In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen- Bellingshausen-Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change.
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Acknowledgements X.L., D.M.H. and C.Y. were supported by the NSF Office of Polar Programs (grant number ANT-0732869), the NASA Polar Programs (grant number NNX12AB69G), and New York University Abu Dhabi (grant number G1204). E.P.G. was supported by the NSF Office of Atmospheric and Geospace Sciences (grant number AGS-1264195). The HadISST SST and SIC data was provided by the British Met Office, Hadley Centre. The Antarctic weather station data was made available by the British Antarctic Survey. The MERRA atmospheric reanalysis data was provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center (GSFC) through the NASA Goddard Earth Sciences (GES) Data and Information Services Center (DISC) online archive (http://disc.sci.gsfc.nasa.gov/mdisc/ data-holdings/merra/merra_products_nonjs.shtml). The ERA-Interim atmospheric reanalysis was provided by the ECMWF. The comprehensive atmospheric model (CAM4) was made available by the National Center for Atmospheric Research (NCAR), supported by the National Science Foundation (NSF) and the Office of Science (BER) of the US Department of Energy (DOE). The idealized atmospheric model (the GFDL dry dynamical core) was developed by the National Oceanic and Atmospheric Administration (NOAA) at the GFDL. Computing resources were provided by the National Energy Research Scientific Computing Center (NERSC) and High Performance Computing (HPC) at New York University (NYU).