Hydrogen peroxide at the Bermuda Atlantic Time Series Station: Temporal variability of seawater hydrogen peroxide

Hydrogen peroxide concentrations, production rates and decomposition rates were measured during each of two 3-week cruises in August 1999 and March 2000 at the Bermuda Atlantic Time Series Station. Patterns of variation in the concentrations of hydrogen peroxide in surface seawater at BATS were drastically different in August of 1999 compared with March of 2000. In August, hydrogen peroxide concentrations were primarily controlled by input from rain, whereas in March, they were controlled by photochemical processes and showed diurnal variations. The highest concentrations in surface water in August followed rain events, whereas in March, they occurred at approximately 1400 after rapid photochemical production. This production in March was followed by an equally rapid loss of H 2O 2, probably driven by a secondary photochemical process, then by much slower decline at night. The combination of photochemical production and consumption processes resulted in a steady-state system over a 24-h period in March but not August. The dark decomposition of surface water hydrogen peroxide incubated in storage experiments was the same during both August and March and followed first order kinetics with a rate constant of 0.009 h − 1. This was in remarkably good agreement with the decay of the atmospheric hydrogen peroxide signal in surface seawater observed in August. The comparable rate constant for deep water from 200 m was about one-third of that for BATS surface seawater in March. Because filtered seawater had lower production rates than unfiltered seawater from the same depth, biological production may contribute to surface seawater hydrogen peroxide at BATS during the March spring plankton bloom, but it is not the dominant source.