Deep-sea black carbon comes from hydrothermal vents – Zoo House News

Hydrothermal vents have been identified as a previously undiscovered source of dissolved soot in the oceans, furthering the understanding of the oceans’ role as a carbon sink.

The ocean is one of the world’s largest dynamic carbon sinks and is vulnerable to increased carbon emissions from human activities. There are even proposals to use the ocean to sequester carbon to reduce carbon emissions. However, many of the processes by which the ocean acts as a carbon sink are not yet fully understood.

Associate Professor Youhei Yamashita and PhD student Yutaro Mori from Hokkaido University, together with Professor Hiroshi Ogawa from AORI, The University of Tokyo, have presented conclusive evidence that hydrothermal vents are a previously unknown source of dissolved black carbon in the deep sea. Their discoveries were published in the journal Science Advances.

“One of the largest reservoirs of carbon on Earth’s surface is the dissolved organic carbon in the ocean,” explains Ogawa. “We were interested in a part of this pool known as dissolved black carbon (DBC), which is unusable by organisms. The source of DBC in the deep sea was unknown, although hydrothermal vents have been suggested to be involved.”

Researchers analyzed the distribution of DBC in the North Pacific and eastern South Pacific ocean basins and compared the data to previously reported concentrations of a helium isotope associated with emissions from hydrothermal vents and oxygen use in these areas.

Their results indicated that hydrothermal vents were an important source of DBC in the Pacific Ocean. This hydrothermal DBC is most likely formed by mixing the hot fluids from hydrothermal vents with cold seawater and is transported long distances – up to thousands of kilometers.

“Most importantly, our research shows that the DBC from hydrothermal vents is an important source of dissolved organic carbon in the deep sea. In terms of DBC inputs to the ocean, hydrothermal vents can contribute up to half as much DBC as what is formed by burning biomass or burning fossil fuels and then transporting it via rivers or atmospheric deposition,” Yamashita concluded. Further research is ongoing required to understand exactly how DBC is formed from hydrothermal vents.