Micropaleontological and geochemical analyses of a sediment core collected in the Laurentian Trough of the Gulf of St. Lawrence were carried out to reconstruct temporal variations in pelagic productivity and benthic environmental conditions. Dinoflagellate cyst assemblages reveal relatively stable pelagic productivity over the last two centuries. Similarly, geochemical (organic C, C org : N) and isotopic (d 13 C org , d 15 N) data reveal that organic matter fluxes to the seafloor have been relatively constant over the same period. In contrast, significant changes are recorded in the benthic foraminifer assemblages. A sediment surface peak in the abundance of Cassidulina laevigata and Brizalina subaenariensis is consistent with the recent record of oxygen depletion in the bottom water. A decrease in the relative abundance of Nonionellina labradorica, concomitant with a relatively higher occurrence of Oridorsalis umbonatus in the upper part of the core, reflects a significant warming of the bottom water. Changes in bottom-water properties are further constrained by a negative trend of the d 18 O in Bulimina exilis carbonate shells over the last century, corresponding to a warming of about 2uC. These results strongly suggest that the recent oxygen depletion in the bottom waters of the Gulf of St. Lawrence is due to changes in water masses that have led to increased bottom-water temperatures and, to some extent, a resultant increase in organic matter respiration rates.Eutrophication is often identified as the main cause of bottom-water hypoxia (, 2 mg L 21 or 62.5 mmol L 21 ) in coastal environments (Cloern 2001). In the Lower St. Lawrence Estuary (LSLE), direct measurements have documented a progressive depletion of dissolved oxygen (DO) in bottom waters (. 250 m), from , 125 to 60 mmol L 21 over the last 80 yr (Gilbert et al. 2005). These observations are consistent with results of micropaleontological and geochemical analyses of sediment cores that show clear evidence of bottom-water oxygen depletion since the 1960s (Thibodeau et al. 2006). Whereas one half to two thirds of the oxygen depletion has been ascribed to a change in ocean circulation in the northwest Atlantic and, thus, variations in the water properties (DO, temperature, salinity) of the bottom waters that enter the Gulf and St. Lawrence through Cabot Strait (Gilbert et al. 2005), the remainder has been speculatively associated with increased organic carbon (C org ) fluxes to the seafloor, possibly due to anthropogenic eutrophication (Thibodeau et al. 2006). Thibodeau et al. (2006) and Gilbert et al. (2007) have shown that increases in sales of agricultural fertilizers, especially nitrogen fertilizers, in the St. Lawrence River drainage basin are concurrent with the depletion of bottom-water oxygen concentrations in the LSLE. Finally, an increase in bottom-water temperatures (Gilbert et al. 2005), leading to increased respiration rates, could also explain the recent decrease of DO concentrations.To determine if eutrophication and the trend ...