1. Ocean Currents

3. Ocean Currents There are two types of ocean currents:
Surface Currents: are wind driven and affect about 10% of the ocean water, but cover the entire ocean surface.
Thermohaline Currents: (heat/salt) = density driven currents. They occur deeper in the ocean and affect ~ 90% of the ocean water.

4. Hot/Cold Currents
Warm Currents: Gulf Stream, Alaskan, Kuroshio, Brazil, South Equatorial, North Equatorial, East Australian, North Atlantic, North Equatorial, East Australian
Cold Currents: West Wind Drift, Humboldt, California, Canary, Bengula, West Australian, Labrador, Gulf Stream,

6. Surface Currents Surface currents are mostly horizontal currents.
These currents follow the pattern of the wind e.g. the Westerlies/ Trade winds
They occur from the surface down to a few hundred meters.
Generally travel clockwise in the northern hemisphere and counter clockwise in the southern hemisphere.

7. Significance of surface currents
Surface currents cause the general “mixing” of the worlds oceans and waters
move nutrients from more productive areas to less productive areas of the oceans.
Important role in migration and the movement of many less active (or passive) organisms.

8. Deep currents
Thermohaline currents are driven by density and temperature changes in water.
These currents are also known as the “ocean’s conveyor belt”
They flow under the surface of the ocean and move significant amounts of ocean water vertically.

9. Significance of deep currents
Form upwelling: the drawing up of cold water from deeper regions to shallow waters throughout the Ocean
Result: all ocean nutrients don’t end up settling on the bottom: surface organisms can benefit from decomposers, cycle nutrients and sustain life.
So what is downwelling? 

10. What affects currents?
Currents flow in complex patterns affected by the placement of the continents and land masses, wind, the water's salinity and heat content (temperature), bottom topography, and the earth's rotation (aka Coriolis Effect: water moves clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere).

12. Gyres
These currents are deflected by the continents and driven by surface winds, causing them to bend and create large current loops called circulation gyres.
The centers often collect floating mats of seaweed and garbage. (Sargasso Sea and the N. Pacific gyre garbage patch.)

15. The key variables that affect water density:
Temperature: Denser water sinks (cold), less dense water rises (warm)
Cold-water currents occur as the cold water at the poles sinks and slowly moves toward the equator, and opposite for warm water.
Salinity – Saltier water = more dense, therefore sinks

16. “The Great Conveyor Belt”
A global "conveyor belt" is set in motion when cold water forms in the Northern Atlantic, sinks, moves south, and circulates around Antarctica, and then moves northward to the Indian, Pacific, and Atlantic basins. It can take a thousand years for water from the North Atlantic to find its way into the North Pacific.

17. Conveyor Belt