The case of the Polarstern

Map of the Atlantic quadrant of Antarctica, showing the Weddell Sea. Note that any large sea and swell in the Weddell Sea would have to come from the northeast. Adapted from USGS, 2007.

The reports from Gambell were discounted until the attention was brought to the work of Liu and Mollo-Christensen (1988). The Polarstern, a German icebreaker, reported significant swell breaking up the pack ice in the Weddell Sea during a winter cruise. This event was reported as a rare occurrence by a scientific crew.

At the onset of the seas, the amplitude of the waves was 1 m, the wavelength was 250 m and the wave period was measured at 18 sec. The wavelength was considerably shorter than it would have been had the transmission of these waves been in open water. The average thickness of the ice was 80 cm, and some floes were as much as 2 m thick. The ship was 560 km into the ice pack. Following breakup of the ice, the wavelength increased to approximately 500 to 600 m, while the wave period remained roughly the same. These waves broke up a nearly solid ice pack into floes mostly less than 50 m across. Again, this was during the Antarctic winter. There was no reported seismic activity which could have contributed in any way to this event.

As the above map shows, significant sea and swell would have to enter the Weddell Sea from the northeast. Around the Antarctic continent, strong winter time anticyclones, persistent low pressure areas to the north of the Antarctic coastal waters and the "Roaring 40's" westerlies at the southern hemisphere mid latitudes would all form a credible pattern satisfying this requirement. The Weddell Sea is nearly all deep water, more than 500 m down to the ocean floor (Canadian Hydrographic Service, 2000.) 

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