Ocean carbon reservoirs and the air-sea flux of CO2 in a changing climate

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The unprecedented rate of increase in atmospheric carbon dioxide, and its potential impact on climate, has stimulated significant development and application of numerical climate and carbon-cycle models. Such models are becoming extremely complicated, with numerous physical and biogeochemical modules coupled in complex, four-dimensional integrations. Moreover many processes in models may be poorly resolved and/or crudely parameterized. The interpretation of these models requires robust and simplifying diagnostic frameworks. In this project, a research team at the Massachusetts Institute of Technology will develop and apply tools to map and quantify the ocean carbon pumps and the physical/biological drivers of the air-sea fluxes of carbon dioxide. They will use these tools to elucidate and quantify mechanisms underpinning the response of the carbon cycle to climate change, through careful analysis of an ensemble of sensitivity studies using the MIT Earth System Model of intermediate complexity (IGSM), as well as available CMIP5, IPCC climate and carbon cycle simulations and projections: (1) Diagnostic frameworks will be used to evaluate the contributions of several ocean carbon pumps (reservoirs) to ocean carbon storage in models and observations as well as to interpret regional drivers of air-sea carbon flux. (2) An ensemble of simulations with the IGSM will be used to explore how key uncertainties in model parameters affect simulations of the ocean carbon pumps in the pre-industrial era. (3) Ensemble simulations will be extended through the 21st Century, additionally exploring uncertainties in climate sensitivity, aerosol forcing and wind pattern changes under several anthropogenic emissions scenarios. (4) The large IGSM ensemble and diagnostic tools will be used as the context for examining climate/carbon cycle projections from state-of-the-art CMIP5 climate models, both in simulations of the present day and future change scenarios. These tools should be useful not only in the analysis of observations and for the project simulations, but also as a framework for the interpretation of all IPCC-class climate and carbon simulations. Broader Impacts: The key broader impact of this study is its significance for the application of climate and carbon cycle models to near-future projections, an important part of the IPCC process. The proposed study will provide an evaluation of model-derived uncertainties which can be used in assessments of current and future states of the climate system. It will provide a framework for elucidating how the changing physical environment may impact the ocean carbon pumps and air-sea fluxes over the next century. All of the diagnostic tools and derivative products will be distributed freely for continued application to assist in the interpretation of the growing inventory of increasingly complex coupled numerical simulations. In addition, the proposed work will provide a stimulating and interdisciplinary project for a post-doctoral researcher.