Rapid sea-level change and coastal evolution on the Pacific margin of Canada

Abstract

Abstract A rapid regression occurred off the northern Pacific margin of Canada approximately between 14,600 and 12,500 14C years B.P., contemporary with the deglaciation of the continental shelf, primarily due to the rapid isostatic rebound. Sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12,400 14C years B.P., after which a rapid transgression occurred. At 12,500 14C years B.P., the shelf tilt across the northern Pacific margin of Canada ranged between 50 m of submergence at Prince Rupert on the British Columbia mainland to greater than 150 m of emergence on the western edge of the Queen Charlotte Islands. This regressive/transgressive cycle lasted only from 5200 to 5500 14C years, a result of the development and collapse of a glacioisostatic forebulge. Sediment supply, wave action and tidal-current energy are the primary factors that controlled the coastal response to these late Quaternary relative sea-level changes. Plate tectonics, on the other hand, played a secondary role in coastal evolution. During deglacial regression, extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break. During the transgression of the shelf, the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits, resulting in the formation of drowned wave-cut terraces, spit platforms and modification of estuarine environments, as the sea level rose in steps. The present unconsolidated coastline is mostly erosional. During the most recent ENSO event, the sea-level rise of up to 0.4 m resulted in as much as 12 m of coastal retreat.