Collaborative Research: SOFeX: Mesoscale Iron fertilization Effects on Plankton Community Structure, Phytoplankton Growth and Zooplankton Grazing

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The Southern Ocean is a critical region for understanding the role of the oceans in global carbon cycling and its potential to regulate climate change. Besides being an area of high influx of atmospheric carbon and deep water formation, the persistently high concentrations of major nutrients in Antarctic circumpolar waters represent the largest pool of unrealized primary production potential in the oceans. This project is part of a larger effort to test the hypothesis that iron availability limits phytoplankton production and biomass accumulation, nutrient utilization and C02drawdown in the Southern Ocean. Drs. Landry, Chisholm and Bidigare, will contribute by investigating the effects of iron enrichment and silicate availability on the species composition and size structure of the plankton community and taxon-specific growth rates and fluorescence responses of the phytoplankton. Functional and taxonomic components of the plankton community from bacteria to mesozooplankton will be quantified by a combination of flow cytometry, taxon-specific pigments, video image-analysis microscopy and optical plankton counting. In addition, they will use dilution and gut fluorescence techniques to determine micro- and mesozooplankton contributions to grazing and to evaluate grazing as an alternate control mechanism preventing significant net growth of some or all of the phytoplankton populations. The research will bring a community perspective to the interpretation of these in situ fertilization experiments which is essential for a mechanistic understanding of the biological and geochemical responses.