9:45 AM - 10:15 AM
★ [U04-02] Exploring life at its limits in the subseafloor biosphere through scientific ocean drilling
Keywords:IODP, The deep subseafloor biosphere
The Integrated Ocean Drilling Program (IODP) Expeditions 329 and 337 were the microbiology and biogeochemistry-dedicated scientific ocean drilling, targeting on very distinct oceanographic settings; in 2010, using the JOIDES Resolution, Expedition 329 explored deep-water sediments (water depth: 3,740~5,695m, sediment depth: ~131m) down to the basement at 7 sites in the ultra-oligotrophic South Pacific Gyre. During Expedition 337 in 2012, the Chikyu explored ultra-deep sediments (water depth: 1,180m, sediment depth: ~2,466m) associated with deeply buried coalbeds in the northwestern Pacific coast. The samples and data collected during these drilling expeditions, as well as rapid technological developments, provided unprecedented opportunities to study the limits and habitability of life in the subseafloor sedimentary biosphere.
The number of microbial cells is measured by newly developed cell separation and fluorescent image-based cell count techniques, revealing that cell abundances in both ultra-oligotrophic and deep coalbed-associated sediment samples are several orders of magnitude lower than those previously observed in shallow sediments of the ocean margins. The finding of very small microbial populations under two distinct extreme subseafloor conditions leads to subsequent questions: What are the environmental constraints for habitability of subseafloor life? What are ecological roles of subseafloor microbial activity in biogeochemical carbon and other elemental cycles? What are genetic and metabolic functions and its diversity of microbial communities? How and why can they live in such deep and extremely energy-limited conditions?