Surface Layer (top 1 km)
- Surface currents depend on
- average surface winds (trade winds,etc)
- Solar heating
- Coriolis effect (Eckman spirals -icebergs move at 90° to wind direction)
- Forms gyres - large circular currents (rhymes with tire).
- Clockwise (CW) gyres in the northern hemisphere oceans.
- CCW gyres in the southern hemisphere.
- Surface currents very complex (eddies, rings, convergence/divergence, geostrophic currents)
- Research ongoing for short-term variations (ENSO, NAO, PDO).
Deep Ocean layers
- Currents form as a result of thermohaline effects = colder, more saline water sinks.
- Temperature differences are low (< 4°C)
- Weak currents but HUGE volumes.
The Great Conveyor
- Surface and deep currents combined.
- Very complex and still far from understood.
- Transport times are long = centuries to 1400 years.
- Important impact on Earth's heat budget. 2000 x 1012 watts northward in Atlantic.
- Important component of Earth's carbon budget (CO2).
- Oceans hold 50x more carbon than land or air reservoirs.
- Cold water dissolves more gases.
- Increasing temp of ocean or increasing turnover of deep water could have HUGE effect on atmospheric CO2.