Study says CO₂ uptake by the ocean greater than thought

The oceanic carbon cycle [credit: IAEA]

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The article title at Phys.org is ‘How bubbles may speed up CO₂ uptake by the ocean’. Looks like another update to climate models is needed to cater for this large data mismatch. As a knock-on effect various published studies may contain miscalculations. Nature once again turns out to be more robust than expected.
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A new study provides evidence that the ocean may have absorbed as much as 15% (0.3–0.4 Pg C yr-1) more CO2 than previously thought, requiring a re-think of future CO2 flux assessments and global climate models.

The exchange of carbon dioxide (CO2) between the sea and air is a significant part of the global carbon cycle and plays a critical role in buffering climate change.

As the ocean is a major absorber of CO2, accurate quantification of this sea-air CO2 flux is vital for forecasting the future climate and developing effective climate change mitigation strategies.

How sea-air CO2 fluxes are measured
Sea-air CO2 fluxes vary regionally and seasonally between uptake and outgassing, meaning that in some areas the ocean is absorbing CO2 and in other areas, releasing it. In turbulent areas where there is more wave action, uptake is generally more due to bubbles of air getting engulfed by waves that enables the seawater to “absorb” the gas trapped within the bubble.

Key findings from the new study
In this first-of-its-kind study, led by Plymouth Marine Laboratory and GEOMAR Helmholtz Center for Ocean Research (Germany) with a partner from Heriot-Watt University, 4,082 hours of high-quality sea-air CO2 flux measurements, collected over 17 ship cruises and covering a variety of ocean regions, were re-analyzed to investigate if bubble-mediated transfer acts in a more asymmetric manner. The work is published in the journal Nature Communications.
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Using a novel “2-dimensional” fitting method, the analysis shows clear field evidence of asymmetric bubble-mediated CO2 in the ship observations. When the team recalculated global sea-air CO2 fluxes (for 1991–2020) using the asymmetric formulation, they found that the global ocean’s CO2 uptake increased by about 15% (0.3–0.4 Pg C yr-1) compared with conventional, symmetric estimates.

The asymmetric increase in CO2 uptake is especially strong in regions with frequent high winds and wave breaking, such as in the Southern Ocean where some of the stronger climate change impacts are already being seen.

Full article here.