Previously Unknown Hydrothermal Vents Identified as Dissolved Black Carbon Source in Oceans

The ocean is one of the world's largest dynamic carbon sinks, and it is vulnerable to increased carbon emissions from human activities.

There are even plans to use the ocean to sequester carbon in order to reduce greenhouse gas emissions.

However, many of the processes by which the ocean functions as a carbon sink remain unknown.

Deep-sea black carbon comes from hydrothermal vents

(Photo : David McNew/Getty Images)

Associate Professor Youhei Yamashita of Hokkaido University and graduate student Yutaro Mori of AORI at Hokkaido University, along with Professor Hiroshi Ogawa at AORI, The University of Tokyo, have discovered conclusive evidence that hydrothermal vents are a previously unknown source of dissolved black carbon in the deep ocean.

Their findings have been published in the journal Science Advances. According to Ogawa, the dissolved organic carbon in the ocean is one of the largest carbon pools on the Earth's surface.

"We were interested in a portion of this pool known as dissolved black carbon (DBC), which cannot be used by organisms."

The source of DBC in the deep sea was unknown, but hydrothermal vents were suspected to be involved.

The researchers looked at the distribution of DBC in the ocean basins of the North Pacific and Eastern South Pacific Oceans and compared it to previously reported concentrations of a helium isotope associated 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 the mixing of hot fluids from hydrothermal vents with cold seawater, and it travels long distances - up to thousands of kilometers.

"Most importantly, our findings show that DBC from hydrothermal vents is a significant 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 formed by biomass burning or fossil fuel combustion and then transported via rivers or atmospheric deposition," Yamashita concluded in a report from Science Daily.

More research is needed to determine how DBC is formed from hydrothermal vents.

Also Read: Black Carbon: How Long Do These Heat-Absorbing Particles Linger in the Atmosphere?

What Is Black Carbon?

Soot, or black carbon, is a component of fine particulate air pollution (PM2.5) that contributes to climate change, as per the Climate and Clean Air Coalition

The incomplete combustion of fossil fuels, wood, and other fuels produces black carbon.

Complete combustion would convert all of the carbon in the fuel to carbon dioxide (CO2), but combustion is never complete, and CO2, carbon monoxide, volatile organic compounds, organic carbon, and black carbon particles are all produced.

Soot is a complex mixture of particulate matter that results from incomplete combustion.

Black carbon is a short-lived climate pollutant, with a lifetime in the atmosphere ranging from days to weeks.

Black carbon can have significant direct and indirect effects on the climate, cryosphere (snow and ice), agriculture, and human health in such a short period of time.

Several studies have shown that reducing black carbon emissions can reduce near-term climate warming, increase crop yields, and prevent premature deaths.

Many developed countries' black carbon emissions have decreased in recent decades as a result of stricter air quality regulations.

In contrast, in many developing countries where air quality is unregulated, emissions are rapidly increasing.

Asia, Africa, and Latin America account for approximately 88% of global black carbon emissions as a result of open biomass burning and residential solid fuel combustion.

Because of its high efficiency at absorbing light and heating its surroundings, black carbon is a significant contributor to global warming.

Black carbon has a warming effect on the climate that is 460-1,500 times stronger than CO2 per unit of mass.

Black carbon, when suspended in the atmosphere, contributes to global warming by converting incoming solar radiation to heat.

It also has an effect on cloud formation and regional circulation and rainfall patterns.

Black carbon and co-emitted particles reduce surface albedo (the ability to reflect sunlight) and heat the surface when they are deposited on ice and snow.

As a result, the Arctic and glaciated regions like the Himalayas are particularly vulnerable to melting.

Related article: Black Carbon Second-Biggest Human Contributor to Climate Change: Study