Sediment fatty acids associated with seafloor methane seepage in the Nankai and Sagami Troughs, off central Japan

Abstract

Microbial abundance and composition represented by sediment fatty acids serve as the biomarkers for seafloor methane seeps even at 'juvenile' stages, while macroscopic animals serve as a visible marker for some 'aged' seeps. Sediment samples were collected using remotely operated vehicles from the bathyal to abyssal seafloors of Nankai Trough and Sagami Trough. A piston core sample from the West Philippine Basin seafloor was used as a non-seep reference. Sediment fatty acids were extracted as either total fatty acids or phospholipid fatty acids. Phosopholipid fatty acids represent the abundance and composition of 'living' microflorae. Compositions of total fatty acids and phospholipid fatty acids were cluster-analyzed to construct dendrograms. As a general result, high presence of fatty acid markers for sulfate-reducing bacteria and methane-oxidizing bacteria was associated with known methane seepage. The fatty acid profiles of a tested (suspected) seep site were closely similar to those of known seeps, which strongly suggests that the tested site is an incipient seep yet-to-be colonized. As methane acts as a greenhouse gas or a biospheric poison, it should be important to probe, i.e., detect and localize, seafloor methane seeps associated with sub-seafloor gas hydrates.

Molecular Dynamics Simulation of Methane Hydrate Formation and Dissociation in the Clay Pores with Fatty Acids

“…Among the microbial intermediates, fatty acids are of special importance because they can be further degraded to methane, 16 and they are considered biomarkers for seafloor methane seepage overlying the hydrate-bearing sediment. 17 However, no significant research has been conducted to verify the effects of fatty acids on the kinetics of methane hydrate formation and dissociation. The SOMs selected in current studies were strongly hydrophilic such as glucose, glycine, and urea, 13,15 and it remains unclear how the fatty acids with hydrophobic carbon chains and hydrophilic carboxyl interact with the hydrate cages in the clay pores.…”

“…Moreover, SOM represents diverse organic molecules as a result of microbial activities in the gas hydrate deposits, which have different functional groups and chemical configurations. Among the microbial intermediates, fatty acids are of special importance because they can be further degraded to methane, and they are considered biomarkers for seafloor methane seepage overlying the hydrate-bearing sediment . However, no significant research has been conducted to verify the effects of fatty acids on the kinetics of methane hydrate formation and dissociation.…”

Microflorae of aquatic moss pillars in a freshwater lake, East Antarctica, based on fatty acid and 16S rRNA gene analyses

“…Extracts were analyzed by Agilent 6890 GC (Agilent Technologies, Little Falls, DE, USA) following Kanekiyo et al (2005). Inter-sample similarities based on fatty acid composition ratios were calculated as Euclidean distances, and cluster analysis was performed using SPSS (SPSS Inc., Chicago, IL, USA).…”