Study confirms Southern Ocean absorbs carbon

New research aircraft observations indicate the Southern Ocean is absorbing more carbon from the atmosphere than it releases, confirming that it is a powerful carbon sink and important buffer for the effects of human-made greenhouse gas emissions. Previous research and modeling had left researchers uncertain about the amount of atmospheric carbon dioxide (CO2) is absorbed by the cold waters surrounding the Antarctic continent.

In a NASA-funded study published in Science in December 2021, scientists used aerial observations of atmospheric carbon dioxide to “show that the annual net carbon flux in the ocean south of 45 ° S is large, with higher summer absorption and less winter degassing than other recent observations have indicated “. They found that the region’s waters absorbed about 0.53 petagrams more (530 million metric tonnes) of carbon than they released each year.

“Airborne measurements show a decrease in carbon dioxide in the lower atmosphere above the surface of the Southern Ocean in summer, indicating carbon uptake by the ocean,” said Matthew Long, senior author of the study and scientist at the National Center for Atmospheric Research (NCAR). Aircraft observations were collected from 2009 to 2018 during three field experiments, including NASA’s Atmospheric Tomography (ATom) mission in 2016.

The animation and still image on this page shows the areas where carbon dioxide was absorbed (blue) and emitted (red) by the World Ocean in 2012. (Go to 1:00 am to focus on the southern hemisphere .) The data are from the ECCO -Darwin Global Ocean Biogeochemistry Model. The research was funded by the National Science Foundation, NASA, and the National Oceanic and Atmospheric Administration.

When human-made carbon dioxide emissions enter the atmosphere, some of the gas is absorbed by the ocean, a process that can slightly slow the build-up of carbon in the atmosphere and increase in temperature. world that accompanies it. This is in part due to the upwelling of cold water from the depths of the ocean. Cooler, nutrient-rich water at the surface absorbs CO2 of the atmosphere, usually with the help of photosynthetic organisms called phytoplankton, before sinking again.

Computer models suggest that 40 percent of the CO produced by humans2 in the Global Ocean was originally absorbed from the atmosphere in the Southern Ocean, making it one of the most important carbon sinks on our planet. But measuring the flow, or exchange, of CO2 from air to sea was a challenge.

Many previous studies of Southern Ocean carbon fluxes relied heavily on measurements of ocean acidity, which increases when seawater absorbs CO.2– taken by floating and drifting instruments. The new research used planes to measure changes in CO concentration2 in the atmosphere above the ocean.

“You can’t go wrong with the atmosphere,” Long said. “While measurements taken at the ocean surface and from land are important, they are too rare to provide a reliable picture of air-sea carbon flow. The atmosphere, however, can integrate fluxes over large areas.

For the new study, the researchers used airborne measurements from three field experiments: Atom, HIPPO and ORCAS. Collectively, the field experiments captured a series of snapshots (or profiles) of the vertical change in carbon dioxide at various altitudes in the atmosphere and in various seasons. For example, during the ORCAS campaign in early 2016, scientists observed a drop in CO2 concentrations during the aircraft’s descent and also detected severe turbulence near the ocean surface, suggesting gas exchange. Such profiles, along with several atmospheric models, helped the team to better estimate carbon flux.

Video from NASA’s Scientific Visualization Studio and data from the ECCO-Darwin Global Ocean Biogeochemistry Model. Article by Sofie Bates of NASA’s Earth Science News team.


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