Younger dryas period

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Series /
( Glacial ) 		  Climatic levels   Period
v. Chr.
Holocene
Preboreal 9,610-8,690
Pleistocene
( Vistula
- Late Glacial )
Younger dryas period 10,730-9,700 ± 99
Alleröd Interstadial 11,400-10,730
Older dryas period 11,590-11,400
Bölling-Interstadial 11,720-11,590
Oldest dryas period 11,850-11,720
Meiendorf-Interstadial 12,500-11,850
( Vistula
- high glacial )
Mecklenburg phase
Vegetation map of the Younger Dryas Period in Europe; however, a wooded biotope may still existed in the Carpathian Basin , contrary to the map

The Younger Dryas , only younger Dryas , Younger Tundra time , Younger tundra or Dryas 3 (in English as Younger Dryas or YD hereinafter) in which was geological a sharp cold relapse ( Stadial ) after Alleröd interstadial at the end of Weichselian ( Quaternary ). The Preboreal of the Holocene followed the Younger Dryas: the Younger Dryas is thus the last period of the last glacial period and the Pleistocene .

Various calculations result in a period of about 10,730–9700 BC for the Younger Dryas period. It began during the Antarctic Cold Relapse .

Naming and conceptual history

The white silver arum , here on Svalbard , can only be found in arctic - alpine locations today

The term Younger Dryas Period was coined by Knud Jessen in 1935. The name Dryas is the botanical generic name of the white silver arum ( Dryas octopetala) , which was widespread throughout Germany and Scandinavia during this time.

Definition, correlation

The Younger Dryas Period (Dr3) corresponds to Greenland stage 1 (GS-1) in Greenland ice cores ( GRIP , NGRIP ). A type locality for the Younger Dryas period was not defined. However, criteria were described by Johannes Iversen using the profile Bølling Sø ( Jutland , Denmark).

In Ireland this period is known as Nahanagan Stadial and in Great Britain as Loch Lomond Stadial .

Dating

After varve years in the Meerfelder Maar , it lasted from 12,680 varve years BC. H. and ended 11,590 years ago. H. After the varves of Lake Van in Turkey, the Younger Dryas ended 10,920 ± 132 years before present . The time that has elapsed since the beginning of the Holocene (and thus since the end of the Younger Dryas Period) is given by the ICS as 11,700 ± 99 calendar years according to the definition of the Holocene GSSP . Converted for the Younger Dryas period, this results in a period of 10,730 to 9640 BC. BC (varven years) or 9700 ± 99 BC. For the end of the Younger Dryas period as defined by the ICS.

Using dendrochronology , the end was determined to be 11,570 BP , which is 9620 BC. Chr. Means. The geocenter in Hanover gives the period 12,700 to 11,560 cal. H. at, i.e. 10,750 to 9610 BC In the Greenland ice cores, the beginning of the Holocene (and thus the end of the Younger Dryas Period) was defined as 11,700 ± 99 years b2k (ie 9700 BC). This means that there are only very small differences between the various methods of absolute age determination.

course

Three reconstructions of past temperatures. The red grip sequence of the northern hemisphere shows the Dryas event (younger and older Dryas) around 13,000 years ago (1.3 × 10 4 ) with a group of clear rashes . In the curves of the southern hemisphere ( Vostok , EPICA from Antarctica ) a decrease in the isotope ratio can be seen almost simultaneously.

The Younger Dryas Period began with a rapid cooling within a decade, which led to new glaciations in the higher latitudes of the northern hemisphere , similar to those of the Older Dryas Period about 1000 years earlier. In Central Europe the cooling reached 10,600 BC. Annual mean temperatures of around -3 to -4 ° C. In the rewarming phase before 9600 BC Then values ​​around + 4 ° C are likely to have been reached.

Core drilling in the Greenland ice (GRIP) and isotope investigations of argon and nitrogen have shown that the temperatures there in the Younger Dryas were around 15  K lower than today. Average temperatures of around -5 ° C were recorded for Great Britain.

Oxygen isotopes

The δ 18 O values , obtained from the Greenland ice (according to Dansgaard 1980), show analogous to the temperature development with the onset of the Younger Dryas up to about 10,000 BC. A drastic decrease of 5 ‰ (from -33 ‰ to -38 ‰). Then, analogous to the temperatures up to the beginning of the Holocene, they rise again to −32 ‰.

Volcanism

A significant volcanic eruption on Iceland left the Vedde ash in northern Europe ( Sweden , Scotland ) - a very important stratigraphic guide horizon in the Younger Dryas, which dates back to 12,121 ± 114 years BP or 10,171 ± 114 BC. Is dated. Furthermore, the previous sulphurous eruption of the Laacher See is discussed as the trigger for this cold period.

Effects

Glaciations in higher regions and periglacial deposits ( loess and solifluction sediments ) in the plain were the result of the drastic drop in temperature. Even discontinuous permafrost conditions set in again.

In Scandinavia the coniferous forests disappeared and the tundra , the habitat of the eponymous white silver root ( Dryas octopetala ), spread. In the mountainous regions of the entire world, the accumulation of snow increased and the tree line fell. More dust was introduced into the atmosphere from the desert regions of Asia . Drought was spreading in the Levant ; this may have caused the Natufi culture to develop agriculture .

The Huelmo-Mascardi cold period in the southern hemisphere, which was almost simultaneous with the Younger Dryas , was less dramatic than the Younger Dryas in the northern hemisphere. It is possible that it is not a global cooling, but the consequence of a development that primarily affected the northern hemisphere (and especially the North Atlantic).

In western North America , the effects of the drop in temperature during the Younger Dryas were less pronounced. However, renewed glacier advances in the Pacific Northwest also show a cooling trend here.

Development of vegetation history

  • Scots pine

  • Downy birches in the broken pine forest

  • Dwarf birch

The lower limit of the Younger Dryas is characterized by a significant increase in non-tree pollen and a relatively high proportion of sun plants (heliophytes). The pollen thus shows a clear cooling phase after the Alleröd interstadial . Due to the low plant cover, a stronger clastic sedimentation occurred in lakes. The air check was generally a marked reduction in the tree line out and a further spread of shrubs and grassland communities (shrub tundra with dwarf birch (Betula nana), a dwarf willow and helio hydrophilic herbs). With the onset of the deterioration in the climate, the most ancient pine forests were cleared and the population of tree birches was also reduced. In Germany and also in Sweden , the vegetation was then characterized in the further course of the Younger Dryas by a gradual increase of the bog birch ( Betula pubescens ) followed by that of the Scots pine ( Pinus sylvestris ), whereas grasses and herbs ultimately declined significantly (according to Behre 2004). Once again spread Betula nana ( Betula nana ), juniper ( Juniperus ), willow ( Salix ), poplar ( Populus ), Artemisia , Sonnenröschen ( helianthemum ) thalictrum ( Thalictrum ) and sorrel ( Rumex ). Juniper, Artemisia , Helianthemum and seaweed ( Ephedra ) populated clearings with unstable soils, while goosefoot plants (Chenopodiaceae), dock and bedstraws ( Galium ) thrived in floodplains . In wet locations were found Cyperaceae (Cyperaceae), horsetails , buttercup family (Ranunculaceae), cruciferous (Cruciferae), Apiaceae (Umbelliferae), meadowsweet ( Filipendula ) and thalictrum.

  • Common mugwort

  • Ephedra distachya

  • Real meadowsweet

  • Large-flowered sun rose

  • Thalictrum tuberosum

  • Galium album

Cultural history

During the Younger Dryas the Natufia developed in the Levant , the Ahrensburg culture in north-western Central Europe , and the Creswellia in England and Wales (12,000 to 8,000 BC). The predominantly ancient Bromme culture (11400 to 10500 BC) in southern Scandinavia and northern Germany also extends into the Younger Dryas.

causes

Melting of the ice sheets

The cause of the rapid cooling during the Younger Dryas is assumed to be a disruption or interruption of the thermohaline cycle in the North Atlantic , i.e. the North Atlantic Current (the extension of the Gulf Stream towards Greenland and Ireland) due to rapidly melting glaciers in the previous warm period. The Hudson Bay event was possibly the triggering factor: a lot of melt water had accumulated in Lake Agassiz behind the ice bar in the Hudson Bay area . It could not flow to the south because the land rises here. When the ice barrier broke, enormous amounts of fresh water suddenly poured into the North Atlantic and stopped the thermohaline cycle. The the Antarctic cold relapse triggering meltwater pulse 1A could therefore also have been the trigger for the younger Dryas.

Only when it had cooled down again did the fresh water supply through the melting ice stop and the usual cycle got going again. However, this theory does not explain why the cooling period in the southern hemisphere began earlier. Researching the exact causes of such a rapid cooling and the equally abrupt end of this palaeoclimatically interesting period is therefore still a challenge for science.

Some scholars, such as Broecker (2002) and Bond and Lotti (1995), consider the Younger Dryas cooling trend to be a Heinrich event , referred to as H0 .

Impact hypothesis

In May 2007, at a meeting of the American Geophysical Union, a group of researchers led by Richard Firestone from the Lawrence Berkeley National Laboratory presented numerous indications that a low-density meteorite explosion over Canada was the cause of the sudden change. According to this, the event around 10950 BC. Shortly before the beginning of the Younger Dryas, the celestial body broke into individual pieces when it entered the atmosphere and, in addition to extensive forest fires, caused species extinction and a destabilization of the ice sheet. This is supported by the unusually large number of deposits of extraterrestrial rock found in carbon-rich sediments, small carbon spheres that are formed by rapid cooling in the air, and the helium-3 isotope, which is extremely rare on Earth. Even optically very conspicuous sediment layers with these geochemical anomalies have now been found in two dozen core drillings throughout North America. They are remotely similar to the KT boundary layer in terms of layer thickness, appearance and color. The apparently continent-wide existence of this layer is a clear indication of a so-called ejecta cover from a major meteorite or airburst event in this region. The chemical composition of the earth's rock components in this layer is very similar to that of rocks in Quebec, Canada . Accordingly, the potential impact site should be there.

The assumption of an impact was supported by the discovery of nanodiamonds as well as gold and silver, the occurrence of which has been proven in many places in North America by various working groups. However, the existence of nanodiamonds in the corresponding sediments has not yet been confirmed in the course of further analyzes. Presumably graphene - graphane oxide aggregates were misinterpreted as nanodiamonds. A well-known critic of the thesis is the impact specialist Mark Boslough .

Although the scenario of an asteroid or comet impact is an often discussed and widely received topic in the specialist literature, it has so far been largely rejected by science due to a lack of convincing evidence. However, according to a study published in 2018, there are a number of new pieces of evidence that point to an impact. In the course of this investigation, around 160 sites worldwide were evaluated, including ice cores from Greenland and the Antarctic. As part of measurements taken by Operation IceBridge , scientists found evidence of a crater with a diameter of around 31 km below the Hiawatha Glacier in northern Greenland. Rock and glacier ice show structures in the radar measurements that indicate that the impact must have occurred after the beginning of the Pleistocene and before its end. For the age of the crater, a time window between 2.6 million years and 12,000 years could be considered. The latter assumption would coincide with the impact hypothesis in time.

The hypothesis received additional support from broad-based interdisciplinary research in the immediate vicinity of the southern Chilean city of Osorno . The authors of the paper published in 2019 found a large number of new indications in this area which, in their opinion, suggest an impact event with serious consequences at the beginning of the Younger Dryas Period, including an abnormally high incidence of forest and wildfires. Another indication of extreme heat development with direct effects on human communities was discovered in the form of impact glasses at the archaeological site of Abu Hureyra in northern Syria. The study published in March 2020 names a fragmented comet with a high potential for destruction as a possible cause, a fragment of which detonated near the settlement.

A stone stele from Göbekli Tepe in Anatolia was interpreted in a study by Martin B. Sweatman and Dimitrios Tsikritsis as a representation of the comet that triggered the younger Dryas period. This thesis is not undisputed.

Another indication that supports the impact hypothesis is the discovery of a platinum anomaly in the South African province of Limpopo , north of Pretoria . The samples obtained by drilling in a peat deposit were evaluated by a research team from Witwatersrand University ( Johannesburg ) and, according to information from the university, could be assigned to the beginning of the Younger Dryas in October 2019. The evidence of a significantly increased occurrence of atmospheric platinum dust is the first such find on African soil and confirms similar analyzes from Patagonia and from more than 25 sites in the northern hemisphere.

literature

(chronologically)

Individual evidence

  1. ↑ Józef Mitka, Wojciech Baba, Kazimierz Szczepanek: Putative forest glacial refugia in the Western and Eastern Carpathians. In: Modern Phytomorphology. Volume 5, 2014, pp. 85-92 ( phytomorphology.org PDF).
  2. ↑ before today, refers to the year 1950 in varven chronology
  3. ^ A b Thomas Litt, Karl-Ernst Behre, Klaus-Dieter Meyer, Hans-Jürgen Stephan and Stefan Wansa: Stratigraphic terms for the Quaternary of the northern German glaciation area. Ice Age and Present (Quaternary Science Journal), 56 (1/2), 2007, pp. 7-65 ISSN  0424-7116 ( quaternary-science.publiss.net  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. PDF).@1@ 2Template: Toter Link / quaternary-science.publiss.net  
  4. ↑ Günter Landmann, Andreas Reimer, Gerry Lemcke, Stephan Kempe: Dating Late Glacial abrupt climate changes in the 14,570 yr long continuous varve record of Lake Van, Turkey. In: Palaeogeography, Palaeoclimatology, Palaeoecology. 122, 1996, pp. 107-118.
  5. ↑ Mike Walker, Sigfus Johnson, Sune Olander Rasmussen, Trevor Popp, Jørgen-Peder Steffensen, Phil Gibbard, Wim Hoek, John Lowe, John Andrews, Svante Björck, Les C. Cwynar, Konrad Hughen, Peter Kershaw, Bernd Kromer, Thomas Litt , David J. Lowe, Takeshi Nakagawa, Rewi Newnham and Jakob Schwander: Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records. In: Journal of Quaternary Science. 24, No. 1, 2008, pp. 3-17 doi: 10.1002 / jqs.1227 .
  6. ↑ The indication BP in the dendrochronology also refers to the year 1950
  7. ^ The Quaternary in Lower Saxony and neighboring areas. ( lbeg.niedersachsen.de ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. PDF).  @1@ 2Template: Webachiv / IABot / www.lbeg.niedersachsen.de
  8. ↑ b2k = before the year 2000
  9. ↑ U. von Grafenstein, among others: Isotope signature of the Younger Dryas and two minor oscil-lations at Gerzensee (Switzerland): palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates . In: Palaeogeography, Palaeoclimatology, Palaeoecology . tape 159 , 2000, pp. 215-229 .
  10. ↑ https://www.clim-past.net/14/969/2018/cp-14-969-2018.pdf Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly Baldini / Brown / Mawdsley 04 Jul 2018
  11. ^ KE Behre: Biostratigraphy of the last glacial period in Europe . In: Quaternary Science Reviews . tape 8 , 1989, pp. 25-44 .
  12. ^ PA Friele, JJ: Younger Dryas readvance in Squamish river valley, southern Coast mountains, British Columbia . In: Quaternary Science Reviews . tape 21 , no. 18–19 , 2002, pp. 1925-1933 , doi : 10.1016 / S0277-3791 (02) 00081-1 .
  13. ^ WZ Hoek: Palaeogeography of Lateglacial Vegetations - Aspects of Lateglacial and Early Holocene vegetation, abiotic landscape, and climate in The Netherlands . In: Netherlands Geographical Studies . tape 230 . Utrecht 1997.
  14. ^ AH Geurts: Weichselian to Early Holocene vegetation development and fluvial adjustment in the Lower Rhine Valley, Germany. Thesis . Utrecht 2011.
  15. ^ Broecker, WS: Massive iceberg discharges as triggers for global climate change . In: Nature . tape 372 , 2002, pp. 421-424 , doi : 10.1038 / 372421a0 .
  16. ^ Bond, GC, Lotti, R .: Iceberg Discharges into the North Atlantic on Millennial Time Scales During the Last Glaciation . In: Science . 267, No. 5200, 1995, pp. 1005 , doi : 10.1126 / science.267.5200.1005 .
  17. ↑ Rex Dalton: Blast in the past? In: Nature . 447, No. 7142, 2007, pp. 256-257, doi: 10.1038 / 447256a .
  18. ^ DJ Kennett, JP Kennett ,. A. West, C. Mercer, SS Que Hee, L. Bement, TE Bunch, M. Sellers, WS Wolbach: Nanodiamonds in the Younger Dryas Boundary Sediment Layer. In: Science. Volume 323, No. 5910, January 2009, p. 942 ( abstract English).
  19. ^ Carey Hoffman: Exploding Asteroid Theory Strengthened by New Evidence Located in Ohio, Indiana. University of Cincinnati, February 7, 2008, accessed December 4, 2016 .
  20. ^ Tyrone L. Daulton, Nicolas Pinter, Andrew C. Scott: No evidence of nanodiamonds in Younger-Dryas sediments to support an impact event . (PDF) In: PNAS Early Edition . 107, No. 34, August 2010. doi : 10.1073 / pnas.1003904107 .
  21. ↑ Nicholas Pinter, Andrew C. Scott, Tyrone L. Daulton, Andrew Podoll, Christian Koeberl, R. Scott Anderson, Scott E. Ishman: The Younger Dryas impact hypothesis: A requiem . (PDF) In: Earth-Science Reviews (Elsevier) . 106, No. 3-4, June 2011, pp. 247-264. doi : 10.1016 / j.earscirev.2011.02.005 .
  22. ↑ Wendy S. Wolbach, Joanne P. Ballard, Paul A. Mayewski, Andrew C. Parnell, Niamh Cahill, Victor Adedeji, Ted E. Bunch, Gabriela Domínguez-Vázquez, Jon M. Erlandson, Richard B. Firestone, Timothy A. French, George Howard, Isabel Israde-Alcántara, John R. Johnson, David Kimbel, Charles R. Kinzie, Andrei Kurbatov, Gunther Kletetschka, Malcolm A. LeCompte, William C. Mahaney, Adrian L. Melott, Siddhartha Mitra, Abigail Maiorana- Boutilier, Christopher R. Moore, William M. Napier, Jennifer Parlier, Kenneth B. Tankersley, Brian C. Thomas, James H. Wittke, Allen West, James P. Kennett: Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 2. Lake, Marine, and Terrestrial Sediments . (PDF) In: The Journal of Geology . 126, February 2018. doi : 10.1086 / 695704 .
  23. ^ Announcement: Brian Clark Howard: City-size impact crater found under Greenland ice. In: National Geographic. November 15, 2018, accessed December 23, 2018 . Research article: Kurt H. Kjær1 u. a .: A large impact crater beneath Hiawatha Glacier in northwest Greenland . In: Science Advances . November 14, 2018, doi : 10.1126 / sciadv.aar8173 .
  24. ↑ Mario Pino, Ana M. Abarzúa, Giselle Astorga, Alejandra Martel-Cea, Nathalie Cossio-Montecinos, R. Ximena Navarro, Maria Paz Lira, Rafael Labarca, Malcolm A. LeCompte, Victor Adedeji, Christopher R. Moore, Ted E. Bunch, Charles Mooney, Wendy S. Wolbach, Allen West, James P. Kennett: Sedimentary record from Patagonia, southern Chile supports cosmic-impact triggering of biomass burning, climate change, and megafaunal extinctions at 12.8 ka . In: Nature Scientific Reports . March 9, 2019. doi : 10.1038 / s41598-018-38089-y .
  25. ↑ Andrew MT Moore, James P. Kennett, William M. Napier, Ted E. Bunch, James C. Weaver, Malcolm LeCompte, A. Victor Adedeji, Paul Hackley, Gunther Kletetschka, Robert E. Hermes, James H. Wittke, Joshua J. Razink, Michael W. Gaultois, Allen West: Evidence of Cosmic Impact at Abu Hureyra, Syria at the Younger Dryas onset (~ 12.8 ka): high-temperature melting at> 2200 ° C . In: Nature Scientific Reports . March 10, 2020. doi : 10.1038 / s41598-020-60867-w .
  26. ↑ Martin B. Sweatman and Dimitrios Tsikritsis, DECODING GÖBEKLI TEPE WITH ARCHAEOASTRONOMY: WHAT DOES THE FOX SAY? , Mediterranean Archeology and Archaeometry, Vol. 17, No 1, (2017), pages 233-250.
  27. ↑ See Jens Notroff et al, MORE THAN A VULTURE: A RESPONSE TO SWEATMAN AND TSIKRITSIS , Mediterranean Archeology and Archaeometry, Vol. 17, No 2, (2017), pages 57-74.
  28. ↑ Communication from the University of Witwatersrand (Johannesburg) , accessed on October 16, 2019
  29. ^ Francis Thackeray, Louis Scott, P. Pieterse: The Younger Dryas interval at Wonderkrater (South Africa) in the context of a platinum anomaly . (PDF) In: Palaeontologia Africana . 54, October 2019, pp. 30–35. doi : 10.5067 / ASTER / ASTGTM.002 .