OCEAN DYNAMICS LABORATORY

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OCEAN DYNAMICS LABORATORY

Prof. Rich Pawlowicz
Dept. of Earth and Ocean Sciences
University of British Columbia,
6339 Stores Rd.,
Vancouver, B.C. Canada
V6T1Z4

Phone: (604) 822-1356
Fax:(604) 822-6088
Email: rich@eos.ubc.ca

Faculty
 
  • Rich Pawlowicz 

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    Current Graduate Students
     

  • Ben Scheifele (M.Sc. Candidate, 2011-)
  • Chuning Wang (M.Sc. Candidate, 2012-)
  • Artem Zaloga (M.Sc. Candidate, 2013-)

  • CurrentPost-doctoral Fellow

  • Mark Halverson (2013-)



  • Past Graduate Students
     

  • Mark Halverson (Ph.D. 2009)
  • Caixia Wang (Ph.D. 2009)
  • Mike Hodal (M.Sc. 2010)
  • Olivier Riche (Ph.D. 2011)

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    Undergraduate Students

  • Darren Thomson (summer 2002)
  • Amber Kelter (fall/winter 2002/3)
  • Kyla Drushka (summer 2004)
  • Marianne Jensen (2004-2005)
  • Megan Wolfe (2005-2006)
  • Melissa Rohde (summer 2006)
  • Adrian Jones (2010-2011)
  • Marianne Williams (summer 2011)
  • Tara Howatt (fall 2012)

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    Student Opportunities

    There are opportunities for study and/or work at both undergraduate and graduate levels. Graduate projects are possible in most of the larger  programs underway; math skills as far as (and including) partial differential equations in the 3rd or 4th year of an undergraduate degree are a prerequisite. Generally there are one or two positions for undergraduates during the summer (NSERC USRAs are welcome).  Physics, computer, and/or math skills are desirable, as is a desire to get your hands dirty doing fieldwork! Contact Rich Pawlowicz for more details.

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    Research Projects

    Coastal Mixing Processes - Bulk Flow, Mixing, and Mass Fluxes

    The Straits of Georgia and Juan de Fuca  form a large estuary on the west coast of Canada. Fresh water from river runoff, primarily from the Fraser river, flows out into the Strait and forms a large, thin buoyant layer only a few meters thick. This plume then flows out towards the Pacific, passing through a small band of islands between the two Straits. These islands are called the Gulf Islands in Canadian Waters, and the San Juan Islands in US waters. Depths in the Strait of Georgia reach 400m, whereas those in the Straits of Juan de Fuca are closer to 200m. Within Haro Strait and Boundary Pass, the major channel through the Gulf Islands, are two shallow areas (or "sills") with depths of about 100m, separated by a deeper region (depth 400m).

    As the surface waters move seaward, they mix with the salty waters below (as shown in the schematic figure above). Thus there is a net seaward flow of salt in the upper waters. In a steady state system there must then be an inflow of salt in the deeper waters. Over most of this region, we can see evidence for this two-layer flow pattern. Note that the because of the mixing, the amount of water actually moving in either of the two layers is much greater than than flowing in the rivers which drive the circulation. How much more is difficult to say - but the ESTUARINE AMPLIFICATION factor is probably 10-20.

    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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    Internal Tides and Mixing

    Acoustic methods have shown great promise in making rapid and accurate measurements of currents. The Acoustic Doppler Current Profiler (ADCP) is a new instrument especially developed for oceanographic use. It allows the almost instantaneous measurement of currents from the surface down to the bottom some 400m away. A complete three-dimensional view of the flow field can now be obtained as fast as a ship can travel. I hope to use data from such an instrument to quantify both the mean and turbulent parts of the flow field, exploring the region to map and understand mixing and internal soliton and bore processes.
    Here's an example, from data collected during the Haro Strait Experiment. The upper panel shows backscatter from a 100kHz echosounder over a period of about 1 hour as we transit an area of boils. The red plumes projecting downwards represent intense concentrations of bubbles sucked down to 100m below the surface.The second panel shows temperatures, measured by to-yo-ing a CTD. These bubble plumes are associated with warm surface water (orange and red colours). The lowest panel shows vertical velocities measured using an ADCP, with red for upward and blue for downward velocities. Vertical velocities are greater than 50 cm/s in the intense plume at the center of the strip, a very large number indeed!
    Recently, using a simple linear analysis,  [Pawlowicz, JGR, 2002]  I found an internal tide of amplitude 1 m/s in velocity and 40m in height in Haro Strait. I am very excited by this - you don't often get such simple explanations for what looked like a very complicated set of observations. However, the amplitude of the wave is big enough that nonlinrear effects must be important. The picture at right shows an ADCP transect down through the crest of this internal tide.  It doesn't look like much, but in fact it is telling us that a fascinating phenomenon called an internal hydraulic drop is occurring.
     
     











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    Flow visualization using Time-Lapse Photography

    Many of these complicated subsurface features have a surface expression - like the boil shown above. In order to get a better understanding of the shape an evolution of such features I have begun experimenting with time-lapse photography . It turns out that there are all kinds of interesting things occurring in Haro Strait! Clicking here or on the still image at left will let you see a 2Mb MPEG movie of features near the southern end of Haro Strait  in July 1999 (Note - you need a full mpeg viewer to correctly view this movie).  The original images taken over a 7 hour period have been rectified onto a map; the green line shows the SW coast of San Juan Island and the magenta lines are the 250m isobaths on either side of the deep channel.  Tidal elevation and currents are shown at right. Note the internal waves propagating across the Strait (diagonal dark lines moving towards the upper right) near slack water, followed by a northward-travelling "bore" near the coast during the flood tide. Thick fast-moving streaks are freighters, thin streaks are smaller craft.

    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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    Lake Dynamics

    Lakes aren't oceans, but some of the lakes in the interior of British Columbia can get pretty big. Working with R. Pieters of the Environmental Fluids Lab we have been
    studying the dynamics of Harrison Lake, which is 60km long and almost 300m deep. The inflowing Lillooet River at the northern end has a strong turbidity signal which can slowly be tracked down the lake through summer months.

    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 at depth.  
     





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    Strait of Georgia Project




    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:




    Conductivity of Natural Waters



    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:rich@eos.ubc.ca