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Transfer of methane from gassy sediments into the water column associated with submarine groundwater discharge: geochemical evidences and implications

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Sauter, E. (2001): Transfer of methane from gassy sediments into the water column associated with submarine groundwater discharge: geochemical evidences and implications , Hanse Conference: Subterranean Coastal Environments - Biogeochemical Processes, Fluxes and Impacts. Held May 22 - 25in Delmenhorst. . .
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Abstract:

Abstract:Organic carbon fluxes through the sediment/water interface in the high-latitude North Atlantic have been calculated from oxygen microprofiles. A wire-operated in situ oxygen bottom profiler was deployed, and oxygen profiles were also measured on board (ex situ). Diffusive oxygen fluxes, obtained by fitting exponential functions to the oxygen profiles, were translated into organic carbon fluxes and organic carbon degradation rates. The mean Corg input to the abyssal plain sediments of the Norwegian and Greenland Seas was found to be 1.9 mgCm-2d-1. Typical values at the seasonally ice-covered East Greenland continental margin lay between 1.3 and 10.9 mgCm-2d-1 (mean 3.7 mgCm-2d-1), whereas fluxes on the East Greenland shelf are considerably higher, with 9.1 to 22.5 mgCm-2d-1. On the Norwegian continental slope Corg fluxes of 3.3 to 13.9 mgCm-2d-1 (mean 6.5 mgCm-2d-1) were found. Fluxes are considerably higher here compared to stations on the East Greenland slope at similar water depths. By repeatedly occupying three sites off southern Norway in 1997 the temporal variability of diffusive O2 fluxes was found to be quite low. The seasonal signal of primary and export production from the upper water column appears to be strongly dampened at the seafloor.Degradation rates of 0.004 to 1.1 mgCcm-3a-1 at the sediment surface were calculated from oxygen profiles. First-order degradation constants, obtained from Corg degradation rates and sediment organic carbon content, are in the range of 0.03 to 0.6 a-1. Thus, the corresponding mean lifetime of organic carbon lies between 1.7 and 33.2 years, which also suggests that seasonal variations in Corg flux are small. The data presented here characterize the Norwegian and Greenland Seas as oligotrophic and relatively low organic carbon deep-sea environments.Keywords: Diffusive oxygen uptake, benthic fluxes, organic carbon, in situ oxygen microelectrodes, North Atlantic, high latitudes.

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