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Hydrothermal Vents: A Surprising Source of Dissolved Black Carbon

Hydrothermal vents have been discovered as an earlier unexplored source of dissolved black carbon in the oceans, adding to the knowledge of the ocean’s role as a carbon sink.

Hydrothermal Vents: A Surprising Source of Dissolved Black Carbon
Research Vessel Hakuho Maru conducted the observations used for this study. Image Credit: Hokkaido University.

The ocean is one of the world’s largest dynamic carbon sinks. It is vulnerable to severe carbon emissions from human activities, and there have even been plans to use the ocean to sequester carbon to reduce greenhouse gas emissions. However, many mechanisms by which the ocean acts as a carbon sink remain unknown.

Associate Professor Youhei Yamashita and graduate student Yutaro Mori at Hokkaido University, along with Professor Hiroshi Ogawa at AORI, The University of Tokyo, have discovered solid proof that hydrothermal vents are a completely undiscovered source of dissolved black carbon in the deep ocean. Their findings have been published in the Science Advances journal.

One of the largest carbon pools on the Earth’s surface is the dissolved organic carbon in the ocean. We were interested in a portion of this pool, known as dissolved black carbon (DBC), which cannot be utilized by organisms. The source of DBC in the deep sea was unknown, although hydrothermal vents were suspected to be involved.

Hiroshi Ogawa, Professor, Atmosphere and Ocean Research Institute, University of Tokyo

The investigators looked at the dispersion of DBC in the ocean basins of the North Pacific and Eastern South Pacific Oceans. They contrasted it to earlier accounted concentrations of a helium isotope linked with hydrothermal vent emissions and oxygen utilization in these areas.

Their research revealed that hydrothermal vents were a significant source of DBC in the Pacific Ocean. This hydrothermal DBC is most likely formed by mixing hot fluids from hydrothermal vents with cold seawater, and it travels over longer distances—up to thousands of kilometers.

Most importantly, our research indicates that the DBC from hydrothermal vents is an important source of dissolved organic carbon in the deep ocean. In terms of DBC inputs to the ocean, hydrothermal vents may contribute up to half as much DBC as that which is formed by biomass burning or fossil fuel combustion and subsequently transported via rivers or atmospheric deposition.

Youhei Yamashita, Associate Professor, Hokkaido University

More studies are needed to determine how DBC is developed from hydrothermal vents.

The research was funded by the Japan Society for the Promotion of Science (JSPS) grants KAKENHI (JP16H02930, JP19H04249, JP22H03714, JP19H05667, JP19H04260).

Journal Reference:

Yamashita, Y., et al. (2023) Hydrothermal-derived black carbon as a source of recalcitrant dissolved organic carbon in the ocean. Science Advancesdoi/10.1126/sciadv.ade3807


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