1. Chapter 8 and 9

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

5. Thermohaline Circulation

6. NASA Imagery

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

9. Subsurface layers in Atlantic
http://oceano.iim.csic.es/co2group/carboocean.html

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

12. http://www.solcomhouse.com/gulfstream.htm

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

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)

19. http://infranetlab.org/blog/wpcontent/uploads/2008/12/north_pacific_gyre
_world_map.png

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

29. http://www.cop.noaa.gov/stressors/climatechange/current/fact-
globecpne.html

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)

31. https://www.e-education.psu.edu/earth540/content/c4_p3.html

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

33. http://www.liv.ac.uk/physocean/research.html

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

38. http://www.pmel.noaa.gov/tao/proj_over/mooring.sht
ml

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

40. http://www.phoenixprojectfoundation.us/

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.

43. Closed System
http://www.nrel.gov/otec/electricity.html

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

45. Open System
http://www.nrel.gov/otec/electricity.html

46. Hybrid System
http://www.nrel.gov/otec/electricity.html

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.

48. http://nelha.org/

49. Other sources of energy in the oceans…
http://www.phoenixprojectfoundation.us/