Microbial communities in the Arabian Sea:  Composition, size spectra and growth rates from individual cell properties
Robert J. Olson
Biology Department
Woods Hole Oceanographic Institution
508 457-2000 x2565
A central mission of the JGOFS project in the Arabian Sea is to determine how efficiently the carbon pump operates in this region, and how it responds to changes in physical forcing.  To approach these problems we need to analyze the structure of the food web and determine how it varies with geographical and temporal gradients in nutrient supply and water column mixing.  The juxtaposition of productive and oligotrophic oceanic systems in the Arabian Sea, and the regular oscillation between very high and low rates of nutrient supply under relatively constant conditions of solar illumination, offers opportunities for us to gain insights into food web regulation processes.

Specifically, we propose to:  (1) Characterize the distribution, abundance, and light scatter properties of the picoplankton and nanoplankton at the four intensive stations and at selected intermediate stations, flow cytometry, and (2) Estimate in situ growth rates of specific groups of phytoplankton, and grazing pressure on these groups, from diel patterns in cell number, light scatter properties and DNA content of individual cells from depth profiles.  This information will help to interpret diel patterns in beam attenuation, a JGOFS core measurement.