1. Interaction of a Dye Tracer with an Upwelling Front during Variable Winds From a cruise of the June 24-July 1, 2003 Andy Dale, Jack Barth, Murray Levine, Steve Pierce (COAS, Oregon State University) Jay Austin (Old Dominion University) NSF funded 2002-2004

2. With thanks to …. Murray Stein and crew of New Horizon Dennis Root (dye hardware etc.) Anatoli Erofeev (visualization software) Cambria Colt (Scripps res. tech.) Help at sea …. Said Ahmed Allan Book Renato Castelao Anthony Kirincich Larry O’Neill Bob O’Malley Michael Ott Inspiration …. Houghton, Ledwell etc. Collaborations with …. Tim Cowles’ group (bio-optical profiler/thin layers) Minibat

3. Offshore Ekman transport What happens to this dye patch during an upwelling-relaxation cycle?? Frontal region

4. Dye released as an alongshelf streak on a density surface….. Minibat survey ….. Shipboard ADCP Drogued ARGOS/GPS drifter Weighted Minibat 1 knot 6-7 knots Also CTD tow-yos at ~ 1 knot Dye tanks and plumbing Minibat and dye diffuser ~1 km

5. NOAA buoy 46029 Dye release 1 (fluorescein) Dye release 2 (rhodamine) 46029 46050 Release 1 Release 2 100 m 200 m Upwelling Downwelling NOAA buoy 46050 R/V New Horizon OREGON

6. Dye 1 - Fluorescein

7. 1 km ADCP velocity at 16m Dye advects south at ~0.6 m/s START FINISH 0.5 m/s Survey of dye patch 20-25 hours post-release. Size of dye patch 20 hours after release ~ 1.5km x 3.5 km Dye patch released.

8. 20 hours after release Wind at buoy 46050 Release Ekman Transport ~0.20 m/s Plots centered on 120m isobath

9. 23 hours after release Wind at buoy 46050 Release

10. 23.5 hours after release Wind at buoy 46050 Release

11. 24 hours after release Wind at buoy 46050 Release

12. 24.5 hours after release Wind at buoy 46050 Release

13. 34 hours after release Wind at buoy 46050 Release

14. 1 2 3 4 5 ?

15. Entrainment to mixed layer Continued entrainment of dye-free water Mean and standard deviation of fluorescein density

16. Dye 2 - Rhodamine

17. Release 33 hours after release Orange bar shows an inertial period

18. 43.1 hours after release Release

19. 62.6 hours after release Release

20. Density Temperature Salinity Rhodamine

21. Mean and standard deviation of rhodamine density Entrainment Relaxation/ restratification

22. Conclusions  During strongly upwelling-favorable winds, steepening of isopycnals combined with wind-induced mixing generates a surface mixed layer which actively entrains water beneath an upwelling front.  When upwelling-favorable winds cease or reverse, restratification is rapid with water from the frontal zone becoming widely distributed across the shelf. Plus …  These dye releases have revealed other interesting phenomena not covered here …. 10 20 30

23. Tow-yo section with bifurcated dye patch … 16 hours after release

24. Density Temperature Salinity Rhodamine

25. Tow-yo section with internal wave train … 13.9 hours after release