In a warming world, what drives cooling and freshening in the South Pacific Ocean?

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As a whole the earth is warming. Yet cooling and freshening have been observed in the Southeastern Pacific, in the well-instrumented period of 2006 to 2013. At the same time freshwater export by meridional transport of Antarctic sea-ice has shown a positive trend that is strongest in the South Pacific Ocean. This project will investigate the mechanism of this recent South Pacific cooling and freshening trend. Of particular interest is the role of sea ice in the generation of fresh water and the modulation of air-sea flux heat fluxes. The proposed work will contribute to understanding of the Southern Ocean (SO) response to climate change, including changes in the upper ocean heat and freshwater content, sea-ice cover and melt water export. These results are relevant for other disciplines such as biogeochemistry, and will guide our understanding of carbon cycle changes. The results will be published in scientific journals and presented at major meetings. The project outreach components include plans to advise one undergraduate student per year through the Scripps Institution of Oceanography Undergraduate Research Fellowship (SURF) Research Experiences for Undergraduates (REU) program as well as plans for a 5-day workshop series for high school science teachers to help them develop tools and strategies for teaching the most up-to-date scientific results that are of significant importance for wide, non-scientific community. The overall goal is to understand the interconnections between sea ice, ocean, and atmosphere, to describe the mechanisms that govern these changes, as well as their interannual to interdecadal variability. Strong changes observed in the Southern Ocean in recent decades represent significant perturbations to the upper ocean heat and freshwater content and seem to have significant impact on carbon content, as well. Changes in sea-ice cover are strongly linked to observed changes in the Southern Ocean hydrography and to changes in air-sea buoyancy fluxes. The physical processes governing the temporal and spatial variability of individual components will be interpreted in relation to the variability in formation rates of the major Southern Ocean water masses. This will facilitate identification of locations where the ocean is most strongly coupled to the atmosphere, and thus most sensitive to atmospheric changes, providing valuable information on the observational requirements on the atmospheric and sea-ice state needed to accurately describe and interpret Southern ocean hydrology. While the proposed work will focus on water mass transformation processes in the Southern Ocean, the results are likely to be applicable for understanding global meridional overturning circulation, and the methods applied here should be extendable to the Northern Hemisphere as well. The project will lead to an assessment of the accuracy of existing flux measurements, an evaluation of the sensitivity of water mass transformation processes to flux definitions and a dissemination of the resulting requirements to the Global Ocean Observing System and the Global Climate Observing system planning groups.