Ice-rafted debris of Late Cenozoic sediments from ODP Leg 104 holes

The abundance and composition of the upper Cenozoic terrigenous coarse-sand fraction (250 µm-2 mm) at ODP Sites 642, 643, and 644 were investigated to date the onset of significant ice-rafting in the Norwegian Sea, establish the regional chronology of ice-rafting, and determine the relative importance of global vs. regional controls on ice-rafting in this area. The first input of ice-rafted debris (IRD) occurs at approximately 2.9 Ma, with significant ice-rafting beginning at about 2.5 Ma. IRD abundances increase significantly in sediments younger than 0.9 Ma at all three holes, indicating climatic deterioration in the late Pleistocene. Differences in the timing of this IRD increase between holes result from regional patterns of IRD supply and surface circulation. Variations in IRD sources and dispersal patterns may also explain the slightly higher background level of IRD abundance at Hole 642B, a seaward site. Major peaks in the generalized IRD records from the Norwegian Sea are tentatively correlated to glacial stages or glacial-to-interglacial transitions in the globally defined oxygen isotope record. This correlation indicates the effect of global conditions on the regional climate of the Norwegian Sea, although the detailed IRD records at these sites are also affected by local/regional processes (e.g., circulation patterns and source area differences).