Decrease of Sea Ice Thickness at Hopen, Barents Sea, During 1966-2007

Seasonal shore-fast sea ice thickness at the island of Hopen in the northwestern Barents Sea was monitored over 40 years from a permanently manned meteorological station. Sea ice thickness variability is an important climate indicator, providing more quantitative information on the state of the ice cover than solely sea ice extent data series. Compared to North America and Siberia, few longer time series of seasonal ice exist in the European Arctic. Fast ice formation at Hopen starts on average just before December, and maximum ice thicknesses are reached in May, before the ice starts to melt and breaks up. Being more exposed to swell, currents, and variable wind regimes than in sheltered bays or fjords, the development of fast ice at Hopen is interrupted various times during several of the seasons observed. Then, the ice is removed and new ice forms. Annual maximum ice thicknesses at Hopen average 0.99 m, with thickest ice measured 2.0 m. Since 2000, no ice thicker than 1.0 m was observed. Over the entire span of the time series (1966-2007), we find a negative trend of the ice thickness anomaly and seasonal maximum ice thickness. This decrease coincides with an increase in both local surface air temperature and surface water temperature at Hopen. The observed sea ice thickness changes are consistent with reductions of sea ice extent in the Barents Sea and the entire Arctic.