Small-scale oxygen fluxes and remineralization in sinking aggregates

Sinking aggregates are the major component of the vertical particulate flux in most regions of the ocean. Controlling factors for aggregate reminerali zation rates and solute exchange with the surrounding water, however, are p oorly quantified because of few empirical data. To study the role of flow a nd diffusion on aggregate remineralization rates, oxygen distributions were mapped within and around aggregates by use of microelectrodes in a flow fi eld similar to that experienced by sinking aggregates. The oxygen distribut ion was asymmetrical with a wake of undersaturated water at the rear (downs tream) of the aggregates. Oxygen concentrations within the aggregates were >80% of air saturation. The diffusive fluxes of oxygen at the aggregate-wat er interface were similar along the equator and at the downstream pole for a wide range of different aggregate sources (field-sampled diatom aggregate s, lab-made diatom aggregates, aggregates formed from freeze-thawed diatoms , and zooplankton detritus aggregates) measured at various temperatures. Re mineralization rates were reaction limited and, hence, determined by substr ate quality and quantity rather than by transport-limited oxygen supply dur ing sedimentation at ambient oxygen concentrations above similar to 25 muM.