Biomarker Fingerprint of Debris Flow Deposits as a Paleoproxy for IRD Sources in the Last Glacial North Atlantic

Abstract

AbstractInvestigating the spatiotemporal dynamics of iceberg discharges during the last glacial period constitutes a major challenge for paleoclimate research. In recent decades, many ice‐rafted debris (IRD) provenance studies, mostly based on the comparison of the inorganic signature of IRD‐rich layers and surrounding continental bedrock, have differentiated main subareas of individual ice sheets as iceberg sources and gauged their dynamic interplay. Diagnosis of specific source ice streams has nonetheless remained limited. Here we propose a new IRD provenance methodology to refine the identification of iceberg sources. It relies on the organic geochemical characterization of glacigenic debris flow (GDF) deposits to obtain the biomarker fingerprint of IRD sources. To test its potential, we analyze the composition of n‐alkanes and chlorophyll‐derived pigments in sediments deposited within six major North Atlantic GDF depocenters fed by ice streams draining the surrounding ice sheets. The biomarker fingerprint of GDF deposits appears to (1) be consistent with a common origin of IRD and GDF deposits through erosion of outcrops and transport by ice streams, (2) differ significantly from that of ambient hemipelagic sediments, (3) be specific and unique to each GDF depocenter, making it possible to distinguish the corresponding specific ice streams, (4) be imprinted in IRD‐bearing marine sediments, and (5) have remained homogeneous enough through the last glacial to be used as a proxy for IRD sources. The biomarker fingerprint of GDF deposits thus shows strong potential to track the specific source ice streams that delivered IRD to the last glacial North Atlantic.