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

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

3. Study Region

4. Summer Winter Seasonal winds – West Coast Rottnest Island

5. Summer Winter Seasonal winds – South Coast Esperance

6. Global distribution of tidal conditions

7. Fremantle water level de-composition U(t) U p (t) U s (t) Sea Level (t) = Mean Sea Level(t) +Tide(t) + Surge(t) U(t) = Z o (t) + U p (t) + U s (t)

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

9. Tidal characteristics

10. Fremantle water level de-composition SolsticeEquinox

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

12. Sub-tidal water levels

13. Water Level Changes

14. Cyclone Track: 1993 (Naomi)

15. Shelf currents: DWCM (100m) Naomi

16. Shelf currents: SWANB (8m) Naomi

17. Southern Surveyor Voyages 2003, 2006

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

19. The Leeuwin Current System

20. WASTAC, 1998 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

21. The Leeuwin Current Ridgway and Condie, 2004

22. The Leeuwin Current

23. Leeuwin Current Winter Summer Seasonal

24. Leeuwin Current La Nina El Nino Inter-annual

25. LC Leeuwin Current System – Water Masses

26. South Indian Central Water Sub- Antarctic Mode water Antarctic Intermediate water

27. Middleton and Cirano, 2003 Circulation: South Coast

28. The Leeuwin Current – South Coast

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

30. Flinders Current Leeuwin 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. May 1981 March 1981 Higher chlorophyll water on the continental shelf April 2002

35. Nov 2000

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