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

Abstract

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 δ 18O of − 29.1‰); this, together with low dexcess 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 icethrust 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 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.

Coastal erosion and mass wasting along the Canadian Beaufort Sea based on annual airborne LiDAR elevation data

“…Glacial sediments were reworked by thermokarst processes and other surficial sediments are of lacustrine, fluvial, or glaciofluvial origin (Rampton, 1982). The sediment composition ranges from organic fine-grained mixtures of clay, silt, and sand in lacustrine deposits to fine-grained marine deposits and tills with pebbles and cobbles in moraines (Bouchard, 1974;Rampton, 1982;Fritz et al, 2012). These sediments are commonly unconsolidated with considerable amounts of ground ice ranging from 30 to 60 volume percent (Couture, 2010).…”

Transformation of terrestrial organic matter along thermokarst-affected permafrost coasts in the Arctic

“…The dominant wind direction is NW, with storms frequently observed in late August and September (Solomon, 2005). Herschel Island is an ice-thrust moraine ridge formed by glaciers during the Late Wisconsin Glaciation (23 to 18 ka BP) and consists of unconsolidated and commonly finegrained former marine and glacigenic sediments (Blasco et al, 1990;Fritz et al, 2012). The island is underlain by continuous permafrost and characterized by polygonal tundra, valleys, and a rolling landscape that reaches a maximum elevation of 183 m above sea level (de Krom, 1990;Rampton, 1982).…”

Holocene ice-wedge polygon development in northern Yukon permafrost peatlands (Canada)

“…2). Unconsolidated sediments and high ground ice volumes make the region vulnerable to ground subsidence and erosion under permafrost thaw conditions (Rowland et al, 2010;Fritz et al, 2012a). Herschel Island is a glacial push-moraine originating from an advance of the Laurentide Ice Sheet into the Northern Yukon during the Late Wisconsin (23e15 kyr BP) (Mackay, 1959;Dyke and Prest, 1987;Fritz et al, 2012a).…”

“…8). Herschel Island and the Yukon Coastal Plain are known to host ice-rich permafrost deposits containing various types of ground ice (Rampton, 1982;Pollard, 1990;Fritz et al, 2012a). Moraines within the Late Wisconsin Laurentide ice limit are often ice-cored with buried glacier ice and massive segregated ice (French, 1998;Fritz et al, 2011).…”

“…Moraines within the Late Wisconsin Laurentide ice limit are often ice-cored with buried glacier ice and massive segregated ice (French, 1998;Fritz et al, 2011). This leads to locally highly variable ground-ice contents in fine-grained, matrix-based diamictons (Fritz et al, 2012a). Differential thaw after deglaciation of the Herschel Island moraine ridge and formerly glaciated parts of the adjacent Yukon Coastal Plain led to thaw subsidence and thaw-basin development (Lenz et al, 2013), especially because of increased summer warmth during the Holocene thermal maximum (Burn, 1997;Kaufman et al, 2004).…”