Geoscience Reference
In-Depth Information
Although the Laurentide ice sheet had retreated north of the St. Lawrence River by twelve thousand years
ago, small ice caps and permanent snowfields remained in Nova Scotia, and perhaps in New Brunswick and
the Gaspé, for another one thousand years, and the glacier may have advanced again during a dramatic cooling
period known as the Younger Dryas event, 12,800 to 11,500 years ago. Temperatures in the North Atlantic re-
gion dropped dramatically, by as much as 5° to 7°C (41° to 45°F), in as little as a decade. Although this strik-
ing example of sudden climate change is not fully understood, it is thought to have been due in part to the in-
flux of vast quantities of cold freshwater from the melting of the glaciers. The cold water temporarily put a lid
on the North Atlantic thermohaline circulation, which brings warmer water into the Northern Hemisphere.
The glaciers are gone, but wind, wave, and ice continue to sculpt the Atlantic coast.
The Younger Dryas event ended approximately eleven thousand years ago, after which the glaciers disap-
peared from the Atlantic coast for good, ushering in the interglacial period in which we are now living—the
Holocene. In the postglacial period the sea level has seesawed in response to complicated forces related to the
retreat and melting of the glaciers. At first, the sea level rose rapidly as the glaciers returned to the oceans vast
reservoirs of water that had been tied up in ice. These changes are referred to as “eustatic.” Coastal river val-
leys were drowned, and in Maine the sea reached 100 kilometers (60 miles) inland from the present-day coast-
