Geochemical record of methane seepage in carbon cycling and possible correlation with climate events in the Qiongdongnan basin, South China Sea

Abstract

At cold seeps, sulfate-driven anaerobic oxidation of methane (SD-AOM) is the dominant biogeochemical process, which can significantly affect the marine carbon-sulfur cycle. In this paper, multiple sedimentary indicators in core QS-1 were reported for methane seepage from Haima seep of the South China Sea (SCS). By combining total carbon (TC), total organic carbon (TOC), total sulfur (TS), total inorganic carbon (TIC), as well as the carbon and oxygen isotope compositions of benthic foraminifera Uvigerina spp. In sediments, our aim was to explore the geochemical evidence on methane seepage activities in this area. We identified three methane release events (MREs) with different intensities and timescales during MIS 1–2, characterized by particular anomalies of negative δ13CTIC (as low as −41.42‰) and δ13CU.spp (as low as −5.50‰), high contents of TS and high S/C ratios, simultaneously. High S/C ratios and negative values of δ13CTIC effectively indicate the intense SD-AOM and SD-AOM-related process in core QS-1. Three MREs, occurred at high or low sea level, may due to the climate-driven increase of hydrostatic pressure and seafloor temperature. The insights for sediment carbon-sulfur trace element, carbon isotopes of TIC contents and benthic foraminifera have obvious implications for tracing past methane seepages and its possible link with climate changes.