Journal
NATURE GEOSCIENCE
Volume 9, Issue 8, Pages 596-+Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NGEO2749
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Funding
- NSF [OCE-1357133, OCE-1357072, PLR-1425989, OCE-1234473]
- New International Fellowship Mobility Programme for Experienced Researchers-NEWFELPRO under the European Union's Seventh Framework Programme for research, technological development and demonstration (FP7-PEOPLE-COFUND-MCA)
- Yellowstone
- National Science Foundation
- Yeti HPC cluster
- Columbia University Research Computing Services
- NSF-XSEDE [OCE130007]
- Division Of Ocean Sciences
- Directorate For Geosciences [1234473, 1357133] Funding Source: National Science Foundation
- Office of Polar Programs (OPP)
- Directorate For Geosciences [1425989] Funding Source: National Science Foundation
- Natural Environment Research Council [bas0100033] Funding Source: researchfish
- NERC [bas0100033] Funding Source: UKRI
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Ocean overturning circulation requires a continuous thermodynamic transformation of the buoyancy of seawater. The steeply sloping isopycnals of the Southern Ocean provide a pathway for Circumpolar Deep Water to upwell from mid depth without strong diapycnal mixing(1-3), where it is transformed directly by surface fluxes of heat and freshwater and splits into an upper and lower branch(4-6). While brine rejection from sea ice is thought to contribute to the lower branch(7), the role of sea ice in the upper branch is less well understood, partly due to a paucity of observations of sea-ice thickness and transport(8,9). Here we quantify the sea-ice freshwater flux using the Southern Ocean State Estimate, a state-of-the-art data assimilation that incorporates millions of ocean and ice observations. We then use the water-mass transformation framework(10) to compare the relative roles of atmospheric, sea-ice, and glacial freshwater fluxes, heat fluxes, and upper-ocean mixing in transforming buoyancy within the upper branch. We find that sea ice is a dominant term, with differential brine rejection and ice melt transforming upwelled Circumpolar Deep Water at a rate of similar to 22 x 10(6) m(3) s(-1). These results imply a prominent role for Antarctic sea ice in the upper branch and suggest that residual overturning and wind-driven sea-ice transport are tightly coupled.
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