1. Mixing & Turbulence
Mixing leads to a homogenization of water mass properties
Mixing occurs on all scales in ocean
molecular scales (10’s of mm)
basin scales (1000’s of km)
Turbulence interactions cascade energy from big to small scales

2. Mixing & Turbulence
10 cm eddies
Small-scale turbulence
Shear-driven

3. Mixing & Turbulence
200 km eddies
Mesoscale
Geostrophic

4. Mixing & Turbulence
4 km eddies
Submesoscale
???

5. Mixing & Turbulence Stirring efficiently mixes property fields
All scales of motion contribute
Nearly all scales interact
Think of a kid’s playroom full of colored balls before the kids come home...
Works if no restoring forces are present

6. Stirring vs. Mixing
A single patch will be chaotically strained by flow
Reversible

7. Stirring vs. Mixing
If this experiment were repeated many times, the average patch will appear to be “diffused”
Concept of eddy diffusion
Eddy diffusion is >> molecular diffusion

8. Buoyancy Dense water sinks - light water floats
Density profile will increase with depth
Upward force due to D’s in r is called the buoyancy force
Buoyancy restricts vertical mixing of water masses

9. Buoyancy & Mixing
Buoyancy is important to vertical mixing for two major processes
Asymmetric mixing in ocean interior
Convection

10. Example r1 >> r2 Water mass 1 T=20 & S=36 Water mass 2
Water mass 2 is buoyant relative to 1 2 1

11. Example r1 ~ r2 No net buoyancy Water mass 1 T=20 & S=36 Water mass 2

12. Buoyancy
Waters of same r mix easily, waters of different don’t (oil & vinegar)
Potential energy differences must be overcome by mechanical energy inputs
Mixing along isopycnal surfaces will be >>> than mixing across them

13. Purposeful Tracer Release
SF6 release in Brazil Basin
Column inventory (mmol m-2)
Top 14 mo
Bottom 26 mo

14. Purposeful Tracer Release
SF6 release in Brazil Basin
Spatial average
Dashed - initial
Solid - 1 yr later
In one year, the SF6 plume has spread 400 m in vertical & 400 km in horizontal

15. Purposeful Tracer Release
SF6 in color
Isopycnal surfaces in white lines
Top 14 mo
Bottom 26 mo

16. Stratified Mixing
Waters mix rapidly along isopycnals & slowly across them
Vertical eddy diffusivity ~ m2/s
Horizontal eddy diffusivity ~ m2/s
Gives rise to constancy in properties following isopycnals

17. Atlantic Temperature
eWOCE gallery –

18. Atlantic Salinity

19. Atlantic Oxygen

20. Atlantic Phosphate

21. Convection
Air-sea cooling & evaporation creates cool & saline surface waters
These waters are then denser than those just beneath them and they sink
Process is called convection
Annual & diurnal time scales

22. Seasonal Temperature Change
OWS Papa
50N 145W

23. Seasonal Temperature Change
OWS Papa
50N 145W

24. Convection & the Conveyor Belt
NADW production drives the conveyor

25. Convection & the Conveyor Belt
AAIW
NADW
AABW

26. Role of Sea Ice Formation of seasonal sea ice also is important
Sea ice salinities are ~2 to 5 psu
Reject brine water when formed
which is salty, cold and dense!!
Source of AABW

27. Seasonal Sea Ice

28. Mixing, Buoyancy, etc. Turbulence drives mixing in the sea
Flow variations on many scales
Buoyancy is important
Drives convection
Asymmetric mixing within the interior
Active area of research