Variability of Fram Strait ice flux and North Atlantic Oscillation

Abstract

We estimate the winter sea ice export through the Fram Strait using ice motion from satellite passive microwave data. Sea ice motion (October‐May) is obtained by tracking the displacement of common features in sequential 85 and 37 GHz brightness temperature fields. The average winter area flux over the 18‐year record (1978–1996) is 670,000 km 2, ∼7% of the area of the Arctic Ocean. The winter area flux ranges from a minimum of 450,000 km 2 in 1984 to a maximum of 906,000 km 2 in 1995. The daily, monthly, and interannual variabilities of the ice area flux are high. There is an upward trend in the ice area flux over the 18 year record. The average winter volume flux over the winters of October 1990 through May 1995 is 1745 km 3 ranging from a low of 1375 km 3 in the 1990 flux to a high of 2791 km 3 in 1994. The sea level pressure gradient across the Fram Strait explains more than 80% of the variance in the ice flux over the 18 year record. We use the coefficients from the regression of the time series of area flux versus pressure gradient across the Fram Strait and ice thickness data to estimate the summer area and volume flux. The average 12 month area flux and volume flux are 919,000 km 2 and 2366 km 3. We find a significant correlation (R = 0.86) between the area flux and positive phases of the North Atlantic Oscillation (NAO) index over the months of December‐March. Correlation between our 5 years of volume flux estimates and the NAO index gives R = 0.56. During the high NAO years a more intense Icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the Fram Strait, thus increasing the atmospheric forcing on ice transport. Correlation is reduced during the negative NAO years because of decreased dominance of this large‐scale atmospheric pattern on the sea level pressure gradient across the Fram Strait.