Ocean Networks Canada has a variety of pressure gauges deployed at most sites. On the VENUS observatory, the primary pressure sensor is the “depth” sensor on our Seabird CTDs, which measured the total water depth above the sensor, plus any atmospheric fluctuation/system passing overhead. The primary signal, evident on most of our plot gallery pages, are the tides, which have amplitudes of a few metres and are semi-diurnal, in that there are generally two high tides and two low tides each day (24-hour period). Superimposed on these tidal variations in total water depth are small signals associated with other long surface waves and atmospheric disturbances.

During a period last week (4 January 2012) there were a number of wave-like perturbations picked up across the pressure sensors on VENUS. Shown in the figure above are portions of the demeaned Seabird CTD pressure records from the Fraser Delta, Eastern Strait of Georgia, and Saanich Inlet sites (mean values of 107, 170, and 95.5 m respectively). As the tide nears high water at noon UTC on January 4, a series of “waves” is evident. In the figure below we have further processed these records to remove the tidal part of the signal (high-pass filtered). What remains is the fluctuating part of the pressure signal, where distinct wave-like oscillations of 4-5 cm height can be seen.

The source of these waves is not immediately known, although atmospheric fronts were passing through at the time, which can establish seiche-like modes in the basins and inlets that would cause oscillatory “sloshing”. The Eastern Strait of Georgia and Fraser Delta signals are nearly exactly in phase, while the Saanich Inlet variations are both out of phase and have a different (longer) period. Such waves do appear in the records occasionally, but usually only in one, or proximal, stations.