DULUTH – Just as fast as it came, it went.

After open water lingered well into February following a warm start to winter, Lake Superior was about 50% covered with ice on Feb. 19, following the polar vortex that kept temperatures below zero across the region. In the warm weeks since, ice has retreated from the North Shore, and the sound of waves lapping at Canal Park has returned.

As of Thursday, just 12% of the big lake had ice on it. Using a new experimental model this year, researchers predicted a low ice season for Lake Superior and the Great Lakes overall, but the solid stretch of low temps helped build ice rapidly as Lake Superior reached its long-term average maximum level of ice this year.

The ice disappeared far faster than it does on average, according to federal records dating nearly 50 years. Lake Superior on average does not fall below 20% ice coverage until April, though last year the lake had even less ice coverage on March 4 and was never more than 22% covered with ice. In 2019, nearly the entire lake was covered in early March; highs and lows of ice coverage are normal but have begun to fluctuate more wildly than they had in the 20th century.

Ice coverage is important for the ecology of the lake, controlling erosion on shorelines, as well as for recreation and industry. "Studying, monitoring and predicting ice coverage on the Great Lakes plays an important role in determining climate patterns, lake water levels, water movement patterns, water temperature structure and spring plankton blooms," the Great Lakes Environmental Research Laboratory wrote last month.

Ice can also "minimize winter evaporation rates, moderate summer water temperatures, and curtail toxic algal blooms, while also providing recreation, transportation and food resources to millions of people," said a recent study from Canada's York University that found if warming trends continue, thousands of lakes in the northern hemisphere could stop icing over altogether. Already Lake Superior ice cover has on average been declining about 5% per decade.

Low ice cover leading up to the March 25 opening of the Soo Locks will be beneficial to the shipping industry, which has been lobbying Congress for a new icebreaker for years to prevent costly delays.

Brooks Johnson • 218-491-6496