Correction of the IRD Influence for Paleo-Current Flow Speed Reconstructions in Hemipelagic Sediments

Abstract

Reconstructions of past changes in deep-sea current intensities are needed to understand ocean-climate interactions in the past. The mean size of the sortable silt fraction (10–63 μm, (Formula presented.)) is one of the most used proxies in this domain. However, in polar and subpolar environments under relatively low flow speed conditions, the presence of Ice-Rafted Detritus (IRD) may alter the (Formula presented.) record and thus bias the interpretation of paleo-current strength changes. In this paper, we examine the influence of IRD on the (Formula presented.) record of three sedimentary cores from the subpolar North Atlantic and the Antarctic margin. The influence of unsorted IRD on (Formula presented.) records is clearly established. To remove this IRD influence on grain-size distributions (GSDs), we propose a new method based on End-Member Analysis approach, and for which a MATLAB script is made available. This method characterizes the GSD of the unsorted IRD input, allowing it to be isolated and discarded, and the current sensitive (Formula presented.) variability to be robustly identified. The method therefore allows the recalculation of a modified sediment GSD free of unsorted IRD influence and the construction of modified (Formula presented.) and sortable silt percentage (the % of the 10–63 μm in the total <63 μm fraction) records. The application of the method to the three studied cores shows that (a) the unsorted IRD component is correctly removed from the grain-size signal and (b) the new (Formula presented.) record is consistent with the XRF-based ln(Zr/Rb) grain-size proxy.