1. Ocean circulation: key questions
Why do currents form?
Circulation of surface & deep ocean are driven by solar radiation, & are closely linked.
So why do they operate on different time scales?
Role of ocean circulation in global climate?

2. Ocean circulation: key points
Closely linked to circulation of atmosphere
Distribution of solar energy drives surface winds, which determines motion of surface ocean & formation of currents
Coriolis also influences ocean circulation, as it does atmospheric circulation
(See systems diagram)

3. Deep ocean
Oceans are vertically stratified, with more dense water at the bottom & less dense water at the top
Deep ocean water moves in response to small changes in density over wide areas, independent of surface ocean circulation
Deep ocean circulation is much slower than surface ocean circulation
Due to surface heating, ocean is stably stratified & vertical mixing is slow

8. Gyres & Ekman spiral
Water does not pile up on the coasts, but rather in the middle of a gyre
Middle of a gyre is a convergence zone
This is due to the Ekman spiral, which results from Coriolis effect & friction
Surface ocean moves in a direction that is 45o to wind, & direction is reversed at 100 m depth
Net transport is 90o to the wind, which is to the center of the gyre
(See diagrams)