Radiocarbon ages, dose rates, water isotopic composition and hydrochemistry of samples from Komakuk Beach and Herschel Island

• Main Authors: Fritz, Michael, Wetterich, Sebastian, Schirrmeister, Lutz, Meyer, Hanno, Lantuit, Hugues, Preusser, Frank, Pollard, Wayne H
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 2012
• Subjects: AWI_PerDyn; International Polar Year (2007-2008); IPY; Permafrost Research (Periglacial Dynamics) @ AWI; Herschel; Herschel Island; Ice; Ice Sheet; International Polar Year; permafrost; Thermokarst; wedge*; Beringia; Yukon
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.809992; https://doi.org/10.1594/PANGAEA.809992

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 16.2 cal ka BP 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 d18O of -29.1 per mil); 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 ~11 cal ka BP 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 11.2 cal ka BP 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 ...