Bacterial productivity and organic matter flux in the Southern Ocean and in the Antarctic Intermediate Water and Mode Water of the Indian Ocean

Bacterial biomass production in the water column across the Antarctic Circumpolar Current in the Crozet Basin was determined to estimate the flux of organic carbon through bacteria. South of the Subantarctic Front and Subtropical Front (SAF-STF) zone, bacterial growth was greatest at the surface and decreased exponentially in the deep layers. North of the frontal zone, however, growth was high at the surface and decreased exponentially to 400 m, but then was greater in Mode Water at 500 m and in the Antarctic Intermediate Water (AAIW) at 1250 m. This indicates that the water masses sinking in the frontal zone and being advected towards the equator from the Southern Ocean contain labile organic matter. The paradigm that the majorsource of organic carbon in the interior of the oceans is due to vertical sinking of particles may need to be changed to include horizontal advection for long distances and perhaps long time scales, at least in the major oceans south of the equator.