THE DECAY OF THE BARENTS ICE-SHEET AS DOCUMENTED IN NORDIC SEAS ICE-RAFTED DEBRIS

A large, marine-based ice sheet that covered the Barents Sea and Svalbard during the height of the Weichselian Glaciation began to disintegrate at 15 ka. The decay produced enormous quantities of icebergs that drifted parallel to the Norwegian continental margin southward and northwestward into the Fram Strait. This drifttrack is reflected by a trace of ice-rafted clastic sedimentary rocks from the bottom of the Barents Sea in deep sea sediments of the Norwegian Sea and the Fram Strait. The petrographic composition of ice-rafted lithic particles (dropstones) > 0. 5 mm in late Quaternary (20 ka-Recent) deep-sea sediments of the Norwegian Greenland Sea was analyzed in order to determine the source areas of the dropstones. The dropstone provenance was deciphered from the regional distribution of some precisely defined lithotypes. During the maximum glaciation between 20 and 15 ka, the Norwegian Sea received crystalline rocks primarily from western Norway, but also from Svalbard and the northwestern British Isles. The Greenland Sea was supplied with clay-, silt- and sandstones from central and northern East Greenland and rocks from circum Arctic areas. At 15 ka, a dramatic shift in provenance from crystalline rocks to clastic sedimentary rocks is recorded in the dropstone composition of the northern and eastern Norwegian Sea. This impulse was the ultimate result of the deterioration of the Barents ice sheet. The dispersal area of clastic rock fragments reaches from the Barents shelf between 72-degrees and 76-degrees-N, and 15-degrees and 20-degrees-E to the Voring Plateau (eastern Norwegian Sea) at 67-degrees-N and 5-degrees-E. The main direction of iceberg drift was to the south and southeast. After an initial period of only 500 years duration and extremely high dropstone deposition rates, the influx from the Barents shelf ceased and gradually changed into the modem surface current system.