| Summary: | Among the approaches developed this last decade to resolve the issue of the controls on particle transfer efficiency to, and organic carbon remineralisation in the mesopelagic zone, stands the study of particulate biogenic barium (Baxs)- barite (BaSO4) distribution in the water column. This approach relies on the formation of nano- to micro- barite crystals in association with sinking decomposing organic matter, in a world ocean mostly undersaturated for barite, and the release of these crystals after remineralization of the organic matter carrier. The water column distribution of barite in suspended matter reflects production of barite to take place mainly below the surface layer and to be ongoing mainly through the mesopelagic zone. However, the exact mechanism by which barite precipitates is still a matter of debate. Barite crystals in suspended matter collected during the BONUS-GOODHOPE cruise (2008) were examined by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM-EDX). The different facies and compositions of marine barite crystals from surface and mesopelagic depths are compared to investigate whether these carry information on the bio-organo-mineralization mechanisms. These results are compared with Baxs and barite profiles determined by ICP-MS and SEM-EDX analysis, respectively.
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