Post-glacial sea-level change along the Pacific coast of North America

Sea-level history since the Last Glacial Maximum on the Pacific margin of North America is complex and heterogeneous owing to regional differences in crustal deformation (neotectonics), changes in global ocean volumes (eustasy) and the depression and rebound of the Earth\u27s crust in response to ice sheets on land (isostasy). At the Last Glacial Maximum, the Cordilleran Ice Sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore. This, combined with different tectonic settings along the coast, resulted in divergent relative sea-level responses during the Holocene. For example, sea level was up to 200 m higher than present in the lower Fraser Valley region of southwest British Columbia, due largely to isostatic depression. At the same time, sea level was 150 m lower than present in Haida Gwaii, on the northern coast of British Columbia, due to the combined effects of the forebulge raising the land and lower eustatic sea level. A forebulge also developed in parts of southeast Alaska resulting in post-glacial sea levels at least 122 m lower than present and possibly as low as 165 m. On the coasts of Washington and Oregon, as well as south-central Alaska, neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea-level changes

A post-glacial sea level hinge on the central Pacific coast of Canada

Post-glacial sea level dynamics during the last 15,000 calendar years are highly variable along the Pacific coast of Canada. During the Last Glacial Maximum, the Earth\u27s crust was depressed by ice loading along the mainland inner coast and relative sea levels were as much as 200 m higher than today. In contrast, some outer coastal areas experienced a glacial forebulge (uplift) effect that caused relative sea levels to drop to as much as 150 m below present levels. Between these inner and outer coasts, we hypothesize that there would have been an area where sea level remained relatively stable, despite regional and global trends in sea level change. To address this hypothesis, we use pond basin coring, diatom analysis, archaeological site testing, sedimentary exposure sampling, and radiocarbon dating to construct sea level histories for the Hakai Passage region. Our data include 106 newly reported radiocarbon ages from key coastal sites that together support the thesis that this area has experienced a relatively stable sea level over the last 15,000 calendar years. These findings are significant in that they indicate a relatively stable coastal environment amenable to long-term human occupation and settlement of the area. Our results will help inform future archaeological investigations in the region