Variability of the spring old ice and fall residual ice boundary in the Arctic Ocean over the current period of climate changes

The present study deals with interannual variability investigation of the April old and the September second-year ice southern boundaries, as well as the impact of the old and the first-year ice amount on the Arctic Ocean ice mass balance. The residual ice includes the old and the residual first-year ice that has survived a summer's melt. The boundaries displacement is analyzed within the Eurasian-Alaskian sector, the most robust part of the Arctic Ocean. It is noted that there is the steady reduction of the April old ice amount and its boundary shift toward the north over the recent two decades. The eastern part of sector studied demonstrates the greater displacement than the western one with the value of about 2,5-5,0 degrees of latitude or 300-550 km. The replacement of the old ice by the first-year ice is shown to occur over the current period of climate changes. In addition, the September residual ice southern boundary have prominent shift to the north in both eastern and western parts of study area. This displacement is 1,0-2,0 degrees of latitude or 110-220 km. Until the end of the 20th century, this region has been covered by ice, but the complete and steady ice clearance exhibits over the two recent decades. Since 2002, the first-year ice prevailed on the Arctic Ocean ice mass balance in April (63% vs 37% of the old ice coverage over the recent five years). It should be noted that the first-year ice amount has increased gradually from year to year.