How the winds in the Southern Ocean alter atmospheric CO2 by upwelling of carbon-rich deep waters

What is it about?

The Southern Ocean is a unique region where carbon dioxide is both taken up by the upper ocean and returned from the deep ocean to the atmosphere. This contrasting response is partly due to the action of the winds, which drive surface waters northward across the Antarctic Circumpolar Current and leads to upwelling of carbon-rich deep waters to the south of the Antarctic Circumpolar Current. We conducted a suite a suite of coarse-resolution, global coupled ocean circulation and biogeochemistry experiments, each experiment integrated for 5,000 years. We found a positive correlation is obtained between the meridional overturning in the Southern Ocean and atmospheric CO2: stronger or northward-shifted westerly winds in the Southern Hemisphere result in greater upwelling of carbon-rich deep waters and oceanic outgassing, which increases atmospheric CO2 by 20 ppm, weaker or southward-shifted winds lead to the opposing result.

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Why is it important?

Understanding the extent that changes in winds in the Southern Ocean alter atmospheric CO2 is important in providing a context for past glacial changes in atmospheric CO2 and the ongoing anthropogenic increase in atmospheric CO2. We also set out a way to understand how the changes in atmospheric CO2 are related to changes in the global ocean carbon inventories. This framework sets out how ocean dissolved inorganic carbon may be separated into a saturated pool (defined relative to the instantaneous atmospheric CO2), a pool affected by biological transfers (involving soft tissue and hard tissue reserves) and a disequilibrium pool. We then are able to interpret the changes in a atmospheric CO2 in terms of the different physical and biological mechanisms that alter these ocean carbon pools in different ways.

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