Detecting a shallow surface layer in Barkley Sound from Lagrangian drifter trajectories

Abstract

(Author abstract.) Fresh surface layers exist on the surface of fjords. In these areas, lighter freshwater from rivers flows over top of denser seawater from the ocean. A fresh surface layer creates stratification, which affects the distributions of biological organisms. It also greatly influences deep-water renewal in fjords since it resists vertical mixing. Low rates of vertical mixing in fjords can cause hypoxic and anoxic conditions at deeper depths. These conditions can kill fish and support bacterial communities that do not use oxygen for respiration. Studying shallower fresh layers can be challenging since their properties can change rapidly over only a few meters. Traditional water column profiling techniques may not adequate to define the existence of these layers. Drifters outfitted with GPS can be used to track water movements at varying depths. Comparing the movements of surface and subsurface water can indicate stability and layer individuality.