Tidal mixing is recognized as a key mechanism in setting water
properties in coastal regions globally. Our study focuses on Canada's
British Columbia coastal waters, from Queen Charlotte Strait to the
Strait of Georgia. This area is bisected by a region of exceptionally
strong mixing driven by some of the strongest tidal currents in the
world. We examine the influence of this tidal mixing on regional
differences in water properties and nutrient ratios. Our results
quantify a spatially-abrupt and temporally-persistent lateral gradient
in temperature, salinity, and density co-located with the region of
strongest mixing. The distributions of density on either side of this
front remain largely distinct throughout the spring-neap tidal cycle,
year-round, and for over 70 individual years for which data are
available. Additionally, nutrient molar ratios north of the front are
statistically distinct from those to the south. Seasonal changes driven
by the arrival of upwelled water differ in both timing and magnitude on
either side of the front. Taken together, these results indicate limited
exchange of water through the region of strongest tidal mixing, and
suggest that Queen Charlotte Strait and the Strait of Georgia are
largely isolated from each other. As such, this area provides a valuable
case study for the degree to which the reduction of estuarine exchange
by tidal mixing can maintain abrupt and substantial regional differences
in physical and biogeochemical water properties. Further, it
demonstrates the potential of tidal mixing to modify nutrient transport
pathways, with implications for marine ecosystems.