Sarah’s research focused on the marine nitrogen cycle, and the links between photosynthesis supported by different nitrogen sources and the drawdown of CO2 by the ocean. Nitrogen is a major constituent of all living organisms and a primary determinant of the ecological success of phytoplankton, the base of marine food chains. Biologically available nitrogen has the potential to limit productivity in the surface ocean and determine the composition of phytoplankton communities, thus affecting the transfer of carbon to higher trophic levels, and eventually into the ocean interior. There exists an oceanographic paradigm stating that primary production supported by nitrogen from outside the well-lit surface ocean is equivalent to the amount of carbon that is exported from this surface layer and sequestered at depth.
Thus discerning the source of N to phytoplankton in various parts of the ocean is potentially very important. Isotope measurements of dissolved and particulate nitrogen pools can tell us about the source of N for photosynthesis, and thus the amount of carbon a particular ecosystem can potentially sequester. She is currently working on measuring species-specific, high-resolution stable isotope signatures of the Sargasso Sea ecosystem using flow cytometry and mass spectrometry. She was also interested in resolving seasonal and temporal changes in phytoplankton N sources, as well as the response of the ecosystem to various perturbations likely to occur as the ocean warms.