CTD and current meter data from the northwestern Gulf of St. Lawrence were analyzed to study the structure and variability of the Gaspé Current. Since the current is buoyancy driven, its properties are strongly influenced by the seasonal variation of the freshwater discharge from the St. Lawrence estuary. From June to November, maximum speed decreases from 110 cm s−1 to 60 cm s−1. High vertical shears exist in the upper 40 m of the water column. During the same period, the width of the current decreases, and the position of the current maximum shifts from near the shore to about 14 km from the shore. These changes in the structure can be understood in terms of geostrophy and baroclinic deformation radius. In the temperature/salinity field the most prominent change from June to November is the continuing increase of surface salinity. Temperature change occurs mainly in the September‐November period, when atmospheric cooling accelerates. The effect of atmospheric cooling is also reflected in the density distribution, with the result that in November currents in the upper 30 m are seaward in the entire section (from Sept‐Iles to Marthe de Gaspé), while in the summer months the currents are seaward in the southern part and westward in the northern part of the section. Momentum balance of the current system is also investigated. It was found that east of Pointe‐des‐Monts, geostrophic balance is maintained, while west of Pointe‐des‐Monts the observations do not seem to be consistent with the assumption of geostrophy.

This work utilizes remotely sensed thermal data to understand how the release of thermal pollution from the Brayton Point Power Station (BPPS) affected the temperature behavior of Narragansett Bay. Building upon previous work with Landsat 5, a multi-satellite analysis is conducted that incorporates 582 scenes from Landsat 5, Landsat 7, and Landsat 8 over 1984–2021 to explain seasonal variability in effluent impacts, contrast data after the effluent ceased in 2011, identify patterns in temperature before and after effluent ceased using unsupervised learning, and track how recent warming trends compare to the BPPS impact. Stopping the thermal effluent corresponds to an immediate cooling of 0.26 ± 0.1°C in the surface temperature of Mt. Hope Bay with respect to the rest of Narragansett Bay with greater cooling of 0.62 ± 0.2°C found near Brayton Point; though, cooling since the period of maximal impact (1993–2000) totals 0.53 ± 0.2°C in Mt. Hope Bay and 1.04 ± 0.2°C at Brayton Point. During seasons with lower solar radiation (winter) and lower mean river input (autumn and late summer), the BPPS effluent impact is more prominent. The seasonal differences between the high impact and low impact periods indicate that river input played an important role in the heat balance when emissions were lower, but surface fluxes dominated when emissions were higher. Putting the BPPS effluent in context, Landsat data indicates that Narragansett Bay warmed 0.5–1.2°C over the period of measurement at an average rate of 0.23 ± 0.1°C/decade and that net warming in Mt. Hope Bay is near zero. This trend implies that Narragansett Bay has experienced climatic warming over the past four decades on the scale of the temperature anomaly in Mt. Hope Bay caused by the BBPS effluent.