Fig. CO7
Ocean currents
Large-scale moving seawater
 Surface ocean currents

 Transfer heat from warmer to cooler areas
 Similar to pattern of major wind belts
 Affect coastal climates

Deep ocean currents
 Provide oxygen to deep sea

Affect marine life
Types of ocean currents


Surface currents
 Wind-driven
 Primarily horizontal
motion
Deep currents
 Driven by differences in
density caused by
differences in
temperature and salinity
 Vertical and horizontal
motions
http://www.global-greenhouse-warming.com/images/thermohaline.jpg
Measuring surface currents

Direct methods
 Floating device tracked through
Fig. 7.1a
time
 Fixed current meter

Indirect methods
 Pressure gradients
 Radar altimeters
○ Satellites measuring bulges which
are due to shape of ocean flow
and currents
 Doppler flow meter (Acoustic
Doppler Current Profiler)
○ Measures shift in frequency of
sound waves to determine current
movement
http://www.pmel.noaa.gov/tao/images/nxcur.gif
Measuring deep currents
Floating devices tracked through time
 Chemical tracers (radioactive isotopes)

 Tritium
 Chlorofluorocarbons

Characteristic temperature and salinity
 Arrays of bottom monitors and cables
Surface currents
Frictional drag between
wind and ocean
 Wind plus other factors
such as…






Distribution of continents
Gravity
Friction
Coriolis effect cause
Gyres or large circular
loops of moving water
http://static.howstuffworks.com/gif/ocean-current-4.jpg
Ocean Gyres

World’s 5 subtropical gyres:
○ North Atlantic Gyre
○ South Atlantic Gyre
○ North Pacific Gyre
○ South Pacific Gyre
○ Indian Ocean Gyre

When talking about location of currents,
we refer to the ocean basin – not the
land!
 For instance, the Gulf Stream is a Western
Boundary current of the North Atlantic
○ Even though it runs along side the eastern US
Ocean gyres
3
2
4
1
4
2

Subtropical gyres
 Center of each is about 30o N or S
3

Major parts
1.
Equatorial currents flow west
2.
Western Boundary currents flow north or south
3.
Northern or Southern Boundary currents – push water east
4.
Eastern Boundary currents flow north or south
Other surface currents

Equatorial countercurrents flow east, counter to equatorial currents in the subtropical
gyres
 As trade winds push equatorial current of subtropical gyre west, water builds
up in western part of ocean basin
 Since coriolis effect is minimal at equator, that build-up of water then flows
east at equator

Subpolar gyres flow eastward
Fig. 7.5
Other factors affecting surface currents



Ekman transport
Geostrophic currents
Western intensification of subtropical gyres
 All of these are connected
Fig. 7.5
Ocean Circulation
Ekman spiral and transport
Surface currents move
at angle to wind
 Ekman spiral describes
speed and direction of
seawater flow at
different depths
 Each successive layer
moves increasingly to
right (N hemisphere)

○ Initial push of water and
then Coriolis effect
comes into play
Ekman spiral and transport

Average movement of seawater under
influence of wind affected by Coriolis effect
 90o to right of wind in Northern hemisphere
 90o to left of wind in Southern hemisphere
Ekman Spiral and Coastal Upwelling/Downwelling
Geostrophic flow

http://maritime.haifa.ac.il/departm/lessons/ocean/
Ekman transport piles
up water within
subtropical gyres
 Surface water flows
downhill (gravity) and
 Also to the right (Coriolis
effect)

Balance of downhill and
to the right causes net
geostrophic flow around
the “hill”
Fig. 7.8
Western intensification
Top of hill of water displaced toward west due
to Earth’s rotation
  water piles up on western side of gyre
 Western boundary currents intensified

 Faster
 Narrower
 Deeper
 Warm
http://maritime.haifa.ac.il/departm/lessons/ocean
Eastern Boundary Currents
Eastern side of ocean basins
 Tend to have the opposite properties of
Western Currents

 Slow
 Wide
 Shallow
 Cold
http://maritime.haifa.ac.il/departm/lessons/ocean
Ocean currents and climate

Warm ocean currents
warm air at coast
 Creates warm, humid
air on coast
 Humid climate on
adjoining landmass
August temperatures
February temperatures

Cool ocean currents
cool air at coast
 Cool, dry air
 Dry climate on
adjoining landmass
Ocean
currents
and
climate
Fig. 7.9
August temperatures
February temperatures
Diverging surface seawater
o
Divergence
o winds move surface
seawater away from
geographical equator due
to Coriolis effect
o
Deeper seawater (cooler,
nutrient-rich) flows up to
replace surface water
o Equatorial Upwelling
o High biological
productivity
Fig. 7.10
Converging surface seawater
o
Convergence
o surface seawater moves
towards an area
o Surface seawater piles up
o
Nutrient depleted surface
water moves downward
o Downwelling
o Low biological productivity
o
Occurs at center of gyres
Fig. 7.11
Coastal upwelling and
downwelling
Winds blowing down
coasts
 Ekman transport moves
surface seawater…

 onshore (downwelling)
or…
 offshore (upwelling)
Fig. 7.12

Upwelling at higher latitudes
 Remember there is no pycnocline at the
poles
○ Therefore, water moving towards the poles
cools and becomes more dense, like all of the
other water at the poles
○ This allows there to be significant vertical
mixing
 Very productive waters – this is where large animals
(such as whales) go to feed
Antarctic circulation




Fig. 7.14
Antarctic Circumpolar
Current (West Wind Drift)
 Encircles Earth
 Transports more water
than any other current
East Wind Drift from
polar easterlies
Antarctic Divergence from
opposite directions of
west and east wind drifts
Antarctic Convergence
piles up and sinks below
warmer sub-Antarctic
waters
Atlantic Ocean circulation

North Atlantic Subtropical Gyre




Gulf Stream (GS)
North Atlantic Current
Canary Current (C)
North Equatorial Current (NE)
○ Merges with S. Equatorial current
to form Antilles and Caribbean
currents 
○ Converge to form Florida Current
(F) thru Florida Strait
○ May form Loop current into Gulf of
Mexico
 Atlantic Equatorial Counter Current
(EC) – between North and South
Equatorial currents
http://www.amnh.org/exhibitions/permanent/ocean/images/01_dioramas/
features/05_sargasso/overview_df.jpg

North Atlantic Subtropical Gyre
 Sargasso Sea
○ Center of gyre – eddy
○ Sargassum “weed” accumulates
in convergence
○ Provides habitat for many
marine animals
http://www.safmc.net/Portals/0/Sargassum/Sargassum_Ross1.jpg
http://upload.wikimedia.org/wikipedia/commons/b/b4/Sargasso.png
Fig. 7.16
Atlantic Ocean circulation

Fig. 7.14
South Atlantic
Subtropical Gyre
 South Equatorial
Current (SE)
 Brazil Current (Br)
 Antarctic
Circumpolar Current
(WW)
 Benguela Current
(Bg)
Gulf Stream
o
o
o
Best studied
Meander is a bend in
current  may pinch off
into a loop
o Warm-core rings form
to north
o Cold-core rings form to
south
Unique biological
populations
Fig. 7.17b
Warm
core ring
Cold core
rings
http://sam.ucsd.edu/sio210/gifimages
Warm
core ring
forming
http://ocw.mit.edu/NR/rdonlyres/Global
Core ring vertical profiles
http://kingfish.coastal.edu/marine/gulfstream
Warm core ring off
“Loop Current” in the Gulf of Mexico
http://storm.rsmas.miami.edu/~nick/
In 2005, winds of Hurricanes Katrina and Rita increase
as they pass over warm loop current in Gulf of Mexico
http://en.wikipedia.org/wiki/
http://ccar.colorado.edu/~leben/
Other North Atlantic currents
Labrador Current
 Irminger Current
 Norwegian Current
 North Atlantic Current

Climate effects of North Atlantic currents
Gulf Stream warms East
coast of U.S. and
Northern Europe
 North Atlantic and
Norwegian Currents
warm northwestern
Europe
 Labrador Current cools
eastern Canada
 Canary Current cools
North Africa coast

Pacific Ocean circulation

North Pacific
subtropical gyre




Kuroshio
North Pacific Current
California Current
North Equatorial
Current
 Alaskan Current
Fig. 7.19
Figure 7.19
Pacific Ocean circulation

South Pacific subtropical
gyre
 East Australian Current
 Antarctic Circumpolar
Current
 Peru Current
 South Equatorial Current
 Equatorial Counter Current
Atmospheric and oceanic disturbances in Pacific Ocean – El
Niño-Southern Oscillation (ENSO)
Relationship of sea surface temp and high altitude
pressure
 Normal conditions

 Air pressure across equatorial Pacific is higher in eastern Pacific
 Strong southeast trade winds
 Pacific warm pool on western side
 Thermocline deeper on western side
 Upwelling off the coast of Peru bring nutrient-rich waters to surface
As, you are looking at these
figures pay attention to
where thermocline is
(remember that raising
thermocline leads to
upwelling which brings
nutrients and oxygen-rich
waters up to surface for
organisms
Normal conditions
Fig. 7.20a

El Niño-Southern
Oscillation (ENSO)
 Warm (El Niño)
○ High pressure in eastern
Pacific weakens
○ Weaker trade winds
○ In strong El Nino events, trade
winds can actually reverse
○ Warm pool migrates eastward
○ Thermocline deeper in eastern
Pacific
○ Downwelling  lowers
biological productivity in East
Pacific
 Corals particularly sensitive
to warmer seawater
 Fish kills
El Niño and La Niña

El Niño-Southern
Oscillation (ENSO)
 Warm (El Niño)
○ Produces heavy rains and
flooding in equatorial western
South America
○ Droughts in western Pacific
○ Droughts in Indonesia and
Northern Australia
 Cool phase (La Niña)
○ Increased pressure difference across equatorial Pacific –
overshoots return to normal from El Niño
○ Stronger trade winds
○ Stronger upwelling in eastern Pacific
 Shallower thermocline
 Higher biological productivity
 Cooler than normal seawater
○ Higher than normal hurricane season in Atlantic
El Niño-Southern
Oscillation (ENSO)
Cool phase (La Niña)
Fig. 7.20c
ENSO events
El Niño warm phase about every 2 to 10 years
 Highly irregular
 Phases usually last 12 to 18 months

Fig. 7.22
ENSO events
Strong events effect global weather
 1982-83, 1997-98
 Mild events only effect weather in equatorial South Pacific
 2002-2003, 2004-2005, 2006-2007
 Effects of strong event can vary
 Can be drier than normal or wetter than normal
 Can be warmer than normal or cooler
○ Can produce thunderstorms and tornados in midwest
○ Can produce droughts in west
○ Pushes jet stream eastward, pushing Atlantic hurricanes east,
away from U.S.
○ Less hurricanes reach US during El Nino, more during La Nina


Flooding, drought, erosion, fires, tropical storms, harmful effects on
marine life

Examples: coral reef death in Pacific, crop failure in Philippines, increased cyclones in
Pacific, drought in Sri Lanka
Fig. 7.21
“Severe” (1997) and “Mild” (2002) El Nino
http://science.nasa.gov/headlines/
Freeze probability lower during La Nina
Freeze probability slightly higher during El Nino
Thermohaline circulation
Caused by density
differences due to
temp and salinity in
different areas
 Below the pycnocline
 90% of all ocean
water
 Slow velocity

http://www.john-daly.com/polar
Thermohaline circulation

Bottom water formation
 Movement caused by differences in density (temperature
and salinity)
 Formed by freezing saltwater  dense brine sinks
○ Cooler seawater denser
○ Saltier seawater denser
http://www.geology.um.maine.edu/ges121/lectures/19-ocean-conveyor
Thermohaline circulation

Originates in high latitude
surface ocean


Near Greenland & Iceland in
North Atlantic
Weddell Sea  Antarctic Bottom
Water (coldest)
○
○
Forms densest oceanic water 
flows on bottom
Moves north in all three ocean
basins
 Once surface water sinks (high
density) it changes little
 Deep-water masses identified on T-S
diagram
Thermohaline circulation
Fig. 7.26
Thermohaline circulation

Selected deep-water masses
 Antarctic Bottom Water
 North Atlantic Deep Water
 Antarctic Intermediate Water
 Oceanic Common Water

Cold surface seawater sinks at polar regions
and moves equatorward
Conveyor-belt circulation

Combination deep ocean currents and surface
currents
Fig. 7.27
Ocean Circulation
Deep ocean currents




Cold, oxygen-rich surface water to deep ocean
Dissolved O2 important for life and mineral processes
Deep ocean currents do bring water across the equator
Changes in thermohaline circulation can cause global
climate change
 Example: warmer surface waters with increased
melting of ice caps  less dense surface waters
○ Bottom water will not form and sink  Gulfstream
may be altered  long-term cooling, particularly in
northern Europe
○ less oxygen deep ocean
Misconceptions
Earth events taking place within the
global environment are not
interconnected, such as El Nino is not
important to people living in the
midwest.
 Humans are the only cause of global
warming.
 The greenhouse effect will cause all
living things to die.

Ocean Literacy Principles








1c - Throughout the ocean there is one interconnected circulation system powered by wind, tides, the
force of the Earth’s rotation (Coriolis effect), the Sun, and water density differences. The shape of
ocean basins and adjacent land masses influence the path of circulation.
1d - Sea level is the average height of the ocean relative to the land, taking into account the
differences caused by tides. Sea level changes as plate tectonics cause the volume of ocean basins
and the height of the land to change. It changes as ice caps on land melt or grow. It also changes as
sea water expands and contracts when ocean water warms and cools.
3a - The ocean controls weather and climate by dominating the Earth’s energy, water and carbon
systems.
3b - The ocean absorbs much of the solar radiation reaching Earth. The ocean loses heat by
evaporation. This heat loss drives atmospheric circulation when, after it is released into the
atmosphere as water vapor, it condenses and forms rain. Condensation of water evaporated from
warm seas provides the energy for hurricanes and cyclones.
3c - The El Niño Southern Oscillation causes important changes in global weather patterns because it
changes the way heat is released to the atmosphere in the Pacific.
3d - Most rain that falls on land originally evaporated from the tropical ocean.
3f - The ocean has had, and will continue to have, a significant influence on climate change by
absorbing, storing, and moving heat, carbon and water.
3g - Changes in the ocean’s circulation have produced large, abrupt changes in climate during the last
50,000 years.
Sunshine State Standards



SC.8.P.8.4
Classify and compare substances on the basis of characteristic physical
properties that can be demonstrated or measured; for example, density, thermal or electrical
conductivity, solubility, magnetic properties, melting and boiling points, and know that these properties
are independent of the amount of the sample.
SC.912.E.7.2
Analyze the causes of the various kinds of surface and deep water motion within
the oceans and their impacts on the transfer of energy between the poles and the equator.
SC.912.P.10.4
Describe heat as the energy transferred by convection, conduction, and
radiation, and explain the connection of heat to change in temperature or states of matter