ABSTRACT: Ground ice studies on Herschel Island in the Western Canadian Arctic

CGRG Bibliography of Canadian Geomorphology
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Abstract

Herschel Island lies approximately 4 km off the Yukon Coastal Plain within the zone of continuous permafrost in the western Canadian Arctic. The island is a terminal moraine resulting from a push of the Laurentide Ice Sheet during the Early to Middle Wisconsin and represents the likely easternmost edge of Beringia. The region presumably remained ice-free during the Late Wisconsin glaciation and has therefore been intensively affected by periglacial processes for at least the last 50 ka BP. Ground ice is ubiquitous on the island and contributes to the shaping of the landscape since deglaciation. Cryostratigraphic, cryolithological and stable isotope analyses (d18O, d D) have been performed on various ground ice types (e.g. ice wedge ice, segregated ice, texture ice, potentially buried glacier ice) recovered to unravel their genetic processes, their relative age as well as responsible freezing processes and different temporal periods of ground ice aggradation and degradation. Since ground ice is a valuable record of paleoclimate information regarding the prevailing temperatures during precipitation and ice formation, it can be used for paleoenvironmental reconstructions. Ice wedges on Herschel Island have begun to form in outwash and morainic deposits of Wisconsin age after deglaciation, when dry and harsh climatic conditions supported frost cracking. A recovered Pleistocene ice wedge – recognised by its truncation by the early Holocene thaw unconformity – is remarkably depleted in its mean d18O isotope signature (-29 ‰) compared to all other occurring ice wedges (–24 to –21 ‰) that penetrate the unconformity or that are not truncated. Thus, significantly colder winter temperatures are assumed during the formation of Pleistocene ice wedges in contrast to Holocene and more recent ones. Evidently, Herschel Island comprises ice wedges that formed likely prior to the Holocene Thermal Maximum (HTM) and afterwards up to the present. Within glacially-affected and ice-rich Herschel Island sediments, bodies of massive ice are exposed whose appearance and isotopic composition is completely different from all other sampled ground ice types. d18O-isotopes are strongly depleted (between -33 and -37‰) thus suggesting a Pleistocene origin with slope and d-excess near the global meteoric water line (GMWL), which indicate that the moisture is likely of meteoric origin without substantial alterations. The question arises, whether the ice body aggraded prior to glaciation as massive segregated ice and was then deformed by glacier ice thrust. Or if the ice wasoriginally basal glacier ice that was buried by supraglacial till as a remnant of the Laurentide ice lobe.

Bibliography of Canadian Geomorphology