DECREASED ICE COVER DURATION ON ARCTIC LAKE LINNÉ, SVALBARD

Arctic regions are highly sensitive to climate change and documenting changes in arctic climate is important because climatically-induced changes in the Arctic can instigate further changes of global consequence. Arctic lakes, influenced by pronounced seasonality, close linkages to the cryosphere, and shifting precipitation regimes, are showing signs of change that include increasing water temperatures, decreased duration of seasonal ice cover, and large scale ecosystem shifts. The Svalbard REU project (http://www.mtholyoke.edu/go/svalbard/) has been continuously monitoring water temperature of Lake Linné, one of the largest lakes on Svalbard, for 10 years. We have more than 50 data loggers recording temperature at 30 minute intervals year-round, from all depths of the lake, as well as 30 minute meteorological data from an automated weather station next to the lake. Lake freeze-over was identified as occurring after lake-wide averaged water temperature dropped to freezing and before temperature stratification occurred, indicating the establishment of continuous ice cover shielding the lake from wind mixing. The timing of lake ice melt-out was identified by the loss of temperature stratification. The temperature signatures of freeze-over and melt-out were corroborated using photographs from two automatic cameras taking twice daily pictures of the lake. Using this approach, we were able to pin-point the timing of the lake freeze-over to within 24 hours and ice melt-out to within a 1 to 5 day range. Our results show that between 2003 and 2011, the timing of freeze-over has shifted 10 days later. There is greater variability in the timing of spring ice melt-out and no significant trend in the melt-out date. Nonetheless, the length of the ice-free period during the summer has decreased by nearly ten days over the last decade. The freeze-over date correlates strongly to air temperature, with higher cumulative degree days correlating to later freeze-over dates. Overall, the frequency and intensity of cold days has not changed, but the warmest days are getting warmer. These results are consistent with published proxy-based temperature reconstructions of the last 1800 years that showed unprecedented warming in the region since the 1980’s. Our Lake Linné ice record shows that this summer warming trend continues.