Organic carbon losses measured by heterotrophic activity of mesozooplankton and CaCO3 flux in the bathypelagic zone of the Arabian Sea

Organic carbon requirements for metabolisms of mesozooplankton in the bathy pelagic zone were calculated for two stations (Western Arabian Sea Sediment Trap, WAST, 16 degrees N 60 degrees E, and Central Arabian Sea Sediment Tr ap, CAST, 14 degrees N 64 degrees E) and two different intermonsoonal perio ds (October 1995 and April 1997) in the Arabian Sea. These requirements wer e compared with inputs of particulate organic carbon (POC) measured from se diment traps. The temporal variability of POC flux is compared to the CaCO3 flux made up by planktic foraminiferans and coccolithophorids. The potenti al oxygen requirement of mesozooplankton was measured by the electron trans port system (ETS) activity and the organic carbon demand calculated using c onversion factors from the literature. Particulate CaCO3 flux was calculate d from multinet hauls and sediment trap samples. Mesozooplankton organic ca rbon demand in the zone between 1050 and 3000 m differed locally and season ally. At WAST, the mesozooplankton required 1778 mu g C m(-2) d(-1) in Octo ber and only 484 mu g C m(-2) d(-1) in April. At CAST, the respective value s were 997 and 211 mu g C m(-2) d(-1). No differences between the stations and time periods were discernible for the zone between 3000 and 3900 m at C AST and between 3000 and 4000 m at WAST; the values ranged between 73 and 9 8 mu g C m(-2) d(-1). The input measured by sediment traps was sufficient t o cover the calculated requirements of the mesozooplankton. The flux of cal careous particles and the mesozooplankton carbon requirements showed a simi lar pattern of temporal variability. At CAST the planktic foraminiferal she ll flux was 33.2 mg CaCO3 m(-2) d(-1) in October and only 5.9 mg CaCO3 m(-2 ) d(-1) at 3000 m depth in April. Flux data derived from multinet hauls are of the same order of magnitude as the sediment trap data and, as multinet data yield a high temporal and spatial resolution, they could serve as a me asure for open-ocean particulate flux. (C) 1999 Elsevier Science Ltd. All r ights reserved.