Application form InterRidge Student and Postdoctoral Fellowship ...

II. PROPOSALPlease describe your proposed research project using sections (a) – (f) below (not to exceeda total of 3 pages, including figures and references):(a) Short summary (100 words maximum; please write this for a broad scientific audience –it will be posted to the IR website if the fellowship is awarded):The hydrothermally active ridge close to continents (Okinawa, JdFR, etc.) has sedimentson the seafloor. The sedimentation settings are often linked to fluid geochemistry (e.g. high CH 4content at sediment-covered sites). However, it has been poorly investigated how and where thefluid-sediment interaction occurs during hydrothermal fluid circulation. In order to elucidate thethermal fluid-sediment interactions under hydrothermal condition, sediment heating experimentswill be carried out in close collaboration with Dr. Seewald at WHOI. The results obtained fromthe experiments will provide the detail information about “thermogenic methane” characteristics,which will clearly differentiate between thermogenic and biogenic “sediment-derived”characteristics.(b) Background and objectives of the proposed research:A hydrothermally active area close to continents, including Okinawa Trough sites, MiddleValley, and Guaymas, has large amount of sediments on the seafloor resulted from riverine flowand high productivity at coastal sea surface. Presence of the sediment, especially sedimentaryorganic matter, is directly involved in geochemical characteristics of hydrothermal vent fluid,such as high CH 4 , NH 4 , Alkalinity, and so on [von Damm et al., 1985; Sakai et al. 1990; Cruseand Seewald, 2006]. Although the linkage between sediment setting and fluid geochemistry hasbeen identified, how and where the linkage occurs during hydrothermal fluid circulation is stillunsolved.To interpret the origin of sediment-derived methane is one of the most effective ways toinvestigate “how and where” the fluid-sediment interaction occurs, because methane can beproduced by thermal as well as biological processes associated with sedimentary organic matter.The origin of the excess methane at sediment-covered hydrothermal sites was explained bymethane production through thermal decomposition of sedimentary organic matter [Ishibashi etal., 1995]. Alternatively, microbial methanogenesis has also been mentioned as the possibleorigin of methane in vent fluids at sediment-covered hydrothermal systems [Pearson et al. 2005;Cruse and Seewald, 2006; Kawagucci et al. submitted]. However, relative contribution of theseprocesses has not been so far clarified due to uncertainties of current tracers to distinguish eachother. Therefore, it is extremely important to develop the useful tracers and confirm theusefulness of the current tracers to distinguish thermogenic from biogenic methane, which willclarify the relative contribution of thermal and biological processes to decompose sedimentaryorganic matter.The [δ 13 C]-[C 1 /C 2 ] map [e.g., Whiticar, 1999] is currently recognized as the best way toidentify the origin of the sedimentary environmental methane. However, typical thermogenicranges of both δ 13 C and C 1 /C 2 ratio (thermogenic area on the map) are problematic and should berevised due to following two reasons. First, since recent geomicrobiological knowledge indicatesa potential of microbial methanogenesis even in the elevated temperature range [Parkes et al.,2007; Takai et al., 2008], environmental methane previously considered as “thermogenic” could