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We summarize 24 years (1978–2002) of ice export estimates and examine, over a 9‐year record, the associated variability in the time‐varying upward‐looking sonar (ULS) thickness distributions of the Fram Strait. A more thorough assessment of the PMW (passive microwave) ice motion with 5 years of synthetic aperture radar (SAR) observations shows the uncertainties to be consistent with that found by Kwok and Rothrock 1999 , giving greater confidence to the record of ice flux calculations. Interesting details of the cross‐strait motion profiles and ice cover characteristics revealed by high‐resolution SAR imagery are discussed. The average annual ice area flux over the period is 866,000 km 2 /yr. Between the 1980s and 1990s, the decadal difference in the net exported ice area is ∼400,000 km 2 , approximately half the annual average. Except for the years with extreme negative NAO, correlation of winter ice area export with the NAO index remains high (R 2 = 0.62). With thickness estimates from ULS moorings, we estimate the average annual ice volume flux (8 years) to be ∼2218 km 3 /yr (∼0.07 Sv). Over the ∼9‐year ULS ice thickness data set, there is an overall decrease of 0.45 m in the mean ice thickness over the entire time series and a decrease of 0.23 m over the winter months (December through March). Correspondingly, the mode of the MY ice thickness exhibits an overall decrease of 0.55 m and a winter decrease of 0.42 m. These are significant trends. Whether these trends are indicative of the thickness trends of the Arctic Ocean is examined, as the time‐varying behavior of the monthly ULS thickness distributions can be related not only to the seasonal cycle in the basal growth and melt, but also to the magnitude and pattern of ice motion in the Arctic Ocean, and the proximity of the ULS moorings to the ice edge.
Kwok et al. (Thu,) studied this question.