Geography and Oceanography - Chapter 14 potx

Deep Ocean Circulation Deep Ocean Circulation Motion in the Ocean, Part 2, “The Great Conveyor Belt” Jack Barth (barth@coas.oregonstate.edu) NASA web site: http://oceanmotion.org Surface Circulation Surface Circulation Surface and Deep Ocean Circulation help move heat from equator to pole Atmosphere & Ocean each responsible for about Atmosphere & Ocean each responsible for about half of heat transfer half of heat transfer How does the Deep Ocean How does the Deep Ocean respond to Surface Circulation? respond to Surface Circulation? ✦ The main gyres move heat and salt ✦ Resulting DENSITY variations lead to vertical flow (sinking) ✦ Formation of “water masses”, characterized by Temperature + Salinity = Density Density Variation in Sea Water Density Variation in Sea Water Isopycnals = constant density Isopycnals = constant density Density Variation in Sea Water Density Variation in Sea Water Nearly all the water in the oceans is cold Nearly all the water in the oceans is cold North Atlantic Surface Circulation North Atlantic Surface Circulation Density-Driven Water Flow Density-Driven Water Flow ✦ Called “ Called “ Thermohaline Circulation Thermohaline Circulation ”, ”, because because temperature temperature and and salinity salinity together determine density of together determine density of seawater seawater “ “ Thermo Thermo ” = ” = temperature temperature “ “ haline haline ” = ” = salt salt Where does the Ocean’s Where does the Ocean’s Deepest Water Come From? Deepest Water Come From? ✦ The densest seawater is The densest seawater is cold cold and and salty salty ✦ This is formed at high latitudes in the This is formed at high latitudes in the North and South Atlantic: North and South Atlantic: North Atlantic Deep Water (NADW) North Atlantic Deep Water (NADW) Antarctic Bottom Water (AABW) Antarctic Bottom Water (AABW) Density of Sea Water Density of Sea Water [...]... products and food production) Disruption to winter travel opportunities and increased icing of northern ports and seas Changes in regional patterns of increases versus decreases in cold- and heat-related deaths and ill-health Movement of populations to southern Europe Need to refurbish infrastructure towards Scandinavian standards http://www.ipcc.ch/publications _and_ data/ar4/wg2/en/ch12s1 2-6 -2 .html... Basins s Sinks and is dammed behind sills – Between Greenland and Iceland and Iceland and the British Isles s NADW periodically spills over sills into the North Atlantic Water Masses and ocean mixing determined by CTD (conductivity, temperature, depth) measurements Mediterranean Water Mediterranean Water Mediterranean Water Deep Atlantic Circulation This southward flow in one layer and northward flow... Weddell, Ross Seas and Adelie Coast L Talley (SIO) Antarctic Bottom Water (AABW) Weddell Sea major site of AABW formation s AABW circles Antarctica and flow northward as deepest layer in Atlantic, Pacific and Indian Ocean basins s AABW flow extensive s – 45°N in Atlantic – 50°N in Pacific – 10,000 km at 0.0 3-0 .06 km h-1; 250 y North Atlantic Deep Water (NADW) s s s Coastal Greenland (Labrador Sea)... Europe from shut-down of the Meridional Overturning Circulation s s s s s s s s Reductions in runoff and water availability in southern Europe; major increase in snowmelt flooding in western Europe Increased sea-level rise on western European and Mediterranean coasts Reductions in crop production with impacts on food prices Changes in temperature affecting ecosystems in western Europe and the Mediterranean... sinks and flows at depth throughout the major ocean basins Deep water upwells to replace the surface water that sinks in polar regions Surface waters must flow to high latitudes to replace water sinking in polar regions This Idealized circulation is called the “Great (Thermohaline) Conveyer Belt” Tracers in the Ocean Track the motion (direction and velocity) 3 14C, cosmic rays in the upper atmos (half-life... (half-life is 12.5 years) CFCs, chlorinated fluoro-carbons – banned in early 1970s 3 CFC Spreading in the Atlantic • 2000 m depth • Deep Western Boundary Current • Red is model result The Great Conveyor Belt Ocean Circulation and Climate s s s s On long timescales, average ocean temperature affects climate Most water is in deep ocean Average temperature of ocean is a function of s process of bottom-water... http://www.ipcc.ch/publications _and_ data/ar4/wg2/en/ch12s1 2-6 -2 .html Carbon Cycle and Global Warming The temperature of bottom water formation determines how much CO2 is dissolved in deep ocean water 3 The rate of overturn of the oceans determines the “burial rate” of C from the atmosphere 3 Organic C accumulates in sediments, depending on the O2 content of deep ocean 3 Carbon Cycle and Global Warming 3 Organic C in sediments is reduced... 3 Organic C accumulates in sediments, depending on the O2 content of deep ocean 3 Carbon Cycle and Global Warming 3 Organic C in sediments is reduced to CH4 (methane gas) 3 Methane gas migrates upward and can be trapped as frozen “gas hydrates” near the ocean floor Gas Hydrates Newport, OR Gas Hydrates Gas Hydrates . Basins ■ Sinks and is dammed behind sills – Between Greenland and Iceland and Iceland and the British Isles ■ NADW periodically spills over sills into the North Atlantic Water Masses Water Masses and. densest seawater is cold cold and and salty salty ✦ This is formed at high latitudes in the This is formed at high latitudes in the North and South Atlantic: North and South Atlantic: North. Pacific and Indian Ocean basins ■ AABW flow extensive – 45°N in Atlantic – 50°N in Pacific – 10,000 km at 0.0 3-0 .06 km h -1 ; 250 y North Atlantic Deep Water (NADW) ■ Coastal Greenland (Labrador