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 ra in squall in the equatorial Pacific Ocean. Iron and hydrogen peroxide were determined at sea using adsorptive cathodic stripping voltammetry (ACSV) an d an enzyme-catalyzed flourometric technique, respectively. The equatorial rainwater was enriched in ACSV reactive iron (average 2.7 nmol Fe kg(-1)) a nd hydrogen peroxide (average 8.5 mu mol kg(-1)) relative to the concentrat ions found in surface seawater (0.05-0.07 nmol Fe kg(-1); 40-70 nmol peroxi des kg(-1)). Wet depositional fluxes during the squall varied from 70 to 10 5 nmol Fe m(-2) h(-1) and from 56 to 880 mu mol peroxide m(-2) h(-1). The i nput of rainwater into the surface layer was documented by using hydrogen p eroxide and iron signals as well as the depression in surface salinity as t racers. 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 pe roxides in rainwater, their wet-depositional fluxes, and their initial sea surface enrichments, were quantitatively consistent with independent predic tions based on applicable iron aerosol and gas-phase peroxide scavenging mo dels for the region. (C) 2001 Published by Elsevier Science B.V.