Scientists have discovered that an invisible layer of scum on the surface of the world’s oceans slows the rate at which oceans absorb carbon dioxide from the atmosphere by up to 50%. The findings could have significant implications for future climate predictions.
Earth’s oceans are the largest long-term sink of carbon on the planet – currently, they absorb about a quarter of all anthropogenic carbon dioxide emissions.
The rate at which the oceans and atmosphere exchange gases including carbon dioxide is regulated by sea turbulence due to wind. Stronger winds create more turbulence, which then increases gas exchange between the atmosphere and the oceans.
In a new study, researchers from Newcastle, Heriot-Watt and Exeter Universities in the United Kingdom found that biological compounds on the sea surface, called surfactants, reduce the exchange of carbon dioxide between the ocean and the atmosphere by as much as half. The team published their findings on Monday in the journal Nature Geoscience.
These organic compounds, which form a greasy film on the surface of the water, are naturally produced by marine plankton and bacteria. Researchers warned that as sea temperature rises due to climate change, the amount of surfactants coating the world’s oceans is expected to increase.
“The warmer the ocean surface gets, the more surfactants we can expect, and an even greater reduction in gas exchange, study author Dr Ryan Pereira, a researcher at Heriot-Watt University in Edinburgh, said in a statement. “[That] is why this is such a critical finding.”
The study, funded by the Natural Environment Research Council (NERC), Leverhulme Trust and European Space Agency, gathered data using satellite imaging and an experimental system to measure the effect of surfactants on gas exchange in different samples of sea water. The team collected the samples in 2014 from 13 different sites in the Atlantic Ocean covering a variety of ecosystems.
“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,” explained Dr Pereira. “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.”
The data could help improve scientists’ understanding of global carbon dioxide levels, said Dr Ian Ashton, a professor at the University of Exeter who led the satellite component of the work.
“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,” he explained.
Study author Rob Upstill-Goddard, professor of marine biogeochemistry at Newcastle University, elaborated on the potential impacts of the team’s findings.
“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,” he said.
“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.”