Abstract
Biomarkers from methane hydrate-bearing sediments can provide vital evidence for microbial activities associated with methanogenesis and their relation to the formation of methane hydrates. However, the former mainly focus on intact polar lipids from these microorganisms, and rarely investigate molecular hydrocarbons such as acyclic isoprenoids and hopanes so far. In this work, the composition of biomarkers in the methane hydrate-bearing sediments in cores SH2B and SH7B from the Shenhu area, the South China Sea (SCS) were identified by gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC×GC-TOFMS). The occurrence of unresolved complex mixtures (UCMs) and 25-norhopane indicate that the organic matters in methane hydrate-bearing sediments underwent a high degree of biodegradation. Although specific biomarkers for methanogens were not identified, the UCMs, 25-norhopane, pristane, phytane, and hopanes can still indicate the microbial activities associated with methanogenesis. These molecular signals suggest that diverse microorganisms, particularly methanogens, were quite vigorous in the methane hydrate-bearing sediments. Further, the biomarkers identified in this study can also be steadily detected from deep oil/gas reservoirs. Considering numerous adjacent oil/gas reservoir systems, fault systems, and mud diapers occurred in the SCS, it can be inferred that microbial activities and deep oil/gas reservoirs may have jointly contributed to the formation of methane hydrate deposits in the SCS.
Highlights
Methane hydrate is a crystalline solid composed of water and methane-dominated hydrocarbon molecules formed under the conditions of low temperature, high pressure, and adequate methane concentrations [1]
GC×GC-TOFMS analysis can clearly identify the biomarkers that cannot be separated by conventional gas chromatography-mass spectrometry (GC-MS)
unresolved complex mixtures (UCMs), 25-norhopane, pristane, phytane, and hopanes have been identified from deeply buried hydrate-bearing sediments in the Shenhu area, in the South China Sea (SCS)
Summary
Methane hydrate is a crystalline solid composed of water and methane-dominated hydrocarbon molecules formed under the conditions of low temperature, high pressure, and adequate methane concentrations [1]. It is mainly distributed in the marine sediments and land permafrost [2]. Methane hydrate has many merits, such as wide distribution and abundant resources. Methane hydrate is considered as one of the most promising clean energy sources in the 21st century, and has become one potential candidate for the future energy resources compared to oil and coal [4]. Of particular interests are microbial communities and their activities that contribute to the vast formation of hydrated methane in deep-sea sediments [6]; and are potentially critical for the stability, composition, and crystal structures of methane hydrates [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
