The National Oceanic and Atmospheric Administration began imaging the Great Lakes’ ice cover in 1973. Since then, the amount of ice has steadily fallen, aside from some seasonal fluctuations.

Typically, the ice coverage across the lakes peaks at an average of 53% in late February or early March. This year, the maximum ice cover was just 16% in the third week of January. It then plummeted to a historic low of 2.7% in early February, according to NOAA. Average ice cover from Jan. 1 through March 17 was 5%, breaking the previous record low of 5.5% for this time period set in 2012.

Meanwhile, the world experienced record heat in January for the eighth-straight month. Chicago’s February was one of the hottest in the city’s history.

“Ice cover is a defining feature of the lakes,” said Aaron Packman, a civil and environmental engineering professor at Northwestern University and the director of the university’s Center for Water Research. “This is a dramatic change in winter season conditions.”

The food chain

Without ice, the Great Lakes absorb sunlight faster, which drives surface warming. NOAA has already predicted that lake surface temperatures will increase 7 degrees by 2050 due to climate change.

For suckers, warmer water acts as a cue to begin spawning runs. As they journey through tributaries, they transport nutrients — their eggs and waste enrich the food web. If migratory fish appear early, it may alter the rest of the ecosystem.

“The suckers show up sooner, but the rest of the food web may not be really ready to take on those nutrients,” said Murchie, who also works as the Shedd’s director of freshwater research. “We don’t know for sure, but we want to keep an eye on it.”

There are other ways a lack of ice could indirectly affect fish. Accelerated surface warming can lead to increased thermal stratification — a process in which colder, denser water settles at the bottom lake. The deepest layer can then lose dissolved oxygen, killing plankton and other organisms.

This can cause a ripple effect across the food chain, resulting in a loss of biodiversity, scientists say.

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