Gas hydrate dissociation during relatively sea level highstands: Evidence from U/Th dating of carbonate from gas hydrate drilling core of the South China Sea

The biggest methane reservoir in marine sediments is thought to exist in the form of gas hydrates, which is susceptible to dissociation triggered by environmental changes. Using mainly seabed-sampled seep carbonates from continental margins, previous studies showed that gas hydrate tends to dissociate during periods of low sealevel (glacial periods). Here, we use two continuous authigenic carbonate layers from a drilling core in the northern South China Sea (~ 800 m water depth). These carbonates were dominated by aragonite and yielded extremely negative δ¹³C but positive δ¹⁸O values, confirming a linkage to gas hydrates dissociation. Three stages of seep activities were divided by uranium-thorium dating carbonate: I): 133,300-130,600 year BP; II): 130,600-128,300 year BP; and III): 128,300-112,700 year BP, respectively. This chronology suggests that gas hydrate dissociation may occur during sea level highstands. We propose that gas hydrate system response to scenarios of climate-driven change in different timescales.