Music today: Little Mermaid, Under the Sea

WELCOME OSU MOMS!!

Deep Ocean CirculationMotion in the Ocean, Part 2, orWho wants to ride the Great Conveyor Belt?

Surface Circulation

How does the Deep Ocean respond to Surface Circulation?The main gyres move heat and saltResulting DENSITY variations lead to vertical flow (sinking)Formation of water masses, characterized by Temperature, Salinity

Density Variation in Sea WaterIsopycnals = constant density

North Atlantic Circulation

Density-Driven Water FlowCalled Thermohaline Circulation, because temperature and salinity together determine density of seawater Thermo = temperature haline = salt

Where does the Oceans Deepest Water Come From?The densest seawater is cold and saltyThis is formed at high latitudes in the North and South Atlantic: North Atlantic Deep Water (NADW) Antarctic Bottom Water (AABW)

Density of Sea Water

Density Rules!

Deep Water Masses

Water Massesand oceanmixing

Mediterranean Water

Mediterranean Water

Mediterranean Water

Deep Atlantic Circulation

Tracers in the OceanTrack the motion (direction and velocity)14C, cosmic rays in the upper atmos (half-life is 5700 years) 3H, nuclear weapons testing (half-life is 12.5 years) CFCs, chlorinated fluoro-carbons

The Great Conveyor Belt

Closing Isthmus of Panama and onset of the Ice Ages?

Consequences of Global FlowOcean turnover is about 1500 years (time for a round trip on the conveyor belt) Deep water (made in the polar Atlantic) contains abundant O2 and CO2The high O2 content promotes oxidation of bottom sedimentsThe CO2 content controls CCD (Carbonate Compensation Depth)

Carbon Cycle and Global WarmingThe temperature of bottom water formation determines how much CO2 is dissolved in deep ocean water The rate of overturn of the oceans determines the burial rate of C from the atmosphereOrganic C accumulates in sediments, depending on the O2 content of deep ocean

Carbon Cycle and Global WarmingOrganic C in sediments is reduced to CH4 (methane gas)Methane gas migrates upward and can be trapped as frozen gas hydrates near the ocean floor

Gas Hydrates

Gas Hydrates

Gas Hydrates

Gas Hydrates

Climate Change ConcernsWhat happens when sea level falls? (negative feed-back)What happens when deep water warms? (positive feed-back)Both effects liberate gas hydrates (CH4), which combines with O2 to form CO2, ultimately reaching the atmosphere

Deep Ocean Circulation The ocean has an enormous capacity to absorb and release greenhouse gasesSo, the rate, temperature and composition of seawater circulating through the deep ocean is vitally important in assessing long term climate change