8.2-kiloyear event

In climatology, the 8.2-kiloyear event was a sudden decrease in global temperatures that occurred approximately 8,200 years before the present, or 6,200 BC, and which lasted for the next two to four centuries. It defines the start of the Northgrippian age in the Holocene epoch. The cooling was significantly less pronounced than during the Younger Dryas cold period that preceded the beginning of the Holocene. During the event, atmospheric methane concentration decreased by 80 ppb, an emission reduction of 15%, by cooling and drying at a hemispheric scale. A rapid cooling around 6200 BC was first identified by Swiss botanist Heinrich Zoller in 1960, who named the event the Misox oscillation (for the Val Mesolcina). It is also known as the Finse event in Norway. Bond et al. argued that the origin of the 8.2-kiloyear event is linked to a 1,500-year climate cycle; it correlates with Bond event 5. Evidence for the 8.2-kiloyear event has been found in speleothem records across Eurasia, the Mediterranean, South America, and southern Africa and indicates the event was globally synchronous. The strongest evidence for the event comes from the North Atlantic region; the disruption in climate shows clearly in Greenland ice cores and in sedimentary and other records of the temperate and the tropical North Atlantic. It is less evident in ice cores from Antarctica and in South American indices. The effects of the sudden temperature decrease were global, however, most notably in changes in sea level. The event may have been caused by a large meltwater pulse from the final collapse of the Laurentide Ice Sheet of northeastern North America, most likely when the glacial lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean. The same type of action produced the Missoula floods that formed the Channeled Scablands of the Columbia River basin. The meltwater pulse may have affected the North Atlantic thermohaline circulation, reducing northward heat transport in the Atlantic and causing significant North Atlantic cooling.