Collaborative Research: Sampling and Analysis of Iron, an International Collaboration

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ABSTRACTOCE-0325031OCE-0326736OCE-0326697OCE-0324727OCE-0326633OCE-0326111Although great progress has been made in recent years to measure dissolved iron concentrations in seawater, significant differences remain between methods as was shown during a recent workshop held on December 5, 2002 in San Francisco. During this worship, evaluation of data obtained for one sample from the South Atlantic and analyzed by more than twenty different laboratories showed a range in iron values of 0.6 nM, nearly as large as the concentration range from the surface to 1000 m in the North Pacific. Given the importance of this element as a micronutrient which can limit primary production, it is imperative that the reasons for the variability in results be identified. For this reason, a Steering Committee of experienced iron analysts will collaborate with research groups with extensive experience in measuring iron both here in the United States as well as Europe and Japan to resolve the differences that remain in measurements of iron in seawater. This group of about 22 laboratories will participate in one cruise to one open ocean station (30'N, 140'W) with low iron concentrations (0.05 to 0.08 nM) and one coastal station with high iron concentrations with the goal of establishing the following: (1) the comparability of various measurements (isotope dilution high resolution inductively coupled plasma mass spectrometry, organic extraction graphite furnace atomic absorption spectrometry, cathodic stripping voltammetry, flow injection analysis-long path length colorimetry, flow injection analysis-luminol chemiluminescence detection, flow injection analysis with DPD); (2) the differences, if any, in the sampling strategies used (Go-Flo bottles on a Kevlar wire, automated, metal free samplers-MITESS, modified "trace metal rosettes", surface pumping systems; (3) the differences in filtration (Nuclepore, Anotop, capsule filters with pore sizes of 0.1 to 0.45 um); and (4) appropriate sample storage and distribution mechanisms. Measurements of iron will be made both at sea and in the laboratory. In addition, surface and 1000 m depth samples will be distributed to other analysts both in the United States and abroad to ensure that all types of analytical methods for iron are considered and possibly for distribution as an interim iron standard. The ultimate goal of this project is to enable the ocean science community to compare measurements of dissolved iron made at different places and times in the ocean with a high degree of confidence in the differences or similarities that are detected.