Smith 9310599 Some of the strongest atomspheric forcing of oceanic properties anywhere on our planet is observed in the Arabian Sea where seasonally reversing monsoon winds drive fast- flowing, vertically extensive currents, complex eddy fields, broad-scale, open ocean upwelling, coastal upwelling and pronounced mixed-layer deepening. Cycles of production in this region are seasonal oscillations. During the southwest monsoon season (June-September inclusive), primary productivity is maximal owing to strong winds which not only cause the uplift of deep water rich in nutrient, but also deliver aeolian dust to the surface layer of this tropical ocean. During the northeast monsoon (October-November inclusive) and intermonsoon periods, primary productivity is markedly reduced. Biomass of zooplankton and secondary productivity are also elevated during the southwest monsoon season. Based upon earlier studies off Somalia, the epipelagic zooplankton off Oman is hypothesized to undergo significant changes in species composition from one monsoon season to another, with biomass during the southwest monsoon dominated by rapidly growing meso- and macrozooplanktonic grazers such as Calanoides and Eucalanus. These grazers exist in reduced abundance at subsurface depths during other seasons. The seasonal appearance of relatively large, fast growing grazers determines, to a large extent, the grazing impact of the zooplanktonic community on the phytoplankton assemblage that develops in the Arabian Sea during the southwest monsoon (upwelling). The grazing impact in turn modulates the flux of carbon to depth and is an important factor in the spatial and temporal patterns in carbon deposition in this region. In the Arabian Sea off Oman, carbon fluxes driven by large, seasonal changes in the grazing community of the upwelling area can be studied in combination with investigation of the grazing contribution to carbon fluxes associated with the perennially oligotrophi c region of the central Arabian Sea. A steep gradient in oxygen concentration located at approximately 150 meters acts to restrict most epipelagic grazers to a surface layer above this depth. The role of the epipelagic meso- and macrozooplanktonic grazers will be studied using: multiple opening/closing nets (MOCNESS) to determine distribution and abundance with particular attention to the oxic-suboxic interface and incubation experiments to determine ingestion, fecal pellet production, and growth rates
