1. The Reality of Sending a Message in a Bottle
Ocean Currents
The Reality of Sending a Message in a Bottle

2. Ocean Current Layers
Surface Currents – top 10% of the ocean; upper 400 m
Deep Currents – lower 90% of the ocean

3. Properties of Ocean Water
How they impact ocean currents
Temperature – remember heat rises!
Salinity – remember salty water sinks!
Density – a function of temperature and salinity

4. World Map

5. Surfers (Why)
Florida
California

6. Ocean Surface Temperatures

7. Temperature vs. Currents

8. Notes Water by the equator is the hottest.
Water by the Poles is the coolest.
Ocean currents are caused by Uneven Heating.
Ocean Currents are Convection Currents.

9. 1. shape of the continents 2. temperature differences
CAUSES OF CURRENTS
1. shape of the continents
2. temperature differences
(colder water is denser)
3. spinning of the Earth
(deflecting currents to right in Northern hemisphere)
4. winds

10. 1 2 4 Currents are affected by: 1 continents
2 temperature 3 Coriolis spin
4 Gulf Stream 4 3
Credits: CNMOC, U. S. Navy; CNMOC, U. S. Navy; NASA; U. S. Geological Survey

11. Current Forces Explained
Sun/solar heating - causes water to expand and move
Winds - push the water; winds blowing for 10 hrs across ocean will cause the surface water to ~2% wind speed; wind has the greatest effect on surface currents
Gravity - pull water downhill or pile against the pressure gradient (high/low); influences tides

13. Winds
Winds driven by uneven solar heating & Earth’s spin, drive the movement of the ocean’s surface currents. The prime movers are the powerful westerlies and the persistent trade winds (easterlies).

14. Wind Driven Ocean Currents

15. Current Forces (cont’d)
Coriolis effect/force - Force due to the Earth's rotation, capable of generating currents. It causes moving bodies to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The "force" is proportional to the speed and latitude of the moving object. It is zero at the equator and maximum at the poles
causes the water to move around the mound of water

16. Surface Currents
Surface current – with surface currents circulation is less dense and influenced by winds
Warm surface currents: wind and Earth’s rotation
Cold surface currents: flow towards the equator
Upwelling current: cold, nutrient rich; result of wind
Western Boundary currents: warm & fast
Eastern Boundary currents: broad, slow, cool & shallow, associated with upwelling
Ex: Gulf Stream = surface current that is the upper 20% of the ocean, western boundary current

17. Properties of Deep Ocean Currents
Deep ocean water characteristics:
Cold
Dense
Salty
Move by density forces and gravity
Move slower than layers above
Thermohaline Circulation: is global ocean circulation. It is driven by differences in the density of the sea water which is controlled by temperature (thermal) and salinity (haline).

18. Graphic - http://www.grida.no/climate/vital/32.htm
Global Conveyer Belt
Thermohaline circulation links the Earth's oceans. Cold, dense, salty water from the North Atlantic sinks into the deep and drives the circulation like a giant plunger.
Graphic -

19. Ocean Currents & Living Things
Currents are important to marine life as they help move food and nutrients making them available for photosynthesis, metabolic requirements and or consumption.