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The response of the Antarctic Circumpolar Current to recent climate change


Observations show a significant intensification of the Southern Hemisphere westerlies, the prevailing winds between the latitudes of 30 and 60 S, over the past decades. A continuation of this intensification trend is projected by climate scenarios for the twenty-first century. The response of the Antarctic Circumpolar Current and the carbon sink in the Southern Ocean to changes in wind stress and surface buoyancy fluxes is under debate. Here we analyse the Argo network of profiling floats and historical oceanographic data to detect coherent hemispheric-scale warming and freshening trends that extend to depths of more than 1,000 m. The warming and freshening is partly related to changes in the properties of the water masses that make up the Antarctic Circumpolar Current, which are consistent with the anthropogenic changes in heat and freshwater fluxes suggested by climate models. However, we detect no increase in the tilt of the surfaces of equal density across the Antarctic Circumpolar Current, in contrast to coarse-resolution model studies. Our results imply that the transport in the Antarctic Circumpolar Current and meridional overturning in the Southern Ocean are insensitive to decadal changes in wind stress.

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Figure 1: Spatial pattern of changes in the ACC.
Figure 2: Temporal evolution of potential temperature and salinity within the ACC.
Figure 3: Change of water-mass properties on isopycnal surfaces.
Figure 4: Temperature and salinity changes across the ACC.
Figure 5: Trend in baroclinic potential-energy anomaly and volume transport.

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We acknowledge the role of J. Dunn in developing and making available the CSIRO ocean data archives, and K. Lorbacher for her assistance in the data analysis. The study was initiated during visits of C.W.B. and A.D. at CSIRO Marine Research Laboratories in Hobart, supported by an Ernst Froehlich Fellowship (C.W.B.) and a grant from DAAD (A.D.). This research was supported in part by the CSIRO Wealth from Oceans Flagship, the Australian government’s Cooperative Research Centre (CRC) programme through the ACE CRC, and the Australian Greenhouse Office. The paper is a contribution to The Future Ocean Cluster at Kiel University.

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Correspondence to C. W. Böning.

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Böning, C., Dispert, A., Visbeck, M. et al. The response of the Antarctic Circumpolar Current to recent climate change. Nature Geosci 1, 864–869 (2008).

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