A high resolution study of NE Atlantic sediments at station Bengal: geochemistry and early diagenesis of Heinrich layers

High resolution geochemical analysis of a piston core from the deep NE Atlantic revealed large differences in the major and trace element signature within the sedimentary record at station Bengal (48 degrees 58 'N, 16 degrees 28 'W, water depth 4804 m). A prominent Heinrich layer (H4) containing large amounts of ice-rafted detritus (IRD) and two less pronounced layers, HI and H2, were identified from Mg/Al, Si/Al, Zr/Al and porosity profiles. H3 and H5 were much less developed, therefore not all identification criteria are applicable. Elevated Si/Al and Zr/Al ratios were probably caused by enhanced eolian loess input. Element/Al ratios of other elements (Cr, Rb, Fe, V, and Zn [not shown]) point to a change in the provenance of the terrigenous material of upper continental crust material delivered during the most intense Heinrich event, H4. The use of Ba/Al, TOC/Al, and carbonate content as paleoproductivity tracers revealed enhanced carbon input to the seafloor before and during HE as well as for the period between H2 and H4. This results in redox boundary compressions in the sediments which has likely resulted in Fe cycling at the sediment-seawater interface as revealed by Fe/Al and P/Al ratios. A loss of Mn by diffusion out of the sediments is probably also caused by this migration of the redox boundary to the sediment-seawater interface. A combination of low detrital Al-ratios in the upper part of H4 and redox enrichments at the base of this HL produced ambiguous signals of the redox metals Fe, Ni, and V. (C) 2001 Elsevier Science B.V. All rights reserved.