Retreat of the Smith Sound Ice Stream in the Early Holocene

Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic-Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon-dated cores 2001LSSL-0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with Delta R = 220 +/- 20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice-proximal (red/grey laminated, ice-proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice-rafted debris) to ice-distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4-8.9 1 sigma) cal. ka BP marks the break-up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic-Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient-rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand-sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67-5.55 1 sigma) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.