Observations Of The Internal Tidal Bore At The Head Of The Monterey Submarine Canyon: 13 Feburary 20

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Observations Of The Internal Tidal Bore At The
Head Of The Monterey Submarine Canyon 1-3
Feburary 2004

• LEUT Scott Peak, RAN
• OC 3570
• Winter 2004

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Introduction

• TIDAL BORES
• A bore is an unsteady flow, often caused by
  tidal forcing and can be equated to a moving
  hydraulic jump.
• Surface tidal bore occurs in some specific
  rivers, usually during exceptionally high tides.
• River banks form a converging funnel shape, the
  river bed gently rises, and the river is of
  considerable length.
• Causes the wave to become highly non-linear and
  steepen thus forming a bore.
• Araguari Pororoca, which occurs in the Amazon
  River in Brazil and can reach up to 6 meters in
  height.

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Tidal Bores
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Internal Tidal Bores

• Exist where
• Interaction between the barotropic tidal currents
  and the continental shelf edge sets up internal
  tides
• a submarine canyon forms a converging funnel
  shape,
• combined with a gently rising sea floor,
• preferably over a considerable distance.

• MONTEREY CANYON!

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Previous OC3570 Study

• Alicia Washkevich
• Summer 2003
• Tidal Bore Exists
• Progressive Wave
• Kristen Watts
• Winter 2003
• Tidal Bore Exists
• Standing Wave

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Purpose

• Analyse data collected from the cruise on R/V Pt
  Sur to observe the processes operating at the
  head of the Monterey Canyon.
• More specifically, find evidence of the passage
  of an internal tidal bore and its classification
  as a progressive wave or a standing wave.

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Data for Report

• Collected on Leg II of the cruise, in the
  vicinity of the head of Monterey Canyon
• A 25 and 28 hour CTD Time Series
• ADCP Measurements
• Shipboard
• TRBM

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Monterey Canyon
TRBM
Moss Landing
Time Series 1
Time Series 2
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CTDs

• Time Series 1
• 25 CTD casts
• 0630 01 Feb 04 0730 02 Feb 04
• Average maximum depth 160m
• Time Series 2
• 28 CTD casts
• 0900 02 Feb 04 1316 03 Feb 04
• Average maximum depth of 210m
• Temperature, salinity, depth / pressure
  measurements

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ADCP (Acoustic Doppler Current Profiler)

• Onboard Pt Sur
• Measures velocity of water from reflection off
  suspended particles
• Continuous operation through time series

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TRBM (Trawl-resistant Bottom Mooring)

• ADCP
• Continuous operation
• through time series
• Pressure measurements
• No velocity measurements

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Data Analysis
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100m
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• Internal wave signal
• Semi-diurnal
• Highly non-linear
• Below 20-30m

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Time Series 1
Time Series 2
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Discussion

• From literature, the arrival of an internal tidal
  bore is characterised by
• wave steepening,
• a sharp drop in temperature and salinity over the
  water column, and
• a significant increase in upslope current
  velocity at the bottom.

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TIDAL BORE
TIDAL BORE
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Standing or Progressive?
No Velocity
Max Velocity
Max Velocity
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Conclusion

• The passage of an internal tidal bore was evident
  from the collected data.
• The tidal bore appears in the form of a standing
  internal wave.
• The formation of internal bores in offshore
  submarine canyons is not fully understood and
  this study only scratches the surface of what is
  a very complex and intricate process.

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Questions?