PROJECT

T-Limit of the Deep Biosphere

Summary

On 12 September 2016, an international team of 25 researchers boarded the drilling vessel (D/V) Chikyu, the world’s largest scientific research vessel, in Shimizu Port in Shizuoka, Japan, to begin a 60-day quest to determine the limits of life below the ocean’s floor. Working with six additional shore-based scientists, the team set out to define the temperature limits to deep life in marine sediments and to clarify key factors, including pressure, limiting Earth’s underground habitable zone.

Three co-chief scientists led the T-Limit expedition: Drs. Verena Heuer (MARUM, University of Bremen), Fumio Inagaki (Kochi Institute for Core Sample Research/Research and Development Center for Ocean Drilling Science, JAMSTEC), and Yuki Morono (Kochi Institute for Core Sample Research, JAMSTEC). The co-chief scientists and many others on the science team are members of the Deep Carbon Observatory.

International Ocean Discovery Program’s (IODP) Expedition 370: T-Limit of the Deep Biosphere off Muroto targeted many of the science goals of the Deep Carbon Observatory, including mapping the abundance and diversity of subsurface marine microorganisms and their interactions with deep carbon.

The state-of-the-art D/V Chikyu traveled to the central Nankai Trough, ~120 kilometers off the coast of Japan where the ocean is 4.7 kilometers deep, and drilled a further 1.2 kilometers beneath the ocean’s floor to collect sediment and rock cores. The total distance from the ocean’s surface to the target sample depth is equivalent to the height of 18 Eiffel Towers.

The Nankai Trough off Cape Muroto offers unique conditions where temperatures can approach ~130°C as cores were collected. Based on previous data from deep-sea hydrothermal vents, researchers expected the upper limit of life in the seafloor near 120°C. The hottest life currently catalogued on Earth includes Geogemma barossii, a single-celled organism thriving in hydrothermal vents on the sea floor. Its cells, tiny microscopic spheres, grow and replicate at 121°C. Scientists found the organism, also known as strain 121, in a sample collected during a 2003 expedition to the Juan de Fuca Ridge off the northwest USA coast and named it after Deep Carbon Observatory scientist John Baross (University of Washington, USA), who provided the sample.

The Trough is located on the Eurasian plate, where heat flow is particularly high, near its boundary with the subducting young, hot Philippine Sea tectonic plate. At the targeted site, the geothermal gradient is about four times steeper than elsewhere in the Pacific Ocean. Reaching these temperatures in other areas would require collecting cores from ~4 kilometers below the seafloor, rather than the 1.2 kilometers target for the T-Limit Expedition.

Researchers found the site in Nankai Trough 15 years ago but returned in 2016 with a renewed purpose and more advanced technologies, coupled with analysis capabilities at top laboratories around the world. In their sample analyses, investigators also are considering existing data to learn how cell concentrations drop to zero, or if life continues at a slower pace or with different forms of microbes with different energy needs.

A unique aspect of this endeavor involved investigations occurring simultaneously onboard the Chikyu and on land at the Kochi Core Center in Kochi, Japan. For the first time, helicopters transported fresh core samples from the Chikyu to the state-of-the-art research facilities in the Kochi Core Center. There, members of the shore-based science team analyzed samples to determine the geochemical and microbiological characteristics of the sediments, and painstakingly counted minuscule and sparse cells.

The team used next-generation DNA sequencing technology to determine which organisms can survive in deep subseafloor sediments and their ancestry. Genetic data like these provided clues showing how resident microbes adapt to such extreme environments.

T-Limit Infographic

 

Research Questions

How deep is Earth’s habitable zone?

How deep is the deep subseafloor biosphere?

How does the deep biosphere affect life at the surface?

Could life have originated deep and moved upward?

Project Leaders

  • Heuer
    Verena Heuer MARUM University of Bremen, Germany
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    Heuer
    Verena Heuer
    MARUM University of Bremen, Germany
  • Dr. Fumio Inagaki
    Fumio Inagaki Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan
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    Dr. Fumio Inagaki
    Fumio Inagaki
    Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan

    Dr. Fumio Inagaki is a geomicrobiologist, who has sailed in scientific ocean drilling expeditions many times as a shipboard scientist (ODP Leg 201, IODP Expeditions 301 and 316) and as co-chief scientist (Expeditions 329, 337, and 370). He was awarded the first Taira Prize by the American Geophysical Union in recognition of his significant contributions to the deep-biosphere frontier research. Among his contributions were the discovery of the occurrence of deep subseafloor microbial communities, in coal-bearing sediments down to ~2.5 km below the ocean floor, which have played important ecological roles in biogeochemical carbon cycling over geologic time. Inagaki is deputy director of JAMSTEC’s R&D Center for Ocean Drilling Science and the Kochi Institute for Core Sample Research, and also heads the Geomicrobiology Group and Geobiotechnology Group, JAMSTEC.  

Research Team

T-Limit scientific party

 

The offshore scientific party:

  • Verena Heuer, MARUM University of Bremen, Germany
  • Fumio Inagaki, Kochi Institute for Core Sample Research/Research and Development Center for Ocean Drilling Science, JAMSTEC, Japan
  • Stephen Bowden, University of Aberdeen, UK
  • Susann Henkel, AWI/MARUM, Germany
  • Takehiro Hirose, JAMSTEC, Japan
  • Kira Homola, University of Rhode Island, USA
  • Hiroyuki Imachi, JAMSTEC, Japan
  • Nana Kamiya, Nihon University, Japan
  • Masanori Kaneko, AIST, Japan
  • Lorenzo Lagostina, ETH Zurich
  • Hayley Manners, University of Southampton/Plymouth University, UK
  • Kyle Metcalfe, Caltech, USA
  • Natsumi Okutsu, AORI, University of Tokyo, Japan
  • Donald Pan, JAMSTEC, Japan
  • Maija Raudsepp, University of Queensland, Australia
  • Justine Sauvage, University of Rhode Island, USA
  • Florence Schubotz, MARUM, University of Bremen, Germany
  • Art Spivack, University of Rhode Island, USA
  • Satoshi Tonai, Kochi University, Japan
  • Tina Treude, UCLA, USA
  • Man-Yin Tsang, University of Toronto, Canada
  • Bernhard Viehweger, MARUM, University of Bremen, Germany
  • David Wang, MIT, USA
  • Yuzuru Yamamoto, JAMSTEC, Japan
  • Kiho Yang, Yonsei University, Korea
  • Yusuke Kubo, JAMSTEC, Japan

The onshore scientific party:

  • Yuki Morono, KCC, JAMSTEC
  • Margaret Cramm, University of Calgary, Canada
  • Tatsuhiko Hoshina, JAMSTEC, Japan
  • Akira Ijiri, JAMSTEC, Japan
  • Harry-Luke McClelland, Washington University in St Louis, USA
  • Emily Whitaker, Texas A&M University, USA
  • Lena Maeda, JAMSTEC, Japan

Contact

Verena Heuer vheuer@uni-bremen.de

Expedition Website 

Updates

Short video of the expedition

Chikyu IODP Expedition 370 explores the temperature limit of the deep biosphere by drilling 1.2 km into subseafloor off cape Muroto, Japan.

DCO T-Limit Blog: Updates from Expedition 370 Scientists

Re-live the two month-long expedition with scientist bloggers Stephen Bowden, Justine Sauvage, and Donald Pan. 

Visit the DCO T-Limit Blog

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