| Younger Dryas |
Article Index for Younger |
Website Links For Younger |
Information AboutYounger Dryas |
| CATEGORIES ABOUT YOUNGER DRYAS | |
| pleistocene | |
| climate | |
| nordic stone age | |
| stone age europe | |
|
The Younger Dryas of the early Holocene . 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). See INTIMATE Project (Integration of Ice, Marine and Terrestrial records), an INQUA Palaeoclimate subcommittee. 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. An '' Older Dryas '' stadial had preceded the Allerød, approximately 1000 years before the Younger Dryas; it lasted 300 years. {Link without Title} There is evidence of asteroid impact event 12,900 years ago in North America which, according to a recently presented hypothesis, could have initiated the Younger Dryas cooling. {Link without Title} 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)Alley, R.B.: "The Younger Dryas cold interval as viewed from central Greenland.", page 213-226. ''Quaternary Science Reviews'' 19, 2000 in sharp contrast to the warming of the preceding interstadial has been experienced since . WAS THE YOUNGER DRYAS GLOBAL? Answering this question is hampered by the lack of a precise definition of "Younger Dryas" in all the records. In western Europe and Greenland, the Younger Dryas is a well-defined synchronous cool period. {Link without Title} But cooling in the tropical North Atlantic may have preceded this by a few hundred years; South America shows a less well defined initiation but a sharp termination. The ; Huybers has argued that there is fair confidence in the absence of the Younger Dryas in Antarctica, New Zealand and parts of Oceania. Similarly the Southern Hemisphere cooling known as the Deglaciation Climate Reversal (DCR) began approximately 1kyr before the YD, between 14kya and 11.5 kya as noted in the Sajama ice core. The Andean climate returned to LGM conditions with colder temperatures coupled with higher precipitation (high lake stands in the Altiplano ). Thompson ''et al.'', 2000. Other features seen include:
CAUSES OF THE YOUNGER DRYAS The prevailing theory holds that the Younger Dryas was caused by a significant reduction or shutdown of the North Atlantic . This theory does not explain why South America cooled first. Previous glacial terminations probably did not have Younger Dryas-like events, suggesting that whatever the mechanism is, it has a random component. However there is evidence that termination II had a post glacial cooling period similar to the younger Dryas but lasting longer and being more severe. There is speculation that the Younger Dryas was precipitated by the so-called Younger Dryas Impact Event . THE END OF THE YOUNGER DRYAS Measurements of oxygen isotopes from the GISP2 Ice Core suggest the ending of the Younger Dryas took place over just 40 - 50 years in three discrete steps, each lasting five years. Other proxy data, such as dust concentration, and snow accumulation, suggest an even more rapid transition, requiring a ~7 °C warming in just a few years. Sissons, J.B.: "The Loch Lomond stadial in the British Isles.", page 199-203. ''Nature'' 280, 1979 Alley, R.B., ''et al.'': "Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event.", page 527-529. ''Nature'' '''362''', 1993 Dansgaard, W., ''et al.'': "The abrupt termination of the Younger Dryas climate event.", page 532-534. ''Nature'' '''339''', 1989 The end of the Younger Dryas has been dated to around 9600 BC (11550 calendar years BP, occurring at 10000 Radiocarbon Year s BP, a "radiocarbon plateau") by a variety of methods, with mostly consistent results: :11530±50 BP -- GRIP Ice core, Greenland Taylor, K.C., ''et al.'': "The Holocene-Younger Dryas transition recorded at Summit, Greenland.", page 825-827. ''Science'' 278, 1997 :11530+40-60 BP -- Kråkenes Lake , western Norway . Spurk, M., ''et al.'': "Revisions and extension of the Hohenheim oak and pine chronologies: New evidence about the timing of the Younger Dryas/Preboreal transition", page 1107-1116. ''Radiocarbon'' 40, 1998 :11570 BP -- Cariaco Basin core, Venezuela Gulliksen, S., ''et al.'': "A calendar age estimate of the Younger Dryas-Holocene boundary at Krakenes, western Norway", page 3, 249-259. ''Holocene'' 8, 1998 :11570 BP -- German Oak / Pine Dendrochronology "Hugheus radiocarbon and climate shifts during the last deglaciation", page 5498, 1951-1954. ''Science'' 290 :11640±280 BP -- GISP2 ice core, Greenland THE YOUNGER DRYAS AND THE BEGINNING OF AGRICULTURE The Younger Dryas is often linked to the adoption of agriculture in the , when hunter gatherers turned to farming. SEE ALSO
NOTES EXTERNAL LINKS
|
|
|