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Inverse modeling of particulate organic carbon fluxes in the South Atlantic

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Citation:
Schlitzer, R. , Usbeck, R. and Fischer, G. (2004): Inverse modeling of particulate organic carbon fluxes in the South Atlantic , in: Wefer, G., Mulitza, S., Rathmeyer, V., (eds.), The South Atlantic in the Late Quaternary - Reconstruction of Material Budget and Current Systems, pp. 1-19, Springer-Verlag, Berlin .
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Abstract:

The biological production of particulate material near the ocean surface and the subsequent remineralization during sinking and after deposition on the seafloor strongly affect the distributions of oxygen, dissolved nutrients and carbon in the ocean. Dissolved nutrient distributions therefore reveal the underlying biogeochemical processes, and these data can be used to determine production-, remineralization and accumulation rates using inverse techniques. Here, an ocean circulation, biogeochemical model that exploits the existing large sets of hydrographic, oxygen, nutrient and carbon data is presented and results for the export production of particulate organic matter, vertical fluxes in the water column and sedimentation rates are presented. In the model, the integrated export flux of particulate organic carbon (POC) for the South Atlantic amounts to about 1300 Tg C yr-1 (equivalent to 1.3 Gt C yr-1), most of which occurring in the Benguela/Namibia upwelling region and in a zonal band following the course of the Antarctic Circumpolar Current (ACC). Remineralization of POC in the upper water column is intense, and only about 7% of the export reaches a depth of 2000 m. Comparison of model particle fluxes with sediment trap data suggests that shallow traps tend to underestimate the downward flux, whereas the deep traps seem to be affected by lateral input of material and apparently overestimate the vertical flux. These findings are consistent with recent radionuclide studies. The rapid degradation of POC with depth leads to geographical patterns of POC fluxes to the seafloor and POC accumulation in the sediment that are very different from the pattern of surface productivity, because of modulation with varying bottom depth. Whereas there is significant surface production in deep-water, open-ocean regions, the benthic fluxes occur predominantly in coastal and shelf areas.

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