Documenting recent sea-level rise and coastal squeeze in eastern Quebec using salt-marsh foraminifera and plant macrofossils

English Abstract:

Global sea-level is expected to continue rising throughout the 21^st century, according to the Intergovernmental Panel on Climate Change (IPCC). Parts of eastern Quebec, Canada, are likely to experience higher than average relative sea-level rise due to ongoing land subsidence associated with the last glaciation. Current and increasing urban development along Quebec coastlines (buildings and roads) gives rise to the threat of coastal squeeze. Our knowledge of recent sea-level rise in the region is limited due to short reliable tide gauge data which only extends back to the 2000s. Proxy data is required in order to investigate patterns of past sea-level changes. We aim to investigate coastal ecosystem changes at Saint-Omer, Baie-des-Chaleurs, caused by late Holocene sea-level rise and to generate a new late Holocene sea-level reconstruction at this site.

We analysed the stratigraphy of a Spartina salt-marsh at Saint-Omer which documents a regression, followed by continuous transgression until today. Silty clay, sand and lean clay units are found at the base of the sequence, between 0.85 and 0.60m. These are overlain by organic rich muds which transitions to an organic rich clay unit that caps the sequence. A sediment core, representative of the salt-marsh sediment sequence found at Saint-Omer, was taken from the high marsh zone and subsampled for plant macrofossils, foraminifera, geochemical analyses and for dating. Training sets of contemporary salt-marsh foraminifera were developed from sampling along surface transects of known elevation. These training sets will be used to build a local transfer function so that surface foraminifera assemblages can be used to estimate palaeo-marsh surface elevations (and thereby sea level) from fossil foraminifera assemblages analysed from the sediment core. These new data will help describe recent changes in local sea level and document the effects of coastal squeeze at Saint-Omer, necessary for future coastal management decisions.