Was the Younger Dryas Triggered by a Flood?

摘要

As Earth's surface warmed at the end of the last glacial period, the Laurentide ice sheet that covered much of North America retreated and a vast melt water lakeLake Agassiz-formed hi the area of today's Great Lakes. But the transition from glacial tointerglacial conditions was not smooth: Between -12,900 and -11,500 years ago, cold conditions returned during the Younger Dryas,It is widely believed that this cold event was triggered by a flood of fresh water that poured into the northern Atlantic (7) and disrupted the thermohaline ocean circulation (2). The accepted scenario (3) is that at some point during the retreat of theLaurentide ice sheet, the northern and eastern shorelines of Lake Agassiz were breached, diverting the outflow from the lake eastward through Lake Superior and into the northern Atlantic via the St. Lawrence lowlands (see the first figure) Teller et al.have argued that the initial flood caused by the sudden drop in outlet elevation, rather than the subsequent steady-state discharge from the lake, was instrumental in causing the Younger Dryas (4).