Small amounts of subsurface warming of oceans can trigger a massive and rapid collapse of ice shelves, according to an analysis of prehistoric “Heinrich events.”
The findings show that warming of water by 3 to 4 degrees was enough to trigger these Heinrich events, in which masses of ice calved off the seaward facing side of a glacier in larger numbers than is typical — in particular, off the Laurentide Ice Sheet, which once covered most of Canada and a large portion of the northern United States of America.
The study, which will be published this week in the journal Proceedings of the National Academy of Sciences, are vitally important in a day and age when scientists are concerned for the fate of the massive ice shelves in Antarctica and Greenland. Understanding what caused these massive Heinrich events in the past could help scientists predict when they may happen in the future.
“We don’t know whether or not water will warm enough to cause this type of phenomenon,” said Shaun Marcott, a postdoctoral researcher at Oregon State University and lead author of the report. “But it would be a serious concern if it did, and this demonstrates that melting of this type has occurred before.”
Marcott noted that if the water under the West Antarctic ice shelves were to warm by about 2 degrees, the melting may increase to more than 30 feet a year. This could cause many of the ice shelves to completely melt by the end of the current century, he noted, and is probably the most likely mechanism to cause such a rapid change in the ice sheets.
“There is now better evidence that the climate was getting colder prior to the Heinrich events, causing surface ocean waters to cool but actually causing warmer water in the subsurface,” Marcott said. “We tried to demonstrate how this warmer water, at depth, caused the base of the ice shelf to warm and collapse, triggering the Heinrich events.”
Marcott pointed to a modern day concern that ocean currents could shift and change direction well before the oceans had warmed a significant amount, which, if the directions shifted and warmer water was directed towards the ice shelves, could increase the rapid melting they found in their computer simulations and recreations of past Heinrich events.