depth interval over which there is a rapid change in density

lower density on surface--> higher density on bottom

• vertical stratification: impt for biology
• transports heat 
•  dissolved oxygen to deep ocean
• stores  CO2 

• aka thermohaline circulation, abyssal circluation, meridional overturning circulation, global conveyor belt
• caused by density difference

• salinity 

• driven by temperature and salinity
• vertical structure of the deep ocean

depth in water column where salinity changes abruptly. usually from shallow waters to deep waters (saltier)

• sun heats only upper ~100m layer
• deep water is cold
• density and T= mirror image
• temp has a greater effect on density

•  strong thermocline--> stratified
• ex. ecuador

• parcels of water exhibiting somewhat narrow range of T and S
• N. Atlantic- deep water
• Antarctic- bottom water

• mixing in the ocean brings deep water to the surface
• indonesian through flow connects the pacific and indian oceans
• the antarctic circumpolar current mixes deep water from all oceans and redistributes it back to each ocean

• wally broecker 
• meridonial overturning circulation
• what drives the circulation of all ocean basins
• drives 90% of ocean currents
• interconnectedness of ocean currents 

• distribution of tritium in the Western N Atlantic in 1972 and 1981)
• half-life 12 years
• T was produced by nuclear bomb tests
• *human pollutants can be used as tracers for deep water circulation

• affected by excess precipitation, runoff, or ice melt
• slowdown/shutdown of ocean conveyor 
• belt disturbing the global heat distribution can disrupt climates 
• varying climate change (by location)

earth emerged from Younger Dryas (lasted 1300 years)

the Conveyor belt was disrupted

Within 10 yrs, temperatures in the N. Atlantic region plummeted nearly 5° Celsius

caused the most recent ice age

• North Atlantic Deep Water 
•  "start" of thermohaline circulation
• stratification by density difference!
• N. Atlantic: high salinity, extremely cold: dense--> water sinks
• evaporation: temp drops, salinity rises
• ice formation: S rises by brine rejection

deep current buoys

increase their density, sink through different layers, go along with currents, transmit information

tells how deep water circulation moves

• oxygen
• nutrients
• CFCs and SF6
• radiocarbon (C-14)
• Tritium (H-3)