Fumio Inagaki, PhD
Director, Principal Senior Scientist
Mantle Drilling Promotion Office (MDP),
Institute for Marine-Earth Exploration and Engineering (MarE3),
Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Work Address: Showa-machi 3173-25, Kanazawa-ku,
Yokohama 236-0001, JAPAN
Guest Professor, Research Organization for Nano & Life Innovation, Waseda University, Japan
Guest Professor, Graduate School of Integrated Arts and Sciences, Kochi University, Japan.
MY RESEARCH INTEREST
Understanding Deep Life, Deep Carbon, and Deep Time
for sustainable planetary habitability of the Earth
Missions to Mantle: The most challenging endeavor in geoscience
To date, the impact of anthropogenic climate and environmental changes on the Earth’s ecosystem and human society is becoming increasingly apparent. Understanding complex feedback-mechanisms that may affect the trajectory of our planetary systems, such as the balance of carbon and energy as the future human population grows, is an urgent need for the sustainability of the ocean and Earth’s health as well as human well-being. From a mid-to-long-term perspective, scientific ocean drilling will provide unique opportunities for the international and multidisciplinary scientific community to gain new insights into geosphere-biosphere interactions from the past and present to the future. For example, ecosystem responses to environmental changes could be deciphered from ancient DNA, biomarkers, and/or indigenous microbial communities that persist in sediment over geologic time. The planetary habitability involving interactions between the Earth’s surface and subsurface biospheres remains largely elusive, in terms of energy, space, and time. Also, it is almost completely unknown what types of pre-biotic/abiotic chemical reactions occur beneath the limit of the deep biosphere and what roles of the chemical evolution are in the emergence and evolution of life.
There are many places to drill and study mantle-ocean-life-atmosphere interactions. For example, at hydrothermally active volcanic hotspots, spreading ridges, outer-rise faulting systems, and even deep subseafloor abyssal plains, relatively low-temperature oxic seawater may deep penetrate the oceanic crust and react with mantle peridotites to supply nutrient and energy substrates for in-situ or shallower life. Because the mantle occupies 83% of the Earth’s volume and 67% of its weight, and given the fact that its energy convection intimately controls the Earth’s dynamism, drilling, characterizing, and observing the oceanic lithosphere down to the upper mantle penetrating through the Mohorovičić discontinuity will be the most comprehensive, challenging, and innovative endeavor on Earth, which will be able to accomplish using state-of-the-art current human technologies.
The Deep Subseafloor Biosphere
Over the past decades, scientific ocean drilling has explored subseafloor environments at various oceanographic and geological settings, which resulted in numerous discoveries on Earth’s planetary sub-systems —the atmosphere, hydrosphere, geosphere, and biosphere. The dynamism fostering the co-evolution of life and the Earth system is principally constrained by extra- and intra-terrestrial energy sources. The lithosphere consisting of sediments, crusts and upper mantle plays a significant role as an interface between the Earth’s asthenosphere and the overlying hydrosphere and atmosphere. Drilling the Earth’s lithosphere down to the upper mantle has significantly expanded our understanding of Earth’s sub-systems and will continue to do so in the future. To date, only little is known about how Earth’s various spheres interact, despite the awareness that such spheres connect and interact with each other. Building this knowledge will provide useful insights at various levels into the past, present and future of our Earth and human society.
With respect to the deep biosphere, accumulating evidence from ocean margin sites indicates that remarkable numbers of anaerobic microbial cells are present at least down to at least ~2.5 km below the ocean floor (Inagaki et al., Science, 2015). In open ocean sites, the occurrence of microbial communities and oxygen was observed in the entire sediment column of the ultra-oligotrophic South Pacific Gyre, qualifying up to ~37% of the global oceanic sediment as aerobic biosphere (D'Hondt et al., Nature Geoscience, 2015). These recent findings through scientific ocean drilling have characterized the deep biosphere as one of the important Earth’s sub-systems, where microbial life inhabiting the vast oceanic lithosphere influences whether several important elements are sequestered for millions of years or returned to the ocean as active agents with an impact on life and climate (Hinrichs & Inagaki, Science, 2012).
Only a better understanding of the Earth’s multi-spheres interactions through scientific ocean drilling will enable informed conclusions regarding the origins and evolution of life, oceans and Earth—the characterization and monitoring of multi-spheres boundaries, including the limits to the deep biosphere, will highlight the organization and interactions of Earth’s sub-systems and provide critical information enabling the discovery and utilization of new functions of Earth’s multi-spheres deep beneath the ocean (Inagaki & Taira, Oceanography, 2019).