Aug/Sept 2006 Equator Date Line Iron, Aluminum and Manganese in the Equatorial Pacific James W. Murray Lia Slemons Joe Resing (NOAA/PMEL) Barbara Paul University of Washington AGU JOINT Assembly 2009

How did I get into this… Always a Voyage to Address the Most Important Questions. Fellow Citation: Surface Chemistry of MnO 2, FeOOH and Natural Marine Particles (Stumm, Balistrieri, Dillard) 234 Th as a Tracer for Ocean Scavenging then Export Production, sediment traps w/ 234 Th and 15 N-New Production (Anderson, Dunne, Wei, Aufdenkampe) Models of Controls on New/Export Production Food Web Structure and Parameterization of Grazing (Frost, Lukos) Iron as a Control on Export Production ( Johnson, Slemons) Stay Tuned – Stable Iron Isotopes as a Tracer for the Source of Iron

Is the Main Flux of Fe from the EUC? Gordon and Coale (1995) An EqPac Hypothesis: The Equatorial Pacific HNLC NO 3 Is there A maximum? Mackey et al. (2002) Depth profiles of total dissolvable Fe

Stations sampled – R/V Kilo Moana 0625 Aug/Sept 2006 Honolulu to Rabaul

Equatorial Undercurrent during Kilo 0625 ADCP From P. Dutrieux (Hawaii)  ө ( EUC) = 25.0 to 25.5

EUC – 61% NGCUC at 145  E NICU – ~10% at 156  E From P. Dutrieux (Hawaii)

Equatorial Zonal Sections nM

Papua New Guinea (145  E) Meridional Section Fe Mn Al Vitiaz2N, 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 m 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

Al D and Fe D along Section P16 (150W) in the Pacific Hiscock, Measures and Landing 2009

New Hypothesis: Variability in Iron and Productivity ENSO 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

OPA-PISCES Model 0.5˚ meridional * 2˚ zonal 31 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 Phase A Dissolved Iron Maximum is not Apparent If the Acid Soluble Iron is Considered to be Bioavailable if results in Unrealistic Model Biological Fields (NO 3 too low; Chl too high) Thus, There is a Source of Iron from the EUC but it is Mostly not Bioavailable

10L Go-Flo Trace Metal Rosette with Vectran conducting cable on trace metal clean winch. Sample processing in lab “bubble” Canadian Geotraces Trace 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 nM 4% precision cruise replicates Internal, external Standards –3 x 2L internal standard –SAFe external standard: 0.12  nM, within 1 rsd of consensus value of nM Lia 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