A 35-year Coast Guard veteran who has spent 12 years on the lakes, Davanzo said this winter is the toughest he's experienced because the ice came so soon and is so thick and widespread, and the weather has been constantly bitter.
The Mackinaw, commissioned in 2006 to replace an older vessel with the same name, is designed specifically for duty on the Great Lakes. It's propelled by two "Azipod" thrusters that can spin 360 degrees and fire jets of water at adjacent ice, weakening it. Sometimes the crew will drive the ship's bow onto an ice sheet to crack it with sheer weight. Or they'll go backward, chopping up ice with the propeller blades.
When the going gets tough, there's the battering-ram option — hurling the reinforced hull directly against walls of ice that can be several feet thick.
The workload typically drops sharply after navigational locks on the St. Marys River, the link between Lakes Superior and Huron, close in mid-January and most large cargo haulers dock for winter. But the ice was so thick this year that a number of freighters were still struggling to complete final deliveries days later. Even now, demand for road salt and heating oil in the Midwest is keeping some icebreakers busy.
One day last month, the Mackinaw spent 16 grueling hours helping a freighter squeeze through a narrow 3.5-mile section of the St. Marys. As the Mackinaw attacks the ice, the engines roar and the ship vibrates. The noise and motion are "like living in an earthquake 16 hours a day," Petty Officer 3rd Class Ryan Alderman said.
Davanzo hopes for rain and warmer temperatures that would melt some ice before the locks reopen in late March, when the Mackinaw will venture onto Lake Superior and clear paths for iron ore and coal haulers.
"But if the weather stays like this," he said, "we could be breaking ice all the way to the middle of May."
Despite the inconvenience, there's a silver lining for shippers. Since the low-water period began in late 1990s, they've been forced to carry lighter loads to avoid scraping bottom in shallow channels and harbors. Heavy snow and rain in 2013 finally raised water levels.
Ice cover blocks evaporation, the leading cause of low water. It also will keep the lakes cooler for a longer time this year, delaying the onset of heavy evaporation season, scientist John Lenters reported in a paper last month, although the benefit is partially offset by stepped-up evaporation shortly before the ice forms.
In Lake Superior, snowbound Isle Royale National Park is home to a dwindling and inbred wolf population that is usually trapped on the island. Biologists hope a newcomer or two will venture to the park now that the lake is almost entirely frozen over. The park's first wolves are believed to have crossed an ice bridge from Canada, 15 miles away, in the late 1940s.
There's also a chance that one or more of the island's wolves could grab the rare opportunity to escape.
"They are inveterate travelers," veteran wolf expert Rolf Peterson said. "And they don't need a reason that would make sense to us."
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