ABSTRACT: Deglacial sea level along Eureka Sound: the effects of ice retreat from a central basin to alpine margins.

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Abstract

Postglacial emergence in the Queen Elizabeth Islands (QEI) displays a prominent ridge reaching 150 m asl that extends through the axis of Eureka Sound. This ridge forms part of the Innuitian uplift which was attributed to the axis of maximum former ice thickness of the Innuitian Ice Sheet (IIS). For more than two decades, the validity of the IIS during the Last Glacial Maximum (LGM) has been debated. This was because fundamentally different ice loads (ranging from the IIS to smaller, non-contiguous, ice caps) were invoked to explain the Innuitian uplift in the absence of unequivocal geological evidence. Recent fieldwork, by independent investigators in different parts of the QEI, now confirms the presence of the IIS during the LGM. This demonstrates the linkage between maximum postglacial emergence and maximum former ice thickness in this region. During the LGM, Eureka Sound was infilled by glaciers that advanced from ice caps on the encircling mountains of Axel Heiberg and Ellesmere islands. Hence, the geographic centre of this part of the IIS (Eureka Sound) was a basin that constituted the centre of glacial loading. Because Eureka Sound subsequently became ice-free, it also experienced the greatest glacial unloading as ice retreated towards the alpine margins (where it persists today). Deglaciation of Eureka Sound occurred sometime between ~10.5 ka and 9.0 ka BP when the sea gutted the axis of the IIS. The rapid breakup of the central axis of the IIS, predominantly by calving, explains the paucity of geological evidence left by its retreat along Eureka Sound. Continued retreat onto land-based margins occasioned lower rates of ablation, hence stabilization and conspicuous deposition around many fiord heads between ~ 9 ka and 8 ka BP. The sea level record throughout Eureka Sound and its adjacent fiords is dominated by this pattern of deglaciation. Marine limit descends from ~150 m asl along parts of Eureka Sound to =100 m asl at many fiord heads. It is emphasized that this pattern of ice retreat took place down-isobase (away from the axis of maximum glacier unloading). This pattern of retreat can only amplify (and never mute) the amount of differential emergence as recorded by non-synchronous marine limits (vs. true isobases). This is because 'restrained rebound' is minimized at the former loading centre (where, uniquely, marine limits are highest and oldest). Differences between the age and elevation of marine limit reported across Ellesmere Island require rapid initial emergence in Eureka Sound (vs. site-specific evidence for slow initial emergence reported elsewhere). Reconstruction of the sea level history around Eureka Sound faces persisting stratigraphic and chronologic problems due to its style of deglaciation.

Bibliography of Canadian Geomorphology