Upwelling spike and marked SST drop after the arrival of cyclone Dorian to the Atlantic Canadian coast

Abstract

In intertidal environments, temperature changes at hourly scales are ecologically relevant because of the physiological stress that organisms must endure as a result. Tides constitute the main source of such changes, as low tides periodically expose intertidal habitats to aerial conditions, which can exhibit extreme high and low temperatures in summer and winter, respectively. This study identifies a source of strong hourly thermal variation that acts upon seawater temperature. Hours after the arrival of cyclone Dorian to the Atlantic Canadian coast in September 2019, intertidal loggers revealed that sea surface temperature (SST) decreased by 10–12 °C. Online data indicated that neither tidal amplitude nor air temperature were responsible for this marked SST drop. Conversely, data on wind speed and direction strongly suggest that a pronounced spike in coastal upwelling caused by this cyclone drove the sharp drop in intertidal SST. Bakun's upwelling index, for instance, peaked at 689 m3 s−1 (100 m of coastline)−1 a few hours after Dorian's landfall. It remains to be seen how this marked SST drop may have affected intertidal organisms, as they were then acclimated to summer conditions. As the frequency and intensity of cyclones are predicted to increase with climate change in temperate latitudes, cyclone-related intertidal thermal ecology might deserve further attention.