Organic Fe Complexation in the Gulf of Mexico

The SWISS (Surface Water Iron Speciation Study) project conducted 3 cruises to the open Gulf of Mexico in 2001 and 2002 (one during the low dust spring season and two during the high dust late summer). The goal of these cruises was to further our understanding of the abiotic cycling of Fe as it relates to atmospheric deposition, redox, photochemistry and organic complexation. Surface (less than 5 m) samples were collected using a clean towed wing. The sample was pumped into a clean work area and filtered. Samples were either frozen for total ligand analysis or ultrafiltered (1 kDa) and frozen for determination of colloidal ligand concentrations. Some subsamples (totals and low molecular weight) were incubated in deck mounted constant temperature (surface seawater) baths in order to determine the importance of photochemistry for the degradation of organic Fe complexing ligands. We will present results from both cruises of 2001. Preliminary data support the hypothesis of photochemical degradation controlling the ligand concentration with the largest percentage of the ligand below 1 kDa.