7
More research efforts have focused on tidal fronts than on any other frontal
types (Mann and Lazier 2006). Typical tidal fronts are seasonal and they establish each year at the same approximate time and location; and are characterized by
strong thermal gradients (Fig. 2.2a).
2.2 Shelf-Break Fronts
A linear zone of cool surface waters, supporting a plankton bloom, frequently
overlies the upper slope and shelf edge over continental shelves and other
banks elsewhere around the world ocean. Not all these fronts are forced by
the same mechanisms but the band of cold waters generally indicate entrainment of deeper, cooler, and nutrient-rich waters towards the surface. A widely
accepted explanation of this observation involves the generation of internal
standing waves on the thermocline at the shelf edge where the tidal stream
encounters rough topography on the seabed (Longhurst 1998), but various
alternative explanations involving small-scale eddies (coupled with episodic
wind stress) have also been proposed. Additionally, the interleaving of water
masses at the front could enhance vertical stability, retaining phytoplankton
Fig. 2.2 Frontal types. a Tidal front; b Shelfbreak front; c upwelling front (southern hemisphere); d estuarine front. f Front; sf shelfbreak; t thermocline; w wind; arrows are currents;
dashed lines are lines of equal density
2.1 Tidal Fronts
More research efforts have focused on tidal fronts than on any other frontal
types (Mann and Lazier 2006). Typical tidal fronts are seasonal and they establish each year at the same approximate time and location; and are characterized by
strong thermal gradients (Fig. 2.2a).
2.2 Shelf-Break Fronts
A linear zone of cool surface waters, supporting a plankton bloom, frequently
overlies the upper slope and shelf edge over continental shelves and other
banks elsewhere around the world ocean. Not all these fronts are forced by
the same mechanisms but the band of cold waters generally indicate entrainment of deeper, cooler, and nutrient-rich waters towards the surface. A widely
accepted explanation of this observation involves the generation of internal
standing waves on the thermocline at the shelf edge where the tidal stream
encounters rough topography on the seabed (Longhurst 1998), but various
alternative explanations involving small-scale eddies (coupled with episodic
wind stress) have also been proposed. Additionally, the interleaving of water
masses at the front could enhance vertical stability, retaining phytoplankton
Fig. 2.2 Frontal types. a Tidal front; b Shelfbreak front; c upwelling front (southern hemisphere); d estuarine front. f Front; sf shelfbreak; t thermocline; w wind; arrows are currents;
dashed lines are lines of equal density
2.1 Tidal Fronts