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Aug/Sept 2006

Iron, Aluminum and Manganese in the Equatorial Pacific. James W. Murray Lia Slemons Joe Resing (NOAA/PMEL) Barbara Paul University of Washington. Date Line. Aug/Sept 2006. Equator. AGU JOINT Assembly 2009. How did I get into this… Always a Voyage to Address the Most

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Aug/Sept 2006

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

  2. How did I get into this… Always a Voyage to Address the Most Important Questions. Fellow Citation: Surface Chemistry of MnO2, FeOOH and Natural Marine Particles (Stumm, Balistrieri, Dillard) 234Th as a Tracer for Ocean Scavenging then Export Production, sediment traps w/234Th and 15N-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

  3. An EqPac Hypothesis: The Equatorial Pacific HNLC Is the Main Flux of Fe from the EUC? NO3 Is there A maximum? Mackey et al. (2002) Depth profiles of total dissolvable Fe Gordon and Coale (1995)

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

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

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

  7. Equatorial Zonal Sections nM

  8. Papua New Guinea (145E) Meridional Section nM Fe Al Vitiaz 2N, 145E Currents at 200 m, P. Dutrieux Mn

  9. Fe max : west Pacific

  10. 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

  11. AlD and FeD along Section P16 (150W) in the Pacific Hiscock, Measures and Landing 2009

  12. New Hypothesis: Variability in Iron and Productivity ENSO variability in strength and depth of NGCUC Ryan et al (2006)

  13. 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

  14. OPA-PISCES Model 0.5˚ meridional * 2˚ zonal 31 vertical levels, 12 in upper 120m

  15. Model iron sources in the western equatorial Pacific

  16. Subsurface dissolved iron at 140°W

  17. Surface nitrate concentrations and primary productivity shifts

  18. Surface chlorophyll

  19. 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 (NO3 too low; Chl too high) Thus, There is a Source of Iron from the EUC but it is Mostly not Bioavailable

  20. Sampling Methods Canadian Geotraces Trace Metal Sampling system 10L Go-Flo Trace Metal Rosette with Vectran conducting cable on trace metal clean winch. Sample processing in lab “bubble”

  21. 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 nM Lia in lab

  22. Vitiaz to NGCUC (before Sepik)

  23. NGCUC (after Sepik) to 145E ; 0.6N

  24. Fe max: central Pacific

  25. Schematic of PISCES iron cycle

  26. Zonal sections of iron and nitrate along the equator

  27. Meridional structure of primary productivity

  28. Patterns of POC export

  29. Thermocline iron and surface nitrate trends

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