OCEAN DYNAMICS LABORATORY
Prof. Rich Pawlowicz
Phone: (604) 822-1356
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To really understand what this amplification factor is (and why), we have to understand the processes of mixing. There are different kinds of mixing - we need to understand things like where, and how much, and when it occurs. Much of the mixing happens in the Gulf Islands region. But should we consider the islands to act as a kind of "egg-beater" as the tides slosh water back and forth? Should we rather think of the mixing as being driven by bottom turbulence? Or is something else important? The bathymetry is dominated by two sills; this has led to speculation that a physical process known as hydraulic control(and the turbulence generated in the hydraulic jumps downstream of the control) may be important.
These are important questions. Unfortunately, they are also difficult to approach directly. The intense turbulence that occurs in this region manifests itself on many scales. This picture shows a ``boil'' some 20m across occuring at the meeting of two streams as they join in the lee of an island. Such features are sometimes powerful enough to spin large ships around, and their time scale is measured in minutes! Because of this variability direct measurements (e.g. from current meters) are not necessarily useful for understanding the larger scales (for more information about what causes these boils see Farmer, Pawlowicz, and Jiang, Dynamics of the Ocean and Atmosphere, 2002).
To look at the big picture new ideas are called for!
During a field program in 1996, I noticed that plots of temperature vs. salinity for the waters in this region showed an interesting curved nature. A simple mixing process would result in a straight T/S correlation. Analysis of this data [Pawlowicz and Farmer, J. Geophys. Res. , 1998] indicates that this curved nature arises from the effects of surface heating, and gives us a handle on trying to estimate bulk mixing rates. In the summer of 1998 I went back into the field to get more data on this effect, and to extend the results over a wider area. The figure at right shows the results. Individual vertical profiles are colour-coded from red (Strait of Georgia) to black (near the mouth of Juan de Fuca Strait). Notice that the slope of the black curves is steeper than the red ones. Using this data as well as some mathematical theory developed for this problem calculated the average in- and out-flow at various points in this region, as well as estimates of bulk mixing [Pawlowicz, Estuarine Coastal and Shelf Sciences, 2001].
One exciting application of this work is to determine the fluxes of other materials - for example, the flux of nutrients. Currently we are trying to use this approach to get a better idea of what the seasonal changes are, and by measuring nutrients (nitrate, silicate, and phosphate) attempting to better understand changes in these biologically important parameters. During 2002-2006 I was one of the primary investigators in the Strait of Georgia Ecosystem Monitoring Project (STRATOGEM) [Pawlowicz, Halverson and Riche, Atmosphere-Ocean, 2007].
Recently this has has gotten me involved in a large multi-investigator project, the Rivers Inlet Ecosystem Study , in remote Rivers Inlet, BC, where we are trying to understand just why the salmon have stopped coming into what was until about 20 years ago the 3rd largest run of sockeye salmon in British Columbia.
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Currently Caixia Wang (Ph.D. Candidate) is trying to use this system to understand the dynamics of internal wave propagation in the Strait of Georgia. The thumbnail at left shows an aerial photo taken from 500m looking down at an internal wave packet. Although internal waves are waves on a deep density interface, they can be seen from the surface because they change the surface waves overhead (making rough and smooth patches which you can see in the upper part of the photograph, or because the water in them is a different colour - the green lines at the bottom of the photograph). The red dot at center left is the Coast Guard Hovercraft SIYAY (length 30m) , outfitted with a CTD to measure temperature/salinity/density profiles, as well as an Acoustic Doppler Current Profiler (ADCP) to measure currents associated with these waves. If you click on the image you can see the internal waves much more clearly.
In 2007 I was part of cruise to Knight Inlet, where I made many more
cool movies of internal waves being formed on
the famous sill there.
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Following this study, we investigated anoxic Nitinat Lake on the West Coast of Vancouver Island (which, despite its name, is actually a fjord filled with seawater). In collaboration with B. Laval (UBC Civil Eng.) and S. Baldwin (UBC Chem and Biological Eng.) we discovered how this fascinating system, which is 200m deep with deadly anoxic water coming as close to the surface as 3m in late summer (and, paradoxically, is the site of the largest chum salmon hatchery in Canada) "works" [Pawlowicz et al., Limnology and Oceanography, 2007].
More recently, I have been working in Powell Lake. Powell Lake looks
normal enough on the surface, and is about 50m above current sea level.
However, it contains seawater at the bottom of
two of its basins. This seawater was trapped after the coastal
land mass rebounded upwards at the end of the last ice age
about 10,000 years ago. This ancient seawater is filled with
various gases (water samples "fizz" like very smelly champagne),
and geothermal heat which result in double-diffusive layering
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|| This is a project we have started at UBC to try
and understand the coupled biology and physics of the Strait of Georgia
and there is far more to say about it than I want to type here (but you
can see Shannon and Carla doing chemistry on the back deck of the hovercraft
at left - hope they don't turn that fan on!). For more details see the Strait of Georgia Project Web page, www.stratogem.ubc.ca.
Spring 2005...48 sampling trips into the Strait of Georgia and DONE!....data summary seen at right:
Working in lakes and the ocean got me interested in trying to understand how these water conduct electricity. This may seem a bit odd, but in fact the electrical conductivity is proportional to the amount of dissolved ions in the water. In fact, measurements of conductivity are the primary (and often only) way that oceanographers and limnologists have to describe the salt content. But no-one really knows how to predict the conductivity for a given chemical composition - until [Pawlowicz, Limnology and Oceanography:Methods, 2008] which describes a numerical I model I wrote to do this.
This work has gotten me involved in SCOR Working group 127, and part of the team developing the new international Thermodynamic Equation of Seawater (TEOS-10) , now THE accepted method for the estimation of the properties of seawater!
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Last changed 30/Aug/2013. Questions and comments to Rich Pawlowicz, mailto:firstname.lastname@example.org