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Physical Oceanography of South Western Marine Region

Physical Oceanography of South Western Marine Region. Charitha Pattiaratchi School of Environmental Systems Engineering The University of Western Australia. Background Wind, tide and wave regime Leeuwin Current Forcing, water masses, eddy generation Continental shelf processes

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Physical Oceanography of South Western Marine Region

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  1. Physical Oceanography of South Western Marine Region Charitha Pattiaratchi School of Environmental Systems Engineering The University of Western Australia

  2. Background Wind, tide and wave regime Leeuwin Current Forcing, water masses, eddy generation Continental shelf processes Forcing, seasonal changes, upwelling Conclusions Outline

  3. Study Region

  4. Seasonal winds – West Coast Summer Winter Rottnest Island

  5. Seasonal winds – South Coast Summer Winter Esperance

  6. Global distribution of tidal conditions

  7. Fremantle water level de-composition U(t) Sea Level (t) = Mean Sea Level(t) +Tide(t) + Surge(t) Up(t) U(t) = Zo (t) + Up(t) + Us(t) Us(t)

  8. Spring and Neap tides First quarter Sun New Moon Full Moon Last quarter Spring tides = King tides Neap tides = Dodge tides

  9. Tidal characteristics

  10. Fremantle water level de-composition Solstice Equinox

  11. Continental Shelf Wave generation Summer: Tropical cyclones Winter + summer: pressure systems

  12. Sub-tidal water levels

  13. Water Level Changes

  14. Cyclone Track: 1993 (Naomi)

  15. Shelf currents: DWCM (100m) Naomi

  16. Naomi Shelf currents: SWANB (8m)

  17. Southern Surveyor Voyages 2003, 2006

  18. Cresswell Current Capes Current Ningaloo Current Leeuwin Current Leeuwin Undercurrent The Leeuwin Current System

  19. The Leeuwin Current System

  20. The Leeuwin Current • warmer, lower salinity • lower nutrient water • flows all year around • stronger in winter • weaker in summer • strength linked to SOI • weaker during El Nino • stronger during La Nina • Relative strength measured by mean sea level Ridgway and Condie, 2004 WASTAC, 1998

  21. The Leeuwin Current Ridgway and Condie, 2004

  22. The Leeuwin Current

  23. Leeuwin Current Seasonal Winter Summer

  24. Leeuwin Current Inter-annual El Nino La Nina

  25. Leeuwin Current System – Water Masses LC

  26. Leeuwin Current System – Water Masses South Indian Central Water Sub-Antarctic Mode water Antarctic Intermediate water

  27. Circulation: South Coast Middleton and Cirano, 2003

  28. The Leeuwin Current – South Coast

  29. Flinders Current (FC) • Dominant current in southern region • Wind stress curl drive FC • Centered at 600m depth, max at 400m • Interconnect with LC at shelf break • Part of FC flows beneath LC, imitate LU Middleton and Platov,2003.

  30. Leeuwin Current/ Flinders Current Leeuwin Current Flinders Current

  31. Leeuwin Current/ Flinders Current Leeuwin Current: Higher in temperature FC/Undercurrent: Higher in salinity Transect P

  32. Flinders Current feeds Leeuwin Undercurrent

  33. Leeuwin Current: Eddies

  34. Higher chlorophyll water on the continental shelf April 2002 May 1981 March 1981

  35. April 2002 Nov 2000 April 2002

  36. The Leeuwin Current – Eddy generation Shark bay Abrolhos Islands Perth Canyon Albany Esperance

  37. The Capes Current: A northward counter current during the summer

  38. Balance of forces: Capes Current

  39. Summary – southern section

  40. Cresswell Current?

  41. Pygmy Blue Whale aggregations: Perth Canyon • Pygmy Blue Whales: • > 25 m long • Found in the Perth Canyon Feb - May • Consume 4-5 tonnes of food per day

  42. Upwelling in South Australia

  43. Conclusions - I • The wind regime is seasonal with summer/spring sea breezes and winter storms. • The wave climate responds to changes in the winds with higher swell waves during winter. • The tides are diurnal and do not follow the moon’s phases for spring and neap tides – lowest water levels occur during the December solstice. • Sub-tidal forcing is important for the whole study region: Shark Bay to Kangaroo Island

  44. Conclusions - II • Leeuwin Current is the dominant surface forcing in the offshore regions – it interacts with particular regions of the coast (e.g. Jurien Bay) due to eddy generation. • In the subsurface the Leeuwin Undercurrent and Flinders Current are important • Continental shelf currents are dominated by wind forcing. There are seasonal changes with upwelling occurring during the summer and downwelling in winter.

  45. http://www.sese.uwa.edu.au/~pattiara/CoastalOceanography

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