ABSTRACT: Weather events and the genesis of a lacustrine sedimentary record in a montane lake, British Columbia, Canada.

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Abstract

Meziadin Lake (560° 5' N, 129° 20'W), British Columbia, Canada, provides an opportunity to examine the physical limnology and sedimentology of a glacially overdeepended lake. The sedimentary record of Meziadin potentially contains the necessary information for reconstruction of shifting synoptic-scale climate in the northern Coast Mountains. The use of this type of paleoclimatic record is viable only when the integrated signal of the glaciated basin drainage hydrology, lacustrine circulation and sedimentation are understood. While climate provide the overlying control for the genesis of a sediment record in a glaciated basin, short-term weather events may provide sufficient forcing to obscure this paleoclimatic proxy. A better understanding of the physical limnology and sedimentology of Meziadin Lake will have a significant impact on future sites for sediment core retrieval and analysis of paleoclimatic record. Field observations at Meziadin Lake were carried out for 12 weeks from late May to early August, 1999. During this time, basin hydrology was examined through the monitoring of the inflow source of Meziadin Lake, providing a continuous record of discharge, while the suspended sediment flux to the lake was calculated from point samples. Lacustrine circulation was examined using a Hydrolab Datasonde 3, providing temperature/conductivity/turbidity profiles from 18 static sites throughout the lake. Lake bottom temperature proximal to the delta was continuously recorded using a submerged datalogger. Sediment trap moorings were established at 11 sites within the lake prior to spring melt. These moorings consisted of a pair of funnel-shaped traps suspended 40 m from the lake surface and another pair located 1 m from the lake bottom. Beginning on June 15, increased discharge due to snow melt in warmer air temperatures was augmented by the most significant rainfall events of the summer, creating a peak in suspended sediment concentration entering the lake. These peaks, timed with a lack of significant thermal stratification, correlate to the an underflow event recorded in temperature/conductivity/turbidity profiles and lake bottom temperature. This event was initiated overnight on June 16 and can be seen in distal regions of the lake at a reduced magnitude as late as June 21. The shape and size of Meziadin Lake, in relation to its inflow create a significant proximal-distal variation in its sedimentation, as well as a Coriolis deflection. Mass accumulations for the summer recorded in proximal sediment traps are in the order of 260 g with mean grain sizes over 2.5f (190 mm), compared to distal mass accumulations of less than 10 g and a mean grain size of 9f (7 mm).

Bibliography of Canadian Geomorphology