Louanchi F.

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Louanchi
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  • Article
    A modeling study of the seasonal oxygen budget of the global ocean
    (American Geophysical Union, 2007-05-09) Jin, X. ; Najjar, Raymond G. ; Louanchi, F. ; Doney, Scott C.
    An ecosystem model embedded in a global ocean general circulation model is used to quantify roles of biological and physical processes on seasonal oxygen variations. We find that the thermally induced seasonal net outgassing (SNO) of oxygen is overestimated by about 30% if gas phase equilibrium is assumed, and we find that seasonal variations in thermocline oxygen due to biology are approximated well using the oxygen anomaly. Outside the tropics and the north Indian Ocean, biological SNO is, on average, 56% of net community production (defined as net oxygen production above 76 m) during the outgassing period and 35% of annual net community production. In the same region the seasonal drawdown of the oxygen anomaly within the upper thermocline (76–500 m) is 76% of the remineralization during the drawdown and 48% of annual remineralization. Applying model-derived relationships to observed O2 climatologies and using independent estimates for tropical and monsoonal systems, we estimate global net community production to be 14.9 ± 2.5 Pg C yr−1.
  • Article
    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)
    (American Geophysical Union, 2007-08-08) Najjar, Raymond G. ; Jin, X. ; Louanchi, F. ; Aumont, Olivier ; Caldeira, Ken ; Doney, Scott C. ; Dutay, J.-C. ; Follows, Michael J. ; Gruber, Nicolas ; Joos, Fortunat ; Lindsay, Keith ; Maier-Reimer, Ernst ; Matear, Richard J. ; Matsumoto, K. ; Monfray, Patrick ; Mouchet, Anne ; Orr, James C. ; Plattner, Gian-Kasper ; Sarmiento, Jorge L. ; Schlitzer, Reiner ; Slater, Richard D. ; Weirig, Marie-France ; Yamanaka, Yasuhiro ; Yool, Andrew
    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.