PHOTOCHEMICAL OXYGEN ACTIVATION - SUPEROXIDE RADICAL DETECTION AND PRODUCTION-RATES IN THE EASTERN CARIBBEAN

Superoxide ion-radical, O2-, the one-electron reduction product of molecular oxygen, is a long-suspected first intermediate in chemical reactions using oxygen as the ultimate electron acceptor. We have detected photochemical production of O2- in a variety of eastern Caribbean waters studied in Spring and Fall by using a chemically direct O2- trapping reaction combined with N-15 and/or O-18 isotopic labelling of reactants to provide sensitivity and specificity. Photochemical superoxide production rates ranged from 0.1-6 nmol L-1 min-1 of full-sun irradiation in Spring end from 0.2-8 nmol L-1 min-1 in Fall. These superoxide fluxes correlate well with independently measured total (NO-scavengeable) radical fluxes in both seasons and account for approximately 1/3 of the total radical production. Hence we confirm that O2- is a quantitatively important, perhaps dominant, reactive transient species in the photochemical radical array. Semiquantitative estimates suggest that O2- dismutation to HOOH and O2 can account for most or all of the photochemical HOOH production in surface waters. O2-production rates also correlated negatively with salinity.