2. How can density drive circulation?
Temperature, salinity, and temperature
changes
Well mixed surface layer of 100 m and
below that density changes rapidly
Due to temperature decreases (100-
1000 m)
Below 1000 m changes are not as great
Density increases as head toward
bottom of ocean
3. Latitude affects density
Warm low-salinity water at equator less
dense than
30 degrees where water cooler and
higher salinity due to lack of rain
60 degrees is even more dense than
equator and 30 degrees N. or S. due to
temperature and salinity
Polar regions in winter when sea ice is
formed have higher salinity and dense
water sinks below all other latitudes
4. What is thermohaline circulation? How is it
driven?
Density driven vertical circulation
controlled by temperature and salinity
If more dense water on top then initiates
downwelling
While less dense water rises called
upwelling = overturn
7. Thermohaline Circulation
If same density in water column then
waves and wind can mix easily
If density changes with depth then does not
over turn and more stable
Large scale thermohaline circulation
system ensures eventual mixing from top
to bottom
Seasonal changes in temperature more
important than seasonal changes in salinity
in altering density in open oceans
8. What are the layers dividing?
Temperature, salinity, and density
North Atlantic Ocean Deep Water = where converge at 60
degrees N.
What is the result of this convergence?
34 0/00 and 2-4 degrees C
Dense water sinks and moves south
Above very salty warm water is trapped by gyre
movement
Between these layers is an intermediate salinity and
temperature
Mediterranean water finds own layer as empties into
ocean
Antarctic Intermediate water is warmer and less salty than
the Atlantic Ocean Deep Water
10. Sea Ice forms Antarctic Bottom water and is the densest water in the
ocean
Sea Ice forms Antarctic Bottom water and
is the densest water in the ocean
This water moves northward and under the
Atlantic Deep water
Trapped on the West side of the Mid-
Atlantic Ridge system
Moves as far North as equator
North Atlantic Deep water splits as reaches
surface and northward part becomes South
Atlantic surface water and Antarctic
Intermediate water and moves southward
11. What differences do you notice between the
different oceans?
Pacific Ocean colder less salty water
Atlantic warmer and more salty
The Arctic Ocean = density controlled by salinity and not
temperature
Combines with Gulf Stream water to form North Atlantic
Deep water
The Pacific Ocean = Conditions uniform below 2000 m
N. Pacific isolated from the Arctic Ocean
Western side cold Bering Sea water converges with
Equatorial currents produces a small volume that sinks to
mid depths
Indian Ocean = Antarctic circumpolar water mainly and
small amounts of Antarctic Intermediate water and warm
salty surface water
13. What is a gyre?
Circular motion of larger ocean currents
Currents driven by trade winds and
Coriolis effect accumulate in the middle
of the gyre and elevate water 3ft or more
Western Intensification western sides of
gyres are narrower and more intense
14.
15. Gyres
Western sides more intense due to =
increased coriolis effect with increased
latitudes, changing wind direction with
latitude, friction between ocean currents
and land masses
Most intense in N. Hemisphere with Gulf
Stream and Kuroshio Currents
Others obscured by deflection currents
or islands
16. Surface currents driven by?
The Pacific Ocean
Trade winds move water away from Central
& S. Am. and push up against Asia
Westerlies move water away from Asia and
push up against west coast of N. Am.
Water that accumulates must move
towards water that has been removed
Creating CA and Kuroshio currents on E.
and W. sides
Note other minor currents that feed into the
N. Pacific Gyre (i.e. Oyashio
17. Gyres are on 5 degrees either side of
equator and Equatorial Countercurrent
runs in the opposite direction (i.e. helps
return surface water that has
accumulated against Asia)
Charts can show surface flows over
specific time but do not reflect
El nino and la nina
18. The Atlantic Ocean
Gulf Stream fed by both N. Equatorial and Gulf
currents
Speeds up to 5ft per second
Volume flow 500x the Amazon River
FL current may exceed Gulf Stream in speed
N. Atlantic Gyre isolates Sargasso Sea
1000 m deep of clear warm surface water
Defined by the currents and N. Atlantic Ridge
Sargasso seaweed or algae provides rich
community in a dessert of open ocean (with
down welling = nutrient poor)
20. S. Atlantic Ocean trade winds move
water to west but Brazil splits the S.
Equatorial Current.
Most goes into Caribbean Sea and Gulf
Why is this important to the U.S.?
21. Cousteau and the Amazon
http://www.imdb.com/video/cbs/vi41306
03545/
The Amazon feeds out into the ocean
and flows North past the Caribbean
Islands and into the Gulf of Mexico
What goes on in the Amazon affects us!
22. The Arctic Ocean
Large clockwise gyre
Some water from Pacific through Bering
Strait
Some water from Atlantic west of
Spitsbergen
West Greenland water flows S. and joins
Labrador Current
23. Indian Ocean
The Indian Ocean
S. Hemisphere ocean
Smallest Gyre
N. Equatorial Current strengthened by
northeast trade winds during dry season
Wet monsoon season winds strengthen the
Equatorial Countercurrent and reduce N.
Equatorial
This seasonal shift unlike in Atlantic or
Pacific gyres
24. Convergent vs. Divergent
What is the difference between
convergence and divergence
currents?
Convergence = combining of currents
where downwelling occurring
Divergence = currents upwell and move
away from each other
25. Convergence Currents
Subtropical convergences at 30-40
degrees N. and S.
Arctic and Antarctic convergences at 50
degrees N. and S.
Three major ocean divergence zones =
two tropical and one Antarctic
Convergence brings oxygen rich surface
water to depths and
26. Divergence brings nutrients up
from the deeper waters
Mixing of waters of different geographic
regions mix with these currents
Thermohaline and wind driven currents are
closely related
Changing sea levels, moving continents,
and shapes of ocean basins have changed
these currents
Climate change also has altered locations
and role of upwelling and down welling
Surface currents driven by winds and
thermohaline help redistribute heat, salinity,
and dissolved gases
27. Coastal Upwelling and
Downwelling
Why are these area important?
Productive areas for nutrients and fish
Trade winds on Western sides of
continents create continual upwelling
Seasonal upwelling and downwelling
occurs along coast lines
Lack of land in S. Hemisphere has less
of this affect
28. Northwest U.S.
From S. CA to Vancouver Island
Southerly winds in winter and Northerly
in summer and thus changing Ekman
transport of water
Net result is upwelling in the summer
and downwelling in the winter
30. What is the Ekman Spiral and Ekman
Transport?
Deeper water moves more slowly with
greater deflection and water at the
bottom moves in the opposite direction
(i.e. spiral motion)
32. Eddies
Where are they found and how are they
created?
Pockets of cold or warm water moving in a
circular motion spinning off major current
(i.e. Gulf Stream)
Current meanders and creates these
pockets on either side
Eddies occur throughout the ocean at all
depths
Each eddy has own chemistry until it mixes
with surrounding water
34. Fish and other marine life use Eddies to escape
predators in the open ocean! (Gulf Stream below)
35. How are currents measured?
Following the water with die, pictures or
a machine
Also measure speed and direction as
passes a fixed point
Satellite images
Buoys
Doppler
Could be used on the surface or
underwater anchored to buoy
36. Image of acoustic doppler being used in Greenland
http://www.whoi.edu/page.do?pid=10897&i=8201&x=247
37. Newer electronic meters emit narrow
frequency sound beams in all four
directions
Echo frequency is related to water speed
and is known as the Doppler Effect
In order to emit frequency in all four
directions, meter is checked against
internal compass
Data can be stored or transmitted to ship or
surface buoy
39. How can oceans provide energy?
Through heat and currents
Oceans have large heat capacity
Ocean Thermal Energy Conversion
(OTEC) works with temperature
differences between surface and up to
1000 m
41. Energy from Heat
Two types: 1) Closed system uses
contained fluid such as ammonia or
Freon with low boiling point or
2) Open system which directly converts
sea water to steam
42. Closed system = warm water passes
over evaporator chamber that contains
fluid. Working fluid is vaporized by heat
from sea water. As vapor heats up it
builds up pressure to spin turbine which
in turn generates power. After fluid has
been heated up then it is returned to
liquid state to start cycle all over again.
44. Open system = requires large quantities
of warm water and must be condensed
by using fresh water.
Requires at least 20 degrees C
difference between surface and depth in
order to generate more power than is
used
47. Latitudes of 25 degrees N. or S. would
be best location for plants due to
average sea temperature of 22 degrees
C
Plant/Lab in Hawaii (NELHA) closed
after seven years in use due to cost
being 10x that of oil or coal
Now experimenting with bringing cold
water from depths and producing fresh
water with lab.
