The paradoxical phenomenon is thought to be caused by relatively cold plumes of fresh water derived from melting beneath the Antarctic ice shelves.

This melt water has a relatively low density, so it accumulates in the top layer of the ocean.

The cool surface waters then re-freeze more easily during Autumn and Winter.

This explains the observed peak in sea ice during these seasons, a team from the Royal Netherlands Meteorological Institute (KNMI) in De Bilt says in its peer-reviewed paper.