PATTERNS OF ICE-RAFTED DETRITUS IN THE GLACIAL NORTH-ATLANTIC (40-DEGREES-55-DEGREES-N)

The observation by Heinrich (1988) that, during the last glacial perio d, much of the input of ice-rafted detritus to the North Atlantic sedi ments may have occurred as a succession of catastrophic events, rekind led interest on the history of the northern ice sheets over the last g lacial period. In this paper, we present a rapid method to study the d istribution of these events (both in space and time) using whole core low-field magnetic susceptibility. We report on approximately 20 cores covering the last 150 to 250 kyr. Well-defined patterns of ice-rafted detritus appear during periods of large continental ice-sheet extent, although these are not always associated within their maxima. Most of the events may be traced across the North Atlantic Ocean. For the six most recent Heinrich layers (HL), two distinct patterns exist: HL1, H L2, HL4, HL5 are distributed along the northern boundary of the Glacia l Polar Front, over most of the North Atlantic between almost-equal-to 40-degrees and 50-degrees-N; HL3 is more restricted to the central an d eastern part of the northern Atlantic. The Nd-Sr isotopic compositio n of the material constituting different Heinrich events indicates the different provenance of the two patterns: HL3 has a typical Scandinav ia-Arctic-Icelandic ''young crust'' signature, and the others have a l arge component of northern Quebec and northern West Greenland ''old cr ust'' material. These isotopic results, obtained on core SU-9008 from the North American basin, are in agreement with the study by Jantschik and Huon (1992), who used K-Ar dating of silt- and clay-size fraction s of an eastern basin core (ME-68-89). These data confirm the large sp atial scale of these events, and the enormous amount of ice-rafted det ritus they represent.