Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion

Journal name:
Nature Geoscience
Volume:
6,
Pages:
376–379
Year published:
DOI:
doi:10.1038/ngeo1767
Received
Accepted
Published online

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded1, with record extent2 in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica’s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends4, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

At a glance

Figures

  1. Austral winter half-year (April-September) trends in sea-ice extent (total Southern Hemisphere) and SST (averaged over 50[deg]-90[deg][thinsp]S).
    Figure 1: Austral winter half-year (April–September) trends in sea-ice extent (total Southern Hemisphere) and SST (averaged over 50°–90°S).

    a,b, Sea-ice extent trends (a) are based on a combination of data from the final analysis2, the preliminary analysis and near-real-time data (2009–2012); SST data (b) were taken from the NCEP (National Centers for Environmental Prediction) merged satellite data set and the in situ SST data set SST OI v2 (ref. 29; the same data sources apply for Figs 2 and 3). The green line represents the 10-year running mean.

  2. Spatial distributions of Antarctic sea-ice concentration and SST trends over the period 1985-2010.
    Figure 2: Spatial distributions of Antarctic sea-ice concentration and SST trends over the period 1985–2010.

    a,b, Sea-ice concentration trends (a) and SST trends (b). Colouring (bright or faint) indicates whether the trends are significant (yes or no) at p<0.1 according to a two-sided t-test. The locations of the Antarctic Peninsula (AP), Amundsen Sea (AS), Ross Sea (RS), Weddell Sea (WS) and Bellingshausen Sea (BS) are indicated in a.

  3. Austral winter half-year (April-September) zonal mean trends (1985-2010) of observed salinity, vertical density gradient and potential temperature, in the Southern Ocean.
    Figure 3: Austral winter half-year (April–September) zonal mean trends (1985–2010) of observed salinity, vertical density gradient and potential temperature, in the Southern Ocean.

    a, Salinity. b, Vertical density gradient. c, Potential temperature. Contours indicate the 1985–2010 mean state (psu, kgm−4, °C). Colouring (bright or faint) indicates whether the trend is significant (yes or no) at p<0.1 according to a two-sided t-test. The near-surface increase in salinity between 65° and 70°S is most likely due to brine rejection when sea ice forms. The sub-surface ocean observations were taken from the Met Office EN3 analysis, which is based on in situ observations30.

  4. Simulated changes in austral winter (April-September) temperature, salinity and sea-ice cover resulting from a 250[thinsp]Gt[thinsp]yr-1 increase in Antarctic mass loss (relative to the control run).
    Figure 4: Simulated changes in austral winter (April–September) temperature, salinity and sea-ice cover resulting from a 250Gtyr−1 increase in Antarctic mass loss (relative to the control run).

    a, Zonal mean potential temperature change. b, Zonal mean salinity change. c, Zonal mean vertical stability change. d, Spatial sea-ice concentration change. In ac contours indicate the 31-year mean states in °C, psu and kgm−4, respectively. Results represent means over the 31-year simulation period. In ac colouring (bright or faint) indicates whether the difference is significant (yes or no) at p<0.1 according to a two-sided t-test.

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Affiliations

  1. Royal Netherlands Meteorological Institute (KNMI), Wilhelminalaan 10, 3732 GK De Bilt, The Netherlands

    • R. Bintanja,
    • G. J. van Oldenborgh,
    • S. S. Drijfhout,
    • B. Wouters &
    • C. A. Katsman

Contributions

G.J.v.O., R.B. and S.D. developed the ideas that led to this paper. G.J.v.O. analysed the observational data. B.W. and R.B. conducted the climate model experiments and analyses. R.B. wrote the main paper, with input from all authors, who discussed the results and implications and commented on the manuscript at all stages.

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