ABSTRACT: Stable isotope and hydrochemical signatures of massive ground ice on Herschel Island (Western Canadian Arctic).

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

Herschel Island (69.583°N; 139.083°W) lies off the Yukon Coastal Plain in the southern Beaufort Sea as a terminal moraine resulting from the Laurentide Ice Sheet during the Early to Middle Wisconsin and represents the likely easternmost edge of Beringia. Massive ground ice bodies in the island’s permanently frozen ground are ubiquitous and contribute to the shaping of the landscape since deglaciation. Stable water isotopes (d18O, dD) have been analysed on various ground ice types. Since ground ice is a valuable record of climate information it can be used for palaeoenvironmental interpretation. Ice wedges on Herschel Island have begun to form in outwash and morainic deposits during the late Pleistocene after deglaciation, when dry and harsh climatic conditions promoted frost cracking. These ice wedges are remarkably depleted in their isotopic signature (d18O of around -29 ‰) compared to Holocene ice wedges (d18O of around –24 to –21 ‰). Within ice-rich permafrost sediments, also massive ice bodies are exposed whose appearance and isotopic composition is completely different from all other sampled ground ice types. Their d18O records are strongly depleted (-33 ‰) thus suggesting a late Pleistocene origin. The slope and d-excess lie near the Global Meteoric Water Line (GMWL) indicating that the moisture source is likely of meteoric origin without substantial alterations. Other massive ice of unknown but supposedly glacial origin was encountered adjacent to large, striated boulders. With about -37 ‰ for d18O, the ice exhibits extremely low isotopic values. The question arises, whether the ice bodies aggraded before or after deglaciation as massive segregated ice or if the ice was originally basal glacier ice buried by supraglacial till. Stable isotope geochemistry is limited to unravel the nature and origin of recovered ground ice. Therefore, hydrochemistry (pH, electrical conductivity, major ions) is used to differentiate between massive segregated ice, buried glacier ice and buried lake ice. Usually, buried ice types have low conductivity values as they derive from meteoric water. Thus, they are dominated by calcium (Ca2+), bicarbonate (HCO3-) and sulphate (SO42-). In turn, massive segregated ice represents frozen ground water and therefore re?ects the sediment ion composition. High electrical conductivity values (>1000 µS cm-1) and a broad mixture of signi?cantly occurring ions with peaks in sodium (Na+), strontium (Sr2+), and chloride (Cl-) are obvious. Therefore, massive segregated ice hydrochemical data resemble the Herschel Island sediments that derive from near-shore marine deposits upthrusted by the Laurentide Ice. Ongoing processing of stable isotope and hydrochemical data from ground ice will enable us (1) to provide solid evidence of the timing and the spatial extent of late Pleistocene glaciations on the Yukon Coastal Plain, and (2) to precise the age of the deposition and the processes responsible for the formation of Herschel Island.

Bibliography of Canadian Geomorphology