Laurentide Ice Sheet dynamics from 35 to 7 ka: strontium-neodymium-lead isotopic provenance of northwest North Atlantic margin sediments

This dissertation presents Sr-Nd-Pb isotopic sediment provenance and radiocarbon data that elucidate the dynamics of the northeastern Laurentide Ice Sheet during the last glacial/deglacial cycle. These data constrain the sources, quantities and timing of Laurentide ice and meltwater inputs during the 500–1,000 year-long intervals, termed Heinrich (H) events, when icebergs inundated the North Atlantic.; Key findings include: (1) Sediment from as far west as Keewatin was transported to the Labrador Sea during H-events, implying that a major ice stream flowed southeast down the axis of Hudson Strait during these events. (2) An ice stream in Cumberland Sound (north of Hudson Strait) advanced onto the shelf repeatedly during the Late Wisconsin. (3) On the Labrador Sea slope, sediment accumulation rates typically increased eight-fold during H-events. (4) The laminated silts and clays comprising the detrital carbonate-rich H-layers imply that turbid glacial meltwater plumes coincided with the increased iceberg flux. (5) Ice and meltwater inputs from Hudson Strait (i.e., H-events) occurred less frequently and at different times than those from the Cumberland Sound ice margin; this asynchrony implies non-climatic or complex climatically forced behavior of the Hudson Strait ice stream. (6) In the Labrador Sea, the isotopic composition of the glacial hemipelagic deposits is interpreted as a binary mixture dominated by Canadian Shield-derived sediment (>80%) with the relative fraction of an East Greenland basaltic end-member varying inversely with overall Laurentide ice sheet extent. (7) Statistical errors on age estimates for down-core time-series are minimized by using an ordinary least-squares-fit regression for depth-age models; however, the placement of dates with respect to lithofacies boundaries is a key consideration. (8) The deglaciation of Hudson Bay and concomitant drainage of proglacial Lakes Agassiz and Ojibway occurred near the onset of the 8.2 kyr cold event, implying that increased freshwater flux to the North Atlantic triggered the cold event by altering the ocean thermohaline circulation.