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102-537: Valdemarsvik is surrounded by water. However, after the end of the last glacial period , it lay beneath the sea level. As a result of post-glacial rebound , the water withdrew as the land rose. The resulting appearance of fertile soil drew settlers in the Bronze Age , around 1500 BC. The surrounding archipelago has had a bloody history: remains of shipwrecks at the bottom of the sea and Viking Age remnants witness of battles from that time. Industrialization occurred during

204-564: 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

306-502: 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

408-572: A jury then assesses. The winning dish is then served at most restaurants in the municipality. The football club Valdemarsviks IF is located in Valdemarsvik. [REDACTED] Media related to Valdemarsvik at Wikimedia Commons Last glacial period The Last Glacial Period ( LGP ), also known as the Last glacial cycle , occurred from the end of the Last Interglacial to the beginning of

510-501: 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

612-468: 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

714-513: A result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland, where the land is rising at a rate of as much as 8–9 mm per year, or 1 m in 100 years. This is important for archaeologists, since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore. The term Würm

816-762: A still lesser extent, glaciers existed in Africa, for example in the High Atlas , the mountains of Morocco , the Mount Atakor massif in southern Algeria , and several mountains in Ethiopia . Just south of the equator, an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro massif , Mount Kenya , and the Rwenzori Mountains , which still bear relic glaciers today. Glaciation of

918-418: Is both a market, with a range of goods to be sold, and a fair, featuring acrobats , cotton candy , live music and various amusement rides . Many of Valdemarsvik's restaurants and cafés are open all year round; other are open during the tourist season. Also, each year there is exists a special "food competition". Dishes are to be made, the ingredients should, as far as possible, be locally produced and which

1020-594: Is derived from a river in the Alpine foreland, roughly marking the maximum glacier advance of this particular glacial period. The Alps were where the first systematic scientific research on ice ages was conducted by Louis Agassiz at the beginning of the 19th century. Here, the Würm glaciation of the LGP was intensively studied. Pollen analysis , the statistical analyses of microfossilized plant pollens found in geological deposits, chronicled

1122-529: Is hypothesized to be 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

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1224-578: 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

1326-789: The Arctic ice cap . The Antarctic ice sheet began to form earlier, at about 34 Mya, in the mid- Cenozoic ( Eocene–Oligocene extinction event ), and the term Late Cenozoic Ice Age is used to include this early phase with the current glaciation. The previous ice age within the Quaternary is the Penultimate Glacial Period , which ended about 128,000 years ago, was more severe than the Last Glacial Period in some areas such as Britain, but less severe in others. The last glacial period saw alternating episodes of glacier advance and retreat with

1428-967: The Central Rocky Mountains ), Wisconsinan or Wisconsin (in central North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps ), Mérida (in Venezuela ), Weichselian or Vistulian (in Northern Europe and northern Central Europe), Valdai in Russia and Zyryanka in Siberia , Llanquihue in Chile , and Otira in New Zealand. The geochronological Late Pleistocene includes

1530-515: The Himalayas , and other formerly glaciated regions around the world. The glaciations that occurred during this glacial period covered many areas, mainly in the Northern Hemisphere and to a lesser extent in the Southern Hemisphere. They have different names, historically developed and depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale (in

1632-561: The Holocene , c.  115,000  – c.  11,700 years ago, and thus corresponds to most of the timespan of the Late Pleistocene . The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The glaciation and the current Quaternary Period both began with the formation of

1734-542: The Last Glacial Maximum occurring between 26,000 and 20,000 years ago. While the general pattern of cooling and glacier advance around the globe was similar, local differences make it difficult to compare the details from continent to continent (see picture of ice core data below for differences). The most recent cooling, the Younger Dryas , began around 12,800 years ago and ended around 11,700 years ago, also marking

1836-585: The Lesotho Highlands and parts of the Drakensberg . The development of glaciers was likely aided in part due to shade provided by adjacent cliffs. Various moraines and former glacial niches have been identified in the eastern Lesotho Highlands a few kilometres west of the Great Escarpment , at altitudes greater than 3,000 m on south-facing slopes. Studies suggest that the annual average temperature in

1938-648: 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

2040-697: The Owen Stanley Range , and the Saruwaged Range . Mount Giluwe in the Central Cordillera had a "more or less continuous ice cap covering about 188 km and extending down to 3200-3500 m". In Western New Guinea , remnants of these glaciers are still preserved atop Puncak Jaya and Ngga Pilimsit . Small glaciers developed in a few favorable places in Southern Africa during the last glacial period. These small glaciers would have been located in

2142-677: 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

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2244-462: 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,

2346-634: The Sierra Nevada in northern California . In northern Eurasia, the Scandinavian ice sheet once again reached the northern parts of the British Isles , Germany , Poland , and Russia, extending as far east as the Taymyr Peninsula in western Siberia. The maximum extent of western Siberian glaciation was reached by about 18,000 to 17,000 BP, later than in Europe (22,000–18,000 BP). Northeastern Siberia

2448-536: The Siskiyou Mountains suggests 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

2550-915: 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

2652-702: The Upper Mississippi River , which in turn was formed during an earlier glacial period. In its retreat, the Wisconsin episode glaciation left terminal moraines that form Long Island , Block Island , Cape Cod , Nomans Land , Martha's Vineyard , Nantucket , Sable Island , and the Oak Ridges Moraine in south-central Ontario, Canada. In Wisconsin itself, it left the Kettle Moraine . The drumlins and eskers formed at its melting edge are landmarks of

2754-481: 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

2856-564: The grooves left by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta, a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills , which is the northernmost point in North America that remained south of the continental ice sheets. The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of

2958-576: The isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea . Then, as postglacial isostatic rebound lifted the region about 9500 BP, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lake , which is identifiable in the freshwater fauna found in sediment cores. The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached

3060-624: 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

3162-584: The 1630s, when Valdemarsvik became a trade port for copper and leather ; one of Sweden's largest tanneries was located in Valdemarsvik. The town's name was first mentioned in 1664. Sailing to the Tjust archipelago  [ sv ] to swim and fish is a popular summertime activity. Boat excursions and jetski rentals are also available. No one I know who has experienced Gryt's archipelago disagrees with me saying: It has been—and is—a blessing to experience this archipelago, this living porch, stretching out into

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3264-485: 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

3366-471: 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

3468-739: The Alpine foreland . Local ice fields or small ice sheets could be found capping the highest massifs of the Pyrenees , the Carpathian Mountains , the Balkan Mountains , the Caucasus , and the mountains of Turkey and Iran . In the Himalayas and the Tibetan Plateau , there is evidence that glaciers advanced considerably, particularly between 47,000 and 27,000 BP, but the exact ages, as well as

3570-725: The Center for Arctic Gas Hydrate, Environment and Climate at the University of Tromsø , published a study in June 2017 describing over a hundred ocean sediment craters, some 3,000 m wide and up to 300 m deep, formed by explosive eruptions of methane from destabilized methane hydrates , following ice-sheet retreat during the LGP, around 12,000 years ago. These areas around the Barents Sea still seep methane today. The study hypothesized that existing bulges containing methane reservoirs could eventually have

3672-474: The Greenland climate was dry during the LGP, with precipitation reaching perhaps only 20% of today's value. The name Mérida glaciation is proposed to designate the alpine glaciation that affected the central Venezuelan Andes during the Late Pleistocene. Two main moraine levels have been recognized - one with an elevation of 2,600–2,700 m (8,500–8,900 ft), and another with an elevation of 3,000–3,500 m (9,800–11,500 ft). The snow line during

3774-409: 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

3876-570: The LGP as the Devensian . Irish geologists, geographers, and archaeologists refer to the Midlandian glaciation, as its effects in Ireland are largely visible in the Irish Midlands . The name Devensian is derived from the Latin Dēvenses , people living by the Dee ( Dēva in Latin), a river on the Welsh border near which deposits from the period are particularly well represented. The effects of this glaciation can be seen in many geological features of England, Wales, Scotland, and Northern Ireland . Its deposits have been found overlying material from

3978-444: 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

4080-505: The North American Laurentide ice sheet. At the height of glaciation, the Bering land bridge potentially permitted migration of mammals, including people, to North America from Siberia . It radically altered the geography of North America north of the Ohio River . At the height of the Wisconsin episode glaciation, ice covered most of Canada, the Upper Midwest , and New England , as well as parts of Montana and Washington . On Kelleys Island in Lake Erie or in New York's Central Park ,

4182-400: 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

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4284-410: The Polish River Vistula or its German name Weichsel). Evidence suggests that the ice sheets were at their maximum size for only a short period, between 25,000 and 13,000 BP. Eight interstadials have been recognized in the Weichselian, including the Oerel, Glinde, Moershoofd, Hengelo, and Denekamp. Correlation with isotope stages is still in process. During the glacial maximum in Scandinavia, only

4386-437: The Southern Hemisphere was less extensive. Ice sheets existed in the Andes ( Patagonian Ice Sheet ), where six glacier advances between 33,500 and 13,900 BP in the Chilean Andes have been reported. Antarctica was entirely glaciated, much like today, but unlike today the ice sheet left no uncovered area. In mainland Australia only a very small area in the vicinity of Mount Kosciuszko was glaciated, whereas in Tasmania glaciation

4488-452: The Wisconsin episode. It began about 30,000 years ago, reached its greatest advance 21,000 years ago, and ended about 10,000 years ago. In northwest Greenland, ice coverage attained a very early maximum in the LGP around 114,000. After this early maximum, ice coverage was similar to today until the end of the last glacial period. Towards the end, glaciers advanced once more before retreating to their present extent. According to ice core data,

4590-431: 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

4692-403: 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

4794-467: 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 ,

4896-449: The area and forced 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

4998-430: 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

5100-581: 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

5202-425: The cooling to 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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5304-404: The date of 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

5406-400: The dramatic changes in the European environment during the Würm glaciation. During the height of Würm glaciation, c.  24,000  – c.  10,000  BP, most of western and central Europe and Eurasia was open steppe-tundra, while the Alps presented solid ice fields and montane glaciers. Scandinavia and much of Britain were under ice. During the Würm, the Rhône Glacier covered

5508-415: 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

5610-539: The end of the LGP and the Pleistocene epoch. It was followed by the Holocene , the current geological epoch . The LGP is often colloquially referred to as the "last ice age", though the term ice age is not strictly defined, and on a longer geological perspective, the last few million years could be termed a single ice age given the continual presence of ice sheets near both poles. Glacials are somewhat better defined, as colder phases during which glaciers advance, separated by relatively warm interglacials . The end of

5712-412: The endless ocean. Other recreational activities include bicycle rentals, golf, cinemas, canoeing, and horse riding. There are museums in the locality that can be visited. The glass artist , sculptor and painter Milan Wobruba  [ sv ] has a studio , where visitors have the opportunity to be involved in glass blowing and the manufacture of glass. An "October Market", held every 4 October,

5814-437: 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,

5916-423: The formation of a single contiguous ice sheet on the Tibetan Plateau, is controversial. Other areas of the Northern Hemisphere did not bear extensive ice sheets, but local glaciers were widespread at high altitudes. Parts of Taiwan , for example, were repeatedly glaciated between 44,250 and 10,680 BP as well as the Japanese Alps . In both areas, maximum glacier advance occurred between 60,000 and 30,000 BP. To

6018-422: 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

6120-482: 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

6222-417: 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

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6324-410: 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

6426-432: 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

6528-447: The last glacial advance was lowered approximately 1,200 m (3,900 ft) below the present snow line, which is 3,700 m (12,100 ft). The glaciated area in the Cordillera de Mérida was about 600 km (230 sq mi); this included these high areas, from southwest to northeast: Páramo de Tamá, Páramo Batallón, Páramo Los Conejos, Páramo Piedras Blancas, and Teta de Niquitao. Around 200 km (77 sq mi) of

6630-444: The last glacial maximum, the Patagonian ice sheet extended over the Andes from about 35°S to Tierra del Fuego at 55°S. The western part appears to have been very active, with wet basal conditions, while the eastern part was cold-based. Cryogenic features such as ice wedges , patterned ground , pingos , rock glaciers , palsas , soil cryoturbation , and solifluction deposits developed in unglaciated extra-Andean Patagonia during

6732-401: The last glacial period, which was about 10,000 years ago, is often called the end of the ice age, although extensive year-round ice persists in Antarctica and Greenland . Over the past few million years, the glacial-interglacial cycles have been "paced" by periodic variations in the Earth's orbit via Milankovitch cycles . The LGP has been intensively studied in North America, northern Eurasia,

6834-410: The last glaciation, but not all these reported features have been verified. The area west of Llanquihue Lake was ice-free during the last glacial maximum, and had sparsely distributed vegetation dominated by Nothofagus . Valdivian temperate rain forest was reduced to scattered remnants on the western side of the Andes. Younger Dryas The Younger Dryas (YD, Greenland Stadial GS-1)

6936-442: The late glacial (Weichselian) and the immediately preceding penultimate interglacial ( Eemian ) period. Canada was almost completely covered by ice, as was the northern part of the United States , both blanketed by the huge Laurentide Ice Sheet . Alaska remained mostly ice free due to arid climate conditions. Local glaciations existed in the Rocky Mountains and the Cordilleran ice sheet and as ice fields and ice caps in

7038-401: The lower Connecticut River Valley . In the Sierra Nevada , three stages of glacial maxima, sometimes incorrectly called ice ages , were separated by warmer periods. These glacial maxima are called, from oldest to youngest, Tahoe, Tenaya, and Tioga. The Tahoe reached its maximum extent perhaps about 70,000 years ago. Little is known about the Tenaya. The Tioga was the least severe and last of

7140-448: The main Wisconsin glacial advance. The upper level probably represents the last glacial advance (Late Wisconsin). The Llanquihue glaciation takes its name from Llanquihue Lake in southern Chile , which is a fan-shaped piedmont glacial lake. On the lake's western shores, large moraine systems occur, of which the innermost belong to the LGP. Llanquihue Lake's varves are a node point in southern Chile's varve geochronology . During

7242-426: 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,

7344-479: The massive Missoula Floods . USGS geologists estimate that the cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred about 40 times over the 2,000-year period starting 15,000 years ago. Glacial lake outburst floods such as these are not uncommon today in Iceland and other places. The Wisconsin glacial episode was the last major advance of continental glaciers in

7446-557: 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

7548-502: The mountains of Southern Africa was about 6 °C colder than at present, in line with temperature drops estimated for Tasmania and southern Patagonia during the same time. This resulted in an environment of relatively arid periglaciation without permafrost , but with deep seasonal freezing on south-facing slopes. Periglaciation in the eastern Drakensberg and Lesotho Highlands produced solifluction deposits and blockfields ; including blockstreams and stone garlands. Scientists from

7650-576: The onset of 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

7752-408: 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

7854-463: The opposite happens when it 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

7956-719: The preceding Ipswichian stage and lying beneath those from the following Holocene , which is the current stage. This is sometimes called the Flandrian interglacial in Britain. The latter part of the Devensian includes pollen zones I–IV, the Allerød oscillation and Bølling oscillation , and the Oldest Dryas , Older Dryas , and Younger Dryas cold periods. Alternative names include Weichsel glaciation or Vistulian glaciation (referring to

8058-481: 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

8160-543: The proglacial rivers' shifting and redepositing gravels. Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow. The Pinedale (central Rocky Mountains) or Fraser (Cordilleran ice sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States. The Pinedale lasted from around 30,000 to 10,000 years ago, and

8262-463: The receding ice. When the enormous mass of the continental ice sheet retreated, the Great Lakes began gradually moving south due to isostatic rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River . With the assistance of several very broad glacial lakes, it released floods through the gorge of

8364-454: 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

8466-399: The same fate. During the last glacial period, Antarctica was blanketed by a massive ice sheet, much as it is today. The ice covered all land areas and extended into the ocean onto the middle and outer continental shelf. Counterintuitively though, according to ice modeling done in 2002, ice over central East Antarctica was generally thinner than it is today. British geologists refer to

8568-466: The sill about 8000 BP, forming a marine Littorina Sea , which was followed by another freshwater phase before the present brackish marine system was established. "At its present state of development, the marine life of the Baltic Sea is less than about 4000 years old", Drs. Thulin and Andrushaitis remarked when reviewing these sequences in 2003. Overlying ice had exerted pressure on the Earth's surface. As

8670-412: 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

8772-544: The strengthened Irminger Current . The Jabllanica mountain range in 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

8874-498: 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

8976-476: The surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores , even times of seasonally open waters must have occurred. Outside the main ice sheets, widespread glaciation occurred on the highest mountains of the Alpide belt . In contrast to the earlier glacial stages, the Würm glaciation was composed of smaller ice caps and mostly confined to valley glaciers, sending glacial lobes into

9078-408: 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

9180-447: The total glaciated area was in the Sierra Nevada de Mérida , and of that amount, the largest concentration, 50 km (19 sq mi), was in the areas of Pico Bolívar , Pico Humboldt [4,942 m (16,214 ft)], and Pico Bonpland [4,983 m (16,348 ft)]. Radiocarbon dating indicates that the moraines are older than 10,000 BP, and probably older than 13,000 BP. The lower moraine level probably corresponds to

9282-451: The tropics, 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

9384-534: 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

9486-589: The western parts of Jutland were ice-free, and a large part of what is today the North Sea was dry land connecting Jutland with Britain (see Doggerland ). The Baltic Sea , with its unique brackish water , is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened. Initially, when the ice began melting about 10,300 BP, seawater filled

9588-547: 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

9690-713: The whole western Swiss plateau, reaching today's regions of Solothurn and Aargau. In the region of Bern, it merged with the Aar glacier. The Rhine Glacier is currently the subject of the most detailed studies. Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura. Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Günz and Mindel glaciation, by depositing base moraines and terminal moraines of different retraction phases and loess deposits, and by

9792-476: 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

9894-603: 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;

9996-578: 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

10098-458: Was at its greatest extent between 23,500 and 21,000 years ago. This glaciation was somewhat distinct from the main Wisconsin glaciation, as it was only loosely related to the giant ice sheets and was instead composed of mountain glaciers, merging into the Cordilleran ice sheet. The Cordilleran ice sheet produced features such as glacial Lake Missoula , which broke free from its ice dam, causing

10200-461: Was more widespread. An ice sheet formed in New Zealand, covering all of the Southern Alps, where at least three glacial advances can be distinguished. Local ice caps existed in the highest mountains of the island of New Guinea , where temperatures were 5 to 6 °C colder than at present. The main areas of Papua New Guinea where glaciers developed during the LGP were the Central Cordillera ,

10302-501: Was not covered by a continental-scale ice sheet. Instead, large, but restricted, icefield complexes covered mountain ranges within northeast Siberia, including the Kamchatka-Koryak Mountains. The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today, probably was covered only by relatively shallow ice, subject to seasonal changes and riddled with icebergs calving from

10404-509: Was offset by 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

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