An invisible layer of biological compounds on the sea surface reduces the rate at which CO2 gas moves between the atmosphere and the oceans, according to a latest research by Exeter, Heriot-Watt and Newcastle universities published in Nature Geoscience. Scientists suggest the findings have major implications for predicting future climate.
The world’s oceans currently absorb around 25% 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 CO2 exchange by up to 50%. Dr Ryan Pereira, a Lyell Research Fellow at Heriot-Watt University in Edinburgh, 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 are not necessarily visible like an oil slick, or a foam, and they are even difficult to identify from satellites, he added.
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 biogeochemistry at Newcastle University, said:
These latest results build on our previous findings that, contrary to conventional wisdom, large sea surface enrichments of natural surfactants counter the effects of high winds. The suppression of carbon dioxide uptake across the ocean basin due to surfactants, as revealed by our work, implies slower removal of anthropogenic carbon dioxide from the atmosphere and thus has implications for predicting future global climate.
The University of Exeter team of Drs Jamie Shutler and Ian Ashton, from the Centre of Geography, Environment and Society (CGES) based at the Penryn Campus, led the satellite component of the work. Dr Ashton said:
Combining this new research with a wealth of satellite data available allows us to consider the effect of surfactants on gas exchange across the entire Atlantic Ocean, helping us to monitor carbon dioxide on a global scale.
