Scientists have found evidence that the horizontal circulation of carbon-rich ocean water in the subpolar Southern Ocean works in tandem with vertical circulation, together controlling how much carbon the region stores in the deep ocean or releases to the atmosphere. These findings contradict the conventional framework for carbon cycling in Antarctic waters, which primarily attributes carbon uptake to vertical circulation while overlooking the contribution of large systems of swirling ocean current called gyres. Reframing the carbon cycle in the Southern Ocean is an essential step to better shape predictions for how future climate change will impact processes such as acidification and sea-ice cover shift. Graeme A. MacGilchrist et al. zeroed in on the Weddell Gyre - an important representative region of the subpolar Southern Ocean - using data obtained from cruises around the outer perimeter of the gyre along with accompanying satellite observations. They discovered that the gyre transports carbon-containing phytoplankton from the open ocean out of the region at a rate of about 80 trillion grams per year, indicating that the gyre plays a key role in Southern Ocean carbon transport. This result suggests that processes far removed from vertical circulation affect the carbon content of deep ocean waters, further hinting that future research efforts should be more broadly focused to include horizontal circulation. Such studies could begin to answer intensely debated questions about the past and future of Earth's climate, including causes of glacial climate periods and future projections of CO2 in the atmosphere, the authors say.
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