IDENTIFICATION OF THE MULTIPLE SOURCES OF ICE RAFTED DEBRIS IN THE NORTH ATLANTIC DURING HEINRICH EVENTS USING A BIOMARKER APPROACH

During the last glacial period the ice sheets surrounding the North Atlantic discharged abruptly massive numbers of icebergs in quasi-periodic episodes. These events are known as Heinrich Events or HE, and are recorded in oceanic Quaternary sediments as prominent layers of ice rafted debris (IRD), whose properties differ from those of adjacent ambient sediments. For instance, the layers contain organic matter of pre-Quaternary origin characterised by a molecular signature more akin to that from a petroleum-like source than from an autochthonous marine input. We have used this to apply a biomarker approach to characterise the provenance of the organic material, and hence the IRD, in four deep sea cores in the North Atlantic containing HLs 1 to 6 (MD95-2024, ODP-609, BOFS-5K and SU90-09). The approach is similar to that applied in the petroleum industry for oil-source rock correlation as well as in oil pollution studies to track the sources of atmospheric pollution or oil spills.

The characteristics of the source material have been determined through the detailed characterisation of the biomarker composition of some of the largest glaciogenic debris flow deposits in the continental margins of the northern North Atlantic. This represents a novel approach to characterise geochemically IRD sources. It is possible because ice sheets drained through specific “outlets” known as trough mouth fans (TMF) in the ocean, and left in the continental margins massive deposits of debris which happen to be relatively rich in organic matter. In this communication we will discuss pros and cons of the use of biomarkers to determine provenance of IRD and the implication of some of the findings to understand further the HEs.