Subsurface Currents in the Strait of Georgia, West of Sturgeon Bank

Abstract

Spectral characteristics of subsurface currents and temperature records spanning 310–533 days from the Strait of Georgia near Sturgeon Bank are examined. Of particular interest are low-frequency fluctuations having a characteristic period of 30 days. Typically, the energy of the low-frequency and tidal currents are equal at 50 m (each about 40% of the total) and 10 and 70%, respectively, at 200 m.Low-frequency currents are observed to be baroclinic and possess a lateral length scale < 10 km. Their generation mechanisms are not identified. Low-frequency fluctuations in sea level and current have poor-to-fair coherence, while those in air pressure and current have poor coherence. Low-frequency fluctuations in wind and current have fair coherence at the eastern mooring and poor coherence at the remaining two moorings.Fluctuations in water temperature have a characteristic period of 300 days. Water temperatures at different locations generally have poor coherence except at the lowest frequencies where they are fair to good. Water temperature and current at the same location have poor coherence.Tidal currents are found to be ellipses, with the largest constituents being M2 and K1. The magnitude, shape, and orientation of the tidal current ellipses are time-dependent. Internal tides are suggested as an explanation.