Benthic Foraminiferal Assemblages from the Laurentian Channel in the Lower Estuary and Gulf of ST. Lawrence, Eastern Canada: Tracers of Bottom-Water Hypoxia

Over the past century, an increase in temperatures anda decrease in dissolved oxygen concentrations have beenobserved in the bottom waters of the Laurentian Channel(LC), throughout the Lower St. Lawrence Estuary (LSLE)and the Gulf of St. Lawrence (GSL), eastern Canada. To documentthe impact of these changes, we analyzed the benthicforaminiferal assemblages and geochemical signatures of foursediment cores taken in the LC. Radiometric measurements(210Pb, 226Ra, 137Cs) indicate that the studied cores encompassthe last 50 years of sedimentation in the LSLE and thelast ∼160 years in the GSL. The sedimentary record showsa 60 to 65% decrease in benthic foraminiferal taxonomicdiversity in the LC since the 1960s. An accelerated change inthe foraminiferal assemblages is observed at approximatelythe same time at all studied sites, around the late 1990sand the early 2000s, towards populations dominated by thehypoxia-tolerant indicator taxa Brizalina subaenariensis,Eubuliminella exilis, and Globobulimina auriculata. Thisevolution of assemblages reflects incursions of the hypoxiczone into the western GSL over the last decades. The resultsof our multivariate analyses highlight the potential ofbenthic foraminiferal assemblages as a proxy of bottom-waterhypoxia.