labs_title

Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project

R.G. Najjar, X. Jin, F. Louanchi, O. Aumont, K. Caldeira, S. C. Doney, J. C. Dutay, M. Follows, N. Gruber, F. Joos, K. Lindsay, E. Maier-Reimer, R. J. Matear, K. Matsumoto, P. Monfray, A. Mouchet, J. C. Orr, G. K. Plattner, J. L. Sarmiento, R. Schlitzer, R. D. Slater, M. F. Weirig, Y. Yamanaka, & A. Yool

The export of organic matter from surface waters to the deep ocean, known as ‘‘export production,’’ is a central process in marine biogeochemical cycling. Here we emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.


Najjar, R. G., X. Jin, F. Louanchi, O. Aumont, K. Caldeira, S. C. Doney, J.-C. Dutay, M. Follows, N. Gruber, F. Joos, K. Lindsay, E. Maier-Reimer, R. J. Matear, K. Matsumoto, P. Monfray, A. Mouchet, J. C. Orr, G.-K. Plattner, J. L. Sarmiento, R. Schlitzer, R. D. Slater, M.-F. Weirig, Y. Yamanaka, and A. Yool, Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2). Global Biogeochemical Cycles, 21, GB3007, doi:10.1029/2006GB002857, 2007.

Fig. 5: Fraction of global total (gray) and particle (black) carbon export in five latitude bands for the 12 OCMIP models (Table 1) and their mean, the inverse method of SO2 [Schlitzer, 2002], and satellitebased estimates (particle only) of GO4 [Gnanadesikan et al., 2004]. For GO4, the three bars refer to usage of the primary production algorithms of Behrenfeld and Falkowski [1997] (left), Carr [2002] (middle), and Marra et al. [2003] (right). Horizontal line is fractional area of given latitude band.

Abstract

Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (±1σ) downward flux of organic matter across 75 m depth is 17 ± 6 Pg C yr−1. Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.