SIGNIFICANCE OF BACTERIA IN CARBON FLUXES IN THE ARABIAN SEA

In the Arabian Sea, temporal contiguity of highly oligotrophic and eut rophic periods, along with high water temperatures, may result in uniq ue features of bacteria-organic matter coupling, nutrient cycling and sedimentation, which are unlike those in the classical oligotrophic an d eutrophic waters. Bacteria-phytoplankton interactions are suggested to influence phytoplankton. aggregation and its timing. It is also hyp othesized that, within aggregates, hydrolytic ectoenzyme activity, tog ether with condensation reactions between the hydrolysis products, pro duce molecular species which are not readily degraded by pelagic bacte ria. Accumulation of a reservoir of such slow-to-degrade dissolved org anic carbon (DOC) is proposed to be a carbon flux and energy buffer, w hich moderates the response of bacteria to the dramatic variations in primary production in the Arabian Sea. Use of the slow-to-degrade DOC pool during the intermonsoon could temporarily render the Arabian Sea net-heterotrophic and a source of CO2 to the atmosphere. Stored DOC is also suggested to balance the observed deficit between mesopelagic ca rbon demand and the sinking particulate organic carbon supply. Knowled ge of the significance of bacteria in carbon storage and cycling in th e Arabian Sea is needed to understand the response of the ocean's biog eochemical state to strong physical forcing and climate change.