ABSTRACT: Late Quaternary paleoenvironmental chance in the Melville Hills, N.W.T.

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

Preliminary results of sediment cores taken from a small lake located at 760 m asl, in the Melville Hills, NWT (69o04.86’ N 121o25.75’ W) provide new information on the timing of deglaciation in the Bluenose Lake area, as well as one of the longest paleoenvironmental records in this region of the arctic. A radiocarbon date of 9700 BP immediately post-dates the onset or organic sedimentation in the lake, confirming that the tops of the Melville Hills, which are suggested to have remained above the Laurentide ice limit during the Late Wisconsinan (Klassen, 1971), were ice free by the beginning of the Holocene. While this does not confirm that the Melville Hills were unglaciated, it suggests that the effects of continental ice were minimal during the early Holocene. By 9700 BP the Laurentide ice front stood about 200 km east of the site after depositing a broad belt of Younger Dryas age moraines around the lower east flank of the Melville Hills (Dyke et al., in review). The Holocene paleoenvironmental record indicates a strong increase in autochthonous productivity near the end of the Younger Dryas. Organic carbon content increased by 20% between 10 000 and 9000 BP. Apparently Holocene climate varied in a quasi-cyclic manner with a period of 2500-3500 years. Variability is indicated by organic carbon, eolian sand, and moss fragment abundances. Intervals of low organic carbon correspond with intervals of increased deposition of well rounded quartz grains of medium to fine sand size, while intervals of high organic carbon correspond with more abundant moss fragments. Clastic and organic sediment flux values, as well as grain size properties and the mass accumulation rate of sand deposited during periods of low organic carbon indicate that the low organic carbon content values did not result from dilution by increased sand influx. This suggests that increased sand flux and decreased organic carbon content resulted from decreased lake productivity as well as increased eolian sediment deposition. Recent studies from western Greenland (Willemse and Törnqvist, 1999) indicate that LOI organic carbon content values in arctic lakes are strongly correlated with the duration of ice cover, and therefore annual average temperature, suggesting colder conditions may have prevailed during the low LOI organic carbon phases. This conclusion is also supported by chironomid-based water temperature reconstructions (Cwynar and Spear, 2001) which demonstrate a correlation between maximum summer water temperature and the organic carbon content of lake sediments. The apparent cyclic nature of these alternating cool and warm intervals suggests that there may be some external forcing mechanism driving long-term climatic change in this region. Although chronological control is currently limited (more dates are pending), recurrent cold intervals centered on ca. 1500, 4000, 7500 and 10500 BP may indicate external climate forcing by ocean or atmospheric circulation. Although recent research has identified several processes which operate at comparable timescales (e.g. Bond et al., 1997; Darby et al., 2001), their role in this record cannot be assessed until dating control on this core is improved. Ongoing analyses include pollen and diatoms, as well as increasing the sampling resolution of organic carbon measurements and macrofossil and sand grain counts.

Bibliography of Canadian Geomorphology