The oceans absorb much more carbon than previously thought

New research from the University of Exeter has revealed that carbon uptake by the ocean has been largely underestimated. According to the experts, previous studies have failed to account for a specific measurement of water temperature that has a critical influence on how much carbon is absorbed.

The amount of carbon exchanged between the atmosphere and the ocean, which is known as carbon flux, is influenced by differences in temperatures at the water’s surface versus a few meters down. Based on this phenomenon, the study found a significantly higher net flux of carbon into the ocean than what has been reflected in climate models, indicating that the ocean is a much larger carbon sink that what was realized. 

The team calculated fluxes from 1992 to 2018 and found that at certain times in specific locations, up to twice as much carbon was exchanged compared to projections from other models.

“Half of the carbon dioxide we emit doesn’t stay in the atmosphere but is taken up by the oceans and land vegetation ‘sinks’,” said study co-author Professor Andrew Watson.

The scientists have compiled a large database of near-surface carbon dioxide measurements called the Surface Ocean Carbon Atlas, which can be used to calculate the flux of CO2 from the atmosphere into the ocean.

“Previous studies that have done this have, however, ignored small temperature differences between the surface of the ocean and the depth of a few meters where the measurements are made,” said Professor Watson.

“Those differences are important because carbon dioxide solubility depends very strongly on temperature.”

“We used satellite data to correct for these temperature differences, and when we do that it makes a big difference – we get a substantially larger flux going into the ocean.”

Professor Watson said the difference in ocean uptake that was calculated in the study amounts to about 10 percent of global fossil fuel emissions.

“Our revised estimate agrees much better than previously with an independent method of calculating how much carbon dioxide is being taken up by the ocean,” said study co-author Dr. Jamie Shutler.

“That method makes use of a global ocean survey by research ships over decades, to calculate how the inventory of carbon in the ocean has increased.”

“These two ‘big data’ estimates of the ocean sink for CO2 now agree pretty well, which gives us added confidence in them.”

The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer