What can bath toys (and this man) tell us about Ocean Currents?

1. What can bath toys (and this man) tell us about Ocean Currents? Chapter 9

2. First ….a key concept to keep in mind: Winds are named from the direction in which they are coming…. for example: A Southerly – is a wind coming from the south but blowing north. 2. Currents are named for the direction in which they flow….. for example: an eastward current - moving to the east (so it’s coming from the west).

3. Why is Ocean Circulation Important? • Transport ~ 20% of latitudinal heat • Equator to poles • Transport nutrients and organisms • Influences weather and climate • Influences commerce Ocean Currents – Wind driven – mainly moves water horizontally……down to 1 km Density or gravity driven - moves water vertically – mixes water masses!

4. Ocean Currents Only 10% of ocean currents moved this way! • Wind driven • Density (gravity) Driven AKA – Surface Currents (down to ~ 1km)  Moves water horizontally Moves water vertically!  Responsible for mixing water masses

5. We can measure currents using:

6. We can measure currents using: Basic Current meters Satellites – TOPEX/Poseidon radar….

7. Surface currents develop because of the friction between wind and water…. Only 2% of the wind’s energy is transferred to the ocean surface. So – 100 knot wind – will create a 2 knot current. A knot is equal to 1 nautical mile or 1.15 land miles (1.85 km)

8. ARGO – For 2000 m Currents

9. A gyre  is any large system of rotating ocean currents, particularly those involved with large wind movements.  Five Subtropical Gyres: 1. North Atlantic 2. South Atlantic 3. Indian Ocean 4. North Pacific 5. South Pacific

10. Western Boundary currents –narrow (<100 km), deep (up to 2km), fast (hundreds of km per day) – moving warm water to the poles Eastern Boundary currents –wide ( >1000 km), shallow (0.5 km), slow (tens of km per day) – moving cool water to the equator…

11. California Canary Somalia Peru Equatorial Benguela Major Upwelling Regions in the Ocean

12. Surface Currents Are Driven by Winds

13. The Ekman Spiral

14. The Movement of Water

15. 90° to the right of wind direction is up here At 15°N 30°– 45° Water continues clockwise? Trade wind Direction of water movement

16. Wind Can Cause Vertical Movement of Ocean Water

17. Wind Can Cause Vertical Movement of Ocean Water (cont’d.)

18. Ekman spiral Ekman spiraldescribes the speed and direction of flow of surface waters at various depths • Factors: • Wind • Coriolis effect

19. Ekman transport Ekman transportis the overall water movement due to Ekman spiral • Ideal transport is 90º from the wind • Transport direction depends on the hemisphere

20. Ekman Transport Water flow in the Northern hemisphere- 90o to the right of the wind direction Depth is important

21. Upwelling and downwelling Vertical movement of water - Upwelling = movement of deep water to surface • Hoists cold, nutrient-rich water to surface • Produces high productivities and abundant marine life • Downwelling = movement of surface water down • Moves warm, nutrient-depleted surface water down • Not associated with high productivities or abundant marine life

22. upwelling downwelling

23. Eddy • A circular movement of water formed along the edge of a permanent current • In an average year, 10-15 rings are formed • 150-300 km in diameter • Speed 1 m/sec • Warm core ring • Rotates clockwise • Found on the landward side of the current • Cold core ring (cyclonic eddy) • Rotates counterclockwise • Forms on the ocean side of the current

25. Hello, My name is Curtis Ebbesmeyer

27. Duckie Progress • January 1992 - shipwrecked in the Pacific Ocean, off the coast of China • November 1992 - half had drifted north to the Bering Sea and Alaska; the other half went south to Indonesia and Australia • 1995 to 2000 - spent five years in the Arctic ice floes, slowly working their way through the glacier • 2001 - the duckies bobbed over the place where the Titanic had sunk • 2003 - they were predicted to begin washing up • in New England, but only one was spotted in Maine • 2007 - a couple duckies and frogs were found • on the beaches of Scotland and southwest England.

28. Deep water Circulation • Also called: • Thermohaline circulation • Abyssal circulation • Meridional overturning circulation • Global conveyor belt • Is caused by Density difference. • Density is a function of • Temperature (“thermo”) & • Salinity (“haline”).

29. Examples of Tracers • Tritium (H-3): half-life ~12 years. • Radiocarbon (C-14): Half-life ~5700 years (especially C-14 from nuclear bomb test). • Oxygen: consumed by organisms in the deep water. • Nutrients: produced by organisms in the deep water. • CFCs (Chlorofluorocarbons-Freons) and SF6 (sulfur hexafluoride): man-made; recently injected to atmosphere, and consequently, into the ocean.

30. Circulation of the Deep Ocean (the other 90% of the ocean) Salinity is the driving mechanism for circulation in the deep ocean. Thermohaline circulation- driven by temperature and salinity. Vertical structure of the deep ocean

31. Temperature variation with depth • Sun heats only upper ~100m layer. • Deep water is cold. • Density & T = mirror image. • Temp. has a greater effect on density.

32. Driving force: • Wind cools surface water (T↓), evaporates water vapor (S↑). • Importance of Deep water circulation • Vertical stratification – important in dynamics and biology. • Heat transport influences Earth’s heat budget and climate. • It provides dissolved oxygen to the deep ocean. • Deep ocean stores anthropogenic CO2 (it takes 1000’s of years for one mixing).

33. Sources of Deep Water • Low latitude: strong thermocline  stratified. • High latitude: vertically well mixed. Temperature High latitude Low latitude Mixing Depth

34. Water Masses • Water masses: Parcels of water exhibiting somewhat narrow range of T & S.

35. Density = function of T&S Increasing density

36. Deep water currents are SLOW – 10-20 km per year! NADW = “Start” of thermohaline circulation Joined by AABW The Atlantic Ocean Stratification by density difference !

37. North Atlantic NADW formation Evaporation: T drops, S rises. Ice formation: S rises by brine rejection. whoi.edu

38. Returning Flow • Mixing in the ocean brings deep water to the surface. • Indonesian Throughflow connects the Pacific and Indian Ocean. • The Antarctic Circumpolar Current mixes deep water from all oceans and redistributes it back to each ocean

39. The Ocean Conveyor Belt By Wally Broecker (Meridional Overturning Circulation)

40. No deep water formation in the N. Pacific…Why? Salinity

41. My favorite subject so far in this course has been: • History of ocean exploration • Plate tectonics • Hurricanes • Atmospheric Circulation

42. More complicated.. Schmitz 1995 The Indian The Pacific The Atlantic