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86-765: The Younger Dryas (YD, Greenland Stadial GS-1) was a period in Earth's geologic history that occurred circa 12,900 to 11,700 years Before Present (BP). It is primarily known for the sudden or "abrupt" cooling in the Northern Hemisphere, when the North Atlantic Ocean cooled and annual air temperatures decreased by ~3 °C (5.4 °F) over North America , 2–6 °C (3.6–10.8 °F) in Europe and up to 10 °C (18 °F) in Greenland , in

172-413: A change to colder climate. Microstructure observation of the sediments shows that fossil soil wedges or frost cracks were observed in the top of Older Dryas deposits, which indicates mean annual air temperatures below −1 to 0 °C and cold winters. This conclusion is also supported by the presence of Juniperus , which indicates a protecting snow cover in winter. This change is also shown on the records at

258-480: A cold oscillation between 14,025 to13,904 years BP, which is reflected in the increased δ O during this period. This cold oscillation was also observed in earlier ice core records (GRIP and GISP2 ) drilled in the early 1990s by GRIP members. A multi-proxy study on late glacial lake sediments of Moervaart palaeolake shows multiple pieces of evidence in various aspects to support Older Dryas. The lake sediment had an erosional surface prior to Older Dryas suggesting

344-404: A cold oscillation in the second late-glacial (LG2) following the first late-glacial readvance (LG1) at around 14,000±700 to 13,700±1200 years BP. The LG2 cold oscillation around 14,000 years BP can correspond to the cooling of Greenland Interstadial 1 (GI-1d-Older Dryas) that happened around the same time period, which is the first chronological evidence that supports the presence of Older Dryas in

430-466: A cold-water indicator) suggests a lower summer temperature compared to previous Bølling period. Recent research on sea surface temperature (SST) for the past 15,000 years in southern Okinawa modelled the Paleoclimate of ocean sediment core (ODP 1202B) using an alkenone analysis. The results show a cooling stage at 14,300 to 13,700 years BP between Bølling and Allerød warm phases, corresponding to

516-487: A difficulty in estimating its time, as it is more of a point than a segment. The segment is small enough to escape the resolution of most carbon-14 series, as the points are not close enough together to find the segment. One approach to the problem assigns a point and then picks an arbitrary segment. The Older Dryas is sometimes considered to be "centered" near 14,100 BP or to be 100 to 150 years long "at" 14,250 BP. A second approach finds carbon-14 or other dates as close to

602-537: A few decades. Cooling in Greenland was particularly rapid, taking place over just 3 years or less. At the same time, the Southern Hemisphere experienced warming. This period ended as rapidly as it began, with dramatic warming over ~50 years, which transitioned the Earth from the glacial Pleistocene epoch into the current Holocene . The Younger Dryas onset was not fully synchronized; in the tropics,

688-546: A heavy breed, similar to a Great Dane , perhaps useful to run down Elephantidae . The large number of mammoth bones at campsites make it clear that even then, the Elephantidae in Europe were approaching the limit of their duration. Their bones were used for many purposes, one being the numerous objects of art, including an engraved star map. Late Upper Palaeolithic culture was by no means uniform. Many local traditions have been defined. The Hamburgian culture had occupied

774-523: A high latitude volcanic eruption could have accelerated North Atlantic sea ice growth, finally tipping the AMOC sufficiently to cause the Younger Dryas. Cave deposits and glacial ice cores both contain evidence of at least one major volcanic eruption taking place in the northern hemisphere at a time close to Younger Dryas onset, perhaps even completely matching the stalagmite-derived date for the onset of

860-463: A lag in timing of the Younger Dryas, indicating a greater influence of warmer Pacific conditions on that range. Effects in the Rocky Mountain region were varied. Several sites show little to no changes in vegetation. In the northern Rockies, a significant increase in pines and firs suggests warmer conditions than before and a shift to subalpine parkland in places. That is hypothesized to be

946-514: A mixture of grassland and cool-weather alpine species. The biome has been called " Park Tundra ," "Arctic tundra," "Arctic pioneer vegetation," or “birch woodlands." It is now in the transition between taiga and tundra in Siberia . Then, it stretched from Siberia to Great Britain , in a more-or-less unbroken expanse. To the northwest was the Baltic ice lake , which was truncated by the edge of

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1032-505: A pathway along the Mackenzie River in present-day Canada, and sediment cores show that the strongest outburst had occurred right before the onset of Younger Dryas. Other factors are also likely to have played a major role in the Younger Dryas climate. For instance, some research suggests climate in Greenland was primarily affected by the melting of then-present Fennoscandian ice sheet , which could explain why Greenland experienced

1118-468: A plant which only thrives in glacial conditions, began to dominate where forests were able to grow during the preceding B-A Interstadial. This makes the Younger Dryas a key example of how biota responded to abrupt climate change . For instance, in what is now New England , cool summers, combined with cold winters and low precipitation, resulted in a treeless tundra up to the onset of the Holocene, when

1204-429: A short-term increase in herbaceous pollen. The changed pollen pattern suggests an increased abundance of grass as well as a retreat of tree and shrubs. The change in vegetation distribution further indicates a colder and drier climate during this period. As for aquatic plant evidence, both aquatic and semi-aquatic botanical taxa show a sharp decrease, suggesting lower lake levels caused by a drier climate. The drier climate

1290-533: Is also reflected by increased salinity indicated by diatom analysis. The change in Chironomids population also indicates a colder climate. Microtendipes is an indicator of intermediate temperature in Late glacial deposits in northern Europe (Brooks and Birks, 2001). The abundance of Microtendipes peaked in the early part of Older Dryas suggesting a cold oscillation. The mollusc data ( Valvata piscinalis as

1376-557: Is no evidence of human occupation of Britain . In Northwestern Europe there was also an earlier Oldest Dryas (18.5–17 ka BP 15–14 ka BP). The Dryas are named after an indicator genus, the Arctic and Alpine plant Dryas octopetala , the remains of which are found in higher concentrations in deposits from colder periods. The Older Dryas was a variable cold, dry Blytt–Sernander period, observed in climatological evidence in only some regions, dependent on latitude. In regions in which it

1462-642: Is not observed, the Bølling–Allerød is considered a single interstadial period. Evidence of the Older Dryas is strongest in northern Eurasia, particularly part of Northern Europe , roughly equivalent to Pollen zone Ic. In the Greenland oxygen isotope record, the Older Dryas appears as a downward peak establishing a small, low-intensity gap between the Bølling and the Allerød. That configuration presents

1548-569: Is not well defined, with estimates varying by 400 years, but its duration is agreed to have been around two centuries. The gradual warming since the Last Glacial Maximum (27,000 to 24,000 years BP) has been interrupted by two cold spells: the Older Dryas and the Younger Dryas (c. 12,900–11,650 BP). In northern Scotland , the glaciers were thicker and deeper during the Older Dryas than the succeeding Younger Dryas, and there

1634-461: Is reconstructed through proxy data such as traces of pollen , ice cores and layers of marine and lake sediments . Collectively, this evidence shows that significant cooling across the Northern Hemisphere began around 12,870 ± 30 years BP. It was particularly severe in Greenland , where temperatures declined by 4–10 °C (7.2–18.0 °F), in an abrupt fashion. Temperatures at the Greenland summit were up to 15 °C (27 °F) colder than at

1720-489: Is sometimes used for dates established by means other than radiocarbon dating, such as stratigraphy . This usage differs from the recommendation by van der Plicht & Hogg, followed by the Quaternary Science Reviews , both of which requested that publications should use the unit "a" (for "annum", Latin for "year") and reserve the term "BP" for radiocarbon estimations. Some archaeologists use

1806-430: Is weak. The scientific consensus is that severe AMOC weakening explains the climatic effects of the Younger Dryas. It also explains why the Holocene warming had proceeded so rapidly once the AMOC change was no longer counteracting the increase in carbon dioxide levels. AMOC weakening causing polar seesaw effects is also consistent with the accepted explanation for Dansgaard–Oeschger events , with YD likely to have been

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1892-632: The Cetacean Odontoceti , the Monodontidae : Delphinidae : Of the Mysticetian Eschrichtiidae : The top of the food chain was supported by larger numbers of smaller animals farther down, which lived in the herbaceous blanket covering the tundra or steppe and helped maintain it by carrying seeds, manuring and aerating it. Leporidae : Ochotonidae : Cricetidae : Sciuridae : Dipodidae : Eurasia

1978-677: The Nahanagan Stadial , and in Great Britain it has been called the Loch Lomond Stadial . In the Greenland Summit ice core chronology, the Younger Dryas corresponds to Greenland Stadial 1 (GS-1). The preceding Allerød warm period (interstadial) is subdivided into three events: Greenland Interstadial-1c to 1a (GI-1c to GI-1a). As with the other geologic periods, paleoclimate during the Younger Dryas

2064-700: The Puerto Princesa cave complex in the Philippines shows that the onset of the Younger Dryas in East Asia was delayed by several hundred years relative to the North Atlantic. Further, the cooling was uniform throughout the year, but had a distinct seasonal pattern. In most places in the Northern Hemisphere, winters became much colder than before, but springs cooled by less, while there was either no temperature change or even slight warming during

2150-464: The Scandinavian ice sheet advanced. Notably, ice sheet advance in this area appears to have begun about 600 years before the global onset of the Younger Dryas. Underwater, the deposits of methane clathrate - methane frozen into ice - remained stable throughout the Younger Dryas, including during the rapid warming as it ended. As the Northern Hemisphere cooled and the Southern Hemisphere warmed,

2236-950: The Swiss Alps and the Dinaric Alps in the Balkans , northern ranges of North America's Rocky Mountains , Two Creeks Buried Forest in Wisconsin and western parts of the New York State , and in the Pacific Northwest, including the Cascade Range . The entire Laurentide ice sheet had advanced between west Lake Superior and southeast Quebec , leaving behind a layer of rock debris ( moraine ) dated to this period. Southeastern Alaska appears to have escaped glaciation; speleothem calcite deposition continued in

2322-520: The White Sea , a cooling occurred at 14,700–13,400/13,000, which resulted in a re-advance of the glacier in the initial Allerød. In Canada , the Shulie Lake phase, a re-advance, is dated to 14,000–13,500 BP. On the other hand, varve chronology in southern Sweden indicates a range of 14,050–13,900 BP. Northern Europe offered an alternation of steppe and tundra environments depending on

2408-485: The boreal forests shifted north. Along the southern margins of the Great Lakes, spruce dropped rapidly, while pine increased, and herbaceous prairie vegetation decreased in abundance, but increased west of the region. The central Appalachian Mountains remained forested during the Younger Dryas, but they were covered in spruce and tamarack boreal forests, switching to temperate broadleaf and mixed forests during

2494-426: The permafrost line and the latitude . In moister regions, around lakes and streams, were thickets of dwarf birch , willow , sea buckthorn , and juniper . In the river valleys and uplands, to the south, were open birch forests. The first trees, birch and pine , had spread into Northern Europe 500 years earlier. During the Older Dryas, the glacier re-advanced, and the trees retreated southward, to be replaced by

2580-641: The thermal equator would have shifted to the south. Because trade winds from either hemisphere cancel each other out above the thermal equator in a calm, heavily clouded area known as the Intertropical Convergence Zone (ITCZ), a change in its position affects wind patterns elsewhere. For instance, in East Africa , the sediments of Lake Tanganyika were mixed less strongly during this period, indicating weaker wind systems in this area. Shifts in atmospheric patterns are believed to be

2666-488: The AMOC on timescales of decades or centuries. The Younger Dryas is the best known and best understood because it is the most recent, but it is fundamentally similar to the previous cold phases over the past 120,000 years. This similarity makes the impact hypothesis very unlikely, and it may also contradict the Lake Agassiz hypothesis. On the other hand, some research links volcanism with D–O events, potentially supporting

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2752-475: The AMOC. Once the Younger Dryas began, lowered temperatures would have elevated snowfall across the Northern Hemisphere, increasing the ice-albedo feedback . Further, melting snow would be more likely to flood back into the North Atlantic than rainfall would, as less water would be absorbed into the frozen ground. Other modelling shows that sea ice in the Arctic Ocean could have been tens of meters thick by

2838-474: The Balkans also experienced ice loss and glacial retreat: this was likely caused by the drop in annual precipitation, which would have otherwise frozen and helped to maintain the glaciers. Unlike now, the glaciers were still present in northern Scotland , but they had thinned during the Younger Dryas. The amount of water contained within glaciers directly influences global sea levels - sea level rise occurs if

2924-490: The Holocene. Conversely, pollen and macrofossil evidence from near Lake Ontario indicates that cool, boreal forests persisted into the early Holocene. An increase of pine pollen indicates cooler winters within the central Cascades. Speleothems from the Oregon Caves National Monument and Preserve in southern Oregon 's Klamath Mountains yield evidence of climatic cooling contemporaneous to

3010-510: The Marine Isotope Stage 6, ~130,000 years BP), III (the end of Marine Isotope Stage 8, ~243,000 years BP) and Termination IV (the end of Marine Isotope Stage 10, ~337,000 years BP. When combined with additional evidence from ice cores and paleobotanical data, some have argued that YD-like events inevitably occur during every deglaciation. The 2004 film, The Day After Tomorrow depicts catastrophic climatic effects following

3096-480: The Northern Hemisphere, the length of the growing season declined. Land ice cover experienced little net change, but sea ice extent had increased, contributing to ice–albedo feedback . This increase in albedo was the main reason for net global cooling of 0.6 °C (1.1 °F). During the preceding period, the Bølling–Allerød Interstadial , rapid warming in the Northern Hemisphere was offset by

3182-629: The Older Dryas event. Another study on an ocean sediment core from the Norwegian Trench also suggests a cooling between Bølling and Allerød warm phases. The glacial polar faunal study on ocean sediment core Troll 3.1 based on Neogloboquadrina pachyderma abundances suggests that there were two cooling events before Younger Dryas in which one of the events occurred within Bølling-Allerød interstadial and can be associated with Older Dryas. The study on late-glacial climate change in

3268-582: The Rieme sites on the Great SandRidge of Maldegem-Stekene at Snellegem in NW Belgium, and many other sites in north-western Europe. δ O measurements show a decreasing trend in δ O at the transition to the Older Dryas, which corresponds to the ice core record of precipitation in the northern hemisphere. Pollen analysis shows a temporary decrease in the pollen levels of trees and shrubs with

3354-849: The Tatra Mountains. Older Dryas species are usually found in the sediment below the bottom layer of the bog. Indicator species are the Alpine plants: Grasslands species are the following: A well-stocked biozone prevailed on the Arctic plains and thickets of the Late Pleistocene. Plains mammals were most predominant: Artiodactyls : Perissodactyls : Proboscidea : So much meat on the hoof must have supported large numbers of Carnivora : Ursidae : Hyaenidae : Felidae : Canidae : Mustelidae : The sea also had its share of carnivores; their maritime location made them survive until modern times: Phocidae : Odobenidae : Of

3440-722: The White Mountains (New Hampshire, USA) refined the deglaciation history of the White Mountain Moraine System (WMMS) by mapping moraine belts and related lake sequences. The result suggests that the Littleton-Bethlehem (L-B) readvance of the ice sheet occurred between 14,000 and 13,800 years BP. The L-B readvance coincided with the Older Dryas events and provides the first well-documented and dated evidence of Older Dryas. Another Glacial chronology and palaeoclimate study on moraine suggests

3526-592: The Younger Dryas event. It has been suggested that this eruption would have been stronger than any during the Common Era , some of which have been able to cause several decades of cooling. According to 1990s research, the Laacher See eruption (present-day volcanic lake in Rhineland-Palatinate , Germany ) would have matched the criteria, but radiocarbon dating done in 2021 pushes the date of

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3612-482: The Younger Dryas with a significant reduction or shutdown of the thermohaline circulation , which circulates warm tropical waters northward through the Atlantic meridional overturning circulation (AMOC). This is consistent with climate model simulations, as well as a range of proxy evidence, such as the decreased ventilation (exposure to oxygen from the surface) of the lowest layers of North Atlantic water. Cores from

3698-568: The Younger Dryas. On the Olympic Peninsula, a mid-elevation site recorded a decrease in fire, but forest persisted and erosion increased during the Younger Dryas, which suggests cool and wet conditions. Speleothem records indicate an increase in precipitation in southern Oregon, the timing of which coincides with increased sizes of pluvial lakes in the northern Great Basin. Pollen record from the Siskiyou Mountains suggests

3784-621: The amount of dust blown by wind had also increased. Other areas became wetter including northern China (possibly excepting the Shanxi region) The Younger Dryas was initially discovered around the start of the 20th century, through paleobotanical and lithostratigraphic studies of Swedish and Danish bog and lake sites, particularly the Allerød clay pit in Denmark. The analysis of fossilized pollen had consistently shown how Dryas octopetala ,

3870-509: The changing abundance pattern of fauna and flora are most commonly used when examining lake sediments. Moraine belts are usually studied in places with palaeoglacier presented. As for ocean sediments, the variations of alkenone levels and faunal abundances were measured to model paleotemperatures in separate studies shown in the following sections. The North Greenland Ice Core Project (GRIP) members drilled an undisturbed ice core from North Greenland (75.1 8N, 42.3 8W). The ice core record showed

3956-572: The coastal waters. It was originally hypothesized that the massive outburst from paleohistorical Lake Agassiz had flooded the North Atlantic via the Saint Lawrence Seaway , but little geological evidence had been found. For instance, the salinity in the Saint Lawrence Seaway did not decline, as would have been expected from massive quantities of meltwater. More recent research instead shows that floodwaters followed

4042-744: The continental interior. The Southeastern United States became warmer and wetter than before. There was warming in and around the Caribbean Sea , and in West Africa . It was once believed that the Younger Dryas cooling started at around the same time across the Northern Hemisphere. However, varve (sedimentary rock) analysis carried out in 2015 suggested that the cooling proceeded in two stages: first along latitude 56–54°N, 12,900–13,100 years ago, and then further north, 12,600–12,750 years ago. Evidence from Lake Suigetsu cores in Japan and

4128-434: The cooling was spread out over several centuries, and the same was true of the early-Holocene warming. Even in the Northern Hemisphere, temperature change was highly seasonal, with much colder winters, cooler springs, yet no change or even slight warming during the summer. Substantial changes in precipitation also took place, with cooler areas experiencing substantially lower rainfall, while warmer areas received more of it. In

4214-522: The disruption of the North Atlantic Ocean circulation that results in a series of extreme weather events that create an abrupt climate change that leads to a new ice age . Before Present In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present". The BP scale

4300-641: The eastern and central areas. While the Pacific Northwest region cooled by 2–3 °C (3.6–5.4 °F), cooling in western North America was generally less intense. While the Orca Basin in the Gulf of Mexico still experienced a drop in sea surface temperature of 2.4 ± 0.6°C, land areas closer to it, such as Texas , the Grand Canyon area and New Mexico , ultimately did not cool as much as

4386-449: The end of the Bølling and the beginning of the Allerød as possible and then selects endpoints that are based on them: for example, 14,000–13,700 BP. The best approach attempts to include the Older Dryas in a sequence of points as close together as possible (high resolution) or within a known event. For example, pollen from the island of Hokkaidō , Japan , records a larch pollen peak and matching sphagnum decline at 14,600–13700 BP. In

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4472-476: The equivalent cooling in the Southern Hemisphere. This "polar seesaw" pattern is consistent with changes in thermohaline circulation (particularly the Atlantic meridional overturning circulation or AMOC), which greatly affects how much heat is able to go from the Southern Hemisphere to the North. The Southern Hemisphere cools and the Northern Hemisphere warms when the AMOC is strong, and the opposite happens when it

4558-404: The eruption back to 13,006 years BP, or over a century before the Younger Dryas began. This analysis was also challenged in 2023, with some researchers suggesting that the radiocarbon analysis was tainted by magmatic carbon dioxide. For now, the debate continues without a conclusive proof or rejection of the volcanic hypothesis. The Younger Dryas impact hypothesis (YDIH) attributes the cooling to

4644-406: The estimated ages can vary using different age dating methods. Numerous studies on chronology and palaeoclimate of last deglaciation show a cooling event within Bølling–Allerød warming that reflects the occurrence of Older Dryas. The determination of paleotemperatures varies from study to study depending on the sample collected. δ O measurements are most common when analyzing Ice core samples whereas

4730-482: The exception was in tropical Atlantic areas such as Costa Rica , where temperature change was similar to Greenland's. The Holocene warming then proceeded across the globe, following an increase in carbon dioxide levels during the YD period (from ~210 ppm to ~275 ppm). Younger Dryas cooling was often accompanied by glacier advance and lowering of the regional snow line , with evidence found in areas such as Scandinavia,

4816-476: The exponential decay relation and the "Libby half-life" 5568 a. The ages are expressed in years before present (BP) where "present" is defined as AD 1950. The year 1950 was chosen because it was the standard astronomical epoch at that time. It also marked the publication of the first radiocarbon dates in December 1949, and 1950 also antedates large-scale atmospheric testing of nuclear weapons , which altered

4902-561: The glacier. Species had access to Denmark and southern Sweden. Most of Finland and the Baltic countries were under the ice or the lake for most of the period. Northern Scandinavia was glaciated. Between Britain and Continental Europe were rolling hills prolifically populated with animals. Thousands of specimens, hundreds of tons of bones, have been recovered from the bottom of the North Sea , called " Doggerland ," and they continue to be recovered. There are many more species found for

4988-484: The glaciers retreat, and it drops if glaciers grow. Altogether, there appears to have been little change in sea level throughout the Younger Dryas. This is in contrast to rapid increases before and after, such as the Meltwater Pulse 1A . On the coasts, glacier advance and retreat also affects relative sea level . Western Norway experienced a relative sea level rise of 10 m ( 32 + 2 ⁄ 3  ft) as

5074-480: The global ratio of carbon-14 to carbon-12 . Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw ) and calibrated (also called Cambridge ) dates. Uncalibrated radiocarbon dates should be clearly noted as such by "uncalibrated years BP", because they are not identical to calendar dates. This has to do with the fact that the level of atmospheric radiocarbon ( carbon-14 or C) has not been strictly constant during

5160-531: The hypothesis, and argue that all of the microparticles are adequately explained by the terrestrial processes. For instance, mineral inclusions from YD-period sediments in Hall's Cave, Texas, have been interpreted by YDIH proponents as extraterrestrial in origin, but a paper published in 2020 argues that they are more likely to be volcanic. Opponents argue that there is no evidence for massive wildfires which would have been caused by an airburst of sufficient size to affect

5246-465: The impact of a disintegrating comet or asteroid. Because there is no impact crater dating to the Younger Dryas period, the proponents usually suggest the impact had struck the Laurentide ice sheet , so that the crater would have disappeared when the ice sheet melted during the Holocene, or that it was an airburst, which would only leave micro- and nanoparticles behind as evidence. Most experts reject

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5332-412: The lack of sea level rise during this period, so other theories have also emerged. An extraterrestrial impact into the Laurentide ice sheet (where it would have left no impact crater) was proposed as an explanation, but this hypothesis has numerous issues and no support from mainstream science. A volcanic eruption as an initial trigger for cooling and sea ice growth has been proposed more recently, and

5418-408: The lack of sea level rise during the Younger Dryas onset by connecting it with a volcanic eruption. Eruptions often deposit large quantities of sulfur dioxide particles in the atmosphere, where they are known as aerosols , and can have a large cooling effect by reflecting sunlight. This phenomenon can also be caused by anthropogenic sulfur pollution, where it is known as global dimming . Cooling from

5504-493: The last and the strongest of these events. However, there is some debate over what caused the AMOC to become so weak in the first place. The hypothesis historically most supported by scientists was an interruption from an influx of fresh, cold water from North America's Lake Agassiz into the Atlantic Ocean. While there is evidence of meltwater travelling via the Mackenzie River , this hypothesis may not be consistent with

5590-801: The lowercase letters bp , bc and ad as terminology for uncalibrated dates for these eras. The Centre for Ice and Climate at the University of Copenhagen instead uses the unambiguous "b2k", for "years before 2000 AD", often in combination with the Greenland Ice Core Chronology 2005 (GICC05) time scale. Some authors who use the YBP dating format also use "YAP" ("years after present") to denote years after 1950. SI prefix multipliers may be used to express larger periods of time, e.g. ka BP (thousand years BP), Ma BP (million years BP) and many others . Radiocarbon dating

5676-557: The main reason why Northern Hemisphere summers generally did not cool during the Younger Dryas. Since winds carry moisture in the form of clouds, these changes also affect precipitation . Thus, evidence from the pollen record shows that some areas have become very arid, including Scotland, the North American Midwest , Anatolia and southern China . As North Africa, including the Sahara Desert , became drier,

5762-453: The most abrupt climatic changes during the YD. Climate models also indicate that a single freshwater outburst, no matter how large, would not have been able to weaken the AMOC for over 1,000 years, as required by the Younger Dryas timeline, unless other factors were also involved. Some modelling explains this by showing that the melting of Laurentide Ice Sheet led to greater rainfall over the Atlantic Ocean, freshening it and so helping to weaken

5848-516: The name (standard codes are used) of the laboratory concerned, and other information such as confidence levels, because of differences between the methods used by different laboratories and changes in calibrating methods. Conversion from Gregorian calendar years to Before Present years is by starting with the 1950-01-01 epoch of the Gregorian calendar and increasing the BP year count with each year into

5934-406: The onset of the Younger Dryas, so that it would have been able to shed icebergs into the North Atlantic, which would have been able to weaken the circulation consistently. Notably, changes in sea ice cover would have had no impact on sea levels, which is consistent with the absence of significant sea level rise during the Younger Dryas, and particularly during its onset. Some scientists also explain

6020-400: The past from that Gregorian date. For example, 1000 BP corresponds to 950 AD, 1949 BP corresponds to 1 AD, 1950 BP corresponds to 1 BC, 2000 BP corresponds to 51 BC. Older Dryas The Older Dryas was a stadial (cold) period between the Bølling and Allerød interstadials (warmer phases), about 14,000 years Before Present , towards the end of the Pleistocene . Its date range

6106-414: The period than in this article. Most families were more diverse than they are today, and they were yet more so in the last interglacial. A great extinction , especially of mammals, continued throughout the end of the Pleistocene , and it may be continuing today. The Older Dryas is a period of cooling during the Bølling–Allerød warming , estimated to be from 13,900 to 13,600 years before present (BP), and

6192-484: The presence of anomalously high levels of volcanism immediately preceding the onset of the Younger Dryas has been confirmed in both ice cores and cave deposits. The Younger Dryas is named after the alpine – tundra wildflower Dryas octopetala , because its fossils are abundant in the European (particularly Scandinavian ) sediments dating to this timeframe. The two earlier geologic time intervals where this flower

6278-528: The region despite being retarded, indicating the absence of permafrost and glaciation. On the other hand, the warming of the Southern Hemisphere led to ice loss in Antarctica, South America and New Zealand. Moreover, while Greenland as a whole had cooled, glaciers had only grown in the north of the island, and they had retreated from the rest of Greenland's coasts. This was likely driven by the strengthened Irminger Current . The Jabllanica mountain range in

6364-535: The result of a northward shift in the jet stream, combined with an increase in summer insolation as well as a winter snow pack that was higher than today, with prolonged and wetter spring seasons. The Younger Dryas is often linked to the Neolithic Revolution , with the adoption of agriculture in the Levant . The cold and dry Younger Dryas arguably lowered the carrying capacity of the area and forced

6450-482: The sedentary early Natufian population into a more mobile subsistence pattern. Further climatic deterioration is thought to have brought about cereal cultivation. While relative consensus exists regarding the role of the Younger Dryas in the changing subsistence patterns during the Natufian, its connection to the beginning of agriculture at the end of the period is still being debated. The scientific consensus links

6536-596: The span of time that can be radiocarbon-dated. Uncalibrated radiocarbon ages can be converted to calendar dates by calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating based on tree growth-rings) and stratigraphy (dating based on sediment layers in mud or sedimentary rock). Such calibrated dates are expressed as cal BP, where "cal" indicates "calibrated years", or "calendar years", before 1950. Many scholarly and scientific journals require that published calibrated results be accompanied by

6622-406: The start of the 21st century. Strong cooling of around 2–6 °C (3.6–10.8 °F) had also taken place in Europe. Icefields and glaciers formed in upland areas of Great Britain , while many lowland areas developed permafrost , implying a cooling of −5 °C (23 °F) and a mean annual temperature no higher than −1 °C (30 °F). North America also became colder, particularly in

6708-493: The summer. An exception appears to have taken place in what is now Maine , where winter temperatures remained stable, yet summer temperatures decreased by up to 7.5 °C (13.5 °F). While the Northern Hemisphere cooled, considerable warming occurred in the Southern Hemisphere. Sea surface temperatures were warmer by 0.3–1.9 °C (0.54–3.42 °F), and Antarctica , South America (south of Venezuela ) and New Zealand all experienced warming. The net temperature change

6794-404: The thermohaline circulation, mineralogical and geochemical evidence or for simultaneous human population declines and mass animal extinctions which would have been required by this hypothesis. Statistical analysis shows that the Younger Dryas is merely the last of 25 or 26 Dansgaard–Oeschger events (D–O events) over the past 120,000 years. These episodes are characterized by abrupt changes in

6880-527: The volcanic hypothesis. Events similar to the Younger Dryas appear to have occurred during the other terminations - a term used to describe a comparatively rapid transition from cold glacial conditions to warm interglacials. The analysis of lake and marine sediments can reconstruct past temperatures from the presence or absence of certain lipids and long chain alkenones , as these molecules are very sensitive to temperature. This analysis provides evidence for YD-like events during Termination II (the end of

6966-560: The western subtropical North Atlantic show that the "bottom water" lingered there for 1,000 years, twice the age of Late Holocene bottom waters from the same site around 1,500 BP. Further, the otherwise anomalous warming of the southeastern United States matches the hypothesis that as the AMOC weakened and transported less heat from the Caribbean towards Europe through the North Atlantic Gyre , more of it would stay trapped in

7052-601: Was a relatively modest cooling of 0.6 °C (1.1 °F). Temperature changes of the Younger Dryas lasted 1,150–1,300 years. According to the International Commission on Stratigraphy , the Younger Dryas ended around 11,700 years ago, although some research places it closer to 11,550 years ago. The end of Younger Dryas was also abrupt: in previously cooled areas, warming to previous levels took place over 50–60 years. The tropics experienced more gradual temperature recovery over several centuries;

7138-580: Was abundant in Europe are the Oldest Dryas (approx. 18,500-14,000 BP) and Older Dryas (~14,050–13,900 BP), respectively. On the contrary, Dryas octopetala was rare during the Bølling–Allerød Interstadial . Instead, European temperatures were warm enough to support trees in Scandinavia, as seen at the Bølling and Allerød sites in Denmark . In Ireland , the Younger Dryas has also been known as

7224-446: Was first used in 1949. Beginning in 1954, metrologists established 1950 as the origin year for the BP scale for use with radiocarbon dating, using a 1950-based reference sample of oxalic acid . According to scientist A. Currie Lloyd: The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U.S. National Bureau of Standards . A large quantity of contemporary oxalic acid dihydrate

7310-644: Was populated by Homo sapiens sapiens ( Cro-Magnon man ) during the late Upper Paleolithic . Bands of humans survived by hunting the mammals of the plains. In the Northern Europe they preferred reindeer, in Ukraine the woolly mammoth . They sheltered in huts and manufactured tools around campfires. Ukrainian shelters were supported by mammoth tusks. Humans were already established across Siberia and North America. Two domestic dogs ( Canis familiaris ) have been found in late Pleistocene Ukraine and were

7396-525: Was prepared as NBS Standard Reference Material (SRM) 4990B. Its C concentration was about 5% above what was believed to be the natural level, so the standard for radiocarbon dating was defined as 0.95 times the C concentration of this material, adjusted to a C reference value of −19 per mil (PDB). This value is defined as "modern carbon" referenced to AD 1950. Radiocarbon measurements are compared to this modern carbon value, and expressed as "fraction of modern" (fM). "Radiocarbon ages" are calculated from fM using

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