ABSTRACT

Stanwell-Fletcher Lake is 400 miles north of the Arctic Circle, covers 131 square miles, and is over 100 m deep. Its size and the severe climate restrict summer melting of ice to the margins. The ice insulates the water, which remains essentially isothermal, warming slightly from 1.3 to 1.6°C. during the summer. Inflowing water is nearer 4°C, and therefore sinks and mixes with the lake water, a process which maintains thermal and chemical homogeneity in the lake and oxygenates the surficial bottom sediment.

Sedimentation is very slow because of the short period of stream flow and the low organic activity in the lake. Silty sand derived from river bed loads accumulates on shallow marginal deltas and shelves. The sediment is poorly sorted because ice cover prevents wave action and removal of the fine material to deeper water. Mud, derived largely from the suspended loads of rivers, settles slowly in the central part of the lake. Faint laminae in the shelf sands may be varves, but the deep water mud is structureless. Evidently seasonal sedimentary variations do not affect the center of the lake, probably because ice cover minimizes transporting currents.

The oxidation-reduction boundary in the sediment is at 5-20 cm, deeper than in temperate lakes, because of oxidation at the lake bottom and slower reduction within the sediment.