Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 4 1 2007 10.5194/bg-4-87-2007 http://www.biogeosciences.net/4/87/2007/ http://www.biogeosciences.net/4/87/2007/bg-4-87-2007.html http://www.biogeosciences.net/4/87/2007/bg-4-87-2007.pdf 87 104 2007-01-25 Marine geochemical data assimilation in an efficient Earth System Model of global biogeochemical cycling A. Ridgwell J. C. Hargreaves N. R. Edwards J. D. Annan T. M. Lenton R. Marsh A. Yool A. Watson School of Geographical Sciences, University of Bristol, Bristol, UK Frontier Research Center for Global Change, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan Earth Sciences, The Open University, Walton Hall, Milton Keynes, UK School of Environmental Sciences, University of East Anglia, Norwich, UK National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, UK We have extended the 3-D ocean based "Grid ENabled Integrated Earth system model" (GENIE-1) to help understand the role of ocean biogeochemistry and marine sediments in the long-term (~100 to 100 000 year) regulation of atmospheric CO2, and the importance of feedbacks between CO2 and climate. Here we describe the ocean carbon cycle, which in its first incarnation is based around a simple single nutrient (phosphate) control on biological productivity. The addition of calcium carbonate preservation in deep-sea sediments and its role in regulating atmospheric CO2 is presented elsewhere (Ridgwell and Hargreaves, 2007). We have calibrated the model parameters controlling ocean carbon cycling in GENIE-1 by assimilating 3-D observational datasets of phosphate and alkalinity using an ensemble Kalman filter method. The calibrated (mean) model predicts a global export production of particulate organic carbon (POC) of 8.9 PgC yr−1, and reproduces the main features of dissolved oxygen distributions in the ocean. For estimating biogenic calcium carbonate (CaCO3) production, we have devised a parameterization in which the CaCO3:POC export ratio is related directly to ambient saturation state. Calibrated global CaCO3 export production (1.2 PgC yr-1) is close to recent marine carbonate budget estimates. 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