Sack Lunch Seminar (SLS)

The Younger-Dryas Cold Reversal: Ice-Earth-Ocean Interactions During a Period of Rapid Climate Change


During the last glacial-interglacial transition, the climate system experienced a series of paroxismic events. The massive armada of ice-bergs associated with Heinrich Event 1, which issued from the eastern flank of the Laurentide ice-sheet, effectively “shut-down” the Atlantic overturning circulation. The AMOC was thereafter spontaneously resurrected, thereby causing the Bølling-Allerød warming of the northern hemisphere and the rapid rise of global sea level associated with Meltwater Pulse 1A. Following a period of slow cooling, the system rapidly returned to almost full glacial conditions approximately 12,800 years ago, a state that persisted for over a thousand years. This Younger-Dryas phase ended with a very rapid warming into the modern Holocene state. The origins of the Younger-Dryas have recently been traced to a massive outflow of freshwater onto the surface of Arctic Ocean through the McKenzie River outlet. The associated freshwater was thereafter advected through Fram Strait by the Trans-Polar Drift onto the surface of the Greenland-Iceland-Norwegian seas where it led to a further sharp reduction in the strength of the MOC. This explanation was originally suggested on the basis of a detailed analysis of freshwater routing during deglaciation, an explanation that has very recently been verified by optical stimulated luminescence (OSL) dating of the terrains of the McKenzie River Delta. I will trace the history of the development of this explanation of post-Last Glacial Maximum (LGM) climate variability, emphasizing northern hemisphere climate impacts and the issues that remain outstanding.