ENS Alicia A. Washkevich, USN An Overview of the Internal Tidal Bore at the Head of the Submarine Canyon in Monterey Bay OC 3570 Cruise 21-28 JUL 2003 Project by: ENS Alicia A. Washkevich, USN

Introduction: OC3570 NPS student cruise 2 Legs: 21-24 JUL & 24-28 JUL Legs traveled from Monterey south to San Luis Obispo and back

Internal Tidal Bore Unsteady flow caused by tidal forcing Common to Monterey Bay Submarine Canyon Narrowing Rising sea floor / slope Long distance Characterized by: Lower temperature and salinity extending down in water column Increased wave height Greater current velocity at the bottom of the water column traveling toward shallow bathymetry

Bathymetry of Monterey Bay Time Series 2 Time Series 1

Instruments / Data Used 25 Hour CTD Time Series Data Shipboard ADCP data Mean Sea Level data from NOAA/NOS CO-OPS

CTD’s Time Series 1 Time Series 2 27 CTD casts 26 JUL 03 0302 – 27 JUL 03 0409 Average maximum depth 162m Time Series 2 27 JUL 03 0459 – 28 JUL 03 0610 Temperature and salinity measurements used and plotted with depth / pressure

Salinity from CTD Time Series 1 T-S Plot Pressure/100 Yearday

Temp from CTD Time Series 1 Pressure/100 Yearday

Salinity from CTD Time Series 2 Pressure/100 Yearday

Temp from CTD Time Series 2 Pressure/100 Yearday

CTD Data Shows: Lower temperature extending down at Yearday 207.7 and 208.1 for Series 1 Lower salinity extending down at approximately same time Lower temperature extending down at Yearday 208.5 and 209.1 for Series 2

ADCP (Acoustic Doppler Current Profiler Onboard Pt Sur Transmits 150 kHz Measures velocity of water from reflection off suspended particles

East/West Velocity cm/s PBOR1 Some Bottom Intensification Yearday -1

North/South Velocity cm/s PBOR1 Depth/100 Yearday -1

East/West Velocity cm/s PBOR2 Depth Yearday -1

North/South Velocity cm/s PBOR2 “sloshing” Depth “spilling” Yearday -1

PBOR2 U vs. V (Overlay) “E/W” “N/S”

PBOR2 Discussion: Not perfectly aligned E/W (slightly oblique) Exception to general trend (One would assume a NE/SW but overlay shows a NW/SE movement) Canyon wall deeper on Southern side, may spill over more to South Sloshing to North and South above canyon wall (freedom of movement) North may be possible reflection

ADCP Data shows: PBOR1 clearly defined Most notable E/W – deep water funneled “in and out” of canyon PBOR2 Slightly offset Less strength Different but possible

Propagating or Standing Wave? U and V components taken at depths of 71, 87, and 103 meters 6 Minute Mean Seal Level Data for Monterey Station # - 9413450 36 36.3’ N 121 53.3’ W

(PBOR1)

(PBOR2)

(PBOR1)

Propagating Internal Wave http://www.es.flinders.edu.au/~mattom/IntroOc/lecture10.html

Sea Level Shows: Bit of a lag Strong velocity at peaks Generally followed shape

CONCLUSIONS: Internal bore was present in the form of a propagating internal wave The bore displayed customary characteristics Lower salinity and temperature extending down into water column Bottom intensification (velocity) Mirrored mean sea level heights with strong velocity at peaks

Questions? Special Thanks to: LT Kristen Watts RAN, Chris Miller, Tarry Rago, Prof. Collins