Phytoplankton-nutrient interactions in the upper ocean

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The ocean covers about 71% of the earth's surface and strongly affects global climate. Floating unicellular algae (phytoplankton) play a critical role in modifying the earth's climate by changing the carbon balance of the ocean, which have a direct impact on atmospheric carbon dioxide concentrations. These photosynthetic organisms take up nutrients (e.g. carbon, nitrogen, silicon, phosphorus) through photosynthesis and return them back to seawater after death and decomposition, thereby controlling the level of carbon dioxide in the ocean and atmosphere. Phytoplankton physiology can also affect nutrient transfer along marine food webs with consequences for the survival of fish and marine mammals. High-latitude oceans are experiencing the most dramatic climatic variations due to global warming. Predicted changes (e.g. in sea ice cover, circulation patterns, water column stratification, temperature, dissolved carbon dioxide, nutrient supply) will impact marine ecosystem structure and function by affecting phytoplankton productivity at the base of the biological system. Therefore, it is critical to evaluate phytoplankton responses to ocean warming and acidification in subarctic and arctic seas. This research program examines the links between phytoplankton physiology and nutrient cycling in the ocean. Studies will be conducted in the laboratory and on oceanographic research cruises to the subarctic Northeastern Pacific and western Arctic Oceans, and utilize interdisciplinary techniques. Specifically, I will advance my research by studying (1) biogenic silica production and silicon isotopes, (2) the balance between planktonic calcification and photosynthesis, and (3) phytoplankton elemental composition. I will explore the sensitivity of nutrient acquisition in marine phytoplankton to nutrient limitation and changing environmental conditions. Results will shed new light on the factors affecting the productivity of marine phytoplankton, and improve our understanding of present and past nutrient cycles, carbon export and food web dynamics in high-latitude marine waters.