Fe, Al and Mn in the Western Equatorial Pacific

1. ADCP 200 m, P. Dutrieux Lia Slemons1 (ossianla@u.washington.edu), James Murray1, Joseph Resing2, Barbara Paul1 Fe, Al and Mn in the Western Equatorial Pacific (1) School of Oceanography, University of Washington, Seattle, WA (2) Pacific Marine Environmental Laboratory, NOAA, Seattle, WA Figure 1: Station map for Kilo Moana EUCFe cruise, Aug. 19 - Oct. 2, 2006. Mackey et al. (2002) total acid soluble iron profiles during three cruise years. Gordon et al. (1997) filtered and particulate iron concentrations from FeLine sampling in July 1990. Figure 3: Meridional sections from Vitiaz Strait along the New Guinea Coast to 2°N along cruise track, marked in the circles area on the velocity map. Red arrows show the velocity at 200 m, the approximate depth of the New Guinea Coastal Undercurrent. Note different concentration colorbar than Fig. 2. All three metals are enriched at the station downstream of the Sepik River. Figure 2: Zonal distributions of total acid soluble iron, aluminum, and manganese. Zonal velocity overlaid in gray contours. Sample points indicated by black diamonds. Abstract Zonal distributions of total acid soluble iron, aluminum, and manganese were determined across the equatorial Pacific from 140W to 145E. A meridional section was determined from 2°N to the New Guinea Coastal Undercurrent to Vitiaz Strait at about 145°E. All three metals have a subsurface maximum in the zonal section that increases toward the west. This maximum was located approximately at the core of the Equatorial Undercurrent (EUC). In addition, Al and Mn had surface enrichments that increased in the west. Fe had no surface enrichment. The subsurface maxima for particulate Fe was slightly below those of Al and Mn and below the core of EUC. In the meridional section at 145°E the concentrations of all three metals were much greater and all three were significantly enriched downstream of the Sepik River of Papua New Guinea. Taken together, these data indicate that the western equatorial Pacific is an important source of trace metals to the EUC, which upwells nutrient-rich water in the eastern equatorial Pacific. Zonal and Meridional Distributions of Methods Samples were obtained using a trace metal clean rosette system loaned by J. Cullen and Canadian GEOTRACES colleagues. The rosette and bottles were cleaned and assembled at the University of Washington and conditioned with open ocean seawater for 5 days. Total acid soluble (pH < 2) and 0.4 m filtered and acidified samples were collected. Shipboard and laboratory iron analyses were conducted by Flow Injection Analysis (FIA) chemiluminescence detection, modified from Johnson et al., 2003. Precision of low-Fe internal seawater standard: +/- 0.09 nM (n=19) Large volume (2L), triplicate samples of unfiltered surface seawater from the R.V. Kilo Moana’s trace metal sampling system and one filtered sample from 175 m were collected at the first station (140°W, 2°N) as internal standards throughout analysis. The average value of the interal standard from 175 m was 0.49 +/- 0.09 nM (1 rsd, n=19). The internal standard from the shipboard sampling system averaged 1.12 +/- 0.17 nM (n=19). Accuracy of low-Fe measurement: within 1 relative standard deviation (rsd) of SAFe low-Fe standard The consensus value for SAFe S1 reference surface seawater is 0.097 +/- 0.043 nM (95%) (Johnson et al., 2007). Our concurrent analyses of SAFe S1 with analyses yielded a value of 0.12 +/- 0.012. Blank: typical analytical blank is 0.52 +/- 0.047 nM, yielding a limit of detection of 0.137 nM for a 5-minute sample load time. Aluminum analyses were conducted by the fluorescence FIA technique of Resing and Measures (1994). The limit of detection of Al was 0.15 nM with a precision of 3.5% Manganese measurement utilized the chemiluminescent FIA technique of Resing and Mottle (1992). The limit of detection of Mn was 0.050 nM and the precision based on cruise replicates was 4.0%. Figure 4: Vertical profiles of total acid soluble and 0.4 m-filtered Al, Fe, and Mn concentrations and zonal velocities at four equatorial stations. At 175°W the total acid soluble Al profile from 175°W is shown. References Gordon, R.M., Coale, K.H., Johnson, K.S. (1997) Iron distributions in the equatorial Pacific: Implications for new production. Limnology and Oceanography 42 (3): 419-431. Johnson K.S. and 10 others (2003) Surface ocean-lower atmosphere interactions in the Northeast Pacific Ocean Gyre: Aerosols, iron and the ecosystem response. Global Biogeochemical Cycles, 17 (2) 1063, doi: 10.1029/2002GB002004. Johnson, K. and 35 others (2007) Developing Standards for Dissolved Iron in Seawater. Eos Transactions, AGU 88 (11) 131. Mackey, D.J., O’Sullivan, J.E., Watson, R.J. (2002) Iron in the western Pacific: a riverine or hydrothermal source for iron in the Equatorial Undercurrent? Deep-Sea Research I 49:877-893 Resing, J.A. and Measures, C.I. (1994) Fluorometric determination of Al in seawater by flow injection analysis with in-line preconcentration. Analytical Chemistry, 66, 4105-4111. Resing, J.A. and Mottle, M.J. (1992) Determination of manganese in seawater by flow injection analysis using preconcentration and spectrophotometric detection. Analytical Chemistry 64, 2682-2687. March 2-7, 2008 Ocean Sciences Meeting Ocean Processes in the Western Tropical Pacific, Session 047 Figure 5: Zonal concentration trend of total acid soluble Al, Fe, and Mn along isopycnal surfaces. Al, Fe, and Mn concentrations were averaged within 0.5 kg/m3 of the designated isopycnal surface.