Cavity Ringdown Spectroscopy, instrument

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Cavity Ringdown Spectroscopy, instrument cost ~$90K vs. ~$400K for mass spec from Gupta, P. 2009, Chapman Conf. poster

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Cavity Ringdown Spectroscopy, instrument. cost ~$90K vs. ~$400K for mass spec. from Gupta, P. 2009, Chapman Conf. poster. Cavity Ringdown Spectroscopy, principles. idea is to compare empty chamber and full-chamber ring-down across several absorption lines - PowerPoint PPT Presentation

Transcript of Cavity Ringdown Spectroscopy, instrument

Page 1: Cavity Ringdown Spectroscopy, instrument

Cavity Ringdown Spectroscopy, instrument

cost ~$90Kvs. ~$400K for mass spec

from Gupta, P. 2009, Chapman Conf. poster

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Cavity Ringdown Spectroscopy, principles- idea is to compare empty chamber

and full-chamber ring-downacross several absorptionlines

- must determine unknowns againsta calibration of ring-downs of known standard values

from picarro.com

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Geothermometry & paleoclimate proxies 10/10/12

The JOIDES Resolution drillship

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Temperature-dependent fractionation - recap

Equilibrium fractionation is temperature-dependent, always.- we’ve discussed the liquid-vapor fractionation for precipitation- today: carbonate-liquid fractionation

red=warmblue=cold;arrows track movement of 18O through phase changes

any solid phase

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Carbonate δ18O – introduction

Minerals (e.g. carbonate, quartz, barite, etc) form from super-saturated solution.

δ18O of these minerals is a fxn of δ18O of solution and temperature of solution

Remember: the δ18O of a solid phase is usually reported in PDB (heavy standard)while δ18O of liquid phase is usually reported in SMOW (light standard)interconversion equation:

Important: You need to know the δ18O of the solution to derive temperature from δ18Osolid

The ocean δ18O is defined as 0‰ (Standard Mean Ocean Water), and it’s a big volume, so how do you change δ18O of seawater?

18 181.03086( ) 30.86SMOW PDBO Oδ δ Friedman and O’Neil (1977)

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The relationship between water-δ18O, temperature, and the equilibrium δ18O of calcite was determined empirically by Sam Epstein et al., (1953) and later modified by Craig (1965):

O’Neil et al. (1969) determined an experimental relationship for the temperature-dependence of for the calcite-water system:

216.9 4.2( ) 0.13( )c w c wT C δ δ δ δ

3 6 210 ln 2.78(10 ) 2.89T

NOTEδc must be wrt PDB,δw must be wrt SMOW

good for low T,paleoceanography

T in Kelvingood for high T

Carbonate δ18O – temperature relationships

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Aragonite δ18O – temperature relationships

Why is the δ18Oarag-water different than the δ18Ocal-water ?

Is the larger for aragonite or calcite?

Zhou & Zheng, GCA, 2003

T-dependence of (T in Kelvin):

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Glacial-Interglacial foraminifera δ18O, revisited

Data from deep-sea(benthic) foraminiferashow +1.5‰ δ18Oshift during LGM

LGM

The million-dollar question in paleoceanography:How much of this shift was due to ice volume (sea level change) and how muchwas due to temperature change?

Schrag modelled the glacial-interglacial shift in porewater δ18O (~1.0‰),so we have 0.5‰ left over for temperature change.

How much did bottom water temperatures change during the LGM? (problem set)

Or you could measure temperature (trace metal concentrations in carbonates),and obtain a “residual” δ18O that gives you the δ18OSW change.

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Complications: Kinetic effects, vital effects and carbonate δ18O

Fact: very few organisms precipitate carbonate in isotopic equilibrium with the surrounding water (the vital effect)

One problem: skeletons are precipitated in super-saturated “micro-environments”, with sources from surrounding water & metabolic products

Another problem: isotopic exchange may be rate-limited in biological reactions

Kinetic isotopeeffects underlievital effect

Can track kinetic effectswith isotope-isotopeplot (δ13C vs. δ18O), check for slope = 2

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Spero et al., Nature 1997

Carbonate ion effect on foram δ18O

Results from culturing living forams:increase CO3

2-, δ18O foram decreases

* Not a very big effect,but casts further doubt on inferring G-I T changesfrom forams

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In order to reconstruct surface temperatures from carbonate δ18O formed during the LGM, you need to 1) remove the ice-volume effect2) constrain the δ18O of your local water mass3) apply the paleo-temperature equation

Glacial-Interglacial climate reconstruction

However, people can use other proxies to get at temperature:1) foraminifera assemblage data (CLIMAP)2) tree lines and snow lines will be lower during cold times3) trace metals in carbonates (Mg/Ca in forams or Sr/Ca in corals)4) alkenones (saturation index of long-chained alkanes in coccolithophores)

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δ18O as tracer of igneous processes

spectrometer lightintake

A “black smoker”from the East Pacific Rise

Applications of oxygen isotopes in igneous rocks:

1) determine temp of formation (water-mineralor mineral-mineral pairs)

2) quantify “water-rock” ratios of altered rocks

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composition of lunar rocks, carbonaceouschondrites, and MORB

Oxygen Isotopic compositions of geological materials

What scale is this?

Why is the ocean so light compared to MORB?

If carbonates precipitatefrom a “light” ocean,why are they so heavy?

Lunar rocksMORB

basic lavasmantle nodules

eclogitesandesitesophiolites

rhyolites & tuffsgranitic rocks

altered igneous rocksmetamorphic rocks

clastic sedimentsmarine limestones

Why does eclogite havea heavier δ18O than MORB?

Why do metamorphic rocksexhibit such a range of δ18O?

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2

*101000ln m n

ab

T

Principle of Geothermometry in igneous applications

The fractionation of oxygen or hydrogen in different minerals of a rock can beused as a geothermometer, provided that:

1. minerals deposited at same time, at equilibrium2. no subsequent alteration3. fractionation factors and T-dependence known experimentally

NOTE: Using multiple mineral pairs will increase confidence in the calculated temperature,if the mineral pair temperatures agree – i.e. they are concordant.

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2.78*101000ln 2.89calcite water T

Remember from last lecture we talkedabout the high-Twater-calcite equation?

General form of geothermometryfractionation equations.

1000ln m n m n m n δ δ Handy conversions:

For phases m and n:

T in Kelvin

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T-dependent fractionation in various mineral pairs

Where must these lines converge?

NOTE: These slopes are different – so all you need to determine T is m-n

The highest fractionation is betweenquartz and magnetite.

In general, 18O is increasingly favoredin higher-quartz minerals, and lessfavored in hydrous minerals (magnetite,amphibole, chlorite).

How could we determine the slope of the Quartz-Muscovite fractionation?

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Today’sHandouts:

Tables of T-dependentFractionation

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Example

Quartz, calcite, and chlorite were all precipitated in a hydrothermal vent setting.

Measured δ18O’s:Quartz: 5.1‰ SMOWCalcite: 3.8‰ SMOWChlorite: -1.5‰ SMOW

Why does quartz have the heaviest δ18O, and chlorite the lightest?

And why is the quartz only 5.1‰ heavier than SMOW?

Did these minerals precipitate at the same temperature?

How would you begin to solve this problem?

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Metamorphism: Water-Rock interactions

Fact: In several places it is possible to measure igneous rocks with δ18O values of -5‰!

These are places were fluid has interacted with the rock (usually at high T) to changethe isotopic composition of the rock.

We can use a mass balance approach to calculate the amount of water that has reacted with a host rock (or “water/rock ratio”) over time (assuming equilibrium):

w rδ δ is the equilibrium values for water and mineral,(need to know temperature independently)

i i f fw w r r w w r rc W c R c W c Rδ δ δ δ and mass balance equation: cw = conc. of O in water

cr = conc. of O in rockW = mass waterR= mass rocksuperscript I = initialsuperscript f = final

and combining these:

*f ir r r

i fw r w

cW

R c

δ δδ δ

for a closed systemWhat does a “closed system” mean?

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Water-Rock interactions II

for an open system

Now we only have a small parcel of water (dW) interacting at any given time, but newwater parcels are injected continuously in time, causing dδr

in this scenario we need to integrate to calculate W/R ratios.

ir r w r wRc d c dWδ δ δ

ln 1f ir r r

i fw r w

cW

R c

δ δδ δ

Probably much more realistic, because water flows through the rock.

In order to solve for W/R interactions, you need to know:1. the temperature of the interaction (hopefully you can get that by a mineral-mineral pair)2. the mineral phases that experienced fluid alteration3. the isotopic composition of the water before it interacted with the rock (δD of rock… why?)4. the isotopic composition of the rock before it interacted with the water (unaltered samples)

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A characteristicsignature of hydrothermalactivity is a “bulls-eye”pattern of δ18O values,with low values in the middle.

Alteration occurs alongan established conduitof weakened structures.

Most gems are the productof low-T, high-fluidmetamorphism –$1M worth of gold minedin the Bohemia complexbetween 1870 and 1940 -happy hunting!

A real-worldexample

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A Cool Early Earth, (2002) Geology. 30: 351-354.

A cool early Earth?

Idea: measure U-Pb dates and δ18O of old zircons- if you find low δ18O relative to today’s ‘primitive’ mantle, then that implies interaction with meteoric waters at low temperatures

This work is done using a laser flourination line plumbedto a dual inlet mass spec

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So what’s causing the relatively high zircon δ18O values at 4.2Ga?

time-line along bottom indicates:(1) accretion of the Earth, (2) formation of the Moon and the Earth’s core, (3) minimum age of liquid water based on high δ18O zircon, (4) Acasta gneiss, and (5) Isua metasedimentary rocks.

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likely interaction with meteoric waters

which implies a period of few impacts