Effects of the Last Deglaciation climate warming on hydrate dissociation in the northern South China Sea

Abstract

Sea level and bottom water temperature variations caused by the Last Deglaciation climate warming impacted the stability of marine hydrates. In order to examine their influence on hydrate dissociation in the northern South China Sea (SCS), we conducted simulations to track the evolution of hydrate saturation and hydrate occurrence zone since the Last Deglaciation in the Dongsha Area, Shenhu Area, Xisha Area and Qiongdongnan Area. The amount of methane generated and subsequently released into seawater and atmosphere was also evaluated within the four areas. The simulation revealed the following results: (1) Hydrate dissociation induced by variations in sea level and bottom water temperature was observed in the Dongsha Area, Xisha Area and Qiongdongnan Area, but not in the Shenhu Area. (2) The water depth at which hydrate dissociation occurred ranged between 480 and 720 m, encompassing a hydrate dissociation area of approximately 1.54 × 10¹⁰ m². This accounted for 6.68% of the northern South China Sea Area. (3) Since the Last Deglaciation, an estimation of 3.08 × 10⁸–1.48 × 10¹⁰ m³ hydrates have dissociated, resulting in the release of 5.05 × 10¹⁰–2.43 × 10¹² m³ methane. The generated methane migrated through the overlying sediments by means of central migration mode. 9.9 × 10⁹–4.76 × 10¹¹ m³ methane entered into the seawater, which will result in the formation of a weak acid affecting the marine environment. Meanwhile, 2.02 × 10⁸–9.72 × 10⁹ m³ methane entered into the atmosphere, which leads to an increase in greenhouse gas concentrations.