Identification of Heinrich layers in core KS 01 north-eastern Atlantic (46 degrees N, 17 degrees W), implications for their origin

Sediments of the North Atlantic contain between 40 degrees and 55 degrees N a series of layers rich in ice-rafted material (Heinrich layers, HL's). In core KS01 from the northeastern Atlantic (46 degrees 00.2'N, 17 degrees 12.1'W) we identified HL1 to 5. Important parts of these layers are abnormally dense. In order to unravel the depositional history of the HL's and the environmental conditions which have allowed such induration, we investigated the O-18 and C-13 contents of planktonic foraminifers and studied the bulk physical and lithological properties of the layers. The detailed investigation of HL1, HL2 and HL4 shows that, at this site, drastic changes in the surface water and at the sediment-water interface occurred during the HL deposition. We distinguished two phases. The first phase, which includes two steps, is characterised by glacial conditions and high productivity (not reflected by planktonic foraminifers). During the second step the detrital carbonate supply increased and organic carbon content maxima occur in these HL's. The second phase is characterised by an important decrease of the surface water salinity and an important reduction of the productivity. The diagenetic precipitation of calcite within microburrows in relation with anoxic and microbial mineralisation of organic matter may have contributed to the induration of the layers.