Najjar, R.G., X. Jin, F. Louanchi, O. Aumont, K. Caldeira, S.C. Doney, J.-C. Dutay, M. Follows, G.M. Kay, E. Maier-Reimer, R.J. Matear, A. Mouchet, J.C. Orr, G.K. Plattner, J.L. Sarmiento, M.F. Weirig, Y. Yamanaka and A. Yool

The Pennsylvania State University, Department of Meteorology, 503 Walker Building, University Park, PA 16802-5013, Tel: 814-863-1586, Fax: 814-865-3663, E-mail: najjar@essc.psu.edu

Export production simulated by the OCMIP-2 models

Results are presented of export production simulated by twelve global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2). A common, simple biological model is utilized in which surface phosphate concentrations are restored towards an observed climatology in the upper 75 m. Organic matter formed as a result is partitioned into dissolved and particulate forms. Oxygen is included by linking to phosphate with a fixed Redfield ratio. Physical transport is the only difference among the models. The downward flux of organic matter across 75 m depth varies from 8 to 20 Gt C yr^-1 among the models, with a mean of 14 Gt C yr^-1 and a standard deviation of 4 Gt C yr^-1. This is in reasonable agreement with satellite-based estimates (12±1 Gt C yr^-1). The range in model export production (±40%) is considerably larger than the range in chlorofluorocarbon uptake (±30%) and anthropogenic CO₂ uptake (±20%). Similar to the results for other tracers, the most pronounced differences among the models occurs in the Southern Ocean. The fraction of organic matter exported across 75 m in dissolved form varies from 14 to 34% with a mean of 23% and a standard deviation of 6%, in reasonable agreement with observational estimates (17%). Seasonal net outgassing of oxygen in the models with seasonal circulation varies from 5.0 to 10×10¹⁴ mol, with a mean of 6.6×10¹⁴ mol and a standard deviation of 1.6×10¹⁴ mol, significantly smaller than observational estimates (10×10¹⁴ mol).