Younger Dryas

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The Younger Dryas stadial, also referred to as the Big Freeze,[1] was a geologically brief (1,300 ± 70 years) cold climate period between approximately 12,800 and 11,500 years ago (between 10,800 and 9500 BC).[2]

The period followed the Bølling/Allerød interstadial at the end of the Pleistocene and preceded the Preboreal of the early Holocene. It is named after an indicator genus, the alpine/tundra wildflower Dryas octopetala. In Ireland, the period has been known as the Nahanagan Stadial, while in the UK it has been called the Loch Lomond Stadial and most recently Greenland Stadial 1 (GS1).[3]

The Younger Dryas (GS1) is also a Blytt-Sernander climate period detected from layers in north European bog peat. It is dated approximately 12,900–11,500 BP calibrated, or 11,000–10,000 BP uncalibrated (radiocarbon dating). An Older Dryas stadial had preceded the Allerød, approximately 1,000 years before the Younger Dryas; it lasted 300 years.[4]

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Abrupt climate change

The Younger Dryas saw a rapid return to glacial conditions in the higher latitudes of the Northern Hemisphere between 12,900–11,500 years before present (BP)[5] in sharp contrast to the warming of the preceding interstadial deglaciation. It has been believed that the transitions each occurred over a period of a decade or so,[6] but the onset may have been faster.[7] Thermally fractionated nitrogen and argon isotope data from Greenland ice core GISP2 indicate that the summit of Greenland was ~15°C colder during the Younger Dryas[6] than today. In the UK, coleopteran fossil evidence (from beetles) suggests that mean annual temperature dropped to approximately 5°C,[8] and periglacial conditions prevailed in lowland areas, while icefields and glaciers formed in upland areas.[9] Nothing of the size, extent, or rapidity of this period of abrupt climate change has been experienced since.[5]

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