Southern Ocean absorbing more carbon dioxide than previously thought, study finds

The ocean carbon cycle [credit: IAEA]

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The role of nature’s ocean carbon cycle is found to have been ‘substantially’ underestimated by the latest research, challenging climate model simulations. This was mostly from summer data, and further efforts to get better winter data are ongoing. Another reality check for overblown climate obsession.
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New research led by the University of East Anglia (UEA) and Plymouth Marine Laboratory (PML) has found that the Southern Ocean absorbs more carbon dioxide (CO2) than previously thought, reports Science Daily.

Using direct measurements of CO2 exchange, or fluxes, between the air and sea, the scientists found the ocean around Antarctica absorbs 25% more CO2 than previous indirect estimates based on shipboard data have suggested.

The Southern Ocean plays a major role in absorbing CO2 emitted by human activities, a process vital for controlling the Earth’s climate [Talkshop comment – according to one hypothesis]. However, there are big uncertainties in the magnitude and variability in this flux.

Until now it has been estimated using shipboard measurements, such as those collected for the Surface Ocean CO2 Atlas (SOCAT) from research ships and sail drones, data from profiling floats deployed in the ocean, and global ocean biogeochemistry models. These different approaches have produced large variations in estimates.

This new study used a novel technique called eddy covariance — with flux systems mounted on ships’ foremasts — to directly measure air-sea CO2 fluxes during seven research cruises in the region.

The results — published in the journal Science Advances – show the summer Southern Ocean is likely to be a strong CO2 sink, challenging the much weaker estimates based on float data and model simulations, which the authors say “substantially underestimate” the observed CO2 uptake.

The authors argue this difference can be explained by considering temperature variations in the upper ocean and a limited resolution, for example averaging over a too-long time scale or sampling over a too-large interval, adding that current models and float data do not account for small, intense CO2 uptake events.
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Dr Mingxi Yang, study co-author and Chemical Oceanographer at PML, said: “The Southern Ocean is a key sink of CO2, but the magnitudes and the locations of this ocean uptake are uncertain. PML’s autonomous and high frequency eddy covariance system has significantly increased the number of direct air-sea CO2 flux measurements in this region.

“This paper offers the first comparison between direct CO2 flux measurements and estimates from coarse data products and global models on a large spatial/temporal scale. It has helped validate these and shed light on ways to improve them.”

Full report here.
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Image: The ocean carbon cycle [credit: IAEA]