Deglaciation history and relative sea level changes since the Last Glacial Maximum in the southern Gulf of St. Lawrence, Canada

During the last glacial period, continents and surrounding shelves in high latitude regions of the Northern Hemisphere were covered by ice sheets. Their retreat during the late Pleistocene and Holocene resulted in isostatic adjustments of the previously glaciated landmass, which influenced post-glacial changes in relative sea level (RSL). Many questions, however, remain about the timing and impact of the ice retreat on the continental shelf environments and RSL after the Last Glacial Maximum, and of short-lived climatic events, such as the Younger Dryas. This study aims to reconstruct the deglaciation history and changes in RSL for the southern Gulf of St. Lawrence off Prince Edward Island on the eastern Canadian continental shelf for the past 14 ka, and to determine the influence of the Younger Dryas on the ice margin. Using information from sub-bottom profiles, sediment cores, and multibeam bathymetry, this study finds that most of the continental shelf was already flooded 13.6 ka ago, as evidenced by the presence of Bølling-Allerød marine sediments at a modern water depth of less than 50 m and ~15 km off the modern coastline. During the Younger Dryas cooling event, sedimentation rates increased from 0.1 to 1 cm a-1, likely as a consequence of readvancing ice masses. We observe an erosional truncation on top of the Younger Dryas sediment package, which presumably indicates a drop in RSL in the early Holocene. Based on our new data, we propose an updated RSL curve for the region that accounts for the presence of sea ice coverage rather than complete ice coverage as well as a geological model highlighting the sedimentation history over the past 14 ka and role of the Younger Dryas. The new paleo-environmental and RSL reconstructions shed light on the potential impact of short-lived climatic events at the former ice margin during deglaciation and reduce uncertainties for about past sea level changes.