Storm waves break up sea ice

Promoted from comments

Kiwi connection on significant anti-alarmist paper

Robin Pittwood apologises for being “way off topic” and mentions a new paper at Nature about wave effects breaking up Antarctic ice.

“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 decay. 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 regions. Our results suggest that the incorporation of explicit or parameterized interactions between ocean waves and sea ice may resolve this problem.”

This fascinating result reveals another non-climatic influence on sea ice and shows yet again that climate science is far from settled.

Saying “credit where credit’s due,” Robin points out the lead author is one Alison Kohout, a hydrodynamics scientist working for NIWA. Of course, NIWA is more than capable of proper objective science.

– Posted from my Android at Ericsson Stadium, about to watch the Warriors (thanks, Carl!).

4 Thoughts on “Storm waves break up sea ice

  1. Hemimck on June 5, 2014 at 3:40 pm said:

    Maybe the heading should actually be “Monster waves break up sea ice”

    What Niwa might have gone on to say is that storms don’t cause large wave sets. Intense storms cause confused short seas. Monster waves are a function of fetch and wind strength. To build the huge 14 second waves that occasionally hit the SW of New Zealand, and presumably the ice shelves, requires a wave-set to be amplified by a continuous gale force wind from directly behind over a distance of several thousand kms of uninterrupted water in a straight line .

    Winds are not usually that co-operative meaning that these events are truly random and nothing to do with AGW

  2. Good one, Hemi. I’m working on an in-depth discussion of the paper and you’ve thrown a spanner in the works. Still, it’s a good spanner! Can you define monster waves? Would they, like, start at about three metres?

  3. HemimcK on June 6, 2014 at 1:58 pm said:

    Hi Richard,

    My knowledge of this goes back to researching the practicality of Ports on the West Coast of the South Island – (they are not). – and is from memory and anecdotal but might give you a start.

    The energy of waves is best represented by its period. Normally the waves round our coast are 5 to 6 seconds and indicate a wave that has travelled 500 to 1000 km in moderate winds. The best records are from the Maui Platform which has recorded 14 second monsters (and I think in energy terms the scale is exponential). Maui is at the end of the longest great circle route over clear water on the globe which passes through the bottom of the Indian Ocean where average waves are the greatest on the globe at 5m. Monster waves and their lesser cousins continue to shape the South Island and grow Fairwell Spit.

    A lesser example is the surf break at Fiji. The fetch there is probably less than 1000 but made up for by the regularity of the South East Trades. I don’t know the period of these but someone might.

    Someone who knows the science of waves might be useful. Good luck with your research.

  4. HemimcK on June 6, 2014 at 2:56 pm said:

    Hi Richard,

    Obviously the above is missing a bit. The energy of waves must be a function of both period and height.

    The literature talks about the actual situation at Kupe/Maui which is a mixed bag of more local wind waves and high energy waves from the southern oceans. The locally generated wind waves are strongest in late winter but the big energy waves can arrive anytime.

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