Low oxygen events in the Laurentian Channel during the Holocene

Geochemical and micropaleontological analyses were carried out on a 35 cm box core (CR06-TCE) spanning the last 6000 years in the Esquiman Channel, a northeast arm of the Laurentian Channel in the Gulf of St. Lawrence. A 0.6‰ decrease of δ18O in benthic foraminifer Globobulimina auriculata shells characterizes the upper 10 cm of the core and suggests a warming of the bottom waters. This change is concomitant with increased percentages of the low-oxygen tolerant benthic foraminifer species Brizalina subaenariensis and the Atlantic water species Oridorsalis umbonatus. Although a precise timing cannot be established, notably because of the smoothing effect of bioturbation, the amplitude of the trend recorded in the Esquiman Channel is coherent with that of the regional warming observed in the bottom water of the main axis of the Laurentian Channel over the last century. Warm bottom water conditions, however, are not exclusive to the recent time interval as shown by data from the lower part of the core, which are also characterized by low δ18O values in G. auriculata and occurrence of both B. subaenariensis and O. umbonatus. Such data suggest the existence of low-oxygen and relatively high temperature conditions in the bottom water of the Esquiman Channel about 4 to 6 kyrs ago likely related to enhanced inflow of Atlantic water in the Gulf of St. Lawrence through the Cabot Strait and the Laurentian Channel. These results highlight the sensitivity of bottom water properties in the Gulf of St. Lawrence to changes in the western North Atlantic circulation.