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Storm-induced sea-ice breakup and the implications for ice extent


The propagation of large, storm-generated waves through sea ice has so far not been measured, limiting our understanding of how ocean waves break sea ice. Without improved knowledge of ice breakup, we are unable to understand recent changes, or predict future changes, in Arctic and Antarctic sea ice. Here we show that storm-generated ocean waves propagating through Antarctic sea ice are able to transport enough energy to break sea ice hundreds of kilometres from the ice edge. Our results, which are based on concurrent observations at multiple locations, establish that large waves break sea ice much farther from the ice edge than would be predicted by the commonly assumed exponential decay1,2,3. We observed the wave height decay to be almost linear for large waves—those with a significant wave height greater than three metres—and to be exponential only for small waves. This implies a more prominent role for large ocean waves in sea-ice breakup and retreat than previously thought. We examine the wider relevance of this by comparing observed Antarctic sea-ice edge positions with changes in modelled significant wave heights for the Southern Ocean between 1997 and 2009, and find that the retreat and expansion of the sea-ice edge correlate with mean significant wave height increases and decreases, respectively. This includes capturing the spatial variability in sea-ice trends found in the Ross and Amundsen–Bellingshausen seas. Climate models fail to capture recent changes in sea ice in both polar regions4,5. Our results suggest that the incorporation of explicit or parameterized interactions between ocean waves and sea ice may resolve this problem.

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Figure 1: Deployment location and track of each wave sensor.
Figure 2: Decay rates of sensors farther than 100 km from the ice edge.
Figure 3: Ice-breaking potential as a function of the distance from the ice edge and the significant wave height at the ice edge.
Figure 4: A comparison between the trends in sea-ice extent and significant wave height between 1997 and 2009.


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We thank Inprod Pty Ltd for instrument design and construction; M. Doble, V. Squire and T. Haskell for contributions toward instrument design; T. Toyota for the provision of ice floe size and ice thickness data; the captain and crew of RSV Aurora Australis and the second Sea Ice Physics and Ecosystem Experiment (SIPEX II) for their assistance in deploying the waves-in-ice instruments; and V. Squire, T. Toyota, L. Bennetts and T. Williams for contributions toward interpretation and editing. The work was funded by a New Zealand Foundation of Research Science and Technology Postdoctoral award to A.L.K.; the Marsden Fund Council, administered by the Royal Society of New Zealand; NIWA, through core funding under the National Climate Centre Climate Systems programme; the Antarctic Climate and Ecosystems Cooperative Research Centre; and Australian Antarctic Science project 4073.

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Authors and Affiliations



A.L.K. and M.J.M.W. had the idea for and designed the study. A.L.K. carried out the experiment. A.L.K., S.M.D. and M.H.M. analysed the data. All authors contributed to data interpretation and writing.

Corresponding author

Correspondence to A. L. Kohout.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Latitudinal profiles of sea-ice concentration.

ERA-Interim reanalysis of satellite observations34 is averaged between 120° E and 129° E for the peak of each large-wave event: 23 September 2012 at 18:00 (blue long-dashed), 1 October 2013 at 12:00 (green long-dashed) and 7 October 2012 at 12:00 (orange short-dashed) (all dates in utc). The solid line is the mean concentration (120 °E–129° E) between 15 September and 15 October for 1979–2012, and the shaded area (yellow) spans the maximum and minimum concentrations over the same time period.

Extended Data Figure 2 Overview of the observations.

Smoothed significant wave height (solid) and smoothed distance from the ice edge (dashed) of the sensor closest to the ice edge (red) and the sensor farthest from the ice edge (blue). The ice edge is derived from the ASI algorithm SSMI-SSMIS sea-ice concentrations29,30,31. Dates are in utc.

Extended Data Figure 3 The power spectral densities during a storm-generated wave event and during calm seas.

a, A storm-generated wave event at 20:00 on 23 September 2012 utc with significant wave heights of 6, 5.5 and 4.2 m at, respectively, 39 (green solid), 51 (red dashed) and 90 km (yellow dotted) from the ice edge. b, Calm conditions at 02:00 on 27 September 2012 utc with significant wave heights of 2, 1.3 and 0.1 m at, respectively, 0 (green solid), 14 (red dashed) and 150 km (yellow dotted) from the ice edge. The shaded regions give the 90% confidence intervals.

Extended Data Figure 4 Trend in the location of the ice edge versus trend in significant wave height for each longitude and each month between 1997 and 2009.

a, The trends during the ice decay season (September to February). b, The trends during the ice growth season (March to August). The Pearson coefficients are given in the top right of each panel (n = 1,727 for each). The linear least-squares approximation during ice decay is −1.28 (Hs trend) + 0.02, with a 95% confidence interval of (−1.39, −1.16) for the slope. During ice growth, it is −1.03 (Hs trend) + 0.01, with a 95% confidence interval of (−1.12, −0.94) for the slope.

Extended Data Table 1 Floe size distribution
Extended Data Table 2 Numbers of data points and missing values for each sensor
Extended Data Table 3 A comparison of dHs/dx values for the full data set and for data more than 100 km from the ice edge

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Kohout, A., Williams, M., Dean, S. et al. Storm-induced sea-ice breakup and the implications for ice extent. Nature 509, 604–607 (2014).

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