Eastern Beringia and beyond: Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 319-320; pp. 28 - 45
• Main Authors: Fritz, Michael, Wetterich, Sebastian, Schirrmeister, Lutz, Meyer, Hanno, Lantuit, Hugues, Preusser, Frank, Pollard, Wayne H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2012
• Subjects: Beringia; Freshwater; Ground ice; Herschel Island; Laurentide Ice Sheet; Marine; Ostracoda; Permafrost; Stable water isotopes; Beringia; Canada, Laurentide Ice Sheet; Herschel Island; Permafrost; Ground ice; Beringia; Stable water isotopes; Laurentide Ice Sheet
• ISSN: 0031-0182; 1872-616X; 1872-616X
• DOI: 10.1016/j.palaeo.2011.12.015

Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry, and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2calkaBP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean δ18O of −29.1‰); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial, and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until ~11calkaBP during a period of low glacio-eustatic sea level. The late glacial–Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2calkaBP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet, ocean, and permafrost that have existed since the Late Wisconsinan. ► Yukon Coastal Plain (northwest Canada) marks the northeastern limit of Beringia. ► Laurentide Ice Sheet formed Herschel Island as recent as 16.2calkaBP. ► Holocene Thermal Maximum caused thawing of ice-rich near-surface permafrost. ► Ice-wedge casts and truncated ice wedges have recorded permafrost degradation. ► Extensive permafrost aggradation proceeded from middle Holocene climate cooling.