The Southern Ocean is still swallowing large amounts of humans’ carbon dioxide emissions

image of sea ice in the Southern Ocean taken from the window of an airplane
Image Source: Equipped with sensors to measure carbon dioxide in the atmosphere, this airplane winged across sea ice in the Southern Ocean (shown) during a 2016 field campaign to measure how much gas the waters were emitting.REBECCA HORNBROOK/NCAR

A study based on aircraft observations of carbon dioxide reveals that the Southern Ocean is still absorbing huge amounts of the carbon dioxide released by human fossil fuel combustion. According to the new findings, the seas around Antarctica may not be absorbing as much CO2 as previously assumed, and in some locations may even be releasing it back into the atmosphere.

We should be relieved that the ocean, which is already growing more acidic and holding record-breaking heat due to global warming, can handle some additional burdens from climate change (SN: 4/28/17, 1/13/21; SN: 1/13/21). A researcher at the National Center for Atmospheric Research in Boulder said the conclusion was “reassuring” to him.

As a result of this, the Southern Ocean is thought to account for approximately half of the global ocean’s annual CO2 intake. As a result, it has a significant impact on the immediate consequences of such emissions. It had previously been thought that the Southern Ocean was a net sink of carbon dioxide, but the float-based estimations had shown that it was in fact an emitter of roughly 0.3 billion metric tons per year. From 2009 to 2018, the Southern Ocean was a net sink of carbon dioxide, taking in around 0.55 billion metric tons of CO2 per year, according to new results published in Science on Dec. 3.

Deep-diving ocean floats, which are part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project, were used in a 2018 study. Data from 35 of the floats collected between 2014 and 2017 revealed that portions of the ocean were actually releasing a significant amount of carbon dioxide back into the atmosphere during winter (SN: 6/2/19). That raised the possibility that the Southern Ocean’s role in protecting the Earth from the effects of climate change may not be as strong as previously imagined.

However, Long and other experts were doubtful of that conclusion. Scientists use the data from the floats to compute the water’s carbon dioxide concentration. The floats measure temperature, salinity, and pH at a depth of around 2,000 meters. There are a number of assumptions that must be made regarding ocean water qualities in order for these calculations to work. Long speculates that this could be distorting the data and leading to overestimations of water-borne carbon dioxide emissions. Airborne measurements are another method for determining the amount of carbon dioxide that is transported from the atmosphere to the ocean. Carbon dioxide data from three distinct aircraft flight series across broad swathes of the Southern Ocean were compiled in a new study, which was published in the journal Science on September 8th, 2011 (SN: 9/8/11). Once the data was gathered, the researchers ran computer simulations to see how much CO2 could be traveling annually between oceans and the atmosphere.

A seasonal trend of less carbon dioxide absorption by the ocean was found by both float-based and aircraft-based investigations, but the overall amount emitted from the ocean was different. A chemist at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., who was not involved in the research, argues that both forms of data are picking up a real trend. In a nutshell, “We’re all in this together.”

SOCCOM data may or may not have been inaccurate. Researchers must, however, compare ship-based measurements of carbon dioxide in the water with pH-based estimations at the same place in order to better appreciate any potential biases. Johnson believes that these kinds of research are currently being place off the coast of California. According to Johnson, both datasets and the few and far between direct shipboard observations in the Southern Ocean are going to be vital for understanding the function that these waters play in the planet’s carbon cycle. Johnson states thus. Despite the fact that aerial studies can confine the overall picture of Southern Ocean carbon dioxide emissions data, floats are more widely dispersed and hence better equipped to identify local and regional variations in carbon dioxide, which atmosphere data cannot do. “The Southern Ocean is the flywheel of the climate system,” Johnson explains, referring to the component of an engine’s mechanics responsible for keeping things running smoothly. “If we don’t get our understanding of the Southern Ocean right, we don’t have much prospect of knowing the rest of the globe.”

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