To better constrain the temperature limit of life in the deep biosphere, the International Ocean Discovery Program (IODP) is preparing Expedition 370 “T-Limit of the Deep Biosphere off Muroto (T-Limit)” with the Japanese drilling vessel Chikyu to revisit Ocean Drilling Program (ODP) Site 1174 in the Nankai Trough subduction zone off Cape Muroto, Japan (10 September - 10 November 2016).
Because of the high heat flow in this part of the Nankai Trough (4731 m water depth), temperatures are likely ~130°C at the sediment/basement interface (1210 mbsf). This makes the site an ideal target for in-depth examination of subseafloor microbial life close to its putative upper temperature limit. ODP Leg 190 has already shown that cell concentrations drop abruptly at sediment depths around 800 mbsf. Exp. 370 now returns to investigate this putative biotic-abiotic transition with technologies that have advanced tremendously over the past 16 years. The expedition's scientists aim to study diversity, activity, and biomass of microbial communities at the biotic fringe as well as the controlling environmental factors. In order to fully exploit the available technologies, the scientific work program onboard Chikyu will be complemented by simultaneous analytical work in the ultra-clean room facilities of the Kochi Core Center (KCC), which is located within reach of a helicopter shuttle for transportation of freshly cored samples. After drilling, multiple-temperature sensors will be installed into the borehole, allowing ~1 year monitoring of formation temperature in situ. For more information see the expedition homepage: http://www.jamstec.go.jp/chikyu/e/exp370/
The International Ocean Discovery Program (IODP) Expedition 370 Scientific Prospectus, T-Limit of the Deep Biosphere off Muroto (T-Limit): Deciphering factors that constrain the extent of the deep biosphere in a subduction zone, is now published on the IODP website (doi:10.14379/iodp.sp.370.2016).