Testing the New Oceanic Dimethylsulfide (DMS) Stress / Bloom Regime Hypothesis in a Global Coupled Ecosystem-Biogeochemistry Numerical Model

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The oceanic production and subsequent ventilation to the atmosphere of dimethylsulfide (DMS) has been suggested as an important climate regulator; but to date, the mechanisms for closing the DMS-climate feedback loop have been qualitative and empirical. In this project, researchers at the Woods Hole Oceanographic Institution will test a new two regime (stress / bloom forced) hypothesis in a global coupled ecosystem-biogeochemistry model. This two regime conceptual model suggests that in the stress forced regime, DMS and dimethylsulfoniopropionate (DMSP, the chemical precursor to DMS) concentrations are forced by stress created by the physical environment such as shallow mixed layers and high cumulative doses of ultraviolet radiation. In contrast, in the bloom forced regime, variability in surface DMS concentrations is associated with mono-species blooms of traditional DMSP producing phytoplankton species. The pecific scientific objectives of the project are to: 1) Develop a global ocean sulfur biogeochemistry simulation by integrating a state of the art marine ecosystem / ocean circulation model with a physically, optically, and biologically forced DMS submodel. 2) Evaluate the ability of the emerging two regime ocean DMS conceptual model (stress forced & bloom forced) to capture the spatial / seasonal / interannual patterns found in in situ surface DMS data. 3) Explore the strength of the DMS-climate feedback mechanism utilizing an existing reactive atmospheric sulfur chemistry / climate model. This integrated research plan will provide improved quantitative estimates, dynamical understanding, and modeling capabilities for air-sea DMS flux variability and an assessment of the resulting atmospheric chemistry and climate feedbacks. The modeling efforts will allow the research team to (1) create seasonally resolved spatial maps of surface DMS concentrations and air-sea fluxes, (2) assess the generality of the stress / bloom forced regime hypothesis, and (3) quantify the direct and indirect radiative forcing resulting from changes in air-sea DMS fluxes. Through the coupled simulations, they will determine the impact of air-sea DMS perturbations through the atmosphere and back on ocean physics, biology, and DMS cycling laying the groundwork to assess the strength of all of the interacting components of the proposed DMS-climate feedback mechanism.This research should have several broader impacts. Given the immediate societal relevance of anthropogenic climate change, it is critical that the scientific community attempt to refine the considerable uncertainties surrounding future climate projections, including the existence and magnitude of the DMS-climate feedback. If all goes as expected, the project should yield a numerical model that will increase our ability to assess the non-linearities associated with this feedback mechanism and how it will play out in potential future climate change scenarios. The model simulations resulting from this project will be made openly available to the research community and public via the web. This proposed research directly addresses one of the key objectives of the U.S. and International Surface Ocean - Lower Atmosphere Study (SOLAS) initiative, will leverage and contribute to a community of SOLAS research activities, and will incorporate results from ongoing field based NSF and NASA funded research programs. Finally, this project will combine teaching and research by supporting a postdoctoral researcher and will enhance and expand interactions with scientists at other institutions.