TRACING THE SOURCE OF IRD IN THE LABRADOR SEA AND (SUBPOLAR) NORTH ATLANTIC BY MEANS OF ORGANIC GEOCHEMISTRY

One of the key issues in understanding the still poorly comprehended mechanisms behind ice-rafted debris (IRD) events is the development of specific provenance indicators that provide information about the precise source areas of the IRD. Here we present an organic geochemical study on the type, distribution and relative abundance of biomarker compounds of extractable organic matter from the different Heinrich Layers (HLs) of the last glacial at multiple locations in the Labrador Sea and North Atlantic.

The results demonstrate that an unique assemblage of organic “petrogenic” compounds, such as (benzo)hopanes, mono- and triaromatic steroids, and palaerenieratene and isorenieratene-derivatives, characterize the HLs in the Labrador Sea and North Atlantic. The presence of aromatic counterparts and dominance of hopanoids and steroids isomers not occurring in regular biological configurations indicate that the biomarker distribution within HLs is incompatible with recent sediments. Rather, these compounds derive from the transportation of ancient organic matter by ice-rafting because of glacial erosion of bedrock in the Hudson Bay Area. Comparison of the biomarker assemblage of HLs with available geologic and newly generated organic-geochemical data allowed narrowing down the assumed source of IRD to a sequence of Upper Ordovician oil shales and limestones outcropping in and close to the Hudson Strait, which have a strikingly similar biomarker signature to that of HLs. Monitoring the presence of these petrogenic compounds in marine sediments thus allows to distinguish organic matter in HLs from adjacent samples and can be used as specific organic-geochemical tracers for the input of detrital material originating from the Hudson Bay Area in northern Canada.