Relative to its size, the skin of the world’s oceans – a thin sliver of surface water thinner than a human hair – has been capturing carbon at an astonishing scale – one and a half times that captured by annual growth in the Amazon rainforest, new research has discovered.

It’s the result scientists have been looking for years; proof of the long-held belief that subtle temperature differences at the ocean surface have been responsible for the absorption of more carbon dioxide from the atmosphere.

Theoretical and laboratory work has long-suggested that the slight temperature difference between the ocean’s skin (a 0.01mm sliver of surface water) and what lies beneath plays a pivotal role in the carbon absorption rate of the ocean. But until now, this had never been successfully observed at sea.

A new study led by researchers from the University of Exeter’s Penryn Campus in Cornwall, and published in the Nature Geoscience journal, however, has now provided the evidence theorists had been waiting for. Using precision measurements, these researchers have confirmed it: the temperature of the ocean skin does indeed aid carbon absorption.

Carried out in the Atlantic, the findings suggest this ocean absorbs 7% more carbon dioxide each year than previously thought. This may sound small but, argues the Exeter researchers, when applied across all of the world’s oceans this additional carbon absorption becomes quite significant: one and a half times that captured by annual forest growth in the Amazon rainforest.

The global ocean itself absorbs about a quarter of humanity’s carbon emissions, slowing climate change in the process. However, these levels of carbon absorption are harming the ocean – it’s these latest findings that will now help improve our understanding of these processes.

“Our findings provide measurements that confirm our theoretical understanding about carbon dioxide fluxes at the ocean surface,” said lead author, Dr Daniel Ford, from the University of Exeter. “With the COP29 climate change conference taking place next month, this work highlights the importance of the oceans, but it should also help us improve the global carbon assessments that are used to guide emission reductions.”

The findings have now been submitted to this year’s Global Carbon Budget assessment.

The ship observations – from two European Space Agency projects – were taken by a carbon dioxide flux systems that measured tiny differences in carbon dioxide in air swirling towards the ocean surface and away again, along with high-resolution temperature measurements.

It was until now that global estimates of air-sea carbon dioxide fluxes typically ignored the importance of temperature differences in the near-surface layer.

Dr Ian Ashton, also from the University of Exeter, said: “This work is the culmination of many years of effort from an international team of scientists. The European Space Agency’s support for science was instrumental in putting together such a high-quality measurement campaign across an entire ocean.”

Funded by the European Space Agency, Horizon Europe, and the Natural Environment Research Council, international partners on the study included sea temperature measurement experts from the European Space Agency and University of Southampton.

Dr Gavin Tilsone from Plymouth Marine Laboratory (PML), said: “This discovery highlights the intricacy of the ocean’s water column structure and how it can influence carbon dioxide draw-down from the atmosphere. Understanding these subtle mechanisms is crucial as we continue to refine our climate models and predictions. It underscores the ocean’s vital role in regulating the planet’s carbon cycle and climate.”

The full paper, titled Enhanced Ocean CO2 Uptake due to Near Surface Temperature Gradients can be accessed via Nature Geoscience.

Last week, more than 40 scientists and world-leading climate and ocean experts signed an open letter to the world’s leaders to act with urgency to address the vastly underestimated role of the ocean and the global climate. 

Organised by Professor Stefan Rahmstorf at the University of Potsdam, the letter was issued at this year’s Arctic Circle conference ahead of COP16  as a stark warning that the Atlantic Meridonial Overturning Circulation (AMOC) – a network of currents responsible for moving energy around the planet and keeping the Earth’s climate stable – was rapidly approaching its ‘tipping point.’

The IPCC had previously acknowledged that the AMOC was slowing down but suggested that its collapse wouldn’t occur until the year 2107, giving nations an extended timeline to mitigate the fallout. However, new science suggests that these projections are a severe underestimation and that the AMOC’s tipping point – the point at which there is no return from its eventual halt – could be at any point between 2025 and 2095.

The collapse of the current, driven by climate change, will result in a number of impacts felt globally, including a shift in tropical rainfall belts, reduced oceanic carbon dioxide uptake (and thus faster atmospheric increase) as well as major additional sea-level rise particularly along the American Atlantic coast, and an upheaval of marine ecosystems and fisheries.

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