By lowering an electronic sensor package through the water using a winch we can measure the changes in water properties with depth. Temperature and salinity are basic parameters for oceanography, and can be used to compute water density. Ocean water is stratified - light water lies on top of heavy water - and changes in density from place to place drive currents. When heavy water appears on the continental shelf it can flow into the Sound, replacing the existing deep water in a process called "renewal".  Measuring the dissolved oxygen content helps in identifying this process - newer water tends to be higher in dissolved oxygen content than older water, because as water sits in one place decomposition of organic debris sinking down uses up oxygen. 

The plots below show water properties at the "Sarita Hole" Station, which is located in a 200m deep "hole" in Trevor Channel, off the Sarita River. Water properties here are representative of those over all of Trevor Channel and the lower reaches of Alberni Inlet.


Surface water temperatures rise over the summer time reaching almost 20C in August, and then fall through the winter down to about 7C in February.  Down to about 50m the temperatures play "catch-up" to the surface, but below 150m they respond to the influences of inflowing deep water and are coldest around June.


Surface salinities (measured more-or-less in ppt) vary a lot, especially in the winter. If we sample soon after a heavy rainfall the surface becomes very fresh, but this fresh layer soon becomes more salty as it mixes with deeper water.  Down deep the increase i salinity seen from May through to July occurs as saltier (and heavier) water flows in. Waters slowly become fresher the rest of the year as fresh water is slowy mixed down.


Although both salinity and temperature can affect water density, the effects of salinity are dominant. So-called "sigma" units are used, so that a density of 1024 kg/m^3 is written as "24".

Dissolved Oxygen

Dissolved oxygen content near the surface tends to remain near a "saturation" level with the atmosphere (around 6-7 ml/l). But note that oxygen levels can become very low at depth. In mid-summer waters below 50m are hypoxic (the white line shows this limit at 2 ml/l). Deep renewal in spring increases these levels slightly but they soon begin to drop again.

(O2 data not available Nov 2005-April 2006)


Phytoplankton are tiny plants (.2-100 microns in size) that grow in the upper levels of the ocean. These PRIMARY PRODUCERS convert carbon dioxide into oxygen! Their levels can be measured using a fluorometer, because chlorophyll - the actual part of the phytoplankton that absorbs sunlight - fluoresces.

Lighthouse Data Comparison

Are the surface waters of Barkley Sound similar to the ocean just offshore? This plot compares our data against the "lighthouse time series" of daily highwater temperature and salinity measured at the Amphitrite Point lighthouse (data available here).  The sheltered waters of the Sound get much warmer (in summer) and fresher (in winter) than ocean waters.

Bottom Renewal

Can we see the bottom renewal at work? The middle plot shows density deep within Trevor Channel ("Sarita Hole 170m") in blue, along with the density of bottom water in Imperial Eagle Channel (red). See how the red numbers are larger than the blue (heavier), "dragging" the blue up, during the summer. At the same time Oxygen levels are dropping, because the heavier ocean water is lower in oxygen. In the winter we get much lighter and oxygen-rich ocean water entering higher up in Trevor Channel (Sarita Hole 80m)

Last Updated Aug 23 2010
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