Sea ice thickness measurements with AWI polar research aircraft Polar 6 (Photo: Esther Horvath)

Several months before the September minimum, scientists from around the globe provided information on the projected minimum sea-ice areas in the “Sea Ice Outlook”. This year, the Alfred Wegener Institute contributed estimates based on two different forecasting methods for Arctic seasonal sea-ice, which produced similar results very close to the actual September minimum: in July, the AWI’s dynamic forecasting model called for a September minimum of 4.93 million square kilometres, while its static model estimated an area of 4.74 million square kilometres.

This year, the spatial distribution of sea-ice differed from the patterns in recent years, and from the long-term pattern. Less ice than in 2016 was recorded in the Chukchi and East Siberian Seas. In contrast, more ice was observed north of Svalbard and in the Beaufort Sea. In some regions on the fringes of the Artic Ocean, surface melting began fairly early, while in large regions of the central Arctic Ocean, melt onset was observed a few days later than the average for 1981 to 2010. The timing of melt onset is not only important with regard to the overall mass of sea ice; it also determines the lifecycle of the organisms in and below the sea ice.

During the past weeks, sea-ice thickness measurements were the main topic of the TIFAX (Thick Ice Feeding Arctic Export) campaign, which involved research aircraft using laser scanners and a towed electromagnetic probe. In the area surveyed, which lies to the north of the Fram Strait between Greenland and Svalbard, the sea-ice thickness was ca. 1.7 metres, roughly 50 centimetres more than was recorded in 2016. This is most likely due in part to a higher percentage of several-year-old ice in the area. Nevertheless, the measured thickness is ca. 30 per cent lower than between 2001 and 2004. As Marcel Nicolaus summarises, “Despite the warm winter, the sea ice wasn’t unusually thin. Our explanation is that the small and thin ice coverage from the previous summer – the second-smallest area ever recorded – grew faster and thicker than in other years, since thin ice grows faster than thick ice.”