“The official Ice-in date for Mirror Lake is December 7th,” Tammy Wooster from the Cary Institute for Ecosystem Studies reports. “I was waiting to share thinking the recent rain might cause it to break up, but it seems locked in for the winter!”
This year’s Ice-in date is part of a data record that goes back to 1967. There is great variability of when Ice-in happens, but the average date for Ice-in over that time is December 6.
Dr. Gene Likens, founder of the Hubbard Brook Ecosystem Study, set the criteria for Ice-in and Ice-out at Mirror Lake after working on lake research in Antarctica. The criteria for Ice-in is when there is an unbroken stretch of ice across the entire surface of the lake for a sustained period of time.
Ice-in “is one of the longest records,” at Hubbard Brook, Likens says. Quite something for a place that holds long-term data in soil temperature, air quality, and rainfall, some going back to 1955. “It’s a significant record,” Likens goes on to say, “and indicates climate change.”
That climate change indication comes not from Ice-in itself, but from another measurement that the establishment of Ice-in makes possible. Ice-out.
In a Friday the 13th interview Likens told us that data shows Ice-out is “25 days earlier, on average.”
“The ice cover on a lake is a major heat budget term for the lake,” Likens says. Acting as a kind of insulating layer between the lake’s ecosystem and the air. Things that live in the lake – fish, plants, microbes – rely on the protection the ice provides to thrive during the winter.
In 2023-2024 Mirror Lake had four ice-in and ice-out days. The first time on record that the Lake had so many freeze/thaw events.
Photo of Mirror Lake on December 7, 2024 by Ian Halm.