NCAR Imperative 1 | ORCAS Field Campaign

The ORCAS | O2/N2 Ratio and CO2 Airborne Southern Ocean field (https://www.eol.ucar.edu/field_projects/orcas) campaign provided scientists a rare look at how oxygen and carbon dioxide are exchanged between the air and the seas surrounding Antarctica. The data collected helps to illuminate the role the Southern Ocean plays in soaking up excess carbon dioxide emitted into the atmosphere by humans.

ORCAS Infographic.
ORCAS Infographic. High resolution image.
     

The science campaign was led by NCAR with other principal investigators from the Scripps Institution of Oceanography, University of Michigan, and the Cooperative Institute for Research in Environmental Sciences (a partnership of the National Oceanic and Atmospheric Administration and the University of Colorado Boulder), University of Miami, and NASA's Jet Propulsion Laboratory.

Measuring oxygen alongside carbon dioxide gives scientists a clearer picture of the ocean processes affecting carbon dioxide than they would get from measuring carbon dioxide alone.  Carbon dioxide in the ocean is drawn into a chain of chemical reactions that buffer the impact of biological and physical ocean processes on carbon dioxide in the overlying atmosphere. Oxygen air-sea fluxes, however, are more directly tied to these same biological and physical factors. So if scientists know what's going on with oxygen, they can better understand the processes affecting carbon dioxide as well.  Additionally, if scientists know how the concentrations of the two gases change relative to one another with location and time, they can disentangle how biology and physics separately affect the ocean's ability to absorb carbon dioxide.

ORCAS flight tracks colored by flight, including satellite chlorophyll and altitude of track.
ORCAS flight tracks colored by flight, including satellite chlorophyll and altitude of track. High resolution image.

Operating out of Punta Arenas, near the southern tip of Chile, the researchers used the NSF/NCAR HIAPER research aircraft to make 14 flights across parts of the Southern Ocean between Jan. 15 and Feb. 28, 2016. A suite of instruments on the modified Gulfstream V jet measured the distribution of oxygen and carbon dioxide as well as other gases produced by marine microorganisms, plus aerosol and cloud characteristics in the atmosphere.

Physics and biology affect the ratio of carbon dioxide to oxygen in the air in different ways. In the austral spring the warmth of the returning Sun drives both carbon dioxide and oxygen out of the Southern Ocean surface and into the atmosphere. But the sunlight also triggers the growth of phytoplankton in the water. As the organisms begin to flourish, they take in carbon dioxide and release oxygen, causing the relative amounts of those two gases in the atmosphere to shift in opposite directions. Observations of these shifts can ultimately tell scientists how much carbon is going where and, more importantly, why.

The Southern Ocean is unique among Earth's oceans. Unimpeded by continental landmasses, and driven by a westerly wind, the Southern Ocean is able to form a circular current around Antarctica. This huge flow, the largest current on the planet, connects the adjacent Atlantic, Pacific, and Indian oceans. The complex interactions between this Antarctic Circumpolar Current and currents flowing in from other ocean basins creates an overturning circulation that brings deep water to the surface where it can exchange gases with the atmosphere before it is returned to depth.

Once it dives toward the ocean floor, that surface water—and any carbon dioxide it takes with it—can stay sequestered in the deep ocean for hundreds or even thousands of years. Data collected by the ORCAS flights will help determine how much carbon dioxide goes along for the ride.  The data generated during the field campaign will be used by the ORCAS team to improve global computer models so they do a better job representing the complexities of the Southern Ocean. The data set, which is managed by NCAR, will be publicly available.  While the measurements made during the ORCAS campaign will help scientists fine-tune what they know so far about the Southern Ocean, it's possible the project will also bring to light entirely new aspects of how the ocean works.