Iron in the Sargasso Sea (Bermuda Atlantic Time-series Study region) during summer: Eolian imprint, spatiotemporal variability, and ecological implications

[1] We report iron measurements for water column and aerosol samples collected in the Sargasso Sea during July-August 2003 ( summer 2003) and April- May 2004 ( spring 2004). Our data reveal a large seasonal change in the dissolved iron (dFe) concentration of surface waters in the Bermuda Atlantic Time-series Study region, from similar to 1 - 2 nM in summer 2003, when aerosol iron concentrations were high ( mean 10 nmol m(-3)), to similar to 0.1 - 0.2 nM in spring 2004, when aerosol iron concentrations were low ( mean 0.64 nmol m(-3)). During summer 2003, we observed an increase of similar to 0.6 nM in surface water dFe concentrations over 13 days, presumably due to eolian iron input; an estimate of total iron deposition over this same period suggests an effective solubility of 3 - 30% for aerosol iron. Our summer 2003 water column profiles show potentially growth-limiting dFe concentrations (0.02 - 0.19 nM) coinciding with a deep chlorophyll maximum at 100 - 150 m depth, where phytoplankton biomass is typically dominated by Prochlorococcus during late summer.