Density-Driven Downwelling and Thermohaline Circulation Motion of the Deep Ocean - p. 144-145 The Global Conveyor - p. 146-147 Water Mass Characteristics - p. 144-145

Why are deep waters more dense than surface waters? p. 123

Temperature Profiles Across Latitude

Thermohaline Circulation Thermohaline circulation is the density-driven circulation of the ocean below the pycnocline both temperature and salinity are important in the production of bottom, deep, and intermediate water masses p. 144

Intermediate, Deep, & Bottom Water Masses water becomes more dense by lowering the temperature or by adding salt: - winter cooling - evaporation (water becomes saltier causing it to sink) - seasonal sea-ice formation (a salty brine is created, which sinks) downwelling is the sinking of dense waters parcels of water sink to their level of neutral buoyancy below the solar-warmed surface waters thereby producing intermediate, deep, & bottom water masses

Thermohaline Circulation p. 144-145

Bottom & Deep Waters p. 144-145 Bottom and deep waters form only in the Atlantic today: 1. northern North Atlantic (Greenland-Norwegian Sea): North Atlantic Deep Water (NADW) 2. southern South Atlantic (Weddell Sea of Antarctica): Antarctic Bottom Water (AABW) Deep waters of the Indian & Pacific oceans are a mix of NADW and AABW called Circumpolar Water (or “Common Water”)

Antarctic Intermediate Water Gulf Stream Med Water Antarctic Intermediate Water North Atlantic Deep Water Antarctic Bottom Water http://sam.ucsd.edu/sio210/gifimages/A16_CTDSAL.gif

Water Masses A water mass is an identifiable body of water that can be recognized by physical and chemical characteristics temperature, salinity, density, dissolved gases, dissolved nutrients the densest water masses are very cold and somewhat salty (AABW, NADW), or cool and very salty (MIW) p. 144-145

Greenland-Norwegian Sea note: it is warmer in the northern North Atlantic than in the southern South Atlantic Ocean surface Weddell Sea

Antarctic Intermediate Water Gulf Stream Med Water Antarctic Intermediate Water North Atlantic Deep Water Antarctic Bottom Water http://sam.ucsd.edu/sio210/gifimages/A16_CTDSAL.gif

Greenland-Norwegian Sea note: it is saltier in the northern North Atlantic than in the southern South Atlantic Ocean surface Weddell Sea

Winter cooling and sea-ice formation produces dense waters which sink to form AABW; some of this water mixes with NADW to form Circumpolar Water which fills the deep Pacific & Indian oceans p. 145

http://en.wikipedia.org/wiki/Image:Antarctic_bottom_water_hg.png

Western Boundary Currents Deep water masses, like near-surface currents, are influenced by the Coriolis effect resulting in strong western boundary currents As deep waters flow equatorward beneath the pycnocline, they hug the lower continental slopes and rises on the western sides of the ocean basins

The Global Conveyor The global conveyor describes the complete circuit of global ocean circulation involving the horizontal & vertical flow of near-surface & deep waters Near-surface waters move independently of deep & intermediate waters because of the pycnocline that separates them Downwelling & upwelling link the surface & deep ocean p. 147

Global Conveyor

Surface currents (red) return to the Atlantic and then sink again (blue) to complete the loop of the Global Conveyor http://nsidc.org/arcticmet/factors/land_sea_distribution.html

Cold water holds more dissolved oxygen than warm water Why is there so much variation in dissolved O2 across the ocean surface? Ocean surface deep & intermediate waters acquire their physical & chemical characteristics at the surface