Declining Arctic Landfast Ice between 1975 and 2003

Landfast ice constitutes about 15% of the total Arctic sea ice cover in winter. Because landfast ice rings the coastline of the Arctic Ocean, it plays a unique role in the Arctic climate system, with impacts on coastal communities and ecosystems, shipping routes, and the storage and release of freshwater. Using the weekly ice charts produced by the U.S. National Ice Center, we analyzed the interannual variation of landfast ice in the Northern Hemisphere from 1975 to 2003. We divided the Arctic and sub-Arctic seas into 17 regions and created a time series of winter landfast ice extent for each region. The duration of the ice season was also computed for each year by finding the dates in the fall and spring when the ice extent rose above or fell below a certain threshold. We find statistically significant decreases in landfast ice extent in the Laptev, Chukchi, and Beaufort Seas, as well as the Canadian Archipelago, over the period examined. Large declines were also found in the Kara and East Siberian Seas, and along the east coast of Greenland. On the other hand, landfast ice extent increased in the Barents Sea and the Sea of Okhotsk. However, the trend for the Northern Hemisphere as a whole is significantly negative. The duration of the landfast ice season has also shortened significantly in the East Siberian, Chukchi, and Bering Seas, but has increased in the Barents Sea. The trend for the Northern Hemisphere as a whole is close to zero. Several factors may be responsible for the observed changes in landfast ice, including surface air temperature, atmospheric circulation patterns associated with the Arctic and the Pacific Decadal Oscillations and increasing river discharge. We explore these various factors to explain the spatial and temporal changes in landfast ice extent and duration.