Analysis and Integration of Acoustic, Optical and Traditional Data from the 1995 Arabian Sea Expedition
1998
Ortner, Peter B
Our research has been directed at understanding the coupled biological and physical mechanisms controlling the fine-scale (1-10 m) vertical distributions of zooplankton, the ecological significance of these distributions, and their effect upon other particles within the upper water column. Among the strongest atmospheric forcing of the upper water column observable anywhere in the world's oceans occurs in the Arabian Sea. Seasonally reversing monsoonal winds drive strong currents, produce complex eddy fields, deepen the mixed layer, and induce both coastal and open ocean upwelling. In much of the region a shallow oxygen minimum is found year round beneath the mixed layer. These physical features directly affect primary production processes but may also be expected to influence the abundance, distribution, and diversity of the animals dependent upon that production. During the 1995 field season the NOAA Ship Malcolm Baldrige made two cruises (an intermonsoonal cruise in April/May and a late monsoon cruise in August) during which we collected direct (MOCNESS) and indirect (acoustic and optical) data specifically addressing the following questions: (1) How do zooplankton size class spectra, vertical distribution, and biomass respond to seasonal mixing and consequent changes in food availability?; (2) Do both coastal and oceanic zooplankton populations respond similarly?; (3) Do the abundance and vertical distribution of mesopelagic organisms respond to seasonal mixing and consequent changes in food availability?; (4) What are the relative biomasses of zooplankton and mesopelagic populations?; and (5) How are the vertical distributions and diel migration patterns of zooplankton and mesopelagic populations modulated by the oxygen minimum?
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