Assessing variability and trends in Arctic sea ice distribution using satellite data

Trends in the annual minimum, minimum monthly-mean, and the sea ice extent at the end of August were investigated for the Barents and western Kara Seas and adjacent parts of the Arctic Ocean during 1966 to 1994 using data from Russian ice maps (1974-1994), Kosmos-Okean and ALMAZ SAR satellite series (1984-1994), and published literature. Four definitions of sea ice extent were examined based on thresholds of ice concentration: >90%, >70%, >40% and >10% (E1, E2, E3, and E4, respectively). Root-mean-square differences between sea ice maps and satellite-image sea ice classifications for coincident areas were subjected to Monte-Carlo analyses to construct confidence intervals for the 20-year ice-map trends. With probability p=0.8, the average 20-year change in the minimum monthly-mean sea ice extent (followed in brackets by the average change in the absolute annual minimum ice extent) was between 30-60% [19-71%], 29-61% [15-67%], 31-63%[18-69%] and 18-48% [7-55%] in the Barents sea; (-24)-(-4)% [(-25)-(12)%], (-27)-(-9)% [(-34)-(-4)%], (-32)-(-15)% [(-39)-(-9)%] and (-33)-(-15)%[(-38)-(-8)%] in the western Kara sea; and (-3)-19% [(-8)-29%], (-4)-18% [(-11)-26%,] (-6)-16% [(-11)(-24)%] and (-7)-15% [(-12)-24%] in the combined Barents and Kara Seas, for sea ice concentration E1-E4, respectively. Including published data from 1966-1983, the trend in minimum monthly-mean sea ice extent for the combined 30-year period showed an average increasing of 11.8% in the Barents Sea and of 47.4% reduction in the western Kara Sea; sea ice extent at the end of August showed an average reduction of 4.7% in the Barents Sea.