Seasonal and spatial changes in the export and deposition of biogenic matter in a submarine canyon system of the Lower St. Lawrence Estuary, eastern Canada

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University of New Brunswick


The Pointe-des-Monts coastal shelf, located on the northern shore of the Lower St. Lawrence Estuary, hosts active submarine canyons. This work documents seasonal and spatial variations in biogenic matter export, inside and outside the canyon system, based on the analyses of 69 sequential sediment trap samples (November 2020 to September 2021) and 29 surface seafloor sediment samples. Our data reveal that small sediment resuspension events in the canyon impact biogeochemical cycling in the deep water-column layer. Sinking phytoplankton fluxes and deposited microfossil abundances were lower in the canyon system, providing no evidence that canyon processes enhance primary and secondary production at Pointe-des-Monts. The potentially harmful taxa Pseudo-nitzschia seriata, Dinophysis acuminata, and D. norvegica were observed in the sediment traps while cysts of cf. Alexandrium spp. were preserved in most surface sediment samples. The sediment trap samples cover an anomalous nearly ice-free winter, providing insight into future climate-related trends in biogenic export.