Collaborative Research: Determining the Elemental Composition of Natural Plankton Cells in the Eastern Equatorial Pacific using Synchrotron X-Ray Fluorescence Microscopy

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Researchers at the State University of New York-Stony Brook, the University of South Carolina, and Oregon State University will use synchrotron based x-ray fluorescence microscopy (SXRF), a cell-specific analytical technique, to measure elemental concentrations of silicon, phosphorus, sulfur, iron, manganese, nickel and zinc. Along with biological, chemical, and physical data collected in the field, results will be used to determine the following: (1) how the elemental stoichiometries of field collected phyto- and protozooplankton change along gradients of iron supply during a cruise through the eastern equatorial Pacific (EEP); and (2) the stoichiometric responses to iron supply in laboratory cultures and in shipboard manipulations of intact plankton communities from the EEP. The iron:carbon uptake ratios in EEP picoplankton will be measured using radioisotopes. Combined, this information will allow the hypotheses that link cellular elemental stoichiometries to cellular iron quotas and growth rates to be addressed. The PIs also will evaluate if cells that can ingest iron-rich picoplankton are better able to maintain higher cellular iron than cells which must acquire iron directly from the dissolved phase. Differences between the elemental compositions of ballasted and flagellated cells will be determined and the importance of protozoa as a source of recycled iron along gradients in iron supply will also be ascertained. Results will be incorporated into coupled physical-biogeochemical models parameterized for use in the EEP.In terms of broader impacts, the PIs will ensure that the SXRF technique is made available to other interested users in the ocean sciences community. To this end, they also plan to establish and test protocols for sample preparation and develop user-friendly quantification software to increase sample output. Two graduate students will be trained as part of this project. Undergraduate students and high school student will be involved in the research via the REU program in association with Stony Brook's Center of Environmental Molecular Science. It is anticipated that interactive educational programs discussing results from this study will be produced for local high schools and contribute to a teacher training workshop.