Estimating the time of pockmark formation in the SW Xisha Uplift (South China Sea) using reaction-transport modeling

TitleEstimating the time of pockmark formation in the SW Xisha Uplift (South China Sea) using reaction-transport modeling
Publication TypeJournal Article
Year of Publication2015
AuthorsLuo M, Dale AW, Wallmann K, Hensen C, Gieskes J, Yan W, Chen D
JournalMarine Geology
Date Published2015/03
ISBN Number0025-3227
KeywordsAnaerobic oxidation of methane; Non-steady-state; Organic matter degradation; Pockmark; Reaction-transport model; south china sea

Carbon cycling and fluid seepage in marine sediments over the late Quaternary were investigated at a now-extinct pockmark located in a mega-pockmark field in the SW Xisha Uplift (NW South China Sea). Measured particulate organic carbon (POC) content, and porewater sulfate (SO42 −), dissolved inorganic carbon (DIC) concentrations and δ34S-SO42 − distributions were used to constrain a non-steady-state reaction-transport model and quantify POC mineralization rates as well as estimate the time when fluid flow ceased at the investigated pockmark. An increase in POC content and δ34S-SO42 − and a decrease in sulfate concentrations in the upper ca. 2 m at the pockmark and a reference core implied an increase in the flux and reactivity of organic matter during the early Holocene around 10 kyr B. P. caused by enhanced primary productivity during the strengthened southwestern summer monsoon. These features were simulated with the model assuming a Holocene increase in POC flux and reactivity. Subsequently, starting from an initial condition reminiscent of a modern active cold seep (Hydrate Ridge), hindcast simulations showed that fluid seepage at the pockmark ceased ca. 39 kyr ago. This corresponds to a relative sea level high-stand, which is believed to be associated with gas hydrate stabilization. The non-steady-state model presented in this contribution can also be used to constrain the time when fluid seepage ceased at other presently extinct cold seeps when suitable sediment and porewater data are available.

Short TitleMar. Geol.
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