[S-CG42] Frontier of Understanding Earth's Interior and Dynamics

[SCG42-02] Exploring the deep biosphere-frontier beneath the ocean: A geobiological perspective on the oceanic crust and the underlying upper mantle

★Invited Papers

*Fumio Inagaki¹ (1.Mantle Drilling Promotion Office, Institute for Marine-Earth Exploration and Engineering (MarE3), Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

Keywords:scientific ocean drilling, deep subseafloor biosphere, planetary habitability

Over the last two decades, multiple scientific ocean drilling explorations have revealed the existence of an abundant and diverse microbiome deep beneath the ocean floor, which is comparable to those living in the top-soils and seawater on the Earth's surface [1]. Although their activity is maintained at levels close to the theoretical limits of sustaining essential life functions on geological time scales, they are revivable [2], temperature-sensitive [3], and contribute to global material cycles associated with plate tectonics. What are the conditions and limits to life in the Earth's interior deep beneath the ocean floor? What are their origins, evolution, and consequences? How will life continue to shape Earth? Given the fact that the subseafloor biosphere is situated on a thin, mobile layer between the ocean and the mantle on our planet Earth, these questions ultimately be linked to the water-life-crust/mantle interactions and its dynamics. Exploring the entire sequence of oceanic crust down to drilling's accessible limit in the upper mantle will significantly expand our current knowledge of planetary systems [4]. Continued international, transdisciplinary collaborations among geoscience communities are essential for illuminating the trajectory of our planet's habitability and sustainability.

[1] Hoshino, T., Doi, H., Uramoto, G.-I., Wömer, L., Adhikari, R. R., Xiao, N., Morono, Y., D'Hondt, S., Hinrichs, K.-U., and Inagaki, F. (2020) Global diversity of microbial communities in marine sediment. Proc. Natl. Acad. Sci. USA, 117, 27587-27597.
[2] Morono, Y., Ito, M., Hoshino, T., Terada, T., Hori, T., Ikehara, M., D'Hondt, S., and Inagaki, F. (2020) Aerobic microbial life persists in oxic marine sediments as old as 101.5 million years. Nature Communications, 11, 3626.
[3] Heuer, V. B., Inagaki, F., Morono, Y., et al. (2020) Temperature limits to deep subseafloor life in the Nankai Trough subduction zone. Science, 370, 1230-1234.
[4] Inagaki, F., and Taira, A. (2019) Future opportunities in scientific ocean drilling: Illuminating planetary habitability. Oceanography, 32, 212-216.