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Identification of Subglacial Paleolakes in Arctic Canada: geophysical surveys in the Great Slave Lake

The aim of this project is to identify and examine paleo-subglacial lake environments that serve as analogues to subglacial lakes buried beneath the Antarctic Ice Sheet. Our project focuses on Christie Bay in the NE arm of Canada’s Great Slave Lake, which is the deepest lake in North America (∼640 m) and 6th deepest lake worldwide. The deep trough in Christie Bay is a fascinating geomorphological feature in the topographically subtle Canadian Shield. It is probably an erosional result of the advance and retreat of Quaternary ice sheets over a fault system that originates with the amalgamation of the North American continent 2 Ga BP.

Figure 1

Figure 1. (A) Surface elevation of the Laurentide Ice Sheet based on interpolated ICE5G model output (Peltier, 2002). Black box outlines area shown in (B). (B) Modelled subglacial meltwater routing beneath KD. Black contours denote hydraulic potentials. Thin blue lines mark the shorelines of modern lakes. The dark blue area illustrates the extent of a subglacial catchment where water flows to the east arm of the Great Slave Lake. The light blue color designates Christie Bay where trapped water formed a subglacial lake.

The deep trough in Christie Bay was a hydrological trap for meltwater produced beneath the Keewatin Ice Dome, which formed over the Slave region during the last glacial maximum (LGM) 20,000 years BP (Figure 1). The glaciological and climatological conditions during the LGM, and a geological setting characterised by 2-Ga-old rock and tectonics, make Christie Bay an ideal Pleistocene analogue to subglacial Lake Vostok in East Antarctica.

With funding from the University Research Fund (2004-06) and the National Science Foundation (2006-08), scientific expeditions to the NE arm of the Great Slave Lake were undertaken with colleagues from University of California, Santa Cruz (Dr. Slawek Tulaczyk) and The large Lakes Observatory in Duluth, Minnesota (Dr. Nigel Wattrus). In 2005 and 2006, we collected more than 500 km of seismic reflection data and sampled the lake sediment with a gravity corer (Figures 2-6).

Figure 2

Figure 2. Aerial photopograph showing islands in the 620-m-deep eastern arm of the Great Slave Lake, Canada.

In the deep trough in Christie Bay, we discovered a 200-m-thick succession of fine-grained sediment, separating glacial tills from draped Holocene sediment (Figure 3). Our integrated analysis of seismic data and sediment cores suggest that the sedimentary succession was deposited when a large subglacial lake occupied the area. Our data show that inflow of sediment-laden meltwater from a subglacial catchment induced dense turbidity currents that collapsed in the deep trough where sediments accumulated at a rate of 1-2 mm/year.

Figure 3

Figure 3. (A) Seismic reflection data acquired with air gun showing acoustic properties in a transect across CB. (B) Close-up showing acoustic attributes of sedimentary units discussed in text. (C) Bathymetry of CB derived from seismic data. Color scale denotes water depths (m) and axes are in km north and east from 62.4° N, 111.6 °W. Black contours show thickness of sediment (m) interpreted to represent a subglacial paleolake (Unit 2). Thick grey lines show location of seismic transects. Pink line denotes transect shown in (A) and thin grey lines represent shorelines. CB and MB refer to Christie bay and McCloud Bay.

Figure 4

Figure 4. Sunset over the Great Slave Lake.

Figure 5

Figure 5. Collecting seismic data (on the deck).

Figure 6

Figure 6. Collecting seismic data (inside the cabin).

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