Séminaire EPOC "Biogeochemical signatures of methane cycle in the marginal sea sediments" - Kyung-Hoon SHIN (Hanyang University, South Korea)

Résumé : The recent methane (CH4) release has revealed the potential impact of gas hydrates (GH) dissociation on the global carbon cycle and climate change. However, only a few studies have traced the biogeochemical ongoing of CH4 in the deep geosphere. Hence, we investigate geochemical signatures for the CH4 cycle in GH bearing sediments (East Sea, Okhotsk Sea and Beaufort Sea in Arctic), located in a tectonically active continental slope with CH4 venting and the formation of shallow GH. Among the suite of archaeal biomarkers, we have focused on GDGTs (including biphytane), archaeol and sn-2-hydroxyarchaeol profiles retrieved from active CH4 venting sites. Our results indicated that these compounds showed significant concentration variations with a pronounced peak in Sulfate-Methane Transition Zone (SMTZ). Especially, the relationship between predominant abundance and depleted their isotopic values (?13C) have linked the maxima to methanotrophic activities, considering that an intense CH4 release occurred from upward CH4 flux as well as the GH dissociation in our study sites. The active CH4 migration via seismically chimney-like structure results in a larger population and higher activities of methanotroph as driving force for the anaerobic methane oxidation (AOM), thereby controlling CH4 cycle. The molecular and isotopic signature of geochemical properties and compound specific isotopic analysis provide a useful tool which help to better understand biogeochemical CH4 cycle in the active CH4 venting systems.

Prof. Shin fera dans la foulée le jeudi 28 un "short talk" à Arcachon à 10h45 intitulé "Amino-acids , a tool for environmental studies"