A patch of cool surface water less than 2mm deep helps oceans absorb carbon dioxide, a British-led team of scientists has determined after months of voyages across the Atlantic Ocean carefully measuring gas and temperature levels.
The subtle difference in temperature between the “ocean skin” and the layer of water below creates an interface that leads to more CO2 be ingested, the scientists observed.
They used highly sensitive equipment to measure the water temperature and to detect and record small differences in the amount of CO2 in the air swirling to the sea surface and away again.
The work is considered important in the development of climate modeling because oceans absorb about a quarter of human carbon emissions.
Daniel Ford, a research fellow at the University of Exeter, said: “With the policeman 29 climate change conference next month, this work highlights the importance of the oceans, but it should also help us guide the global carbon assessments used to drive emissions reductions.”
Ford was aboard the research ship RRS Discovery, which was sailing between Southampton and Punta Arenas in Chile. He said: “The voyage involved seven weeks of getting all the different instruments working together to collect the wide variety of measurements used in the study.
“We went through very rough seas in the North Atlantic and near the Falklands, which was challenging, but we had a reprieve when we were near the equator with mirror-glass ocean.”
The 2 mm sliver of water is slightly colder due to the “cool skin effect”, which is caused by heat leaving the water as it is in direct contact with the atmosphere.
The results, published in the Nature Geoscience journal, was passed on to the Global carbon budget assessmenta worldwide consortium of scientists set up to establish a common understanding of the Earth’s carbon cycle.
Prof Jamie Shutler, an ocean and atmospheric scientist at the University of Exeter, said the “ocean skin” was very slightly cooler than the layer of water below. The recording of CO2 is controlled by the concentration difference in gases across these layers.
Shutler said the consequences were first suggested in the early 1990s. “But the most important missing piece – the field evidence – eluded us,” he said.
Gavin Tilstone, from Plymouth Marine Laboratory, said: “This discovery highlights the complexity of the ocean’s water column structure and how it can affect CO2 withdrawal. Understanding these subtle mechanisms is crucial as we continue to refine our climate models and predictions. This highlights the ocean’s important role in regulating the planet’s carbon cycle and climate.”
