Deep Coalbed Biosphere off Shimokita

Over the past decade, scientific ocean drilling has revealed the presence of abundant microbial population in marine subsurface sediment. The deep subseafloor biosphere on the continental margins is thought to be playing important roles in Earth's environment, such as biogeochemical carbon and energy cycles. However, what kinds of deep microbes contribute to the deep carbon cycle, how deep microbial activities are present in marine subsurface sediment, and what energy substrates are available for maintenance of microbial activities and long-term survival in deep environment remain unknown.

The IODP Expedition 337 by Scientific Deep-Sea Drilling Vessel Chikyu aims to perform riser-drilling over 2,200 m below the seafloor off Shimokita Peninsula of Japan, northwestern Pacific Ocean. To understand the deep life and hydrocarbon system in marine subsurface, Expedition 337 explores the deeply buried coal formation that may produce natural gas and tackles some fundamentally important scientific questions related to the Earth and Life co-evolution.

Learn More about the Research Let’s ask the Co-Chief Scientist Dr. Inagaki

Fumio Inagaki
JAMSTEC Kochi Institute for Core Sample Research, Geomicrobiology Group & Submarine Resources Research Project, Geobio-Engineering and Technology Group, Group Leader Senior Scientist
Q.What was the motivation to do a drilling research off Shimokita?

After the construction of Chikyu, she launched her shakedown expeditions in 2005 and 2006, right at this sea area off Shimokita.
During the shakedown expedition, we tested sediment-core sampling from the seabed to 365 m below the seafloor. I was luckily involved in that opportunity and found tremendous amount of microbial cells in there.
How and why such abundant microbial life can live in deep sediment?
What are ecosystem roles in Earth's environment?
How deep microbial cells are living there?
There are many important scientific questions raised from the first drilling experience of Chikyu.

Q.What is unique about the drilling site?

Pilot studies of subsurface structure in this area showed a widespread coal seam buried in the Pacific Ocean from southern Hokkaido to Tohoku area in Japan.
The deep coalbeds are supposed to be 50 million years-old or more. Some parts of these coalbeds have not been fully matured yet, called as lignite (brown coal) or bituminous coal, which posse lower resource values and hence not worth industrially exploring so far. However, these lignite coals are still producing some nutrients and energy substrates in maturing process, which may support generation of natural gas (methane) and deep microbial life.
Because the coal was originally made of plants, we could say the deeply buried coalbed as "subseafloor forest", but we still don't know the deep life ecosystem in the "subseafloor forest" and if present, what is the ecological roles in deep carbon cycles--there is a natural gas and methane hydrates in relatively shallow marine sediment.
Another important characteristic in this area is the origin of sediment and rock formation.
As coals are derived from terrestrial plants, deep coal formation is ancient terrestrial deposit, perhaps 50 million-year old Eocene period.
We assume there is a terrestrial-marine transition zone at around 1600 meters below the seafloor, so called "unconformity layer", we will see marine sediment overlying the terrestrial coal formation.
Given such a dynamic sedimentary system, the drilling research will make it ideal for scientists to study the co-evolution of the geological formation history of the northwestern Pacific margin and the deep subseafloor biosphere that associates with "subseafloor forests".

Q.What kinds of analyses are you scientists going to do during Expedition 337?

Shipboard scientistic party of Expedition 337 is an international team, covering a broad range of scientific expertise, specialized in geology, physical property specialist, paleontology, sedimentology, resource geology, organic and inorganic geochemistry, microbiology and molecular ecology.
We will analyze cored materials, fluids and gas samples obtained by riser drilling. For example, after core recovery, samples are immediately scanned by a shipboard medial X-ray CT scanner to analyze internal structures.
This nondestructive testing will allow us to know what types of samples we have obtained and where some invisible specific events are placed in the retrieved core, highly useful for the subsequent sub-sampling and analyses.
Using these samples, we will study chemical composition of gas, fluid and solid sedimentary minerals, including organic matter like coals. For the deep life component, we will use a computer image-based life detection and enumeration technique that has been developed by my laboratory.
During Expedition 337, we will also extract environmental DNA directly from the obtained samples and analyze some important microbial genes related to taxonomic identification and biological carbon cycles.
This onboard molecular program will provide us a "fingerprint" of the deep biosphere and microbial metabolic functions. In addition, using chemical tracers, we will incubate some samples under in-situ condition (e.g., ~55 degree C, 400 pressure bar) and detect microbial activities that may contribute to the degradation of organic matter and production of bio-gas. So far, the world deepest record of subseafloor life detection is 1,626 m below the seafloor.
In this expedition, we will drill down to 2,200 m at least, so will expand our knowledge of the limit of deep biosphere.

Q.What is challenging about this expedition?

It will be full of challenges! In terms of technological challenge, there will be 2 major target points during Expedition 337.


Challenge to drill down to 2,200 m below the seafloor by a Chikyu riser-drilling system and to get high-quality scientific samples from the deeply buried coal formation. This will be the deepest penetration-depth record in a half-century of scientific ocean drilling history.


Challenge to get deep formation fluids using a new borehole wire-line instrument in situ. We try to obtain a few hundreds milliliter of fluids from the deep seated coal-sand formation and bring it back to Chikyu under the in-situ pressure condition.
If succeeded, it will be highly valuable for many onboard geochemical and microbiological analyses and significantly expand our knowledge of the nature of deep biosphere and coalbed-hydrocarbon system.

In addition, making this expedition safe with successful operations of the ship crews and drilling team will be of our biggest challenging goals, of course.

Scientific Objectives

Among the least characterized Earth systems that can be addressed by scientific ocean drilling are deeply buried hydrocarbon reservoirs in sediments along continental margins.
In particular, the role of microbial activities for the formation and fate of these reservoirs remains poorly understood. Expedition 337 will focus on microbial and biogeochemical processes related to a deeply buried Eocene lignite-coalbed at ~2,000 m below the seafloor as well as the paleoenvironmental history recorded at this deep site.
Using the riser-drilling system on Chikyu, we will perform drilling down to 2,200 meters below seafloor.
The cored materials will include a regional unconformity of terrestrial-marine sedimentary transition zone and the underlying Eocene lignite-sand layers.
The wireline logging and in-situ sampling of deep formation fluids in lignite-sand layers are also planned.
The expedition will unravel deep subseafloor life and the biosphere in a habitat that has never been targeted by previous scientific ocean drilling.
Core samples at selected intervals, drill cuttings, and mud gas samples will be collected for scientific analyses, including onboard carbon isotopic analysis and geochemical tracer incubation experiments.

  • To explore the deep subseafloor microbial ecosystem
  • To understand the geobiological hydrocarbon system in marine subsurface