Aug/Sept 2006

Equator

Date Line

Iron, Aluminum and Manganese in the Equatorial Pacific

James W. MurrayLia SlemonsJoe Resing (NOAA/PMEL)Barbara PaulUniversity of Washington

AGU JOINT Assembly 2009

How did I get into this…Always a Voyage to Address the MostImportant Questions.

Fellow Citation: Surface Chemistry of MnO2, FeOOH and Natural Marine Particles (Stumm, Balistrieri, Dillard)

234Th as a Tracer for Ocean Scavengingthen Export Production, sediment traps w/234Thand 15N-New Production (Anderson, Dunne, Wei, Aufdenkampe)

Models of Controls on New/Export ProductionFood Web Structure and Parameterization of Grazing (Frost, Lukos)

Iron as a Control on Export Production ( Johnson, Slemons)

Stay Tuned – Stable Iron Isotopes as a Tracerfor the Source of Iron

Is the Main Flux of Fe from the EUC?

Gordon and Coale (1995)

An EqPac Hypothesis: The Equatorial Pacific HNLC

NO3

Is thereA maximum?

Mackey et al. (2002)Depth profiles of total dissolvable Fe

Stations sampled – R/V Kilo Moana 0625

Aug/Sept 2006Honolulu to Rabaul

Equatorial Undercurrent during Kilo 0625

ADCP From P. Dutrieux(Hawaii)

ө(EUC) =25.0 to 25.5

EUC – 61% NGCUC at 145ENICU – ~10% at 156E

From P. Dutrieux(Hawaii)

Equatorial Zonal SectionsnM

Papua New Guinea (145E) Meridional Section

Fe

Mn

Al

Vitiaz 2N, 145E Currents at 200 m, P. Dutrieux

nM

Fe max : west Pacific

Key Features of Observations

• There are maxima for Fe, Al and Mn with the EUC.

The Al maximum correlates best with the EUC.

The Fe maximum is 50-100m deeper. • Fe and Mn maxima in EUC are mostly

particulate• Al in EUC is dissolved• Concentrations of Fe, Al and Mn in the EUC

increase to the west• High surface values for dissolved Al and Mn in

the west, but not for Fe. Al and Mn concentrations decrease from west to east

AlD and FeD along Section P16 (150W) in the Pacific

Hiscock, Measures and Landing 2009

New Hypothesis: Variability in Iron and ProductivityENSO variability in strength and depth of NGCUC Ryan et al (2006)

Future work – we need to understand

• What controls the details of the distributions 1. Why is the surface maxima for Al and Mn (mostly

dissolved) but not for Fe? Is it river, atm origin? 2. Why is the EUC maximum for Al shallower than for Fe?

Why are EUC maxima for Fe mostly particulate but Al is dissolved? Are these from Sediment sources? 3. How (where) does the NGCUC connect to the EUC?

• Is there seasonal variability of Fe to the NGCUC that corresponds to variable speed and depth of the NGCUC?

• Northern end-member (Marianas to Mindanau to NECC)?• Stable Iron Isotopes to Distinguish Between Riverine Versus Sediment

Resuspension

ToolsTools : : Models

OPA PI SCES

PO43-

Diatoms

MicroZoo

P.O.M

D.O.M

Si

I ronNano-phyto

Meso Zoo

NO3-

NH4+

Small Big

Euphotic Layer (10-200m)

OPA-PISCES Model

0.5˚ meridional * 2˚ zonal31 vertical levels, 12 in upper 120m

Model iron sources in the western equatorial Pacific

Subsurface dissolved iron at 140°W

Surface nitrate concentrations and primary productivity shifts

Surface chlorophyll

Conclusions of Model Study:

There is a Maximum of Iron in the EUC

It is primarily in the Acid Solublele Particulate PhaseA Dissolved Iron Maximum is not Apparent

If the Acid Soluble Iron is Considered to beBioavailable if results in Unrealistic Model Biological Fields(NO3 too low; Chl too high)

Thus, There is a Source of Iron from the EUC but it isMostly not Bioavailable

10L Go-Flo Trace Metal Rosettewith Vectran conducting cable ontrace metal clean winch.

Sample processing in lab “bubble”

Canadian GeotracesTrace Metal Sampling system

Sampling Methods

Analytical Methods

• Flow Injection Analysis– Fe chemiluminesence

• detection limit 0.06 nM (3*rsd ZLT blank, 4 min load)• Precision of 0.5 nM internal standard: 0.09 nM

– Al fluorometric • detection limit 0.15 nM with 1-min load• 3.5% precision

– Mn colorimetric• Detection limit 0.050 nM • 4% precision cruise replicates

• Internal, external Standards– 3 x 2L internal standard– SAFe external standard: 0.12 0.012 nM,

within 1 rsd of consensus value of 0.097 nMLia in lab

Vitiaz to NGCUC (before Sepik)

NGCUC (after Sepik) to 145E ; 0.6N

Fe max: central Pacific

Schematic of PISCES iron cycle

Zonal sections of iron and nitrate along the equator

Meridional structure of primary productivity

Patterns of POC export

Thermocline iron and surface nitrate trends