Geographical sites:

  • Sahara (click here to focus in map) (see also GeoNames #2461445)
    Geonames_icon Western Sahara territory Geocontext: Africa/El_Aaiun
  • North Atlantic (click here to focus in map) (see also GeoNames #3411923)
    Geonames_icon North Atlantic Ocean ocean Geocontext: America/Danmarkshavn
  • Libya (click here to focus in map) (see also Pleiades #716588)
    Pleiades_icon Libya region Geocontext: coastal and inland region W Nile EGY/LBY
    Description: An ancient place, cited: None
  • Greenland (click here to focus in map) (see also GeoNames #3425505)
    Geonames_icon Greenland dependent political entity Description: GL
  • Norway (click here to focus in map) (see also GeoNames #3144096)
    Geonames_icon Kingdom of Norway independent political entity Geocontext: Europe/Oslo
  • China (click here to focus in map) (see also GeoNames #1814991)
    Geonames_icon People’s Republic of China independent political entity


Text #9338

"The 5.9 Kiloyear event", in Wikipedia.

The 5.9 kiloyear event was one of the most intense aridification events during the Holocene Epoch. It occurred around 3900 BC (5,900 years BP), ending the Neolithic Subpluvial and probably initiating the most recent desiccation of the Sahara.

Thus, it also triggered worldwide migration to river valleys, such as from central North Africa to the Nile valley, which eventually led to the emergence of the first complex, highly organized, state-level societies in the 4th millennium BC. It is associated with the last round of the Sahara pump theory.

A model by Claussen et al. (1999) suggested rapid desertification, associated with vegetation-atmosphere interactions following a cooling event, Bond event 4. Bond et al. (1997) identified a North Atlantic cooling episode 5,900 years ago from ice-rafted debris, as well as other such now called Bond events that indicate the existence of a quasiperiodic cycle of Atlantic cooling events, which occur approximately every 1,470 years ± 500 years. For some reason, all of the earlier of the arid events (including the 8.2 kiloyear event) were followed by recovery, as attested by the wealth of evidence of humid conditions in the Sahara between 10,000 and 6,000 BP. However, it appears that the 5.9 kiloyear event was followed by a partial recovery at best, with accelerated desiccation in the millennium that followed.

For example, Cremaschi (1998) describes evidence of rapid aridification in Tadrart Acacus of southwestern Libya, in the form of increased aeolian erosion, sand incursions and the collapse of the roofs of rock shelters. The 5.9 kiloyear event was also recorded as a cold event in the Erhai Lake (China) sediments.

In the eastern Arabian Peninsula, the 5.9 kiloyear event may have contributed to an increase in relatively greater social complexity, corresponding to an end of the local Ubaid period.

Text #9332

"Bond Event", in Wikipedia.

Bond events are North Atlantic climate fluctuations occurring every ≈1,470 ± 500 years throughout the Holocene. Eight such events have been identified, primarily from fluctuations in ice-rafted debris. Bond events may be the interglacial relatives of the glacial Dansgaard–Oeschger events, with a magnitude of perhaps 15–20% of the glacial-interglacial temperature change.

Gerard C. Bond of the Lamont–Doherty Earth Observatory at Columbia University, was the lead author of the 1997 paper that postulated the theory of 1,470-year climate cycles in the Holocene, mainly based on petrologic tracers of drift ice in the North Atlantic.

The existence of climatic changes, possibly on a quasi-1,500 year cycle, is well established for the last glacial period from ice cores. Less well established is the continuation of these cycles into the holocene. Bond et al. (1997) argue for a cyclicity close to 1470 ± 500 years in the North Atlantic region, and that their results imply a variation in Holocene climate in this region. In their view, many if not most of the Dansgaard–Oeschger events of the last ice age, conform to a 1,500-year pattern, as do some climate events of later eras, like the Little Ice Age, the 8.2 kiloyear event, and the start of the Younger Dryas.

The North Atlantic ice-rafting events happen to correlate with most weak events of the Asian monsoon for at least the past 9,000 years,[4][5] while also correlating with most aridification events in the Middle East for the past 55,000 years (both Heinrich and Bond events). Also, there is widespread evidence that a ≈1,500 yr climate oscillation caused changes in vegetation communities across all of North America.

For reasons that are unclear, the only Holocene Bond event that has a clear temperature signal in the Greenland ice cores is the 8.2 kyr event.

The hypothesis holds that the 1,500-year cycle displays nonlinear behavior and stochastic resonance; not every instance of the pattern is a significant climate event, though some rise to major prominence in environmental history. Causes and determining factors of the cycle are under study; researchers have focused attention on variations in solar output, and “reorganizations of atmospheric circulation.” Bond events may also be correlated with the 1800-year lunar tidal cycle.

0 ≈0.5 ka Little Ice Age
1 ≈1.4 ka Migration Period
2 ≈2.8 ka early 1st millennium BC drought in the Eastern Mediterranean, possibly triggering the collapse of Late Bronze Age cultures.
3 ≈4.2 ka 4.2 kiloyear event; collapse of the Akkadian Empire and the end of the Egyptian Old Kingdom.
4 ≈5.9 ka See 5.9 kiloyear event;
5 ≈8.2 ka See 8.2 kiloyear event;
6 ≈9.4 ka Erdalen event of glacier activity in Norway, as well as with a cold event in China.
7 ≈10.3 ka 8 ≈11.1 ka transition from the Younger Dryas to the boreal.

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