Biological Barrier Could Halve Ocean Carbon Uptake

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An invisible layer of biological compounds on the sea surface reduces the rate at which carbon dioxide gas moves between the atmosphere and the oceans, scientists have reported.

Scientists from Heriot-Watt, Newcastle and Exeter universities published their research in the journal Nature Geoscience and say the findings have major implications for predicting future climate.

The world’s oceans currently absorb around a quarter of all anthropogenic carbon dioxide emissions, making them the largest long-term sink of carbon on Earth.

Atmosphere-ocean gas exchange is controlled by turbulence at the sea surface, the main cause of which is waves generated by wind. Greater turbulence means increased gas exchange and, until now, it was difficult to calculate the effect of biological surfactants on this exchange.

The Natural Environment Research Council (NERC), Leverhulme Trust and European Space Agency funded team developed a novel experimental system that directly compares “the surfactant effect” between different sea waters collected along oceanographic cruises, in real time.

Using this and satellite observations the team then found that surfactants can reduce carbon dioxide exchange by up to 50 percent.

Dr. Ryan Pereira of Heriot-Watt University said: “As surface temperatures rise, so too do surfactants, which is why this is such a critical finding. The warmer the ocean surface gets, the more surfactants we can expect, and an even greater reduction in gas exchange.

“What we discovered at 13 sites across the Atlantic Ocean is that biological surfactants suppress the rate of gas exchange caused by the wind. We made unique measurements of gas transfer using a purpose-built tank that could measure the relative exchange of gases impacted only by surfactants present at these sites.

“These natural surfactants aren’t necessarily visible like an oil slick, or a foam, and they are even difficult to identify from the satellites monitoring our ocean’s surface.

“We need to be able to measure and identify the organic matter on the surface microlayer of the ocean so that we can reliably estimate rates of gas exchange of climate active gases, such as carbon dioxide and methane.”

Professor Rob Upstill-Goddard, professor of marine biogeoc

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