Massive Natural Gas Hydrate Dissociation During the Penultimate Deglaciation (~130 ka) in the South China Sea

Abstract

There is widespread and growing scientific interest in the impact of massive gas hydrate dissociation on the global environment and climate in geological history. Based on that a global negative excursion of carbon isotopic compositions in marine (foraminifera) and terrestrial (the organic carbon and calcite) sedimentary records occurred during the penultimate deglaciation (~130 ka), we believe that methane released by hydrate dissociation may play a role in accelerating the initial increase of atmospheric methane. In order to prove that massive natural gas hydrate dissociation occurred in this period, we aim to seek for evidence of gas hydrate dissociation from seep carbonate. Here, X-ray diffraction, carbon and oxygen isotopic compositions, trace elements, and U-Th dating analyses were conducted on the deeply-buried authigenic carbonate obtained by drilling in the northern continental slope of the South China Sea. Authigenic carbonate formed at ~130 ka showed obvious characteristics of negative excursion of carbon isotope, positive excursion of oxygen isotope, and enrichment of redox sensitive elements such as Mo, U and As. These results, in particular the high oxygen isotopic compositions of carbonate, point to massive gas hydrate dissociation in the northern continental slope of the South China Sea during the penultimate deglaciation. It is further speculated that massive gas hydrate dissociation might have also occurred on a global scale, contributing to the increase of atmospheric carbon dioxide and methane concentrations during the penultimate deglaciation, and may eventually cause global carbon isotope negative excursion.