Inferences concerning climatic change from a deeply frozen lake on Rundfjeld,Ellesmere Island,Arctic Canada

A small lake on top of Rundfjeld, central Ellesmere Island, at an elevation of approximately 830 m, is frozen to the bottom, and the thickness of lake ice present is at least 5.45 m. Under present climatic conditions the lake does not thaw to the bottom, even during the warmest summers; i.e., 3 to 4 m of ice still floored the deepest part of the lake in mid-August 1987. A radiocarbon age determination via accelerator mass spectrometry (AMS) on a sample of the filamentous green alga Mougeotia sp., recovered from the lake ice at a depth below 4 m, gave 5730±70 BP (TO-530). The date indicates that the lake was probably completely open for an unspecified period of time during the warmest part of the Hypsithermal Interval. This situation is in agreement with data derived from a variety of other sources in Ellesmere Island and adjacent Greenland.