Raised Gravel Beaches as Proxy Indicators of Past Sea-Ice and Wave Conditions, Lowther Island, Canadian Arctic Archipelago

Abstract

ABStRACt. this study investigates whether raised beach sequences preserved on emergent coasts of the central Canadian Arctic Archipelago contain a proxy record of past sea-ice conditions and wave intensity. We hypothesize that periods of reduced sea ice (increased open water) expose shorelines to more prolonged and higher wave energy, leading to better-developed beach ridges. Surveys of raised beach sequences on Lowther Island revealed the following patterns: a) high, wide, single-to multicrested barriers backed by deep swales or lagoons characterize both the active and lowest relict shorelines; b) small, narrow, discontinuous ridges of poorly sorted gravel extend from 1.0 to 7.5 m asl, except from 4.5 to 5.0 m asl; c) ridge morphology is similar to the active and first relict ridges between 7.5 and 11 m asl; d) a near-featureless zone with minor terraces and ridges above 11 m extends to above 30 m asl. these distinct morphological and sedimentary units are interpreted as a function of wave climate and thus of summer sea-ice conditions. this model suggests periods

Coastal changes in the Arctic

“…In contrast to temperate and tropical coasts, coastal dynamics in the Arctic are generally limited to the short summer ice-free season of a few months' duration. Under the rapid climatic changes currently observed in the Arctic, early and more rapid sea ice retreat in the spring and later annual freeze-up are now resulting in longer open water seasons and coastal dynamics are consequently changing (St-Hilaire-Gravel et al 2010;Forbes & Hansom 2011). How sea ice and other changing drivers (storm frequency and distribution, air and water temperatures) shift coastal dynamics is the object of considerable study, and can be expected to vary at different spatial and temporal scales, depending on coastal morphology and interactions between land and sea.…”

“…In this context of forced regression, successive thin beach ridges are formed by local reworking of emerging nearshore deposits. Recent work by St-Hilaire-Gravel et al (2010) investigates whether raised beach sequences preserved on emergent coasts of the central CAA contain a proxy record of past sea-ice conditions and wave intensity. The study shows that morphological units within the raised-beach sequences of Lowther Island (Figs 13 & 14) are consistent around the island despite significant variations in underlying slope, orientation and the source and quantity of sediment supply from one site to another.…”

Palaeoshoreline records of glacial isostatic adjustment in the Dry Valleys region, Antarctica

“…In addition to these factors, the presence of ice has a strong influence on shoreline formation in polar environments (e.g. Butler 1999;St-Hilaire-Gravel et al 2010).…”

Glaciated Coasts

“…By contrast, a falling rela tive sea level in regions of postglacial rebound and uplift leads to progressive abandonment of thin coastal deposits as they are raised above the level of wave action. The limited time for erosion and longshore reworking of coastal sediments mini mizes the reworking of glacigenic sources, although the sand and gravel fractions of glacimarine deposits may be reworked onshore by waves or coastal ice (Reimnitz et al, 1990;St-Hilaire-Gravel et al, 2010). On the other hand, fluvial sedi ment supply to the coast may be enhanced in the context of forced regression (falling relative sea level) by reworking of emerged paraglacial delta deposits (Forbes and Syvitski, 1994).…”