios

Radiocarbon (Cal BP)

92

5.3 Otolith Geochemistry, Environmental conditions and Fish

Migration

This section of the discussion will deal with how the geochemical records

obtained from each otolith can be used to infer evaporation, temperature and

migration experienced over the course of each fish’s life. A basic model has

been constructed from the experimental studies on lab reared fish described in

Chapter 2 (Background). Oxygen isotope ratios in fish otoliths are strongly

related to ambient water ratios but also experience a temperature effect leading

to higher oxygen isotope ratios deposited in colder conditions and lower under

warmer conditions (Elsdon and Gillanders 2002, Faure and Mensing 2005).

Strontium and barium are deposited in association with ambient concentrations

and are also affected by temperature with higher temperatures leading to higher

ratios of both Ba/Ca and Sr/Ca in studies of freshwater fish (Collingsworth et

al. 2010).

Within each hearth site the otoliths are dated quite close together except for

hearth #953. The two otoliths from this hearth will be treated as separate finds

with #953-6 being most likely related to the hearth, whilst #953-5 is out of

context (see above). For consistency and practicality, trends in the graphed

oxygen isotope and elemental abundance ratios across the age lines of the fish

otoliths will be referred to in terms of years before death (ybd).

5.3.1 Hearth #926

The otoliths from hearth #926 show increasing trends in oxygen isotope ratios

in the years leading up to each fish's death. The point at which this trend starts

93

differs with #926-4 showing an increase in ratios beginning 6 ybd. Otolith

#926-3 shows a more gradual rise from 7 ybd and #926-1 showing a staggered

increase from around 8 ybd (see Figure 5.4 A). They all reach a similar point at

5 ybd and continue in close association up to the assumed mutual time of

death.

Figure 5.5: Comparison of the oxygen isotope ratios from three of the

otoliths from hearth #926 (A), Sr/Ca ratios (B) and Ba/Ca ratios (C).

The numbers in brackets are the ages for otolith #926-4. Otolith edge is

on the left.

0.0

5.0

10.0

15.0

20.0

01234567891011

Hearth #926

Sr/Ca ratios

Otolith 1

Sr/

Ca

(m

mo

l.m

ol)

Ages (years)

Otolith 3

Otolith 4

0.00

0.05

0.10

0.15

0.20

0.25

0.30

01234567891011

Hearth #952

Ba/Ca ratios

Otolith 1

Ba

/Ca

(m

mo

l.m

ol)

Ages (years)

Otolith 3

Otolith 4

A

B

C

94

Oxygen isotope incorporation into fish otoliths is mainly reliant on the ambient

oxygen isotope ratios of the water. Increases in otolith oxygen isotopes are

either due to an evaporative trend causing greater concentration of 18

O over 16

O

or cooler temperatures. From the oxygen isotopes alone an interpretation could

be made whereby entry into Lake Mungo is represented by the start of

increasing geochemical trends. This would indicate that #926-1 and #926-4

entered Lake Mungo at 6ybd and #926-3 entered slightly earlier.

The oxygen isotope ratios may appear to be more closely related to each other

than the elemental abundances because only one or two spots were obtained as

representative of the whole year where as more samples were taken for

elemental analysis. The oxygen isotopes ratios are only an average of the

composition of the water for the later years but more detail is found in the

elemental ratios.

For the otoliths of hearth #926 increasing ratios of Ba/Ca and Sr/Ca are

recorded in the last years of growth (see Figure 5.4 B and C) but there are

points where the Sr/Ca ratios of the otoliths deviate substantially in the years

when the fish are supposedly in the same body of water. Otolith #926-3 and

#926-4 show an increase in Sr/Ca ratios at 3 ybd. Otolith #926-1 shows an

increase in Sr/Ca ratios from around 4 ybd and this meets the ratios for #926-3

and #926-4 briefly at 2 ybd before continuing to increase. There is also an

increase in otolith #926-1 Sr/Ca measurements at 5 ybd which is not seen in

otolith #926-3 and only related to a slight increase in #926-4. If the timing of

each fish’s entry into Lake Mungo is at the point of increase in oxygen isotopes

then either there is a delay in the effect of changed conditions on the Sr/Ca

95

ratios or entry is recorded more closely by the Sr/Ca ratios. Either way, there

are differences in the levels of oxygen isotope and Sr/Ca ratios in the years

when fish are supposed to be in the same body of water. This may be down to a

physiological effect that varies between the fish or it could be due to the

difficulties in identifying age lines and associating these to laser tracks and

SHRIMP SI spots.

In the Ba/Ca ratios there is a slight increase from around 4ybd but this is a less

noticeable rise than in the Sr/Ca and oxygen isotope ratios. In contrast to the

Sr/Ca ratios, where otolith #926-3 and #926-4 showed close associations, there

is instead a close relationship between Ba/Ca for otoliths #926-1 and #926-4.

Otolith #926-3 shows an increase in Ba/Ca at 4 ybd and then fluctuating ratios

up until death. Although both #926-1 and #926-4 also meet and increase from 4

ybd they do not increase to the same levels or show the same fluctuation

intensities. The increasing concentration of elements along with oxygen

isotopes supports the interpretation of an evaporative trend taking place.

Pinpointing fish entry into Lake Mungo or interpreting further detail into

environments and fish movements is more difficult given the concerns

associated with the identification of age lines. Further discussion of migration

can be found later in this chapter with a comparison of the Sr isotope ratios

across each of the otoliths.

96

5.3.2 Hearth #952

Hearth #952 is the only other hearth from which multiple otoliths of the same

radiocarbon age were obtained. The oxygen isotope ratios from these two

otoliths show an increasing trend in later life from around 3 ybd (see Figure

5.6). If migration into Lake Mungo is implied by the increase in oxygen

isotopes then #952-7 enters Lake Mungo just before #952-8. One problem with

this theory is that although the oxygen isotopes increase at a similar rate, there

is a lack of association between the actual values until the very last year of life.

This could be due to an aging offset, or the averaging of values across these

years or perhaps these fish were only concurrently in Lake Mungo from their

last year. It is unlikely that once the evaporation trend took hold that the fish

could have migrated and so it is more likely that the aging is inaccurate.

Turning now to the Sr/Ca and Ba/Ca ratios there are very similar Sr/Ca ratios

in the early fish years then a deviation at 3 ybd where #952-8 ratios increase

and #952-7 ratios stay low. At 1 ybd both otoliths show increasing Sr/Ca ratios

up to a similar point. Following this the Sr/Ca ratios for otolith #952-7 continue

to rapidly increase whilst those of #952-8 stay low. This could be the result of

the last growth layer being missed in otolith #952-8. The Ba/Ca ratios show the

same trend except that in both otoliths they end at a very similar point without

showing the last rapid increase for #952-7 as seen in the Sr/Ca ratios.

97

Figure 5.6: Comparison of the oxygen isotope (A) Sr/Ca (B) and

Ba/Ca ratios (C) of the two otoliths from hearth #952. The numbers

in the brackets are the ages for otolith #952-8. Otolith edge is on the

left.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

012345678910

Hearth #952

Sr/Ca ratios

Otolith 7

Sr/

Ca

(m

mo

l.m

ol)

Ages (years)

Otolith 8

0.00

0.05

0.10

0.15

0.20

0.25

0.30

012345678910

Hearth #952

Ba/Ca ratios

Otolith 7

Ba

/Ca

(m

mo

l.m

ol)

Ages (years)

Otolith 8

A

B

C

98

From these trends it can be inferred that the fish represented by otolith #952-8

experienced evaporative conditions from 3 ybd, as evident in the increasing

δ18

O, Sr/Ca and Ba/Ca ratios. #952-7 on the other hand has increasing Ba/Ca

and Sr/Ca from only 1ybd but oxygen isotope ratios increasing from 3 ybd.

#952-7’s entry into the lake may have occurred slightly later than that of #952-

8 thus causing the disparity between the two points of increase or there could

be an offset between these geochemical data sets. This offset could have been

be caused by the loss of the outer layer of growth, difficulties in identifying age

lines and in relating these to sampled areas.

5.3.3 Individual Otoliths

Of the other otoliths in this study #953-6 and #982-11 show increases in their

oxygen isotope, Sr/Ca and Ba/Ca ratios in their last years of life in a similar

fashion to those of hearths #952 and #926 (see Figure 5.5 and 5.6).

Otolith #953-6 shows an increase in oxygen isotope ratios and elemental

abundances from 1 ybd. Oddly there is a higher comparative increase in the

Ba/Ca and oxygen isotope ratios then in the Sr/Ca ratios (see Figure 5.7).

These are also the highest Ba/Ca ratios seen in the later years of all the otoliths

in this study. This could be a physiological effect where Ba/Ca is being taken

up more than Sr/Ca ratios or the water body began with a very low level of

Sr/Ca compared to Ba/Ca. In the early years of growth #953-6 has quite closely

associated Sr/Ca and Ba/Ca trends and the point of deviation is at 5 ybd. This is

also the point where the oxygen isotopes increase dramatically before falling

again at 4ybd. Without a comparative elemental and oxygen isotope dataset it

99

is difficult to make inferences about fluctuations aside from interpreting the

broad similarity of later year increase in geochemical ratios as seen in the other

otoliths from hearths #926 and #952. This fish experienced an evaporative

trend in later life and may have stayed in the river for a longer period than the

fish already described, only to move into Lake Mungo in its final year.

Figure 5.7: The oxygen isotope ratios (A) and Sr/Ca and Ba/Ca

measurements (B) taken across the age lines of otolith #953-6. Otoliths

edge is on the left.

0.0

1.7

3.3

5.0

6.7

8.3

10.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0123456789


Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mo

l) Ba/C

a (mm

ol.m

ol)

Age (years)

A

B

100

The oxygen isotope ratios measured across otolith #982-11 show an increase

from 7 ybd with slight drops at 5 ybd, 3ybd and a slight flattening between 1

and 2 ybd (see Figure 5.8).

The Sr/Ca ratios increase from 5 ybd and then follow the fluctuations of the

oxygen isotope ratios. Ba/Ca ratios stay fairly flat with a slight increase from 3

ybd. This point of difference could relate to a temperature change, given that

Ba/Ca is supposed to show an opposite effect of temperature to oxygen

isotopes. If the peaks prior to this major difference are all temperature events

0.0

3.3

6.7

10.0

13.3

16.7

20.0

0

0.05

0.1

0.15

0.2

0.25

0.3

0123456789101112


Sr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mol)

Ba/C

a (mm

ol.m

ol)

Age (years)

Figure 5.8: The oxygen isotope ratios and Sr/Ca and Ba/Ca ratios of

the otolith from hearth #982 Otolith edge is on the left.

A

B

101

then the lack of opposite action in the Ba/Ca ratios for these may be due to

problems with correct age line identification leading to an offset of a year or

so. There may also be a different temperature effect operating on the Ba/Ca

ratios for golden perch otoliths than those previously found in other fish.

Otolith #953-5 will only be briefly considered as it is an out of context sample

that has been dated to 6,000 years younger than the others in this study and

may not be related to a human occupation event. There is an increasing trend of

oxygen isotope ratios from around 7 ybd, which is followed by a sudden drop

in ratios at 3 ybd (see Figure 5.9). After this there is a final slight increase but

not to the same level as seen early in the fish’s life. This could be evidence of

the fish surviving an early evaporative trend which was then broken by floods

or it could be the results of a period of increased precipitation. This may have

allowed the fish to escape, only for it to enter Lake Mungo where another

slight evaporative trend occurred. As a surface find this otolith cannot be

directly associated with human occupation and it is possible that it was blown

by wind or moved by rain to its resting point on the dunes. It may not have

been fished but died of natural causes. Also it comes from a later period of

fluctuating lake conditions and without other reference samples for this time an

assessment of surrounding environmental conditions and migration cannot be

firmly established.

102

Figure 5.9: The oxygen isotope ratios (A) and Sr/Ca and Ba/Ca ratios of

otolith #953-5 (B) and strontium isotopes (C). Otolith edge is on the left.

0.0

5.0

10.0

15.0

20.0

25.0

0

0.08

0.16

0.24

0.32

0.4

012345678910

Elemental AbundancesSr/Ca

Ba/Ca

Sr/

Ca

(mm

ol.

mol)

Ba/C

a (mm

ol.m

ol)

Age (years)

A

B

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

012345678910Age (years)

#953-5

87S

r/8

6S

r

C

103

Otolith #1168-9 is the one outlier of this data set. Although it was found in a

hearth site and radiocarbon dates place it in close association with the other

hearths there is no evaporative trend evident in the elemental ratios as has been

found in the other otolith results. No oxygen isotope measurements were taken

from this sample due to time constraints and as such interpretation is based

solely on elemental abundances and strontium isotopes.

The Sr/Ca and Ba/Ca ratios of otolith #1168-9 show an opposite trend to all the

other otoliths in this study. The elemental ratios increase early in the fish’s life

and then follow a decreasing trend until death. Strontium isotopes start at

0.7126 and increase at a similar point to the decreases in the Sr/Ca and Ba/Ca

ratios. The maximum height reached in the Sr/Ca ratios is not as high as those

for the other otoliths in the study but the Ba/Ca ratios are in general higher

particularly in the early life. Higher Ba/Ca is often associated with freshwater

in studies of fish going between marine, estuarine and fresh environments

(Gillanders 2005). This fish may have started out in a freshwater environment

with large temperature effects or regular flood pulses. It could then have

entered an environment with lower levels of Ba/Ca. Either this fish was not in

Lake Mungo for the evaporative trend seen in the other otoliths at this time

period and was actively fished from a different lake not experiencing

evaporative conditions or it survived the evaporative trend and human fishing

at this time only to be caught later in the same lake. The strontium isotope

values suggest that the fish moved from one lake basin in early life,

characterised by the 0.7126 value, to a basin with a higher value in later life.

104

Without geochemical data from other otoliths from this hearth site or oxygen

isotopes from this otolith any interpretation remains speculative.

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800900

#1168-9

87S

r/8

6S

r

Figure 5.10: Otolith #1168-9 graphed elemental ratios, Sr/Ca and Ba/Ca,

(A) and strontium isotope values (B). The otolith nucleus is on the right

and otolith edge on the left.

0.0

5.0

10.0

15.0

20.0

0

0.05

0.1

0.15

0.2

0.25

0.3

2,2502,3002,3502,4002,4502,500


Sr/Ca

Ba/Ca

Sr/

Ca (

mm

ol.

mo

l)

Ba/C

a (m

mo

l.mo

l)

Time (seconds)

A

B

105

The increasing trends in oxygen isotope ratios seen in the majority of otoliths

seem to occur over a number of years. This implies that fish in Lake Mungo

were experiencing an evaporative trend for quite a number of years. It is

possible that even after this there was still plenty of water left in the lake.

Determining how much water was left could have implications for the theory

of fish being collected due to low lake levels causing sluggish behaviours

(Bowler, 1998). This would not be the case if Lake Mungo was still fairly full

of freshwater when fish were being collected and eaten. In order to test how

long a lake of this size would take to evaporate under a certain set of climatic

conditions an experiment could be conducted using current pan evaporation

observations for the area (see Bureau of Meteorology website, evaporation,

2012). This is beyond the scope of this research project but is a further

application for the oxygen isotope ratios measured here and will be

recommended as an area for further study (see Recommendations section of

Chapter 6).

5.4 Temperature Assessment

In each of the otoliths there are visible short term fluctuations in the oxygen

isotopes and Ba/Ca ratios in the early years of the fishes’ lives (see Figures 5.5-

5.10). In some cases the Sr/Ca ratios also fluctuate as seen in otoliths from

hearth #952 but not to the same extent as the Ba/Ca or oxygen isotope ratios.

Ba/Ca ratios are commonly higher in freshwater environments (Gillanders

2005) and the relatively high fluctuating values of the early years of these

otoliths may indicate a period of time when were in the river where seasonal

106

affects are the main controls over water composition and hence otolith

incorporation.

Peaks in the oxygen isotopes in the otoliths could be related to cooler water

temperatures whilst troughs may be related to hotter temperatures. There

should be an opposite affect for temperature recorded between the Ba/Ca and

oxygen isotopes but this is not the case in these results. Either there is an offset

associated with aging that has led to a presentation of similar fluctuations when

they are actually opposite or there is species specific association that has not

been identified in experimental studies. Even with studies into the effects of

temperature on the elemental and oxygen isotope composition of golden perch

otoliths it would still be very difficult to determine absolute past temperatures.

The main reasons for this are that we do not know the original composition of

the ambient water and the lakes are now dry, so a modern water proxy for

comparison is also unattainable.

The elemental and isotopic ratios in the majority of otoliths in this study have

shown an increasing trend associated with the later years of fish life. This has

been interpreted as an evaporative trend experienced after fish entered Lake

Mungo. The point at which this begins is interpreted as the timing of migration

into Lake Mungo but the strontium isotope ratio results may help to elaborate

on this.

5.5 Strontium isotopes

All Sr-isotope values drop to 0.7126 near the edge of the otoliths except for

#1168-9 which has already been discussed above (Figure 5.10) and there are

107

variances in #953-5 which have also been discussed. In the majority of the

otoliths a change in the ambient 87

Sr/86

Sr ratios occurs at a similar time to

increases in the oxygen isotope, Ba/Ca and Sr/Ca ratios and is likely to reflect

the final migration of fish into Lake Mungo. The Sr-isotope ratios of otolith

#1168-9 show a drop to 0.7126 in the early section which may relate to early

occupancy in Lake Mungo and then it being actively fished elsewhere

The age at which oxygen isotopes, Ba/Ca and Sr/Ca ratios begin to increase

differs between the hearth sites and within them. This may be due to each

individual fish entering Lake Mungo at different times. The strontium tracks

can be associated with otoliths ages for #926-4, #953-5, #952-8 and #982-11

(see Figure 5.11). In each of these the decrease in strontium isotope values is

close to the age of increase in the oxygen isotopes and elemental abundances.

108

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

012345678910Age (years)

#953-5

87S

r/86

Sr

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0123456789101112Age (years)

#982-11

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800

Time (seconds)

#926-3

87S

r/8

6S

r8

7S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800Time (seconds)

#926-1

87S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800Time (seconds)

#926-2

87S

r/8

6S

r8

7S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700800900

Time (seconds)

#1168-9

87S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700

Time (seconds)

#952-7

87S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

01234567Age (years)

#952-8

87S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0100200300400500600700

Time (seconds)

#953-6

87S

r/8

6S

r

0.7122

0.7124

0.7126

0.7128

0.713

0.7132

0.7134

0123456789Ages (years)

#926-4

87S

r/8

6S

r

Figure 5.11: The mean strontium isotope values from across each of the

otoliths. All are on the same y-axis scale and otolith edge is on the left.

109

In otoliths #926-1, #926-3 and #926-4 the strontium isotope values start at

0.7126 then increase and fluctuate around 0.7128 before returning to 7.126 in

later life (see Figure 5.11). In otolith #926-4 the last decrease is associated with

increasing Sr/Ca, Ba/Ca and oxygen isotope ratios, and so is interpreted as the

timing of fish entry into Lake Mungo. The earlier values may be showing that

the fish were in Lake Mungo for part of their early life, left there and returned

later on or that these fish began life in an area with a similar strontium isotope

signature to Lake Mungo. While it can be expected that it will take a

considerable time for the Sr isotopes to leach from the lake bed into the water,

the observation that all fish end up with very similar Sr isotope ratios indicate

that Sr isotope analysis is a potential tool for reconstructing fish migration.

Future recommendations for determining this will be presented in chapter 6

(Conclusions and Recommendations).

5.6 Discussion Summary

The geochemical methods applied to fish otoliths in this study show promising

results for creating life history maps of water conditions experienced over the

course of a fish’s life. A number of points can be taken away from this

discussion:

The difficulties in associating otolith age lines with sample areas and

the slight loss of otolith outer layers due to preparation procedures

highlights the need for obtaining clear ages before analyses.

110

The otoliths were well suited to radiocarbon dating and the hearths

showed very close associations.

The AAR data on the otoliths were not suited for attaining detailed

chronological information.

Past temperatures are difficult to determine without knowing the

original composition of the water but sharp fluctuations in the early

years of otolith Ba/Ca and oxygen isotope ratios can potentially be used

to identify seasonal temperature variations.

The relative timings for fish migration into Lake Mungo can be

determined by the use of multiple proxies Ba/Ca, Sr/Ca oxygen

isotopes and strontium isotopes as well as knowledge about the lake’s

hydrological setting.

Evaporative trends leading up to fish capture by humans supports

Bowler’s (1998) easy prey hypothesis.

The opposite trend in #1168-9 can be explained in terms of it either

being associated with flood waters in Lake Mungo after the evaporative

trend seen in the other otoliths or it being obtained from a different

Lake or river and brought to this hearth site. Without oxygen isotope

ratios or other otoliths from this hearth site these interpretations are

mostly speculative.

111

Chapter 6

Conclusions and Recommendations

The main aim of this study was to investigate the potential applications for fish

otoliths for associating human occupation events and environmental conditions

at Lake Mungo on a similar temporal scale. Five major conclusions were

drawn from the results of this study and they are as follows.

Dating techniques for otoliths were found to have varying levels of suitability.

This study has shown that otoliths are well-suited for radiocarbon dating. Fish

otoliths from the same hearth site showed closely associated dates and when

these were modelled based on the stratigraphic position of the hearths an even

closer association was obtained, to within a 500 year period. By combining the

archaeology and geology of the hearth sites with the geochemistry of the fish

otoliths, we can place human occupation at between 19,500-19,000 cal BP

which coincides with the end of the LGM. Radiocarbon also identified otolith

#953-5 as out of context by dating it as 6,000 years younger than the others.

Amino acid racemisation was less successful showing too great a scatter of D/L

ratios for similar aged otoliths to be of use in gaining detailed age information.

AAR is concluded to be an inappropriate method for dating fish otoliths at

Lake Mungo to obtain high resolution geochronological information.

Samples of the otolith geochemistry taken across the annual layers of otolith

growth allowed for the reconstruction of major events in each fish’s life

112

history. The large increase in oxygen isotopes and Sr/Ca and Ba/Ca ratios seen

in the years leading up to each fish’s death are concluded to be the result of an

evaporative trend. The close association of oxygen isotopes in the otoliths from

hearth site #926 suggests that these fish were living in the same body of water

in their later years. There were some slight concerns with aging which may

have led to the offsets between the elemental abundance tracks of the otoliths

from this hearth and these would need to be remedied in any further

applications.

Identifying otolith age lines before analysis is very important for establishing

strong associations between sampled areas, results and time since fish death.

The main recommendations for avoiding such discrepancies and minimising

the loss of otolith outer layers during preparation processes is to obtain thin

sections first, to take high quality photos of these and to keep the track

lines/spots of different analyses as close to each other as possible.

Elemental abundance measurements were able to gain high resolution of data.

Interpretations were, however, limited to what is currently known about the

effects of ambient water composition, fish metabolic processes and temperature

on elemental deposition in otoliths. This study was unable to determine

whether fluctuations in the Ba/Ca and oxygen isotopes of the early years of fish

otolith growth were due to temperature or floodwaters. Ba/Ca ratios appear to

fluctuate in line with the oxygen isotopes. This contradicts the literature,

which states that Ba/Ca ratios and oxygen isotope patterns should deviate. This

might be an effect of aging offsets as have been discussed above but still

highlights to need for species specific studies on the influence of temperature

113

on elemental incorporation into the otoliths of the golden perch (Macquaria

ambigua). As key species present at the Lake Mungo site this information is

necessary for any further assessment of ambient environmental conditions from

fish otoliths to be made.

Strontium isotope ratios showed a decrease to 0.1726 in the majority of otoliths

at approximately the same time as the evaporative trend began. This is

concluded to be the point of fish migration into Lake Mungo, but in order to

firmly establish this as the signature of Lake Mungo and of not any of the other

lakes a strontium map of the area needs to be developed. Sr-isotope ratios taken

from the current lake bed and surrounding regional geology could be analysed

for strontium isotope ratios and a comparison could then be made to those

obtained from otoliths in this and future studies.

Otolith #1168-9 showed an opposite trend in its elemental abundance and

strontium isotope tracks to all other otoliths. This fish appears to have been

born or arrived in Lake Mungo very early on and then managed to escape from

the evaporative conditions possibly due to flooding. The fish then made its way

into a different body of water with freshwater conditions where it was actively

fished. Perhaps fish were acquired from a larger area than just Lake Mungo or

there may be some post-depositional processes affecting hearth #1168. Further

studies of remains acquired from this hearth would help to assess whether this

is a freak occurrence, a problem with the sampling strategy or a definite trend.

This study demonstrates the applicability of fish otolith geochemistry for

linking human occupation events with environmental conditions and placing

114

these in time. Radiocarbon dating enabled us to place the hearth sites to near

the end of the LGM (19,500-19,000 Cal BP). The majority of otoliths showed

an evaporative trend in the oxygen isotope ratios of their later years. The point

at which this trend begins generally coincides with a dip in the strontium

isotope ratios and increasing trends in the Sr/Ca and Ba/Ca ratios which

provides a fairly secure indication of migration. In future studies the

application of pan evaporation observations to this oxygen isotope and

elemental abundance data set could be used to extrapolate how long Lake

Mungo would have taken to evaporate given certain climatic conditions.

Offsets for aging need to be taken into account for the exact timing of these

events; however, overall human occupation at Lake Mungo is able to be

associated with the collection of fish from an evaporating body of water near

the end of the LGM. This study has demonstrated the benefits of cross

disciplinary research for gaining new levels of insight into past human

occupation at Lake Mungo.

115

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124

Appendices

Images of sampled areas of otoliths in relation to age lines (in blue):

Otolith #926-1

Otolith #926-3

Otolith #926-2

Otolith #953-5

125

Otolith #952-7

Otolith #953-6

Otolith #952-8

Otolith #982-11

Otolith #1168-9

126

Radiocarbon modelling script

Plot()

{

Outlier_Model("General",T(5),U(0,4),"t");

Sequence()

{

Boundary("Start all");

Phase("all")

{

R_Date("WLWHAMFS_982-11", 16225, 55)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_1168_305-9", 16070, 50)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_952-7", 16060, 55)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_953-6", 16190, 55)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_953-5", 11840, 45)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_926-2", 16095, 55)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_926-1", 16240, 65)

{

Outlier(0.05);

};

R_Date("WLWHAMFS_926-4", 16250, 50)

{

Outlier(0.05);

};

R_Combine("926_3")

{

Outlier(0.05);

R_Date("WLWHAMFS_926-3 duplicate", 16000, 50);

R_Date("WLWHAMFS_926-3", 16015, 50);

};

127

R_Date("WLWHAMFS_952-8", 16075, 50)

{

Outlier(0.05);

};

Date("Date");

Interval("Interval");

};

Boundary("End all");

};

};

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