I was volunteered to present a simplified version of my research to a group of visiting politicians yesterday. I was given exactly 3.5 minutes to present starting at 3:13 pm, I guess politicians live in a precise world (as we all expected they showed up somewhat late). So here is what I said:
The focus on my research in on how the tides interact with Fraser Ridge (a sub-surface bump in the Strait of Georgia). One really interesting effect is the formation of lee waves on the flood tide. Ocean waters tend to be stratified, which means the water is organized so the denser water sits lower than the less dense water. As tides move this water over an obstacle like Fraser Ridge, water is forced to speed up because of the constricted space and it gains momentum. On the lee side of the obstacle the momentum can carry less dense water down deep. Eventually, friction causes the water to slow and the less dense water bounces back up in a formation called a lee wave. Effects like these lee waves can provide an explanation why some coastal sites form productive ecosystems.
What is interesting about Fraser Ridge is that a rare glass sponge reef has made its home there. Glass sponge reefs were once common in the world’s oceans at the same time that dinosaurs roamed the earth. Like the dinosaurs, we thought glass sponge reefs were extinct. In the 1990s, living glass sponge reefs were discovered in a few locations off the coast of BC and it turns out they make great habitat for young rock fish. Glass sponges are filter feeders fixed to the bottom so they need enough flow to bring in their food, remove their waste and keep them from being buried in sediment. Periodic formation of lee waves can provide the flow they need.
At my study site, a lee wave forms on each flood tide. The sponges have chosen to live on the steepest slope which corresponds to the strongest currents, turbulence and sharpest lee wave.