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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 ∼1–2 nM in summer 2003, when aerosol iron concentrations were high (mean 10 nmol m −3 ), 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 ∼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.
Sedwick et al. (Wed,) studied this question.