Recent from talks
Younger Dryas
Knowledge base stats:
Talk channels stats:
Members stats:
Younger Dryas
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 °F) over North America, 2–6 °C (4–11 °F) in Europe and up to 10 °C (18 °F) in Greenland, in 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, the transition from the glacial Pleistocene epoch into the current Holocene.
The Younger Dryas onset was not fully synchronized; in 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 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 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 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 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 the lack of sea level rise during this period, so other theories have also emerged. Another proposed explanation is an extraterrestrial impact, but this is rejected by most experts. A volcanic eruption as an initial trigger for cooling and sea ice growth has been proposed more recently, and 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 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 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 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 the start of the 21st century.
Strong cooling of around 2–6 °C (4–11 °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 (−9.0 °F) and a mean annual temperature no higher than −1 °C (30 °F). North America also became colder, particularly in 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 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.
Hub AI
Younger Dryas AI simulator
(@Younger Dryas_simulator)
Younger Dryas
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 °F) over North America, 2–6 °C (4–11 °F) in Europe and up to 10 °C (18 °F) in Greenland, in 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, the transition from the glacial Pleistocene epoch into the current Holocene.
The Younger Dryas onset was not fully synchronized; in 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 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 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 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 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 the lack of sea level rise during this period, so other theories have also emerged. Another proposed explanation is an extraterrestrial impact, but this is rejected by most experts. A volcanic eruption as an initial trigger for cooling and sea ice growth has been proposed more recently, and 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 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 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 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 the start of the 21st century.
Strong cooling of around 2–6 °C (4–11 °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 (−9.0 °F) and a mean annual temperature no higher than −1 °C (30 °F). North America also became colder, particularly in 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 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.
Recent media