Aquatic Sciences Meeting, Albuquerque 2001

SS02 Photochemical Reactions In Surface Waters: A Major Issue in the 21st Century? (Environmental Connections)

Date: Friday, February 16, 2001, Time: 10:15:00 AM

Location: San Miguel

Obernosterer, I, , Netherlands Institute for Sea Research, Den Burg, Netherlands, ingrid@nioz.nl

Ruardij, P, , Netherlands Institute for Sea Research, Den Burg, Netherlands, rua@nioz.nl

Herndl, G, J, Netherlands Institute for Sea Research, Den Burg, Netherlands, herndl@nioz.nl

DOM - photoreactivity across the subtropical Atlantic Ocean

Diurnal dynamics of dissolved organic matter (DOM) fluorescence and hydrogen peroxide (H2O2) concentrations were followed in the upper 100m water column at 5 stations across the subtropical Atlantic Ocean. The DOM fluorescence decreased over the course of the day, while H2O2 concentrations increased, especially in the diurnally stratified surface water layers extending to 10-50m depth. In situ H2O2 net production varied between 5.5 nmol L-1 h-1 at 5m depth and 1 nmol L-1 h-1 at 40m depth resulting in a H2O2 net production of ~ 38 µmol m-2 d-1 in the upper 50m water column. Photochemical oxygen demand varied between 0.9 and 2.8 µmol O2 L-1 d-1 and was found to be consistently higher (1.3-8.3 fold) than bacterial respiration (measured in 0.8µm-filtered seawater in the dark). A simple one-dimensional physical model was combined with a photochemical/biological model in order to describe the photochemical production of H2O2 at different depth layers over the course of the day. The model reflects well the observed diurnal H2O2 dynamics. It further provides evidence that mainly biological breakdown determines the loss of H2O2 in the upper 50m water column during the day, however, in the late afternoon, vertical mixing is important in transporting H2O2 from the uppermost 5 m layer to the 10 – 20m layers.

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Aquatic Sciences Meeting, Albuquerque 2001

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