Proposal Abstract:
Ocean ecosystems are part of a complex geophysical-biogeochemical web that transforms matter and energy and sets the conditions for life. Feedback between different parts of this web is mediated to a significant degree by the exchange of radiatively important, biogenic trace gases. One such feedback involves marine plankton, the volatile sulfur compound dimethylsulfide (DMS), and global climate. In this feedback, DMS produced by marine phytoplankton and the food web enters the troposphere and is oxidized there to sulfate particles, which influence cloud albedo and, consequently, climate. Large-scale climate change, in turn, affects phytoplankton abundance and food web processes in the oceans and thereby closes the feedback loop. The strength-and even the sign-of this feedback loop is still unresolved, largely because of the exceedingly complex network of biogeochemical and ecological processes that affect the concentration of DMS. Fascinating new interactions in this cycle are still being discovered with some regularity, but mechanistic and prognostic mathematical models of this system have yet to incorporate many of these developments. Furthermore, there have been no field studies in which all of the relevant rates and concentrations in the marine DMS cycle have simultaneously been measured, nor have complex interactions or measurements been included for important geophysical or chemical parameters, hampering the ability of models to accurately map spatial and temporal variations in surface DMS concentrations. This effort will: 1) Measure and model all known relevant fluxes of concentrations of DMS and related species during intensive field studies in two ocean biomes: a subtropical gyre and the Southern Ocean; 2) Develop a global marine DMS model built upon the proposed field measurements and other existing measurements and models; and 3) Use such a model to evaluate the potential for feedbacks between climate and the marine DMS cycle. The DMS biogeochemical system represents a tractable research subject that can aid in understanding the complexities involved in biosphere-geosphere regulation at the regional and global scales. The DMS system also serves as an excellent, research- accessible model for food-web dependent biogeochemical processes. This investigation of the complex controls on the DMS cycle should shed light on the critical factors influencing the ecological distributions of organisms in the sea and the biogeochemical cycles of major nutrient elements. Advancing the knowledge of DMS biogeochemistry will allow better predictions of the local, regional and global scale responses to anticipated shifts of climate, and provide valuable insights into the connections within the biogeochemical-geophysical web that sustains life on Earth.