Week 6 (new)
What primary physical factors control density of seawater and therefore drive the vertical circulation of deep water?
In other words, what drives thermohaline circulation?
Vertical currents are driven by density (thermo = temp, haline = salinity), low temp + high salinity = more dense,
gravity pushes denser water to the bottom and less dense water rises
vertical circulation; caused by the process of
heating in the lower latitudes close to equatorial regions, and cooling in the higher latitudes near the polar regions
What processes act in the ocean to alter the density of seawater?
Denser water created by: cooling of surface water (more heat given to atmosphere), increasing salinity by
evaporation, formation of sea ice, & mixing water w/ different salinity & temp; rain adds water, ice & evaporation
remove water to increase salinity
Where do you expect
these processes to occur?
Densest water is deepest, formed by surface conditions that made water cold & salty (high latitudes & where
evaporation is higher than precipitation), surface water masses are warmer and lower salinity, intermediate water is
in between the 2. Upwelling & downwelling effect density of water, upwelling = by equator, west coast of US,
South America, & Africa,
Where does deep water form in the ocean, and why there?
Antarctic bottom water = most distinctive deep water mass, 34.7% salinity & -0.5C temp & 1.03 density (densest
water in the world); migrates north along sea floor, forms in Weddell Sea during winter, salt concentration mixes w/
frigid water rapidly; dense bottom water also forms in northern polar ocean but topography of Arctic Ocean prevents
it from escaping except thru deep channels formed by submarine ridges near Scotland, Iceland & Greenland, known
as North Atlantic deep water, forms when relatively warm & salty north Atlantic ocean cools as cold winds from
northern Canada sweep over it, heat is released & water sinks; several other deep water masses near poles
What route does deep water take to fill the oceans, where does it mix (and with what) along the way, and how long
does it take to reach its destination?
Antarctic bottom water travels north, very slowly (faster in Atlantic than Pacific); as it sinks toward continental shelf
it mixes with nearly equal parts of water from southern Antarctic circumpolar current; moves from poles to equator
in roughly 20 years
What is tritium and how does it relate to the circulation of the ocean?
Radioactive form of hydrogen, released by nuclear tests, isotopes can be used to examine ocean circulation &
How is it that two water masses can have the same density, but different salinities?
Different combinations of temp & salinity can make same density