SEA ICE THICKNESS DISTRIBUTION IN THE GREENLAND SEA AND EURASIAN BASIN, MAY 1987

Upward sonar data from a 3400-km track in the Greenland Sea and the Eurasian Basin of the Arctic Ocean, obtained by a British submarine in May 1987, have been statistically analyzed. Mean ice thicknesses in the Greenland Sea show significant melting with downstream distance, at an average rate of 0.38 m per degree of latitude, equivalent to about 2140 km3 yr-1 of freshwater input between 80-degrees-N and 75-degrees-N. In the region north of Fram Strait, between 82-degrees-N and 80-degrees-N, there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises (1976, 1979, 1985), while between Greenland and the North Pole there was a significant thinning in 1987 relative to 1976. In Fram Strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy. Ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the Greenland Sea is due to preferential melting of thicker ice. Pressure ridge draft distributions also fit a negative exponential, while their spacings fit a lognormal distribution. Lead width distribution follows a power law with an exponent of -1.45 for narrow leads and -2.50 for wider leads, if leads are defined as having a 1-m maximum draft (-1.67 and -2.76 for a 0.5-m maximum draft). Lead spacings follow a negative exponential distribution for moderate spacings (400-1500 m) but with an excess of lead pairs at small and very large spacings.