Marine geochemical data assimilation in an efficient Earth System Model of global biogeochemical cycling A. Ridgwell1, J. C. Hargreaves2, N. R. Edwards3, J. D. Annan2, T. M. Lenton4, R. Marsh5, A. Yool5, and A. Watson4 1School of Geographical Sciences, University of Bristol, Bristol, UK 2Frontier Research Center for Global Change, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan 3Earth Sciences, The Open University, Walton Hall, Milton Keynes, UK 4School of Environmental Sciences, University of East Anglia, Norwich, UK 5National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, UK
Abstract. 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.
The GENIE-1 Earth system model is capable of simulating a wide variety of
dissolved and isotopic species of relevance to the study of modern global
biogeochemical cycles as well as past global environmental changes recorded
in paleoceanographic proxies. Importantly, even with 12 active
biogeochemical tracers in the ocean and including the calculation of
feedbacks between atmospheric CO2 and climate, we achieve better than
1000 years per (2.4 GHz) CPU hour on a desktop PC. The GENIE-1 model thus
provides a viable alternative to box and zonally-averaged models for
studying global biogeochemical cycling over all but the very longest (>1 000 000 year) time-scales.
Citation: Ridgwell, A., Hargreaves, J. C., Edwards, N. R., Annan, J. D., Lenton, T. M., Marsh, R., Yool, A., and Watson, A.: Marine geochemical data assimilation in an efficient Earth System Model of global biogeochemical cycling, Biogeosciences, 4, 87-104, doi:10.5194/bg-4-87-2007, 2007.