Deep Water Circulation Also known as thermohaline circulation.

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