“It was coming here to Barrow and going to the sea ice north of here that kept me focused on sea ice for the last 15 years,” Andy Mahoney told Frontier Scientists. Mahoney is a sea ice geophysicist and University of Alaska Fairbanks assistant research professor in geophysics.
Thick sea ice
Level sea ice might grow to be 13-16 feet [4-5 meters] thick offshore of Barrow, Alaska. Mahoney described “One consolidated solid sheet of ice. And that would be a significant obstacle to an ice breaker or a hazard for a fixed structure in the ice or a drill platform.”
Extremely thick sea ice
Add winds and ocean currents capable of driving parts of the ice pack in different directions, and the ice structure gets more interesting. Mahoney: “The other way you can get ice thick is to pile it on top of itself, so you dynamically thicken the ice. This creates pressure ridges that stick up above the ice,” as well as “much deeper below the water.” Ice floes slam into each other and deform, or change shape. At times one floe will ride up and slide onto the edge of another, referred to as rafting. Other times pressure ridging pushes blocks of ice both above and below abutting ice floes. Pressure ridges can be immense. “If they are in shallow enough water then they can actually be grounded on the seafloor and gouge the seafloor.” Part of Mahoney’s aim is to take measurements at places where sea ice impacts the sea floor near Barrow. “Once a ridge becomes grounded it acts like a traffic jam and more ice can keep piling on,” he told Frontier Scientists. “These things can end up being very thick.” In his work he’s witnessed pressure ridges 65-98 feet [20-30 meters] thick.
Mobile ice is a hazard
When thick ice is on the move it can pose threats to ocean travelers, ships and nearby structures. Mahoney said “The ice that caused Shell to stop drilling after they had only been drilling for one day— that ice likely came from the Hanna Shoal region,” a shallow water area some 77 miles [125 kilometers] northwest of Barrow in the Chukchi Sea. Shallow water helps sunlight better benefit plant life, and plants in turn support other creatures. “It is a very biologically productive area,” Mahoney said, and “Very important for walrus as a haul out.” Walrus haul out on ice, dragging themselves up onto sea ice for rest periods in between bouts foraging for food along the sea floor. Near Hanna Shoal they benefit from extremely thick sea ice. Mahoney stated “Because it is very shallow in that region, during the wintertime these very large pieces of ice get grounded, even more ice piles on, and these features become even bigger.” The ice lingers into summer. “They can’t drift away because they are sitting on the seafloor.” Mahoney explained, but the floes eventually might break away from the sea floor. When the extremely thick ice floes “melt sufficiently so they can uplift, then they potentially become a marine hazard.”
Scraping ocean floor sea ice tracking oil shipping concerns
Laura Nielsen 2015
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
