Allerød oscillation

The Allerød oscillation (Danish: Allerødtiden) was a warm and moist global interstadial that occurred at the end of the last glacial period. It raised temperatures in the northern Atlantic region to almost present-day levels, before they declined again in the succeeding Younger Dryas period, which was followed by the present interglacial period.

In some regions, especially in northern Eurasia, there is evidence for a cold period known as the Older Dryas interrupting the interstadial. In such regions the shorter oscillation ending with the Older Dryas is known as the Bølling oscillation, and the Allerød period is the interstadial following the Older Dryas.

The Allerød period was named after a type site in Furesø municipality in Sjælland, Denmark (near Copenhagen), where deposits created during the period were first identified in work published in 1901 by Hartz and Milthers. This Blytt-Sernander period corresponds to Pollen zone II.

The start of the Allerød depends on whether an Older Dryas is present and how much time is to be allotted to the latter. A conventional date of 14,000 BP is typical. Roberts (1998) uses 13,000 BP for the end of the period.

The Greenland oxygen isotope record shows the warming identified with the Allerød to be after about 14,100 BP and before about 12,900 BP. C-14 dates from an excavation on the shore of Lake Neuchatel, Switzerland, furnish a date of 14,000 BP, calibrated, for the start of the Allerød. Pollen cores from Berezina plain, Belarus, give 11,800–10,900 BP uncal. Various researchers have similar ranges: 12,000–11,000, 11,700–11,000, etc. They all seem to roughly concur. The interstadial ended abruptly with a cold period that reduced temperatures back to near-glacial levels within a decade.

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