HR: 1340h
AN: OS23A-1039    [Abstracts]
TI: Dynamic Cycling of Barium in Marine Sediments: A Case study From a Gas Hydrate Potential Region Offshore Southwestern Taiwan
AU: * Wu, S
EM: l4894109@mail.ncku.edu.tw
AF: Chen-Feng You, No.1, University Road, Tainan City 701, Taiwan (R.O.C.), Tainan, 701, Taiwan
AU: You, C
EM: cfy20@mail.ncku.edu.tw
AF: Chen-Feng You, No.1, University Road, Tainan City 701, Taiwan (R.O.C.), Tainan, 701, Taiwan
AB: The dissociation and dissolution of gas hydrate in marine sediments affects importantly of Ba and methane cycle. Three piston cores, MD052911, MD052912 and MD052913, collected during Marion Dufresne cruise from a potential gas hydrate area offshore southwestern Taiwan, were used for dissolved SO42- and Ba2+ analyses in pore waters, as well as exchangeable Ba2+ in sediments, to study hydrate gas venting history. The formation of barite front was identified in each core at shallow depth and theirs respective accumulation ages were estimated using a simple diffusion model. Dissolved SO42- and Ba2+ indicate that the sulfate hydrate transition (SHT) depth is located at 900, 1100 and 760 cm in MD052911, MD052912 and MD052913, respectively. Dissolved Ba2+ increased largely below the depth where sulfate depletion occurred and reached a maximum concentration of 14.8, 12.4 and 6.2 £gM at 660, 1800 and 760 cm, respectively. The detected sedimentary barite front coincides with the modern boundary of upward diffusion of pore water Ba2+, occurring right above the SHT boundary in all three cores and reaches a Ba concentration of 23, 54 and 40 ppm, respectively. Estimated upwardly diffusive Ba2+ flux is 1.93*10-6, 8.86*10-7 and 6.55*10-7 mmol/cm2/yr, which may take 25,000, 110,000 and 213,000 years respectively to accumulate such barite front. Sulfate reduction rate (SRR) in the study area, average ~70 £gM/yr, falls in a similar range as those of regions with intermediately low methane flux and SHT depth of 10-40m. The calculated downward sulfate fluxes, 1.78*10- 3 - 3.2*10-3 mmol/cm2/yr, agree with observations at methane-rich margins where methane were dominantly consumed by oxidation. The authigenic barite fronts formation above the SHT serves as a useful tool to assess the flux variation of upward methane at present and in the past. The unique low concentration of detritus barite in sediments offshore Taiwan cause rather low Ba2+ in pore waters and low exchangeable Ba2+ (23-54 ppm) in sediments compared with Blake Ridge and Gulf of Mexico. This, in turn, offers a sensitive opportunity to apply a diffusion estimation for studying gas venting history using barite front formation in sediment column.
DE: 3004 Gas and hydrate systems
DE: 4217 Coastal processes
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4825 Geochemistry
DE: 4863 Sedimentation (1861)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting