8.2 kiloyear event
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In
climatology Climatology (from Greek , ''klima'', "place, zone"; and , ''-logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. This modern field of study ...
, the so-called "8.2-kiloyear event" was a sudden decrease in global temperatures that occurred approximately 8,200 years before the present ( BP), that is, 6,251 BC. It defines the start of the
Northgrippian In the geologic time scale, the Northgrippian is the middle one of three ages or stages of the Holocene Epoch or Series. It was officially ratified by the International Commission on Stratigraphy in June 2018 along with the earlier Greenlandi ...
age in the
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
epoch. Milder than the
Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...
cold period before it but more severe than the Little Ice Age after it, the 8.2-kiloyear cooling was a significant exception to general trends of the Holocene climatic optimum. During the event,
atmospheric methane Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising. The 20-year globa ...
concentration decreased by 80 ppb, an emission reduction of 15%, by cooling and drying at a hemispheric scale.


Identification

A rapid cooling around 6200 BC was first identified by Swiss botanist Heinrich Zoller in 1960, who named the event the ''Misox oscillation'' (for the
Val Mesolcina The ''Valle Mesolcina'', also known as the ''Val Mesolcina'' or ''Misox'' (German), is an alpine valley of the Grisons, Switzerland, stretching from the San Bernardino Pass to Grono where it joins the Calanca Valley. It is the valley formed by ...
). It is also known as the ''Finse event'' in
Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and the ...
. Bond ''et al.'' argued that the origin of the 8.2-kiloyear event is linked to a 1,500-year climate cycle; it correlates with
Bond event Bond events are North Atlantic ice rafting events that are tentatively linked to climate fluctuations in the Holocene. Eight such events have been identified. Bond events were previously believed to exhibit a roughly cycle, but the primary perio ...
5. The strongest evidence for the event comes from the North Atlantic region; the disruption in climate shows clearly in
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...
ice cores and in
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
ary and other records of the temperate and the tropical North Atlantic. It is less evident in ice cores from
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
and in South American indices. The effects of the sudden temperature decrease were global, however, most notably in changes in
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...
.


Cooling event

The event may have been caused by a large meltwater pulse from the final collapse of the
Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million year ...
of northeastern North America, most likely when the glacial lakes
Ojibway The Ojibwe, Ojibwa, Chippewa, or Saulteaux are an Anishinaabe people in what is currently southern Canada, the northern Midwestern United States, and Northern Plains. According to the U.S. census, in the United States Ojibwe people are one of ...
and Agassiz suddenly drained into the North Atlantic Ocean. The same type of action produced the
Missoula floods The Missoula floods (also known as the Spokane floods or the Bretz floods or Bretz's floods) were cataclysmic glacial lake outburst floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the las ...
that formed the
Channeled Scablands The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods ...
of the Columbia River basin. The meltwater pulse may have affected the North Atlantic
thermohaline circulation Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temp ...
, reducing northward heat transport in the Atlantic and causing significant North Atlantic cooling. Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but decreases of around have been reported. In Greenland, the event started at 8175 BP, and the cooling was 3.3 °C (decadal average) in less than 20 years. The coldest period lasted for about 60 years, and its total duration was about 150 years. The meltwater causation hypothesis is, however, considered to be speculation because of inconsistencies with its onset and an unknown region of impact. Researchers suggest that the discharge was probably superimposed upon a longer episode of cooler climate lasting up to 600 years, and it was merely one contributing factor to the event as a whole. Further afield from the Laurentide Ice Sheet, some tropical records report a cooling, based on cores drilled into an ancient
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...
in
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
. The event also caused a global CO2 decline of about 25 ppm over about 300 years. However, dating and interpretation of other tropical sites are more ambiguous than the North Atlantic sites. In addition, climate modeling work shows that the amount of meltwater and the pathway of meltwater are both important in perturbing the North Atlantic thermohaline circulation. The initial meltwater pulse caused between of
sea-level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cryo ...
. Based on estimates of lake volume and decaying ice cap size, values of circulate. Based on sea-level data from the Mississippi Delta, the end of the Lake Agassiz–Ojibway (LAO) drainage occurred at 8.31 to 8.18 ka and ranges from 0.8 to 2.2 m. The sea-level data from the Rhine–Meuse Delta indicate a of near-instantaneous rise at 8.54 to 8.2 ka, in addition to 'normal' post-glacial sea-level rise. Meltwater pulse sea-level rise was experienced fully at great distance from the release area. Gravity and rebound effects associated with the shifting of water masses meant that the sea-level fingerprint was smaller in areas closer to the Hudson Bay. The Mississippi Delta records around 20%, Northwestern Europe 70% and Asia records 105% of the globally averaged amount. The cooling of the 8.2-kiloyear event was a temporary feature, but the sea-level rise of the meltwater pulse was permanent. In 2003, the
Office of Net Assessment The United States Department of Defense's Office of Net Assessment (ONA) was created in 1973 by Richard Nixon to serve as the Pentagon's "internal think tank" that "looks 20 to 30 years into the military's future, often with the assistance of outsi ...
(ONA) at the
United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...
was commissioned to produce a study on the likely and potential effects of a modern climate change. The study, conducted under ONA head Andrew Marshall, modeled its prospective climate change on the 8.2-kiloyear event, precisely because it was the middle alternative between the Younger Dryas and the milder Little Ice Age.


North Africa and Mesopotamia

Drier conditions were notable in
North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...
, and East Africa was significantly affected by five centuries of general
drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, an ...
. In
West Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion of the larger geographical region of Asia, as defined by some academics, UN bodies and other institutions. It is almost entirely a part of the Middle East, and includes Ana ...
, especially
Mesopotamia Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the ...
, the 8.2-kiloyear event was a 300-year
aridification Aridification is the process of a region becoming increasingly arid, or dry. It refers to long term change, rather than seasonal variation. It is often measured as the reduction of average soil moisture content. It can be caused by reduced precip ...
and cooling episode, which may have provided the natural force for Mesopotamian irrigation agriculture and surplus production, which were essential for the earliest formation of classes and urban life. However, changes taking place over centuries around the period are difficult to link specifically to the approximately 100-year abrupt event, as recorded most clearly in the Greenland ice cores. In particular, in
Tell Sabi Abyad Tell Sabi Abyad ( ar, تل صبي أبيض) is an archaeological site in the Balikh River valley in northern Syria. It lies about 2 kilometers south of Tell Hammam et-Turkman.The site consists of four prehistoric mounds that are numbered Tell Sab ...
, Syria, significant cultural changes are observed at c. 6200 BC; the settlement was not abandoned at the time.


Northern Europe

In western Scotland, the 8.2 kiloyear event coincided with a dramatic reduction in the Mesolithic population.Wicks, K. & Mithen, Steven. (2014). The impact of the abrupt 8.2 ka cold event on the Mesolithic population of western Scotland: A Bayesian chronological analysis using ‘activity events’ as a population proxy. ''
Journal of Archaeological Science The ''Journal of Archaeological Science'' is a monthly peer-reviewed academic journal that covers "the development and application of scientific techniques and methodologies to all areas of archaeology". The journal was established in 1974 by Acad ...
''. 45. 10.1016/j.jas.2014.02.003.


See also

* 4.2-kiloyear event * 5.9-kiloyear event *
African humid period The African humid period (AHP) (also known by other names) is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, ...
* Antarctic Cold Reversal *
Bond event Bond events are North Atlantic ice rafting events that are tentatively linked to climate fluctuations in the Holocene. Eight such events have been identified. Bond events were previously believed to exhibit a roughly cycle, but the primary perio ...
* Little Ice Age *
Older Peron The Older Peron was the name for a period identified in 1961 as an episode of a global sea-level (i.e. eustatic) high-stand during the Holocene Epoch The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years B ...
*
Piora Oscillation The Piora Oscillation was an abrupt cold and wet period in the climate history of the Holocene Epoch; it is roughly dated to c. 3900-3000 BC. Some researchers associate the Piora Oscillation with the end of the Atlantic climate regime, and the st ...
*
Sahara pump theory The Sahara pump theory is a hypothesis that explains how flora and fauna migrated between Eurasia and Africa via a land bridge in the Levant region. It posits that extended periods of abundant rainfall lasting many thousands of years (pluvial p ...
*
Sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
* Storegga Slide *
Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...


References


External links

* {{DEFAULTSORT:8.2 Kiloyear Event History of climate variability and change 7th millennium BC