Research Highlight
Sliver of cool surface water helps the ocean absorb more carbon

Subtle temperature differences at the ocean surface allow more carbon dioxide (CO2) to be absorbed, new research shows.
Scientists studied the “ocean skin” – a sliver less than 2mm deep at the ocean surface that is fractionally cooler than the rest.
Theoretical and lab work have suggested this temperature difference should increase the amount of CO2 absorbed by the ocean – but this had never been successfully observed at sea before.
The new study, led by researchers from the University of Exeter’s Penryn Campus in Cornwall and involving a number of scientists from Plymouth Marine Laboratory (PML), used precision measurements to confirm that the temperature of the ocean skin does indeed aid carbon absorption.
Carried out in the Atlantic as part of the PML-led Atlantic Meridional Transect (AMT) research expeditions, the findings suggest this ocean absorbs about 7% more CO2 each year than previously thought. It might sound small, but when applied across all oceans this additional carbon absorption is equivalent to one and half times the carbon captured by annual forest growth in the Amazon rainforest.
The global ocean absorbs about a quarter of humanity’s carbon emissions, slowing climate change whilst also adding additional pressures on the ocean, and the new findings help improve our understanding of these processes.
“Our findings provide measurements that confirm our theoretical understanding about CO2 fluxes at the ocean surface,” said lead author Dr Daniel Ford from the University of Exeter and former PhD student at PML.
“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”.
Dr Gavin Tilstone, Co-author and Bio-optical Oceanographer at Plymouth Marine Laboratory (PML) said:
“This discovery highlights the intricacy of the ocean’s water column structure and how it can influence CO2 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 team have included this advancement within their data submission to this year’s Global Carbon Budget assessment.
The ship observations, from two European Space Agency projects, were taken by a CO2 flux systems that measured tiny differences in CO2 in air swirling towards the ocean surface and away again, along with high-resolution temperature measurements.
Until now, global estimates of air-sea CO2 fluxes typically ignore the importance of temperature differences in the near-surface layer.
Dr Ian Ashton from the University of Exeter said: “This work is the culmination of many years of effort from an international team of scientists. We can use satellite observations to observe the ocean skin, so combining this new knowledge with satellite data helps us to improve our global estimates of air-sea CO2 exchange.”
Related Information
The study was funded by the European Space Agency, Horizon Europe and the Natural Environment Research Council.
Access the full paper: Enhanced ocean CO2 uptake due to near surface temperature gradients
Author(s)
Gavin Tilstone
Gavin is a co-author of the paper and bio-optical Oceanographer at Plymouth Marine Laboratory (PML).
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