Statistical Study of Sea-Ice Variability at the Planned Locations of Leg 151 Drilling Sites

Abstract

Leg 151 of the Ocean Drilling Program (ODP) was conducted in the Fram Strait during the summer of 1993. Eight sites, extending between the latitudes of 78°22'N and 81°06 N, had been selected by ODP as desirable drill sites. Prior to the drilling season, the authors conducted a statistical study of 26 years of data from the United Kingdom's Meteorological Office ice charts to determine the likelihood of encountering ice-free conditions during the months of August and September at each of the sites. We examined 1897 charts covering July-October of 1966-1991; although charts are issued twice-weekly, they were compiled daily during 1969-1979 and the daily charts were archived so that a large data set was available. We recorded the ice concentration at each of the eight sites from each of the charts, using the results to derive the probability of a site remaining ice free for 2-12 consecutive days during August-September and determine the most favorable time of year for a site to remain ice free for at least 4 consecutive days. We found that there was a significant amelioration of ice conditions in 1971, which continued through to 1990, so data from 1971 to 1990 were used in the final analysis. We found that three of the sites in southern Fram Strait were very favorable for drilling, one was favorable, two were unfavorable, and two were so difficult as to be probably unreachable by an unstrength-ened vessel. The actual experiences of the JOIDES Resolution and the chartered icebreaker support ship Fennica during Leg 151 are reviewed; they corresponded well with the predictions of our analysis.