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Deep Water CirculationAlso known as thermohaline circulation
Deep Water?Where:
◦below pycnocline – high layer of density change in the vertical dimension layer
◦about 90% of global oceanCompared to Shallow Currents
they move very slow. When surface water becomes
dense enough it sinks initiating deep ocean currents
T-S diagramTemperature-Salinity◦Origin of water can
be determined by specific characteristics of water.
◦Densest seawater is cold and a little salty AABW NADW
Sources of Deep WaterAntarctic Bottom
Water (AABW): ◦ densest water mass
(very cold) ◦ forms around
Antarctica and sinks to seafloor
North Atlantic Deep Water (NADW)◦ Less dense than AABW◦ Norwegian Sea water
sinks and mixes with other North Atlantic water masses North Atlantic Intermediate Water (NAIW)
Formed at Arctic Convergence Zone Above NADW
Antarctic Intermediate Water (AAIW) ): Formed at Antarctic Convergence Zone Above NADW
Deep Water Layers
Worldwide Deep-Water CirculationMixes Shallow Water with Deep
Water.◦Upwelling
Brings nutrients up
◦Downwelling Brings O2 Down
The “Conveyor Belt”Combination of surface ocean
circulation and deep-ocean circulation◦North Atlantic: Gulf Stream transports
warm seawater pole ward◦Cooling of this water means it sinks and
flows southward◦ Joins deep water around Antarctica◦Mixed water flows northward into Pacific
and Indian oceans◦Upwelling water flows west and north into
Atlantic Ocean
The “Conveyor Belt”
Turning off the Conveyor beltIf surface water did not sink,
oceans would be warmer◦More Tropical Storms and Hurricanes◦Less Fish
If ocean were warmer, NADW might not sink as readily◦No up welling◦No downwelling
Less transfer of warm water to high latitudes.
Summary – Deep Water Circulation
Huge volumes of seawater move at slow speeds
T-S diagram helps identify sources of water
Two Main Sources of Deep Water◦Antarctic Bottom Water ◦North Atlantic Deep Water
Mixes with Surface Water at High Latitudes where the pycnocline is weaker.
Summary - The “Conveyor Belt”Mixes Deep and Shallow Currents
◦Happens where the pycnocline is weaker
◦Allows for Upwelling and Down welling
Sinks in North AtlanticRises in Indian and North PacificTurning it off would be bad
◦Warmer oceans – more storms.◦Less heat transfer to poles◦Less up and downwelling.
“The day After Tomorrow”
A map of Deep Water Movement
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