The distribution of hydrogen peroxide in the Southern and central AtlanticOcean

The near-surface distribution and processes controlling the distribution of hydrogen peroxide were examined in the South and central Atlantic Ocean du ring a transect from Uruguay to Barbados in May and June 1996. Four kinds o f held experiments were conducted during the cruise including diel observat ions, dark decay experiments, photochemical production experiments, and hyd rogen peroxide-enrichment experiments. Significant diel variations (similar to 25 nM) of hydrogen peroxide were observed, with surface-water concentra tions increasing during the day and decreasing at night. With a dark decay half-life of 5.5 days and a net rate of photochemical production of 8.3 nM/ h at local noon, it appears that both decay rate and photo-production rate of hydrogen peroxide are much smaller in oligotrophic seawater than in coas tal seawater. The experimental results indicate that: (1) the decay reactio n is a second-order reaction over all, first-order with both the concentrat ion of hydrogen peroxide and the concentration of colloidal material; (2) s eawater in the study area could restore its ambient levels of hydrogen pero xide in about 4d after external perturbations. A total of 20 vertical profiles were obtained at 11 stations that can be cl assified as: surface maximum, surface mixed, and sub-surface maximum. Gener ally, the concentration of H2O2 decreased with depth to less than 5 nM belo w 200 m. Hydrogen peroxide also was determined in some water samples from b elow 200 m, which revealed a slight increase of hydrogen peroxide with dept h. In the surface waters of the open ocean, hydrogen peroxide increased wit h latitude from about 24 nM in the south (33.8 degreesS) to about 80 nM in the north (8.9 degreesN). This latitudinal variation of hydrogen peroxide c orrelated with model-calculated solar irradiance, satellite-measured wet de position, depth of the mixed layer, and possibly total organic carbon. The water-column hydrogen peroxide inventory varied from 1.5 to 6.3 x 10(-3) mo l/m(2). Although the greatest shallow water concentrations were observed at stations in the Amazon plume, these stations showed a dramatic decrease in hydrogen peroxide with depth and integrated-water-column hydrogen peroxide was not significantly higher than at open ocean stations. (C) 2001 Elsevie r Science Ltd. All rights reserved.