The Southern Ocean’s surface is cooled during the wintertime, forming a dense water layer containing oxygen and nutrients called subantarctic mode water (SAMW), which is then introduced into global ocean circulation. There is a lack of measurements and observations of the SAMW properties as it forms during the winter, but a new study, supported by a partnership between CPO’s Climate Observations and Monitoring (COM) Program, Climate Variability and Predictability (CVP) Program, and NOAA’s Global Ocean Monitoring and Observing (GOMO) Program, introduces a comprehensive characterization of the water formation.
NOAA-funded scientist Seth Bushinsky of the University of Hawaiʻi at Mānoa along with Ivana Cerovečki of the Scripps Institute of Oceanography use Argo float observations spanning a 7-year period to investigate biogeochemical properties and water density in two main regions where SAMW forms: the Pacific and Indian sectors of the Southern Ocean. Distinct differences between the two regions are seen in the results, published in AGU Advances, showing that SAMW formed in the Pacific is colder, fresher, and higher in oxygen, nitrate, and dissolved inorganic carbon than its Indian Ocean counterpart. Previous work has not yet produced enough observations to investigate sub-regional or interannual variability, so this study uses a model which takes into account biogeochemical properties, ocean processes, and sea ice to approximate finer-scaled features. The model results accurately recreate relationships seen in observations, providing confidence that it is a useful tool to improve our understanding of the link between SAMW and climate patterns. An additional finding demonstrates that carbon dioxide levels are nearly equal between the ocean surface and atmosphere at the time of SAMW formation, so this process does not represent a mitigation pathway to store present-day carbon.
These results advance the interpretation of ocean measurements and model studies investigating the role of these waters in the global carbon cycle. The project is funded by a collaboration between COM, CVP, and GOMO to increase the use and value of ocean observations, advance our understanding of climate variability and change, and enhance NOAA’s ability to model and predict the Earth System.
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