CGRG Bibliography of Canadian Geomorphology
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Author : Barber, D.
Date : 2000.
Title : Patterns of glacial sediment transport to the NW Labrador Sea: data from geochemical provenance studies.
Publication : 30th International Arctic Workshop, Program and Abstracts, 2000. Institute of Arctic and Alpine Research, University of Colorado at Boulder
Issue :
Page(s) : 16-17.
Abstract
During the Late Wisconsin glaciation, the marine margin of the northeastern Laurentide Ice Sheet advanced repeatedly into the Labrador Sea and discharged immense quantities of icebergs to the North Atlantic. These episodes of locally accelerated ice flux, known as Heinrich events (Bond et al., 1992; Andrews et al., 1993), dramatically altered the ice sheet configuration and likely also caused changes in oceanic and atmospheric circulation (Broecker, 1994). A primary conduit for these discharges was Hudson Strait (Andrews and Tedesco, 1992). Cumberland Sound, a deep embayment along the southeast Baffin Island coast, also served as an important path for ice flow to the northwest Labrador Sea (Jennings et al., 1996; Kirby, 1997; Kaplan et al., 1999). A number of studies cf. (Gwiazda et al., 1996; Hemming et al., 1998) have confirmed that sediment in Heinrich layers of the North Atlantic are dominated by erosional products from the Churchill Province of the Canadian Shield. However, due to the widespread outcrop of Churchill rocks on SE Baffin Island, northern Labrador and Quebec, as well as in the Keewatin region, a broad Churchill provenance designation does not tightly constrain the glacial erosion and transport pattern during Heinrich events. For this reason, Sr, Nd and Pb isotopic analyses were made of sediments along the hypothesized former ice sheet flow paths in Hudson Bay, Hudson Strait, Cumberland Sound and northern Labrador, with the goal of determining more specific isotopic compositions to use as sediment-source "fingerprints." By analyzing lithostratigraphy and sediment provenance using elemental abundances, mineralogy and Sr-Nd-Pb isotopes in cores and till samples from Hudson Bay, Hudson Strait, Cumberland Sound and the Baffin Island shelf, characteristic sediment source signatures were identified for multiple Laurentide ice flow paths. Provenance indicators were analyzed in radiocarbon-dated cores from the deep Labrador Sea to elucidate past changes in ice margin proximity and sediment sources. The Sr, Nd and Pb data indicate that subglacial processes transported isotopically distinct sediment a distance of 800 km, from western Hudson Bay to the northwest Labrador Sea slope, with no significant change in the isotopic composition of this sediment along the transport path. During Heinrich events, slope sediment accumulation rates typically increased 8-fold, indicating the proximity of the advanced ice margin. Sedimentary structures in the detrital carbonate-rich Heinrich layers on the upper slope imply that sediment-laden meltwater plumes coincided with times of increased iceberg flux. The inferred asynchrony between advances of the adjacent Cumberland Sound and Hudson Strait ice streams implies non-climatic or complex climatically forced behavior of the NE Laurentide Ice Sheet.
Bibliography of Canadian Geomorphology