Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability

Journal name:
Nature Geoscience
Year published:
DOI:
doi:10.1038/ngeo2751
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Accepted
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Antarctic sea-ice extent has been slowly increasing in the satellite record that began in 19791, 2. Since the late 1990s, the increase has accelerated, but the average of all climate models shows a decline3. Meanwhile, the Interdecadal Pacific Oscillation, an internally generated mode of climate variability4, transitioned from positive to negative5, with an average cooling of tropical Pacific sea surface temperatures5, a slowdown of the global warming trend6, 7, 8 and a deepening of the Amundsen Sea Low near Antarctica1, 9, 10, 11, 12 that has contributed to regional circulation changes in the Ross Sea region and expansion of sea ice10. Here we show that the negative phase of the Interdecadal Pacific Oscillation in global coupled climate models is characterized by anomalies similar to the observed sea-level pressure and near-surface 850hPa wind changes near Antarctica since 2000 that are conducive to expanding Antarctic sea-ice extent, particularly in the Ross Sea region in all seasons, involving a deepening of the Amundsen Sea Low. These atmospheric circulation changes are shown to be mainly driven by precipitation and convective heating anomalies related to the Interdecadal Pacific Oscillation in the equatorial eastern Pacific, with additional contributions from convective heating anomalies in the South Pacific convergence zone and tropical Atlantic regions.

At a glance

Figures

  1. IPO connection to tropical precipitation, Antarctic sea-ice trends and 850[thinsp]hPa wind trends.
    Figure 1: IPO connection to tropical precipitation, Antarctic sea-ice trends and 850hPa wind trends.

    a, Observed precipitation (1979–2014) regressed onto IPO index (inset); sign convention is negative IPO phase. b, Antarctic sea-ice extent trends (106km2decade−1), 1979–99, with 95% confidence bars. c, Same as b except for 2000–2014. d, Same as b except for CMIP5 model averages, 1979–99; MMEM, multi-model ensemble mean. e, Same as d except for composite trends for ten CMIP5 ensemble members with observed global-averaged surface temperature trend and negative IPO phase13. f, For each panel, the two bars at the left are the number of grid points, 1979–99 observations, with sea-ice concentrations (SIC) increasing more than 10%, and the number of those grid points with positive (‘+ve) 850hPa v-component winds; two bars at right, the same as those at the left except for the period 2000–2014. g, Observed DJF zonal mean positive (‘+ve) 850hPa v-component wind trends (ms−1decade−1), 70°S to 50°S, 2000–2014 (red solid), 1979–1999 (blue dashed), noise estimate (grey shading, one standard deviation of 850hPa v-component winds at each latitude). h, Same as g except for positive (‘+ve) 850hPa v-component wind anomalies (ms−1) from the CAM3 model experiment (negative heat source at 135°W, Equator), 30-year average (red solid), three different control run 30-year averages (blue dashed).

  2. Observed trends of SLP, sea-ice concentration and 850[thinsp]hPa winds.
    Figure 2: Observed trends of SLP, sea-ice concentration and 850hPa winds.

    ad, For the era of negative IPO, 2000–2014, sea-ice concentration (SIC) (trends greater than 2.5% decade−1 are plotted as colour shading, values significant at the 5% level are stippled), SLP (hPa decade−1) and 850hPa wind trends (scaling vector at lower right in each panel, ms−1decade−1) for DJF (a), MAM (b), JJA (c) and SON (d). Negative values indicating a deepening of the ASL are denoted by ‘L. (Statistical significance of the SLP trends is generally at the 5% level in most of the negative maxima, with values shown in Supplementary Fig. 7.)

  3. SLP and 850[thinsp]hPa wind anomalies for the eastern equatorial Pacific negative heating experiment at 135[deg][thinsp]W, Equator.
    Figure 3: SLP and 850hPa wind anomalies for the eastern equatorial Pacific negative heating experiment at 135°W, Equator.

    Negative SLP anomalies (hPa) shaded blue; positive orange; stippling indicates significance at the 5% level; scaling vector for 850hPa winds (ms−1) at lower right of each panel. ad, Negative values indicating a deepening of the ASL are denoted by ‘L, for DJF (a), MAM (b), JJA (c) and SON (d).

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Affiliations

  1. National Center for Atmospheric Research, Boulder, Colorado 80307, USA

    • Gerald A. Meehl,
    • Julie M. Arblaster &
    • Haiyan Teng
  2. Monash University, Melbourne 3008, Australia

    • Julie M. Arblaster
  3. University of Washington, Seattle, Washington 98195, USA

    • Cecilia M. Bitz
  4. Bureau of Meteorology, Melbourne 3001, Australia

    • Christine T. Y. Chung

Contributions

G.A.M. directed this work with contributions from all authors. G.A.M., J.M.A., C.M.B., C.T.Y.C. and H.T. performed the analyses. All of the authors discussed the results and contributed to writing the manuscript.

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The authors declare no competing financial interests.

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