Peroxide variations in the Sargasso Sea

This paper presents a time series study of H2O2 distributions and variability at an oligotrophic station in the North Atlantic. Hydrogen peroxide was examined over eleven consecutive days at 1 and 3 m. The average concentration exceeded 100 nM with daily variations of about 40 nM at both depths. Surface water peroxide concentrations increased following an evening rain shower and remained elevated by about 40 nM throughout the remainder of the study. Atmospheric input of H2O2 appears to represent a disturbance to the kinetic balance of H2O2 production and loss and thus produces long term H2O2 trends while the system approaches the steady state concentrations dictated by mixing regime and in situ processes. Vertical profiles showed H2O2 distributions which closely follow density profiles with concentrations dropping rapidly to less than 5 nM below the thermocline when a distinct seasonal mixed layer was present. Results suggest H2O2 as a useful tracer for freshwater input and mixing processes in the upper ocean.