Arctic Gravel Beach Morphodynamics under Changing Relative Sea Level and Environmental Forcing, Canadian Arctic Archipelago.

摘要

This thesis examines the morphodynamic response of Arctic gravel beaches to changes in relative sea level (RSL) and environmental forcing. More specifically, it considers the interplay between the four dominant controls on Arctic coastal dynamics -- RSL, wave and sea-ice climate, sediment supply and basement topography -- along an east-west transect in the central and eastern Canadian Arctic Archipelago (CAA) encompassing a wide range of RSL trends and environmental forcing. Data sources include coastal surveys, both onshore and offshore, airphotos, satellite images, and archived climate data. From west to east, these studies make the following contributions. The potential of gravel beach morphology and sedimentology as a proxy for past sea-ice conditions is explored on the raised-beach sequences of Lowther Island, central CAA. Despite significant variations in slope, orientation, sediment source and supply around the island, beach morphology is strikingly similar within discrete elevational zones. These morphological patterns are explained in terms of variability in sea-ice intensity, which, through its impact on wave climate, has most likely been the predominant control on the gravel beach morphology of Lowther Island for the past 6500 years. A multi-temporal analysis of the gravel-dominated coastline of the Resolute area, central CAA, reveals that gravel beaches in that area are moderately low-energy systems susceptible to reworking by moderate storms, recurring at intervals of 1-10 years, but are nevertheless quite resilient in the face of such storms. The prograding, seaward-rising ridge crests at the Cape Charles Yorke foreland, northern Baffin Island (eastern CAA) result from a combination of rising RSL and abundant sediment supply. A more recent shift from progradation to erosion on the gravel beach ridges of the foreland may be a response to decreasing sediment supply, increasing accommodation space, increased wave energy, and/or accelerated RSL rise, which acts as a passive control on wave reach and accommodation space. Collectively, the thesis results contribute to a better understanding of the importance of i) sea ice in the development of Arctic gravel beaches; ii) the short and long-term coastal impacts of storm events; and iii) the morphological outcomes of the interplay between rate and direction of RSL change and sediment supply. These results provide new insight for more effective management of coastal dynamics and related hazards as they affect Arctic coastal communities and infrastructure.