Phytoplankton Populations in the Equatorial Pacific: Distributions and Growth Rates from Individual Cell Properties

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Central to the mission of the US Joint Global Ocean Flux Study in the equatorial Pacific is an understanding of the composition of the planktonic food web, and the efficiency with which it transports carbon to the deep ocean. One of the specific questions being posed is whether or not iron availability is limiting productivity in this area. This project will address several dimensions of the overall equatorial Pacific plan through the flow cytometric analysis of the phytoplankton component of the food web. Specifically, the project will: (1) Measure the distribution, abundance, and light scatter properties of the picoplankton, and of the larger phytoplankton, on a transect across the equator; (2) Measure the daily changes in cell number, forward light scatter (size), and DNA content of individual cells, which can be translated into estimates of net and gross population growth rates; (3) Use the measured daily changes in cell number and light scatter per cell to help interpret beam attenuation measurements; (4) Test the hypothesis that iron limits phytoplankton growth in the equatorial Pacific by measuring changes in forward light scatter per cell, carbon-14 incorporation per cell, and the distribution of DNA per cell of specific components of the phytoplankton, in response to iron enrichment. //