Spatial and Temporal Variations in the Extent and Thickness of Arctic Landfast Ice

Analyses of landfast ice in Arctic coastal areas provide a comprehensive understanding of the variations in Arctic sea ice and generate data for studies on the utilization of the Arctic passages. Based on our analysis, Arctic landfast ice mainly appears in January-June and is distributed within the narrow straits of the Canadian Archipelago (nearly 40%), the coastal areas of the East Siberian Sea, the Laptev Sea, and the Kara Sea. From 1976-2018, the landfast ice extent gradually decreased at an average rate of -1.1 +/- 0.5 x 10(4) km(2)/yr (10.5% per decade), while the rate of decrease for entire Arctic sea ice was -6.0 +/- 2.4 x 10(4) km(2)/yr (5.2% per decade). The annual maximum extent reached 2.3 x 10(6) km(2) in the early 1980s, and by 2018, the maximum extent decreased by 0.6 x 10(6) km(2), which is an area approximately equivalent the Laptev Sea. The mean duration of Arctic landfast ice is 44 weeks, which has gradually been reduced at a rate of -0.06 +/- 0.03 weeks/yr. Regional landfast ice extent decreases in 16 of the 17 subregions except for the Bering Sea, making it the only subregion where both the extent and duration increases. The maximum mean landfast ice thickness appears in the northern Canadian Archipelago (>2.5 m), with the highest increasing trend (0.1 m/yr). In the Northeast Passage, the mean landfast ice thickness is 1.57 m, with a slight decreasing trend of -1.2 cm/yr, which is smaller than that for entire Arctic sea ice (-5.1 cm/yr). The smaller decreasing trend in the landfast ice extent and thickness suggests that the well-known Arctic sea ice decline largely occurred in the pack ice zone, while the larger relative extent loss indicates a faster ice free future in the landfast ice zone.