Ocean carbon uptake widely underestimated

09 September 2020
ocean science

The world's oceans soak up more carbon than most scientific models suggest, according to new research. Previous estimates of the movement of carbon between the atmosphere and oceans, known as "flux", have not accounted for temperature differences at the water's surface and a few metres below. The new study includes this – and finds significantly higher net flux of carbon into the oceans.

The study was co-funded by the ICOS-coordinated EU Horizon 2020 project RINGO, 'Readiness of ICOS for Necessities of Integrated Global Observations'. The study involved scientists from the ICOS community and was led by the University of Exeter, one of the participating institutes of ICOS.

The study calculates carbon dioxide (CO2) fluxes from 1992 to 2018, finding up to twice as much net flux in certain times and locations, compared to uncorrected 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'," says Dr Andrew Watson, Professor at the University of Exeter's Global Systems Institute and the ICOS United Kingdom Focal Point.

"Researchers have assembled a large database of near-surface carbon dioxide measurements – the Surface Ocean Carbon Atlas – that 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 metres where the measurements are made. 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 adds: "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.

"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," tells Professor Watson.

The paper, published in Nature Communications, is entitled: "Revised estimates of ocean-atmosphere CO2 flux are consistent with ocean carbon inventory." The paper is available at: http://dx.doi.org/10.1038/s41467-020-18203-3

One of the main authors, Dr Jamie Shutler, will give an oral talk at the Virtual ICOS Science Conference 2020 on Thursday 17th of September at 16:00-17:30 CET. The talk at the RINGO session (Session no 17) is titled “Semi-automated near-real time (NRT) data pipeline for calculating atmosphere-ocean CO2 fluxes”. Registration to the conference if of free of charge. Visit the ICOS Science Conference webpage here.