Older Dryas
The Older Dryas[a] was a stadial (cold) period between the Bølling and Allerød interstadials (warmer phases),[1] about 14,000 years Before Present, towards the end of the Pleistocene.
The Older Dryas was a variable cold, dry Blytt–Sernander period, observed in climatological evidence in only some regions,[4] dependent on latitude.
In the Greenland oxygen isotope record, the Older Dryas appears as a downward peak establishing a small, low-intensity gap between the Bølling and the Allerød.
A second approach finds carbon-14 or other dates as close to the end of the Bølling and the beginning of the Allerød as possible and then selects endpoints that are based on them: for example, 14,000–13,700 BP.
During the Older Dryas, the glacier re-advanced, and the trees retreated southward, to be replaced by a mixture of grassland and cool-weather alpine species.
Numerous studies on chronology and palaeoclimate of last deglaciation show a cooling event within Bølling–Allerød warming that reflects the occurrence of Older Dryas.
As for ocean sediments, the variations of alkenone levels and faunal abundances were measured to model paleotemperatures in separate studies shown in the following sections.
A multi-proxy study on late glacial lake sediments of Moervaart palaeolake shows multiple pieces of evidence in various aspects to support Older Dryas.
δ18O measurements show a decreasing trend in δ18O at the transition to the Older Dryas, which corresponds to the ice core record of precipitation in the northern hemisphere.
The mollusc data (Valvata piscinalis as a cold-water indicator) suggests a lower summer temperature compared to previous Bølling period.
Recent research on sea surface temperature (SST) for the past 15,000 years in southern Okinawa modelled the Paleoclimate of ocean sediment core (ODP 1202B) using an alkenone analysis.
[8] The results show a cooling stage at 14,300 to 13,700 years BP between Bølling and Allerød warm phases, corresponding to the Older Dryas event.
[8] Another study on an ocean sediment core from the Norwegian Trench also suggests a cooling between Bølling and Allerød warm phases.
Plains mammals were most predominant: Artiodactyls: Perissodactyls: Proboscidea: So much meat on the hoof must have supported large numbers of Carnivora: Ursidae: Hyaenidae: Felidae: Canidae: Mustelidae: The sea also had its share of carnivores; their maritime location made them survive until modern times: Phocidae: Odobenidae: Of the Cetacean Odontoceti, the Monodontidae: Delphinidae: Of the Mysticetian Eschrichtiidae: The top of the food chain was supported by larger numbers of smaller animals farther down, which lived in the herbaceous blanket covering the tundra or steppe and helped maintain it by carrying seeds, manuring and aerating it.
[25] Two domestic dogs (Canis familiaris) have been found in late Pleistocene Ukraine and were a heavy breed, similar to a Great Dane, perhaps useful to run down Elephantidae.
The large number of mammoth bones at campsites make it clear that even then, the Elephantidae in Europe were approaching the limit of their duration.
During the Older Dryas, contemporaneous with the Havelte Group of the late Hamburgian, the Federmesser culture appeared and occupied Denmark and southern Sweden, following the reindeer.
