Postdoctoral Scholar: Dierdre Toole

Research Statement

The biogeochemical cycling of reduced sulfur compounds between the upper water column and the marine boundary layer has been implicated in a climate feedback loop. This hypothesized climate regulation mechanism suggests that as phytoplankton communities are subject to temperatures and radiation exposure above their normal tolerance levels, they will respond accordingly by increasing production of reduced organic sulfur compounds. Once ventilated to the atmosphere, these reduced sulfur compounds are oxidized to forms which may function as new cloud condensation nuclei, or promote the growth of existing condensation particles, directly and indirectly reducing the solar radiation and temperature at the oceanic surface. One of the most important sources of atmospheric sulfur is the biogenic production of dimethylsulfide (DMS) in the marine environment. DMS, and its precursor, are produced and processed in an exceedingly complex and dynamic network of physical, chemical, biological, and optical interactions across a variety of trophic levels that involve much more than phytoplankton production.

Central to closing this climatic feedback loop however is a measure of the processes that modulate DMS cycling and an understanding of how changes in radiative forcing will alter these processes within oceanic foodwebs. Dierdre’s research thus far has focused on laboratory, field, and modeling studies all designed to unravel the complexities of DMS cycling, particularly with respect to light-mediated responses. Her research has primarily focused on the open-ocean Sargasso Sea region but has also taken her throughout the North Atlantic and the Southern Ocean. Her doctoral research consisted of analyzing a three-year time-series of DMS in terms of concurrently sampled properties, determinations of the spatial / temporal variability and mechanism of the light response of key DMS loss processes including photolysis, microbial consumption, and sea-to-air flux, 1-d modeling to assess the extent to which DMS variability in an open-ocean region can be constrained and characterized by optical and physical factors, and building the optical algorithms and tools necessary to model DMS cycling.

Her postdoctoral research will be an extension of this research focusing on the climate responses and potential feedbacks of changing oceanic DMS concentrations. She will quantify and explore the implications of the DMS climate feedback loop hypothesis with state of the art global marine ecosystem and physics models. In-situ field data, laboratory experiments, and satellite products will be used extensively for parameterization development, forcing, and model validation. Simulations will be conducted under present and future climate conditions, and the resulting climate responses and potential feedbacks of changing air-sea DMS flux will be assessed through coupling with atmospheric chemistry/physics/cloud models. She will also continue to participate in a variety of field campaigns to quantity the impacts of ultraviolet radiation stress on phytoplankton DMS production.