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Research Overview

The "biological pump" is the suite of processes by which marine organisms sequester carbon in the deep ocean, out of contact with the atmosphere.  It both drives and responds to global climate change on decadal to millennial timescales.  My research uses numerical models to understand various processes that control the strength of the biological pump and their sensitivity to environmental change: plankton ecology and physiology; cycling of growth-limiting nutrients; and the respiration of organic particles by diverse microbial communities in the ocean interior, especially in low-oxygen habitat.  My modeling work is always motivated and guided by observations, and I collaborate closely with observational oceanographers to interpret new and exploratory datasets.

My previous research has largely focused on the cycling of nitrogen, the primary limiting nutrient for phytoplankton communities throughout most of the global ocean.  I have explored the biological basis and geochemical consequences of diverse nitrogen stoichiometry among phytoplankton, and the feedbacks between nitrogen-fixing and denitrifying organisms that govern the productivity of the ocean as a whole.  Recently, I have expanded my research into two new areas.  First, I am interested in the cycling of trace metals (Fe, Zn, Cd) that serve as "micronutrients" and enzyme co-factors for phytoplankton.  The ongoing GEOTRACES program is revealing the oceanic distributions of these metals for the first time, and my modeling efforts are designed to provide new insights to the cycling rates and processes responsible.  Second, I am interested in the fate of organic carbon exported from the surface ocean.  By combining simple models with large datasets from Underwater Visual Profilers, I am to better understand the controls on organic particle sinking and respiration rates, and the depths at which carbon is sequestered.

Research Interests

• Ocean biogeochemical cycles, trace element oceanography, marine ecosystems and their response to climate change