p263 1-18 omit 4, 11
1. Winds drive the horizontal circulation in the surface ocean, whereas differences in density (mainly due to
temperature and salinity) cause vertical circulation. The main ocean gyres are caused by global zonal winds. Deepocean circulation is caused mainly by the sinking of cold, relatively salty (dense) surface seawater in high latitudes. Solar
energy is responsible both for winds (atmospheric pressure gradients) and for changes in temperature and salinity
of surface seawater (evaporation and melting ice).
2. Currents can be measured directly by floating objects (instruments) or instruments fixed in place that measure
the water that moves past them. Currents are also measured indirectly by determining the distribution of density, by
understanding the dynamic topography of layers of water, and by using Doppler flow meters to measure the movement
of particles in water. Chemical tracers can be used to determine flow direction and estimate flow velocity of deep-ocean
currents. ALSO: the movements of all kind of flotsam (floating debris) & jetsam (jettisoned debris) can be traced as well!
3. If there were no continents, theoretically:
- the trade winds (easterly winds) would push surface seawater (from 0o to about 30o N and S) westward
- westerlies would push surface seawater (from about 30o to 60o N and S) eastward;
- polar easterlies would push high-latitude seawater westward.
4. OMIT.
5. - Atmospheric pressure is high at the center of the subtropical gyre.
- Atmospheric pressure is low at the subpolar gyre.
- Subtropical gyres in the Northern Hemisphere rotate clockwise, Subpolar gyres rotate counterclockwise.
[Note that ocean gyres, being pulled down by gravity, rotate in the same direction as atmospheric high pressure systems,
also pulled down by gravity]
6. How does Ekman transport produce a “hill” of water in the subtropical gyres? The gyres rotate clockwise because of
surface wind currents, and Ekman transport means that the net movement of water when wind is blowing over it is 90 deg
to the RIGHT (in N. hemisphere) of wind direction. In a clockwise pattern this means water is forced to the center of the
rotating water, aka the gyre.
7. (see p238, fig 8-7) The apex of these geostrophic “hills” of surface seawater is displaced toward the western sides of
ocean basins because of the Coriolis effect and the relative intensity of the effect with changes in latitude (the
Coriolis effect is stronger closer to the poles)
8. [p241 fig 8-9, p242 8-11, p243 8-12 and 8-13 all illustrate upwelling] If surface waters are moved away from each
other or away from a coastline, upwelling results.
9.The flow of the Amazon River is 0.2 Sv (1 Sv = 1 million m3/second)
Antarctic Circumpolar Current = 130 Sv (Amazon x 650)
Gulf Stream = 40-100 Sv (Amazon x 100-500)
10. The Brazil Current is slower and transports less volume than the Gulf Stream because the Brazil Current is impeded
by the Falkland Current. The Labrador Current that meets the Gulf Stream is much smaller than the Falkland Current.
ALSO, the Brazil current is created by a split in the South Equatorial Current (half of the SE moves south to form the
Brazil, the other half moves north and forms the Caribbean current.) The Gulf Stream is not the result of a split.
11. OMIT Whether it is a warm ring or a cool ring, whether it rotates clockwise or counterclockwise is a function of
which meander is pinched off. (heh heh, he said “pinched off”) IN OTHER WORDS: The three sides of the Gulf Stream
meanders that bulge to the RIGHT (colder water bulging into warmer water) flow SE then NE then NW. If the last side of
that meander – SW – severs the meander, the severed cold water loop simply continues rotating counter-clockwise. The
reverse is true for the warmer water bulging LEFT of the Gulf Stream NW then NE then SE. If that last side – again SW –
severs the meander, that warm water ring simply continues the clockwise rotation started in the meander.
12. During an El Niño event:
- Pacific Warm Pool moves eastward across the equatorial Pacific, toward Peru.
- Equatorial Countercurrent is faster.
- Thermocline is deepened in eastern Pacific (reduced upwelling.)
- Reduced upwelling results in low biologic productivity (less marine life).
- Sea level rises along the eastern Pacific.
- Velocity of southeast trade winds decreases (or winds reverse).
- There is low atmospheric pressure over South America, high pressure over Indonesia.
- Weaker Walker Circulation Cell results in slower trade winds.
Global effects:
- changes in wind circulation (direction and vigor)
- changes in patterns of precipitation
- changes in atmospheric pressure
- changes in intensity of tropical cyclones
13. El Niño conditions occur every 2 to 10 years (average about 5). From 1950 to 2000 (Figure 8-22) there were 12
major El Niño events, or one event every four years. El Niño events are irregular.
14. La Niña events are the opposite of El Niño events.
- Pacific Warm Pool moves westward across the equatorial Pacific.
- Thermocline is shallower in eastern Pacific (enhanced upwelling).
- Enhanced upwelling results in high biologic productivity (more marine life) etc
.
La Niña events occur in conjunction with El Niño events…more or less.. According to Figure 8-22, when El Niño
events are larger (higher ENSO index), La Niña events are smaller (lower ENSO index).
15. The monsoons are caused by the difference in heat capacities of land and ocean. In the summer in the Indian
Ocean, the Asian continent warms more quickly than the ocean. IN ESSENCE, MONSOONS ARE JUST
MASSIVE SEA BREEZES. Lower atmospheric pressure over land means that winds blow onshore (southwest
monsoon). The North Equatorial Current is replaced by the Southwest Monsoon Current (flowing from west to east
across North Indian Ocean). During winter, the Asian continent cools more quickly than the ocean. Higher atmospheric
pressure over land means that winds blow offshore (northeast monsoon). The North Equatorial Current flows from east to
west.
16. Thermohaline circulation describes the sinking of dense water masses. Density of seawater is controlled by
temperature, salinity, and pressure. Because deep-ocean water masses form at the surface of the ocean, we can
discount pressure. Temperature controls density more significantly than does salinity. Densest water masses, then,
are cold. Deep-ocean currents form in high latitude regions because deep ocean water masses must be cold. (see
“conveyor-belt circulation” diagram)
17. Two major deep-water masses are North Atlantic Deep Water (NADW), formed in the North Atlantic by
complex mixing of water from the Norwegian Sea, Gulf Stream, and other water masses in the North Atlantic (including
Mediterranean Intermediate Water), and Antarctic Bottom Water (AABW) formed by sinking of very cold, dense
surface seawater around Antarctica.
18. Antarctic Intermediate Water (AIW) forms at the Antarctic convergence. It is cold because is originates around
60oS, it is less salty because this is an area of high precipitation, and it has high dissolved oxygen because it is cold.
[As you know from experiences with cold and warm soda, cold water can contain more dissolved gases than
warmer water.] North Atlantic Deep Water (NADW) is far from its source (in the North Atlantic) so that the oxygen
once contained within it has been used by respiration, decomposition, and mineral oxidation. NADW is saltier because of
its complex mixing with Gulf Stream, Norwegian Sea, and Mediterranean waters in the North Atlantic. AAIW and
NADW have about the same temperatures (see Figure 8-26). AAIW is denser than the surface water above it, so it is
cooler than surface water.