Gravity survey on ice offshore South-East Greenland

Abstract

In the early spring an effort was made to extend some lines of marine gravity data from the shelf into the coast north of Ammassalik. A net of marine gravity data covers the shelf off East Greenland, reaching from about 59°N to 74°N (fig. 1). South of Scoresby Sund the gravity data are mostly coIlected in regions floored by oceanic crust, though some of the lines cross the ocean-to-continent boundary. Between Ammassalik and Scoresby Sund the oceanto-continent transition zone (OCT) runs dose to the coast (Larsen, 1984), and is probably related to the onshore Tertiary basaltic dyke swarm described by Wager & Deer (1938) and Myers (1980) (fig. 2). An offshore continuation of the dyke swarm was proposed by Larsen (1978). The aim of the gravity project was to obtain three tie-lines connecting the offshore marine gravity data to onshore gravity data to be obtained by the Geodetic Institute during the summer of 1986 (fig. 1). Such tie-lines would provide crucial information on the gravity field over the dyke swarm and might aid in a more precise location ofthe initial line of rifting in this region. The survey area is covered with ice most of the year. Gravity surveys on ice have been carried out both in the Bothnian Bay (Lehmuskoski & Makinen, 1978) and on ice-islands in the polar pack ice (Crary et al., 1952; Kristoffersen, 1982). Thus a helicopter survey with portable gravimeter and readings on the ice was planned for the South-East Greenland survey as this would provide gravity data from the area ofinterest at lowest cost. The ice cover off East Greenland is usually most extensive in April (Larsen, 1985) and the field operation was therefore scheduled for that month.