16,000 years of climate and environmental change from east Beringia (Northern Yukon Territory, Canada)

The northern Yukon Territory was only partly glaciated during the Last Glacial Maximum, whereas large parts remained ice-free. Unglaciated landscapes and exposed shelf areas extending continuously between east Siberia and the Mackenzie River in Canada formed the vast subcontinent Beringia. Beringia provided a glacial refugium for high-latitude flora and fauna and a migration corridor for species and early men. Despite its apparently outstanding position for the understanding of the regional landscape and climate development, the late Quaternary history of the easternmost margin is largely unknown and relies on few continuous records. \nLacustrine deposits from the northern Yukon have recorded sedimentation, vegetation, and summer temperature changes since ~16 cal ka BP in the easternmost part of unglaciated Beringia. We applied an interdisciplinary approach using geophysical, sedimentological, and palynological analysis together with multivariate statistics to get a comprehensive understanding of the climatic and environmental history in the close proximity to the Laurentide Ice Sheet (LIS). \nDepositional environments changed rapidly during the late glacial–Holocene transition near the collapsing LIS and were triggered by a late-glacial drainage diversion of the Babbage River, probably leading to episodic spillovers of Laurentide meltwater into bedrock-controlled lake basins. Depositional conditions remained relatively stable during the Holocene and became decoupled from vegetation changes responding to climatic change. \nHerb-dominated tundra persisted until ~14.7 cal ka BP with mean July air temperatures ≤5°C colder than today. Temperatures rapidly increased during the Bølling/Allerød interstadial towards modern conditions, favoring establishment of Betula-Salix shrub tundra. Pollen-inferred temperature reconstructions recorded a pronounced Younger Dryas (YD) cold reversal in east Beringia that had not been inferred in area distant to the North Atlantic and Pacific oceans, so far. Summer temperatures during the YD dropped by ~1.5°C and repressed shrub growth in favor of dry and cold-adapted herb communities. Pollen assemblages show little evidence of an early Holocene Thermal Maximum, probably due to a moisture-limited spread of thermophile plants. \nNorthern Yukon Holocene moisture availability increased in response to a retreating Laurentide Ice Sheet, postglacial sea level rise, and decreasing summer insolation that in turn led to establishment of Alnus-Betula shrub tundra from ~5 cal ka BP until present, and conversion of a continental into a coastal-maritime climate near the Beaufort Sea. \nThis study is the first paleoenvironmental reconstruction at the eastern margin of the vast Beringian subcontinent that mutually addresses glacial chronology, vegetation and summer temperature change in combination with sedimentation history.

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