Ocean’s ‘cold skin’ increases carbon uptake

Oct. 25 () –

New research reveals that the ‘cold skin’ of the ocean allows the oceans to absorb more atmospheric carbon dioxide than previously believed.

These findings could improve global carbon assessments and shape more effective emissions reduction policies, according to the ESA, which part-funded the research.

The global ocean absorbs about a quarter of carbon emissions from human activities, which is extremely important to help curb climate change. However, on the other hand, this benefit comes at a cost: as the oceans absorb more carbon, their waters become more acidic, which endangers the health of marine ecosystems.

Improving our understanding of the complex processes that drive carbon fluxes between sea and air and refining estimates of how much carbon the global ocean sequesters are crucial for making accurate assessments of the carbon budget and taking informed climate action.

Scientists have thought that the ocean skin (a 0.01 mm strip of surface water, thinner than a human hair, which is typically a little colder than the water below) should increase the amount of carbon dioxide absorbed from the atmosphere.

This is because colder water is more efficient at absorbing carbon dioxide. The concentration of gas between this thin upper layer and the water, about 2 mm deeper, is what controls the exchange of gases between the atmosphere and the ocean. However, this has never been widely measured at sea, until now.

Thanks to the research, scientists from the University of Exeter, Plymouth Marine Laboratory and the University of Southampton in the United Kingdom evaluated in situ measurements taken from ships as they crossed the Atlantic Ocean.

The measurements were taken using flow systems that detected small differences in carbon dioxide in the air as it swirled toward the ocean surface and away again, along with accurate temperature readings of the ocean’s extremely thin skin.

Based on these measurements, the new findings, published today in the journal Nature Geoscienceconfirm that ocean skin temperature increases carbon absorption.

The results suggest that the ocean absorbs about 7% more carbon dioxide each year than previously thought due to the cold surface skin. This may not seem like much, but when integrated across all oceans, this additional carbon uptake It is equivalent to one and a half times the carbon captured by annual forest growth in the Amazon rainforest.

Currently, global estimates of carbon dioxide fluxes between air and sea often ignore the importance of temperature differences in the near-surface layer.

Daniel Ford, from the University of Exeter, said in a statement: “Our findings provide measurements that confirm our theoretical understanding of carbon dioxide fluxes at the ocean surface.”

“With the COP29 climate change conference taking place next month, this work highlights the importance of the oceans, but should also help us improve the global carbon assessments used to guide emissions reductions.”