Gas Hydrate Dissociation During Sea‐Level Highstand Inferred From U/Th Dating of Seep Carbonate From the South China Sea. Issue 23 (6th December 2019)

• Record Type: Journal Article
• Authors: Chen, Fang; Wang, Xudong; Li, Niu; Cao, Jun; Bayon, Germain; Peckmann, Jörn; Hu, Yu; Gong, Shanggui; Cheng, Hai; Edwards, R. Lawrence; Ning, Youfeng; Jin, Meng; Huang, Huiwen; Wu, Cong; Sun, Yuedong; Chen, Hong; Zhou, Yang; Chen, Duofu; Feng, Dong
• Is Part Of: Geophysical research letters. Volume 46:Issue 23(2019)
• Page Start: 13928
• Page End: 13938
• Publication Date: 2019-12-06
• Subjects: methane seep gas hydrate seep carbonate; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL085643
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Gas hydrates represent a huge reservoir of methane in marine sediments, prone to dissociation in response to environmental changes. There is consensus that past events of gas hydrate dissociation in the marine environment mainly occurred during periods of low sea level. Here, we report geochemical data for 2‐m‐thick layers of seep carbonate collected from a hydrate‐bearing drill core from ~800‐m water depth in the northern South China Sea. The aragonite‐rich carbonates reveal positive δ 18 O values, confirming a genetic link with gas hydrate dissociation. Uranium‐thorium dating of seep carbonates indicates that gas hydrates at the study site dissociated between 133, 300 and 112, 700 years BP, hence coinciding with the Last Interglacial (MIS 5e) sea‐level highstand. We put forward the concept that a climate‐driven increase in temperature was responsible for a period of pronounced gas hydrate dissociation. Plain Language Summary: The gas hydrate reservoir is a dynamically changing system extremely susceptible to variations of seafloor temperature and pressure. Therefore, gas hydrate dissociation and subsequent methane seepage frequently occur during times of global climate change, especially during sea‐level lowstands with reduced seabed pressure. However, this conclusion was mainly based on dating of seep carbonates sampled from the seabed. As a consequence, one cannot exclude that previous results have been compromised by a sampling bias since seafloor samples are easier to collect. Authigenic seep carbonates from drill cores represent a continuous record of gas hydrate dynamics. Our uranium‐thorium dating of seep carbonate from drill cores provides a unique example of the effects of temperature and pressure on the stability of the hydrate system in the Dongsha area, northern South China Sea (SCS), during the last interglacial stage (MIS 5e, about 130, 000 years BP). Representing the most similar and most contemporary analog to the current interglacial, the study of a methane release event in the SCS during MIS 5e will shed light on the expected trend of methane release events in the future, while providing insight into the response of low‐latitude oceans to climate change. Key Points: U/Th dating of seep carbonates from a gas hydrate‐bearing sediment drill core provides constraints on the timing of methane seepage Carbonates precipitated from 18 O‐enriched pore fluids derived from methane hydrate dissociation Methane hydrate dissociation occurred during sea‐level highstand (MIS 5e) possibly induced by increasing bottom‐water temperatures