Sediment dynamics during Heinrich event H1 inferred from grain size

Throughout the last glacial period, massive volumes of icebergs were discharged periodically through Hudson Strait during so-called Heinrich (H) events. These icebergs transported sediments that were subsequently deposited in distinct layers across the North Atlantic as they melted. The objective of this research was to measure and describe sedimentation associated with a meltwater plume discharged during the H1 ice-rafting event at about 17 ka by examining sediment texture. The H1 layer was sampled in 11 piston cores that cover about 4000 km of the slope between Hudson Strait and the Gulf of Maine. Disaggregated inorganic grain size (DIGS) distributions were determined using a Coulter Counter. Additionally, the CaCO3 content and the > 63 μm fraction were measured and DIGS distributions were sorted using entropy analysis. Entropy analysis proved to be a useful tool for distinguishing between sediment delivery mechanisms. Textural interpretation of sediment dynamics during the H1 event was broadly consistent with facies interpretations. H1 layer sediments were mainly delivered by plume and ice-rafting, with some samples showing higher-energy sorting. In general, plume deposition was dominant within 1000 km of Hudson Strait, and distal sediments were mainly delivered by ice-rafting. Entropy analysis of DIGS distributions provides a robust means of understanding fine fraction (< 100 μm) sediment dynamics in H events.

► Plume delivery dominates in H1 layer sediments within 1000 km of Hudson Strait.
► Distally, H1 sediments are principally delivered by ice-rafting.
► Higher-energy sorting produces distinctive DIGS spectra more abundant at H1 event end.
► Entropy analysis provides evidence of fine (< 100 µm) sediment dynamics in H events.