The duration of ice cover on lakes has a significant influence on the physics, chemistry and ecology of a water body. On a larger scale, changes in lake-ice duration influence the hydrologic-cycle and can affect the regional surface energy balance. However, our understanding of the annual timing of ice-out and freeze-up in high-Arctic lakes is limited by a lack of regular observations. The importance of understanding climatic controls on lake-ice dynamics has been underscored by a number of studies that have linked recent shifts in diatom communities to changes in the duration and extent of ice cover. Therefore, this project was designed to gain a better understanding of lake-ice dynamics in the High Arctic, with the specific objectives of: (1) reconstructing annual variability in summer lake-ice conditions using archived space-borne synthetic aperture radar (SAR) data, and (2) identifying climatic controls on the timing of ice break-up/freeze-up and evaluateing the response of lake ice to climate change using a model that simulates lake-ice growth and decay.

This study is focused on Upper and Lower Murray Lakes (81°20’N, 69°30’W) on northern Ellesmere Island in the Canadian High Arctic, where ongoing research is focused on reconstructing past climate variability using lake sediments. Over 300 archived SAR data scenes were acquired for the period 1997 through 2007 (Figure 1). SAR data provides a unique tool for tracking lake-ice conditions in remote regions, producing high-resolution images and acquiring data regardless of sun or cloud conditions. These data have provided near-continuous coverage of melt season conditions at Upper and Lower Murray Lake with approximately biweekly resolution. Analysis of the SAR data provides insight regarding the rate and timing of ice decay in individual years (Figure 2). These data indicate that moat formation is typically evident by early July and complete ice-free conditions generally occur by mid to late August. Refreezing of the lake surface is more difficult to observe in the SAR data, but likely occurs by late September. Ice-free conditions in Lower Murray Lake generally lag behind those in Upper Murray Lake by 1 to 2 weeks, presumably due to increased shading of the lake surface by more narrow valley walls, and reduced meltwater inflow which facilitates ice break-up. Although both lakes typically experience several weeks of open water each summer, during 3 of the last 11 years only partial melting of lake ice occurred on one or both of the lakes (with as much as 80% of the ice cover remaining at the end of the melt season).

Preliminary efforts to model lake-ice growth and decay show reasonable agreement with the satellite based observations. Sensitivity experiments will be used to identify the natural variability in ice break-up and freeze-up dates that should be expected, and to illustrate the impacts of different climate conditions. The very brief/intermittent nature of open water conditions in the recent satellite record is consistent with early model results that suggest only a slight decrease in melt season temperatures in the past would have promoted permanent ice cover on Upper and Lower Murray Lakes. In contrast, projected warming in the High Arctic associated with increased greenhouse gas emissions is likely to significantly increase the duration of ice-free conditions in the High Arctic.