An Equatorial Pacific rain event: influence on the distribution of iron and hydrogen peroxide in surface waters

The wet deposition of iron and peroxides was monitored during an intense rain squall in the equatorial Pacific Ocean. Iron and hydrogen peroxide were determined at sea using adsorptive cathodic stripping voltammetry (ACSV) and an enzyme-catalyzed flourometric technique, respectively. The equatorial rainwater was enriched in ACSV reactive iron (average 2.7 nmol Fe kg−1) and hydrogen peroxide (average 8.5 μmol kg−1) relative to the concentrations found in surface seawater (0.05–0.07 nmol Fe kg−1; 40–70 nmol peroxides kg−1). Wet depositional fluxes during the squall varied from 70 to 105 nmol Fe m−2 h−1 and from 56 to 880 μmol peroxide m−2 h−1. The input of rainwater into the surface layer was documented by using hydrogen peroxide and iron signals as well as the depression in surface salinity as tracers. The squall created a patch of lower-salinity surface seawater that was relatively enriched in ACSV reactive iron (0.2–0.3 nmol Fe kg−1) and peroxides (200–300 nmol kg−1). The observed concentrations of iron and peroxides in rainwater, their wet-depositional fluxes, and their initial sea surface enrichments, were quantitatively consistent with independent predictions based on applicable iron aerosol and gas-phase peroxide scavenging models for the region.