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Special Session 4: Biogeochemical cycling of trace elements in the ocean: GEOTRACES and beyond |
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An isotopic perspective to estimate fluxes of the aerosol dust deposition in the South China Sea
SS4-01-S
Rongrong Cen* , Xiamen University
Yihua Cai, Xiamen University
Presenter Email: crr5565@126.com
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| Measurements of 230Th and 232Th concentrations have been made on several water column profiles from the South China Sea. Both 232Th and derived 230Th profiles of the sampling sites near the Dongsha Island, on the continental shelf and slope of marginal seas, showed concentration maxim at ~ 0.5 - 0.8 km depth ( derived 230Th concentrations were higher than the estimates of reversible-scavenging model (RSM) ), minimum concentrations at ~ 1 - 3 km depth, and generally increasing concentrations within about 1 km of the seafloor. Th appear to have concentration maxima implicating a sediment source from the nearby continental margin. Source-to-sink sediment transport further out to sea from the continental shelf. Resuspension of sediments may enhance the release of dissolved Th near the seafloor. 232Th profiles near the Luzon Strait have generally increasing concentrations until at ~ 2km, then the concentrations go down because of bottom scavenging. And derived 230Th concentrations stayed lower value than those predicted by RSM. Oceanic 230Th is sourced mainly from the decay of dissolved 234U. Dissolved 232Th is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust. Assuming steady-state, the releasing rate of 232Th by mineral dissolution is constrained by a Th removal rate derived from 230Th - 234U disequilibria. Given the concentration and fractional solubility of Th in the lithogenic material, we can use calculated fluxes of dissolved 232Th in turn to estimate fluxes of the aerosol dust deposition. From our data, terrigenous 230Th in the sampling sites were calculated to be 12% - 50% of the total 230Th. |
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