Gas Hydrate and Biogeochemical Processes


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Gas hydrate formation and associated biogeochemical processes is actively altering deep sea environments offshore SW Taiwan.  Abundant methane from organic carbon fermentation and thermogenic source fed assorted forms of microbial community at various depths in sediments as well as near the sea floor.  Methane migration could induce biogeochemical processes (Figure 1) including sulfate reduction, anaerobic methane oxidation (AOM), iron and manganese recycling, authigenic carbonate and iron sulfide minerals formation, and gas hydrate formation/dissociation.  Offshore SW Taiwan, situated in a complex tectonic settings with two types of tectonic modes, active and passive margin, adjacent to each in a short distance near Taiwan, is ideal environment in studying gas venting and types of biogeochemical processes under different tectonic settings.  Shown in Figure 2 are symbiosis mussel (Bathymodiolus platifrons) overlying by another symbiosis galatheid crab (Shinkaia crosnieri) intertwined with limpet gastropoda (Bathyacmea tertia) and shrimp (Alvinocaris longirostris) on top one of our research environment, the Formosa Ridge, using ROV Hyperdolphin on board r/v Natsushima on a joint cruise with the JAMSTEC. Figure 3 shows a layer of bacteria mat (Beggiatoa) feeding by hydrogen sulfide produced from sulfate reduction with methane diffusion upward reaching the sea floor.

Figure 1. Major biogeochemical processes offshore SW Taiwan.

Figure 2. A chemosynthesis community on top of the Formosa Ridge.

Figure 3. Beggiatoa bacteria mat near the Formosa Ridge.

2. Chemical weathering of small rivers drainage basins:

Physical denudation as a result of rapid island uplift and frequent earthquake is actively altering Taiwan’s landscape as well as delivering a very high amount of particles into seas surrounding Taiwan.  In conjunction, frequent typhoons and monsoon floods are also affecting river water and particle compositions.  One of our research topic focuses on spatial and temporal variations of Taiwan’s small rivers.  We have been study chemical compositions of river dissolve and particles in trying to understand the impact of weather pattern on small rivers in the subtropical environment.