Bølling–Allerød warming

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Bølling-Allerød warming
)
ice cores.[1]

The Bølling–Allerød interstadial (Danish:

interstadial period that occurred during the final stages of the Last Glacial Period. This warm period ran from 14,690 to 12,890 years before the present (BP).[2] It began with the end of the cold period known as the Oldest Dryas, and ended abruptly with the onset of the Younger Dryas, a cold period that reduced temperatures back to near-glacial levels within a decade.[3]

In some regions, a cold period known as the Older Dryas can be detected in the middle of the Bølling–Allerød interstadial. In these regions the period is divided into the Bølling oscillation, which peaked around 14,500 BP, and the Allerød oscillation, which peaked closer to 13,000 BP.

History

North Greenland Ice Core Project Oxygen Isotope Data
Calcium concentration and d18O isotope ratios from the Greenland NGRIP, GRIP, and GISP2 ice cores on the GICC05 time scale
Methane (CH4) record from the North Greenland Ice Sheet Project (NGRIP) ice core, Greenland

In 1901, the Danish geologists Nikolaj Hartz (1867–1937) and Vilhelm Milthers (1865–1962) provided evidence for climatic warming during the last glacial period, sourced from a clay-pit near Allerød, Denmark.[4][5]

Effects

It has been postulated that teleconnections, oceanic and atmospheric processes, on different timescales, connect both hemispheres during abrupt climate change.[6] The Bølling–Allerød was almost completely synchronous across the Northern Hemisphere.[7]

The Meltwater pulse 1A event coincides with or closely follows the abrupt onset of the Bølling–Allerød (BA), when global sea level rose about 16 m during this event at rates of 26–53 mm/yr.[8]

Records obtained from the Gulf of Alaska show abrupt sea-surface warming of about 3 °C (in less than 90 years), matching ice-core records that register this transition as occurring within decades.[9] Antarctic Intermediate Water (AAIW) cooled slightly during this interstadial.[10]

δ18O records from Valmiki Cave in southern India indicate extreme shifts in Indian Summer Monsoon intensity at Termination 1a, which marks the start of the Bølling–Allerød and occurred about 14,800 BP.[11]

Scientists from the Center for Arctic Gas Hydrate (CAGE), Environment and Climate at the

methane reservoirs could eventually have the same fate.[12]

Ice-sheet retreat

A 2017 study attributed the second Weichselian Icelandic ice sheet collapse, onshore (est. net wastage 221 Gt a−1[clarification needed] over 750 years) and similar to today's Greenland rates of mass loss, to atmospheric Bølling–Allerød warming. The study's authors noted:

Geothermal conditions impart a significant control on the ice sheet's transient response, particularly during phases of rapid retreat. Insights from this study suggests that large sectors of contemporary ice sheets overlying geothermally active regions, such as Siple Coast, Antarctica, and northeastern Greenland, have the potential to experience rapid phases of mass loss and deglaciation once initial retreat is initiated.[13]

The melting of the glaciers of Hardangerfjord began during this interstadial. Boknafjord had already begun to deglaciate before the onset of the Bølling–Allerød interstadial.[14]

Flora

Ice uncovered large parts of north Europe and temperate forests covered Europe from N 29° to 41°

Corylus. Poaceae
was to be found in more open regions.

Fauna

During this time late

saiga, antelope, bison, woolly mammoth and woolly rhinoceros were attested, and were hunted by early man. In the alpine regions ibex and chamois were hunted. Throughout the forest were red deer. Smaller animals, such as fox, wolf, hare and squirrel also appear. Salmon was fished. When this interstadial period ended, with the onset of the Younger Dryas, many of these species were forced to migrate south or become regionally extinct
.

In the Great Barrier Reef, the Bølling–Allerød warming is associated with a substantial accumulation of calcium carbonate.[15]

Causes

Ocean circulation

In recent years research tied the Bølling–Allerød warming to the release of heat from warm waters originating from the deep North Atlantic Ocean, possibly triggered by a strengthening of the Atlantic meridional overturning circulation (AMOC) at the time.[16][17]

Study results which would help to explain the abruptness of the Bølling–Allerød warming, based on observations and simulations, found that 3°–5 °C

Ocean warming occurred at intermediate depths in the North Atlantic over several millennia during Heinrich stadial 1 (HS1). The authors postulated that this warm salty water (WSW) layer, situated beneath the colder surface freshwater in the North Atlantic, generated ocean convective available potential energy (OCAPE) over decades at the end of HS1. According to fluid modelling, at one point the accumulation of OCAPE was released abruptly (c. 1 month) into kinetic energy of thermobaric cabbeling convection (TCC), resulting in the warmer salty waters getting to the surface and subsequently warming the sea surface by approximately 2 °C.[18]

Volcanism

See also: Glaciovolcanism

Isostatic rebound in response to glacier retreat (unloading) and an increase in local salinity (i.e., δ18Osw) have been attributed to increased volcanic activity at the onset of Bølling–Allerød. The association with the interval of intense volcanic activity hints at an interaction between climate and volcanism, with one possible route being enhanced short-term melting of glaciers via albedo changes from particle fallout on glacier surfaces.[9]

Greenhouse gases

Estimates of

anthropogenic global warming signal from the past 50 years, and with a radiative forcing of 0.59–0.75 W m−2.[19] A previously unidentified contributor to atmospheric CO2 was the expansion of Antarctic Intermediate Water, which is poor at sequestering the gas.[20]

Human cultures

Humans reentered the forests of Europe in search of big game to hunt. Some theories suggest that humans as well as the changing climate were the driving force that led many of these species to

Natufian settled around the Eastern Mediterranean coast to exploit wild cereals, such as emmer and two-row barley
. In the Allerød they would begin to domesticate these plants.

See also

Sources

  1. PMID 28059138
    .
  2. ISSN 0148-0227
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  3. ISBN 978-1-59420-079-3
    .
  4. ISBN 978-1-4020-4551-6
    .
  5. ^ Hartz, N.; Milthers, V. (1901). "Det senglaciale Ler i Allerød Teglværkgrav" [The late glacial clay of the clay-pit at Alleröd]. Meddelelser Fra Dansk Geologisk Forening (Bulletin of the Geological Society of Denmark) (in Danish). 2 (8): 31–60.
  6. doi:10.1038/ngeo2848
    .
  7. ISSN 1476-4687
    .
  8. ^ Gornitz (2012). "The Great Ice Meltdown and Rising Seas: Lessons for Tomorrow". NASA. Archived from the original on 2012-07-16.
  9. ^
    doi:10.1016/j.epsl.2016.07.033
    .
  10. PMID 38104174
    .
  11. ISSN 0031-0182
    . Retrieved 1 January 2024 – via Elsevier Science Direct.
  12. ^ "Like 'champagne bottles being opened': Scientists document an ancient Arctic methane explosion". The Washington Post. June 1, 2017.
  13. S2CID 73574698
    .
  14. S2CID 133355572
    . Retrieved 29 September 2023.
  15. PMID 35042895
    .
  16. S2CID 4460693
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  17. doi:10.2312/polfor.2016.013
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  18. doi:10.1175/JCLI-D-15-0675.1
    .
  19. doi:10.5194/cp-7-473-2011
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  20. S2CID 247501785
    . Retrieved 21 January 2023.

External links
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