Deepwater Intrusions in the Puget Sound

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Deep-water Intrusions in the Puget Sound

• Sally Warner
• Coastal Estuarine Fluid Dynamics class
• Friday Harbor Labs
• Summer 2006

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Project goals

• Was an intrusion of dense ocean-water occurring
  during our 36-hour cruise?
• What processes were working to allow or prevent
  this intrusion?

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Estuary dynamics
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Fjord dynamics
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Intrusions
Why are intrusions essential to fjords?
What controls the onset of intrusions?
What happens in the Puget Sound?
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Puget Sound and Admiralty Inlet
depth
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The Intrusion
30.8 psu
30.8 psu water intruding down the estuary side of
the sill
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Barotropic vs. Baroclinic Forcing
Barotropic excursion distance
31.2
Tidal current
t1
t0
t2
time
Advection distance of 31.2 psu water 3.89 and
4.03 km in 5.3 and 5.0 h.
Barotropic excursion lengths 0.95 and 1.60 km
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ADCP velocity
ubarotropic 27 cm s-1
ubaroclinic 25 cm s-1
t3
Baroclinic circulation is essential for the
propagation of the intrusion
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Historical Data sx vs. mixing
38 historical transects and our cruise
Bottom water renewal is controlled by changes
in the intensity of mixing due to fortnightly
variations in the tidal amplitude. Geyer
Cannon (1982) The onset of intrusions is a
result of the fluctuations in the horizontal
density gradient caused by salinity variations
across the sill. Cannon et. al. (1990)
Our cruise slack 14 h s 1.5 psu,
sx0.03 psu km-1
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• Conclusions
• Yes, an intrusion was occurring when we visited
  Admiralty Inlet
• Reduced tidal velocities allowed baroclinic
  circulation to develop which carried 30.8 psu
  water over the sill.
• Both the spring/neap change in tidal energy and
  variation in the horizontal salinity gradient are
  important mechanisms controlling intrusions of
  deep water into the Puget Sound, as seen from
  historical data.