IMPACT OF ATYPICAL AIR TEMPERATURES ON DEVELOPMENT AND PERSISTENCE OF WINTER STRATIFICATION AND ICE COVER ON SUBALPINE LAKES, WESTERN MAINE

Unseasonably warm air temperatures experienced in the northeast during both late fall 2011 and mid-March 2012 resulted in a truncated seasonal ice cover of many large Maine lakes. Late ice formation (or incomplete ice cover) and early ice-out, determined visually, were a coherent regional response for these low elevation lakes. In combination with decreased snowfall, especially in December and early January, winter recreation and tourism industries in subalpine and alpine environments were negatively impacted. To assess the response of high elevation lakes in western Maine and northern New Hampshire to these anomalous warm air temperatures, we examined sub-hourly measurements collected at three depths (surface, 2m, and bottom) at more than a dozen sites and compared them to temperature signatures of major seasonal events from 2007-2011. Warmer November and December 2011 air temperatures resulted in multiple episodes of destratification following the end of fall mixing; typically, the lake maintains inverse stratification once it has developed and the bottom temperatures indicate that water is at maximum density. The development of permanent seasonal ice was also delayed; data loggers and a time-lapse camera at a single location show that ice developed and melted several times during December. In spring 2012, unusually warm air temperatures resulted in early thinning of the ice and early ice-out. Ice thinning and the accumulation of meltwater on the surface of the ice were recorded by surface data loggers at most locations that were frozen into the ice. Ice-out dates for our study sites were two weeks earlier than some previous years, and surface water warmed rapidly following ice-out but prior to the end of winter stratification. Both ice duration and the duration of winter stratification were truncated by warmer air temperatures. Continued monitoring of these subalpine lakes will build a rich dataset for this environment, and will help evaluate the frequency of early ice-out events and its impact on lake temperature and habitat quality.