Fram Strait Ice Fluxes and Atmospheric Circulation: 1950–2000
Abstract Observations reveal a strong correlation between the ice fluxes through the Fram Strait and the cross-strait air pressure difference. Using this difference, ?P, as a parameter, the mean ice export from the Arctic Ocean through the Fram Strait is estimated to be ?2900 km3 yr?1 over the past 50 yr. The variability of the annual efflux, which is solely determined by the variability in wind stress, is characterized by a standard deviation of 667 km3. Although the 1950s and 1990s stand out as the two decades with maximum flux variability, significant variations seem more to be the rule than the exception over the whole period considered. There is no temporal trend in the series, indicating long-term stationary conditions, and, consequently, that the mean annual ice efflux corresponds to the mean annual ice formation in the Arctic Ocean. Comparisons indicate that flux anomalies have a high predictive skill for subsequent anomalies, both in the reservoir and in the recipient. As the wind forcing is the major agent for the ice efflux, the downstream and upstream anomalies seem to be initiated in association with variations in the high-latitude atmospheric circulation. This is more the case as the correlation between the ice efflux and the remote air pressure difference between Iceland and Portugal approaches zero (0.1) when considering the whole 50-yr period. A noticeable fall in the winter air pressure of ?7 hPa is observed in the Fram Strait and the Barents Sea during the last five decades. The regional uniformity in the fall renders, however, a temporally invariant magnitude of ?P, indicating no clear effect of the Arctic ocillation on the efflux variability. Decadal alternating variations of ?P indicate the existence of alternating minima and maxima in the annual wind-induced efflux. The corresponding decadal maximum change in the Arctic Ocean ice thickness is of the order of 0.8 m. These temporal wind-induced variations may help explain observed changes in portions of the Arctic Ocean ice cover over the last decades. Due to an increasing rate in the ice drainage through the Fram Strait during the 1990s, this decade is characterized by a state of decreasing ice thickness in the Arctic Ocean.