fig. co7. ocean currents large-scale moving seawater surface ocean currents transfer heat from...
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Fig. CO7
Ocean currents
Large-scale moving seawater Surface ocean currents
Transfer heat from warmer to cooler areas
Similar to pattern of major wind beltsAffect coastal climates
Deep ocean currentsProvide oxygen to deep sea
Affect marine life
Types of ocean currents
Surface currentsSurface currentsWind-drivenPrimarily horizontal
motion Deep currentsDeep 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 time
Fixed current meter
Indirect methodsPressure gradientsRadar 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
Fig. 7.1a
http://www.pmel.noaa.gov/tao/images/nxcur.gif
Measuring deep currents Floating devices tracked through time Chemical tracers (radioactive
isotopes)TritiumChlorofluorocarbons
Characteristic temperature and salinityArrays of bottom monitors and cables
Surface currents
Frictional drag between wind and ocean
Wind plus other factors such as…Distribution of
continentsGravityFrictionCoriolis effect cause
GyresGyres 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
Subtropical gyres Center of each is about 30o N or S
Major parts1. Equatorial currents flow west2. Western Boundary currents flow north or south3. Northern or Southern Boundary currents – push water
east4. Eastern Boundary currents flow north or south
1
2
3
4
3
24
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 effect90o to right of wind in Northern hemisphere90o to left of wind in Southern hemisphere
Ekman Spiral and Coastal Upwelling/Downwelling
Geostrophic flow 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 flowgeostrophic flow around the “hill”
Fig. 7.8
http://maritime.haifa.ac.il/departm/lessons/ocean/
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
FasterNarrowerDeeper
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 CurrentsSlowWideShallowCold
http://maritime.haifa.ac.il/departm/lessons/ocean
Ocean currents and climate Warm ocean
currents warm air at coastCreates warm,
humid air on coastHumid climate on
adjoining landmass
Cool ocean currents cool air at coastCool, dry airDry climate on
adjoining landmass
August temperatures February
temperatures
Ocean currents and climate
Fig. 7.9
August temperatures February
temperatures
Diverging surface seawatero 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 watero Equatorial Upwellingo High biological
productivity
Fig. 7.10
Converging surface seawater
Fig. 7.11
o Convergence o surface seawater
moves towards an areao Surface seawater piles
up
o Nutrient depleted surface water moves downwardo Downwellingo Low biological
productivity
o Occurs at center of gyres
Coastal upwelling and downwelling
Winds blowing down coasts
Ekman transport moves surface seawater…onshore
(downwelling) or…offshore (upwelling)
Fig. 7.12
Upwelling at higher latitudesRemember 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 mixingVery productive waters – this is where large
animals (such as whales) go to feed
Antarctic circulation
Fig. 7.14
Antarctic Circumpolar Antarctic Circumpolar Current (West Wind Current (West Wind Drift)Drift) Encircles Earth Transports more
water than any other current
East Wind DriftEast Wind Drift from polar easterlies
Antarctic DivergenceAntarctic Divergence from opposite directions of west and east wind drifts
Antarctic ConvergenceAntarctic Convergence piles up and sinks below warmer sub-Antarctic waters
Atlantic Ocean circulation North Atlantic Subtropical
Gyre Gulf Stream (GS)Gulf Stream (GS) North Atlantic Current North Atlantic Current Canary Current (C)Canary Current (C) North Equatorial Current (NE)North Equatorial Current (NE)
○ Merges with S. Equatorial current to form Antilles and Caribbean currents
○ Converge to form Florida Florida Current (F) Current (F) thru Florida Strait
○ May form Loop current Loop current into Gulf of Mexico
Atlantic Equatorial Counter Atlantic Equatorial Counter Current (EC)Current (EC) – between North and South Equatorial currents
No. Atlantic current
F
North Atlantic Subtropical Gyre Sargasso SeaSargasso Sea
○ Center of gyre – eddy ○ Sargassum “weed”
accumulates in convergence ○ Provides habitat for many
marine animals
http://upload.wikimedia.org/wikipedia/commons/b/b4/Sargasso.png
http://www.amnh.org/exhibitions/permanent/ocean/images/01_dioramas/features/05_sargasso/overview_df.jpg
http://www.safmc.net/Portals/0/Sargassum/Sargassum_Ross1.jpg
Fig. 7.16
Atlantic Ocean circulation
South Atlantic Subtropical Gyre South Equatorial South Equatorial
Current (SE)Current (SE) Brazil Current Brazil Current
(Br)(Br) Antarctic Antarctic
Circumpolar Circumpolar Current (WW)Current (WW)
Benguela Current Benguela Current (Bg)(Bg)
Fig. 7.14
Fig. 7.17b
o Best studiedo Meander is a
bend in current may pinch off into a loopo Warm-core
rings form to north
o Cold-core rings form to south
o Unique biological populations
Gulf StreamGulf Stream
http://sam.ucsd.edu/sio210/gifimages http://ocw.mit.edu/NR/rdonlyres/Global
Warm core ring forming
Warm core ring
Cold core rings
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://ccar.colorado.edu/~leben/http://en.wikipedia.org/wiki/
Other North Atlantic currents
Labrador CurrentLabrador Current Irminger CurrentIrminger Current Norwegian CurrentNorwegian Current North Atlantic CurrentNorth 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
North Pacific subtropical gyreKuroshioKuroshioNorth Pacific North Pacific
CurrentCurrentCalifornia CurrentCalifornia CurrentNorth Equatorial North Equatorial
CurrentCurrentAlaskan CurrentAlaskan Current
Pacific Ocean circulationPacific Ocean circulation
Fig. 7.19
Figure 7.19
Pacific Ocean circulation South Pacific
subtropical gyreEast Australian CurrentEast Australian CurrentAntarctic Circumpolar Antarctic Circumpolar
CurrentCurrentPeru CurrentPeru CurrentSouth Equatorial South Equatorial
CurrentCurrentEquatorial Counter Equatorial Counter
CurrentCurrent
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 thesefigures pay attention to where thermocline is (remember that raising thermocline leads to upwelling which brings nutrients and oxygen-richwaters up to surface fororganisms
Normal conditions
Fig. 7.20a
El Niño-Southern El Niño-Southern Oscillation (ENSO)Oscillation (ENSO)Warm (El Niño)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 PacificCorals particularly
sensitive to warmer seawater
Fish kills
El Niño and La Niña
El Niño-Southern El Niño-Southern Oscillation (ENSO)Oscillation (ENSO)Warm (El Niño)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)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 thermoclineHigher biological productivityCooler 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 Severe” (1997) and “Mild” (2002) El
NinoNino
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 WaterAntarctic Bottom WaterNorth Atlantic Deep WaterNorth Atlantic Deep WaterAntarctic Intermediate WaterAntarctic Intermediate WaterOceanic Common WaterOceanic 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 changeExample: 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