AN ANALYSIS OF VARVED SEDIMENTS FROM MURRAY LAKE, ELLESMERE ISLAND, NUNAVUT, CANADA

Sediment cores recovered from High Arctic Murray Lake are used to reconstruct the sediment history of the basin since approximately 6.5 ka years b.p. when there was significant glacier activity in the watershed area. In addition, well preserved varves from the upper 55 cm of the record are used to reconstruct climatic and environmental changes for the past 1000 years.

Murray Lake (81^o20’N, 69^o30’W) lies on the eastern edge of the Hazen Plateau and approximately 5 km from Archer Fjord on Ellesmere Island, Nunavut, Canada. The watershed area for the lake is approximately 284 km² with 7% of it glaciated by the Murray and Simmons Ice caps. Murray Lake is the southern lake of a southward draining pair. The lakes are each approximately 6 km2 and lie at 107 and 106 m asl at the bottom of a u-shaped valley. Murray Lake’s northern basin (the deepest basin in the pair) is 47 m deep and is slightly stratified, although not anoxic. Runoff into the lake is dominated by nival melt from the west, and a combination of nival and glacial melt from the Simmons and Murray Ice Caps to the east

Two short (55 cm) cores and two vibracores, measuring 5.2 and 3.6 meters long, were recovered from the northern basin in 47 m of water. Analyses of the cores shows a sequence of sediments that is undisturbed, finely laminated and clastic. The analysis of thin sections from the short cores reveals 1000 sub-millimeter laminae-couplets that appear annual. The sediment sequence from the long cores overlaps with the short cores and shows a sedimentation that has a uniformly micro-laminated structure for the upper 2.2 m. Below 2.2 meters, the sedimentation abruptly changes to much larger (0.5-1 cm) couplets consisting primarily of course grained silts with clay caps. The laminae continue unbroken until 4.5 m where the laminae are interrupted by pulses of sand 1-10 cm thick.

Digital images of the thin sections are used to count and measure varves to develop a reproducible chronology. In addition, image analysis techniques enable a reconstruction of grain size and a measure of horizontality on an annual basis for the past 1000 years. The chronology is constrained with four radiocarbon dates from macrofossils at separate intervals. Detailed paleomagnetic data is also used to match the record to four other records in the region.