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Saulwood Lin, National Taiwan University (Taiwan)
CharShine Liu, National Taiwan University (Taiwan)
Tsanyao Yang Yang, National Taiwan University (Taiwan)
Hideaki Machiyama, Japan Agency for Marine Science and Technology (Japan)
Katsnori Fujikura, Japan Agency for Marine Science and Technology (Japan)
Yue-Gao Chen, National Taiwan University (Taiwan)
Yeecheng Lim, National Taiwan University (Taiwan)
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An active gas hydrate related seep environment with live chemosynthetic community was recently found in the Northern South China Sea continental (passive) margin at a water depth of about 1100m. Abundance of mussels (Bathymodiolus platifrons) and galatheid crab (Shinkaia crosnieri) using Towcam pictures reached 300 specimens per square meter, however, ROV survey showed layers of mussels and crabs piled on top of each other rendering abundance difficult to calculate. Other identified community members included shrimp (Alvinocaris longirostris), gastropod (Bathyacmaea tertia) and bacteria mat. The biological community appeared on the summit of the Formorsa Ridge with obvious spatial variations. From the outer perimeter, normal mud predominated the surrounding ridge flank. Bacteria mats begin to appear nearing the summit, following by dead, bleached bivalve shells, authigenic carbonate, and benthic community.
Three unique features were found, multiple plumes in the water column, pulsation gas/fluid venting and hydrothermal type bio-community. Multiple gas plumes in the water column as well as bubbles emitting from sea floor indicated gas and fluid are continuously carrying methane to the surface. Part of the methane was oxidized and registered strong signals in the authigenic carbonate and mussel shells with stable carbon isotopic values ranging from -45 to -55 per mil. The occurrence of galatheid crab is unusual since it was normally found in the hydrothermal environment. Furthermore, the abnormal abundance of galatheid crab requires unusual supplying of methane and sulfide as their energy source. Source of dissolved sulfide is probably from rapid sulfate reduction with pore water dissolved sulfide reaching 10 mM. With upward advection of fluid carrying methane through rapid sulfate reduction zone, dissolved sulfide is capable of providing and becoming the energy source for the near surface biological community.
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