PRJNA217520
Subseafloor sediments hosting gas hydrates Targeted Locus (Loci)
Sediment samples were obtained from the Andaman Sea at Site 17A during the National Gas Hydrates Program (NGHP) Expedition 01 in 2006 (Scientists ''06) and microbiology described in (Briggs et al. ''12). This site exists in a back arc basin that contains mainly marine deposited nanofossil ooze that was deposited at a rate of 5.6 cm/kyr. The uniquely low geothermal gradient (2.1° C/100 m) allows gas hydrate to exist deep into the sediment column (300 to 600 meters below seafloor or mbsf) making the gas hydrate deposits found at this location among the deepest discovered to date. Geologic horizons demarcate this gas hydrate occurrence zone (GHOZ) as evidenced by increasing porosity from 50% to 63% at 300 mbsf and a seismically observed bottom-simulating reflector where the methane is believed to exist as a free gas at 600 meters below seafloor (mbsf). Biogenic methane is present above 600 mbsf and transitioning to mixed thermogenic/ biogenic methane. In addition, the Andaman Sea sediments are unique because the total organic carbon (TOC) is less than 1% by weight, while other similar continental margins where microbiology has been examined contain 1-11% TOC (Meister et al. ''05).