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
... [Show full abstract] 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