Provenance of icebergs during Heinrich event 3 and the contrast to their sources during other Heinrich episodes

The sources of ice-rafted debris (IRD) from Heinrich layer 3 (H 3) in the North Atlantic were studied by means of Pb isotopic analyses of single- and multiple-grain samples of ice-rafted feldspars from core V28-82 (49 degrees 27'N, 22 degrees 16'W). Pb ratios of H 3 grains point to multiple continental sources and are similar to the isotopic composition of the background sediment. This similarity, as well as previous observations about the age and the Sr and Nd isotopic composition of the fine fraction of H 3 in cores of the same area, are all consistent with the hypothesis that in the eastern North Atlantic along the latitude band of maximum IRD deposition (40 degrees-50 degrees N), H 3 is a product of foraminifera dissolution and/or low productivity. In contrast, analyses of composite samples of H 1, H 2, H 4, and H 5 plot in Pb-206/Pb-204 versus Pb-206/Pb-204 coordinates along the Churchill province line, supporting the premise that the Hudson Strait was the major pathway of iceberg drainage during these four events. Since an advance of the Laurentide ice sheet during H 3 is demonstrated by increases in detrital carbonate at the level of H 3 in cores from the western North Atlantic, the results obtained here suggest that if indeed that advance took place, the iceberg discharge melted mostly in the western basin.