Using the δ18O-Salinity Relationship to Identify Freshwater Inputs to a North Atlantic Estuary

Abstract

The δ18O-Salinity relationship allows us to define distinct end members in Bedford Basin, a system supplied by the North Atlantic Ocean. An isotopic analysis was performed on water in and around Bedford Basin to resolve contributions of offshore water, river water, and precipitation throughout the year. All freshwater inputs were found to co-vary when an annual cycle was defined, however there is a significant seasonal difference between the δ18O of winter and summer freshwater inputs, leading to their selection as end members. Bedford Basin surface (1 m) samples confirm a dominant input of offshore water (~88%) and minimal freshwater input, dominated by “summer” precipitation, while deep samples (60 m) show even less freshwater from land (<3%). At 60 m, the zero-salinity intercept of the δ18O-S relationship suggests that offshore freshwater dominates stable bottom waters (-15.55‰), and only bottom waters mixed with Bedford Basin surface water show freshwater from land (-7‰).