Seminar Details

Taxon-specific stoichiometry of phytoplankton populations in the North Atlantic Ocean




Dr. Steven Baer - Bigelow Laboratory for Ocean Sciences


The Redfield ratio describes the elemental stoichiometry of marine particles, with global averages of 106:16:1 for carbon:nitrogen:phosphorus. This relationship, and deviations from it, has been used to infer biogeochemical rates and therefore are a major component of global models. The degree to which this canonical ratio is driven by autotrophic biomass or the chemical environment has been difficult to tease apart. By using flow cytometry cell sorting, autotrophic taxa were separated and their carbon, nitrogen, and phosphorus quotas were determined. The results highlight the range of physiological states of small autotrophic picoplankton (<20 microns), and the influence of phytoplankton biomass and community composition on the C:N:P ratios of marine particles. This seminar will focus on picoplankton across a broad latitudinal range in the North Atlantic Ocean, with some preliminary results from other sites around the world. We found evidence of physiological flexibility and the importance of community composition in the determination of particle stoichiometry. The lack of a homeostatic relationship between the ambient nutrient field (nitrate:phosphate concentrations) implies that other mechanisms, such as species-specific adaptation to oligotrophic phosphorus concentrations, control elemental particle ratios. These results will greatly improve our understanding of the link between phytoplankton physiology, marine nutrient fluxes, and global biogeochemical modeling efforts.

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