Climate Fact: Drainage Re-route and the AMOC
While the present interglacial period (Holocene epoch) is defined as the period from approximately 11,700 years ago to present, the Laurentide Ice Sheet, which at glacial maximum extended from the North Pole all the way to the Ohio River, occupied the Hudson Bay until about 8,400 years ago. Before this time, runoff from Canada’s western plains drained into the St. Lawrence River. As the ice sheet retreated, this runoff began to drain into the Hudson Bay instead. About 8,470 years ago, the ice dam at Lake Agassiz, a glacial lake that sat over parts of Manitoba, Ontario, Saskatchewan, North Dakota and Minnesota, broke. For at least half-a-year, the lake’s water surged into Hudson Bay at a rate of 65 million cubic yards per second. This freshwater ultimately made its way into the Labrador Sea, where the Atlantic Meridional Overturning Circulation (AMOC) takes place. This circulation, which is the engine behind Earth’s thermohaline circulation (THC), is powered by temperature and salinity contrasts. The sudden influx of freshwater weakened the THC, resulting in less heat from the tropics making its way to the North Atlantic, causing cooling there. This event corresponds to the timing of a noticeable drop in temperature observed in ice cores from Greenland.
Seasons: Spring, Summer, Fall
Source: Carlson, AE et al. “Routing of western Canadian Plains runoff during the 8.2 ka cold event.” Geophysical Research Letters 36 (2009): L14704.)
