Abstract

A major change in the North Atlantic pattern of ice-rafting deposition, during the last interglacial-glacial cycle, occurred approximately 75,000 B.P. Prior to this time, deposition for a period of almost 50,000 yr during isotopic stage 5 was greatest in the northwest near Greenland and Newfoundland. The main glacial pattern was very different; the main depositional axis shifted abruptly to a zonal axis along lat 46° to 50°N, reflecting the passage of ice farther from the pole before reaching water warm enough in which to melt. This pattern remained essentially unchanged for 65,000 yr during the main Würm glaciation.

The peak interglacial depositional pattern can best be explained by analogy with the modern oceanic flow, except for the addition of a concentrated eastward component along lat 50°N. The glacial pattern is also best explained by counterclockwise flow. Laurentide and Greenlandic ice entering the western North Atlantic from the Labrador Sea moved to the east and southeast directly into the glacial depositional maximum. Scandinavian ice dropped part of its bed load near Norway, looped to the southwest into the North Atlantic in a counterclockwise passage south of Iceland, and finally melted along the primary depositional maximum.

Total input rates of ice-rafted sediment to the Atlantic and Norwegian Sea increased slightly at 115,000 B.P. (the glacial inception), rose markedly at 75,000 B.P. (the major glacial transition), and continued to rise late in the Würm toward the late-glacial maximum. North Atlantic ice-rafting deposition is thus positively correlated with ice-sheet size.

During Quaternary time, roughly 70% of ice-rafted deposition of continental detritus in the world's oceans has occurred in the subpolar North Atlantic south of Iceland. During the past 3 m.y., a mass of wet unconsolidated drift estimated at 200,000 km3 has been moved from the continents to the deep Atlantic by ice-rafting alone. This is equivalent to a layer of drift 16 m thick over all parts of the continents thought to have supplied ice-rafted detritus to the North Atlantic.

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