What 92 years of data say about ice cover

Warming air temperatures are changing ice cover in seasonally frozen lakes worldwide. The timing of ice formation and melting, called ice phenology, affects lake temperatures, seasonal stratification, and lake ecology, though much about these dynamics remains unknown.

Using a 92-year record of ice phenology from Mohonk Lake in New York, Oleksy and Richardson uncover new insights into the relationship between changing ice cover and lake dynamics, with implications for bodies of water worldwide. Shorter and more variable ice cover leads to perturbations in the water’s seasonal temperature dynamics, potentially leading to significant changes in lake biogeochemistry and biology.

The work is published in the Journal of Geophysical Research: Biogeosciences.

The authors paired records of the first day of complete ice cover in the fall (ice-on) and completely ice-free water in the spring (ice-off) dating back to 1932 with weekly under-ice measurements dating back to 1985. They used these data to build models of how climatic factors affect ice phenology and under-ice dynamics, including temperature stratification and mixing.

Their data show that the date of ice-on has moved later in the fall by 2.2 days per decade, but there is no clear trend for ice-off dates in the spring. Ice cover duration decreased by about a month during the 92-year study period, and the length of the duration of ice cover grew significantly more variable.

These trends are changing how water layers of different temperatures form in the winter, a process with significant implications for lake ecology, they write.

Later ice formation in the fall leads to cooler water layers that don’t stratify as readily, and more variable ice-off leads to a longer period of mixed water layers in the spring. This could affect summer lake conditions, with implications for lake inhabitants such as phytoplankton. The researchers plan to study these implications further in future work.

The authors also note that although historical visual data about ice-on and ice-off are valuable, they can be measured in different ways—for instance, some lake-monitoring programs consider ice-off to be the first day with 0% ice cover in some lakes (the same definition as that used in this study), whereas others consider ice-off to be the first day a lake is navigable by boat.

Further, visible assessments of ice-on and ice-off often don’t always reflect what is happening beneath the ice.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.