Palynological records from glacial lakes, northern Priokhotye (western Beringia)

Abstract

Palynological analyzes of sediments from glacial lakes in Northern Priokhot'ye provide the first continuous records of regional vegetation responses to climate change at the end of the Pleistocene and during the Holocene. The pollen stratigraphy from these coastal sites is like that described for more northern regions of Western Beringia. Herb dominated tundra with Poaceae-forb meadows characterized the Late Pleistocene and was replaced c. 12,100 cal BP by Betula shrub tundra and then by shrub Betula-Alnus tundra. In the Middle Holocene (c. 8900-4700 cal BP), Larix-Betula platyphylla forests with an undergrowth of Pinus pumila, shrub Betula, and Alnus became widespread. Pinus pumila also formed a high shrub tundra zone above altitudinal treeline. Finds of Betula platyphylla macrofossils suggest that summer temperatures were 2–4 °C warmer than today between c. 7700 and 6700 cal BP. Variations in Pinus pollen percentages during the Middle and Late Holocene suggest changes in altitudinal treeline related to intervals of relatively cooler or warmer climates. The timing of the postglacial thermal maximum and possible shifts in altitudinal treeline suggest paleoclimatic patterns that are more like southern areas of the Russian Far East than northern regions of Western Beringia. A Late Holocene tephra was found for the first time in the lake sediments and peat exposures of Northern Priokhotye. The most likely source of this important chronostratigraphic horizon is the Shiveluch volcanic eruption (Kamchatka Peninsula) dated to 2500–2600 BP (2580–2730 cal BP).