Heinrich Events: unpacking the convoluted freshwater connection

Abstract Layers of ice-rafted debris found in sediment cores from the North Atlantic – so-called Heinrich Events – are usually inferred to be associated with a large increase in freshwater flux due to the enhanced production and subsequent melting of icebergs. This freshwater flux association is strongly motivated by the temporal alignment with large-scale ocean circulation-mediated climatic changes as supported by climate model hosing experiments. However, the critical relationship between ice and sediment flux has yet to be physically resolved. We directly examine this relationship with a fully coupled ice sheet and glacial sediment processes model for the last glacial cycle North American ice complex. Our key finding is that sediment flux, and therefore Heinrich Layers, are a convoluted proxy of freshwater flux from calving and englacial sediment concentration. Heinrich Event-sized ice discharges can occur without significant ice-rafted debris deposition, suggesting that some large-scale calving events may be missing from the Heinrich Layer record and offering an alternative explanation for Heinrich Events with anomalously low ice-rafted debris volume.