week 6 - ocean circulation Flashcards
three types of water masses with different densities
- stable
- unstable
- neutral
stable water mass
low density on top, high density on the bottom
- mixing is inhibited
unstable water mass
high density on top, low density on bottom
- mixing is spontaneous
neutral water mass
density is medium/same on the top and bottom
- mixing is easy
thermocline
a region of rapid temperature change
- separates the top mixed layer (turbulent) from the bottom deep water (calm)
pyconocline
rapid change in density
where is heat greater?
at lower latitudes
-because of this, winds are generated to restore equilibrium
- warm air rises near the equator and travels toward the poles (deflected by coriolis effect)
coriolis effect
things moving in the northern hemisphere appear to be deflected to the right, and to the left on the southern hemisphere
major winds
- westerlies
- trade winds
ekman transport
the net motion of water at a 90 degree angle to the prevailing wind direction
what causes coastal upwelling on the southern hemisphere and downwelling on the northern hemisphere?
southerly winds parallel to the coast (winds coming from the south)
what causes coastal upwelling on the northern hemisphere and downwelling on the southern hemisphere?
northerly winds parallel to the coast (winds coming from the north)
equatorial divergence
winds moving toward each other deflect the water away from each other (45 degrees)
- happens at the equator
- causes upwelling (ekman suction)
upwelling
bringing water from the deep to the surface while surface water is being moved away due to the wind
subtropical convergence
when winds are going in the opposite direction, the water moves toward each other (ekman pumping)
- westerlies and trade winds
- causes downwelling
downwelling
because water cannot pile on top of itself, it is forced to go downward, creating downwelling
basics of subtropical gyres
- happens at the equator
- coastal winds go north with deflection and westerlies deflect water to the right
- all deflected water points to the same center, which creates a mound of water and high pressure
- because everything is deflected to the right, it creates a circle
- creates a pressure gradient force with high pressure on the inside and low pressure on the outside
clockwise on the north, counterclockwise on the south
four components of subtropical gyres
- equatorial current driven by tradewinds
- western boundary current (hot) deflected
- west wind drift driven by westerlies
- eastern boundary current (cold) deflected
5 major ocean gyres
- indian ocean gyre
- north pacific gyre
- south pacific gyre
- north atlantic gyre
- south atlantic gyre
basics of deep currents (6 things)
- driven by bouyancy (density) forces
- gravity is the driving force - also known as thermohaline circulation
thermo = heat, haline = salt - both of these affect density
- flow is much slower than surface currents (1000 years for deep water to circulate)
- formation of deep water is due to evaporation and formation of sea ice
- makes the water more dense and thus sinks to the bottom
two places of deep water formation
- north atlantic deep water (NADW)
- forms near greenland; evaporation and cooling causes surface water to sink and flow south - anarctic bottom water (AABW)
- densest deep water
- cold, dense water from sea ice formation in the weddell sea sinks and mixes with NADW form AABW
how can water masses be distinguished?
by their temperatures and salinities
what are surface currents driven by?
winds
what is deep ocean circulation driven by?
gravity
