9311244 Goericke The U.S. Arabian Sea JGOFS program offers the unique opportunity to study the response of an oceanic ecosystem to strong and seasonally predictable physical forcing in an environment with strong spatial gradients. Biological conditions in the Arabian Sea vary from extreme oligotrophy to extreme eutrophy. Primary production and concentrations of chlorophyll a, for example, change by one to two orders of magnitude over space and time. We propose to study the effects of the seasonally varying physical forcing on the phytoplankton community as a whole and on individual populations of microalgae, using primarily pigment-based methods. We will test the hypothesis, suggested by data from other environments, that phytoplankton community structure and growth rates during most of the year. The exception is the area off Oman during the SW monsoon when oceanic upwelling occurs. At this time the community is expected to be dominated by diatoms growing at high rates. Phytoplankton community structure will be monitored by measuring the concentration of taxon-specific chlorophylls and carotenoids by high-pressure liquid chromatography. It is proposed to carry out theqe analyses as part of the JGOFS core measurements. Using the pigment 14c-labeling method we propose to measure phytoplankton carbon-biomass, phytoplankton growth rates and taxon-specific growth rates to study the physiological response of the phytoplanton community to the seasonally varying physical forcing. Carbon to Chl a ratios will be calculated from phytoplankton biomass and chl a and used to calculated seasonal maps of phytoplankton carbon-biomass for the Arabian Sea from remotely sensed ocean and biomass will allow us to determine factors which control the growth and abundance of the individual phytoplankton population, such as coccolithophores or prochlorophytes, and their contribution to carbon cycling in this environment.
