Deciphering patterns of postglacial sea level at the junction of the Laurentide and Innuitian Ice Sheets, western Canadian High Arctic

Abstract

Recent sampling of deglacial and postglacial raised marine sediments across Melville and Eglinton islands in the western Canadian High Arctic yielded over 200 new radiocarbon dates on molluscs, driftwood and other organic materials. From this database, eight relative sea-level curves and an isobase map for the 9.5 cal ka BP shoreline were constructed. The forms, chronology and pattern of the relative sea-level curves across the study area reflect the complex glacial history of this region, including the asynchronous retreat of the formerly coalescent Laurentide and Innuitian Ice Sheets. Zone I relative sea-level curves, which show continuous emergence to present, were observed in areas closer to greater Last Glacial Maximum ice sheet loading; at more distal sites, transitional Zone I/II curves display emergence followed by submergence in the mid- to late-Holocene (still ongoing) related to forebulge migration and collapse. An independent record of late Holocene submergence is provided by radiocarbon-dated driftwood, which is accumulating at modern sea level due to re-deposition during transgression. Geomorphic evidence of submergence at the modern coastline is widespread but does not distinguish areas that experienced a late Holocene lowstand and subsequent transgression from those that are currently at their lowstand. Of special interest are the relative sea-level histories of two areas that experienced earlier deglaciation by the Laurentide Ice Sheet, while remaining in the peripheral depression of the more stable and adjacent Innuitian Ice Sheet. The flat-topped relative sea-level curves from these sites appear to record unusually slow rates of glacioisostatic emergence for ∼1500 years immediately following deglaciation. The relative sea-level data presented in this paper provide important comparisons for sea level models, which have been shown to fit poorly with previously published data from this region.