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Chapter 8: Ocean Circulation
Fig. 8-26
Ocean currents move large amounts of water and heat
Wind-driven surface ocean circulation
Density-driven deep-ocean circulation Both
redistribute heat from warmer regions to cooler Fig. 8-
16
Measuring ocean currents
Direct measurement Floating
objects/instruments Fixed instruments
Indirect measurement Distribution of density Satellite data Doppler flow meter Chemical tracers Distinctive water masses
Surface currents Frictional drag due to winds Surface currents similar to global
winds Continents affect surface current
patterns Other factors:
Gravity Friction Coriolis Effect
Subtropical gyres
Large circular flow Clockwise in northern oceans, e.g., North Atlantic
Counterclockwise in southern oceans, e.g., South Atlantic
4 main currents in each gyre
Ekman spiral and Ekman transport
Ekman transport moves surface seawater about 90o to the right of the wind in the Northern Hemisphere
90o left in Southern Hemisphere
Fig. 8-6a
Western intensification “Hill” of seawater is steeper on western side Western currents are fast, narrow, deep
Subtropical gyres Ekman transport
piles up “hill” of seawater at about 30o N and S
Water flows downhill under gravity and veers right (Northern hemisphere) due to Coriolis Effect
Circular flowFig. 8-7
Upwelling
Ekman transport moves seawater offshore
Ekman transport moves seawater away from another water mass
Fig. 8-11a
Cooler, nutrient-rich water rises vertically toward sea surface
High biologic productivity
Downwelling opposite Fig. 8-11b
Surface currents
Pattern similar in major ocean basins
Northern ocean gyre moves clockwise
Southern ocean gyre moves counter-clockwise
Antarctic circulation
Antarctic Circumpolar Current (or West Wind Drift) Greatest volume Connects main oceans
East Wind Drift Antarctic Divergence
(upwelling)
North Atlantic Circulation
North Equatorial Current Gulf Stream North Atlantic Current
Gulf Stream and North Atlantic Currents warm Europe
Canary Current
North Equatorial Current
Gulf Stream
North Atlantic Current
Canary Current
South Atlantic Ocean
South Equatorial Current Brazil Current Antarctic Circumpolar Current
Greatest volume Connects three main oceans
Benguela Current
South Equatorial current
Brazil Current
Benguela Current
North Pacific Ocean
North Equatorial Current Kuroshio Current North Pacific Current California Current Strong Equatorial Counter
Current
South Pacific Ocean
South Equatorial Current East Australian Current Antarctic Circumpolar Current Peru Current Strong Equatorial Counter
Current
ENSO El Niño-Southern Oscillation
Irregular shift in ocean and atmosphere characteristics every 2-10 years
Affects global climate Harmful and beneficial
consequences
El Niño ENSO Warm Phase Most obvious in Equatorial Pacific Pacific Warm Pool moves eastward across
Equatorial Pacific Changes in pattern of upwelling/downwelling
in eastern Pacific Ocean
Fig. 8-2
ENSO warm phase effects
Warmer seawater higher sea level Warmer seawater less upwelling in
eastern Pacific Lower biologic productivity
Warmer seawater kills some marine life
Shift in atmosphere pressure Shift in areas of precipitation
La Niña ENSO Cool Phase
Stronger tradewinds Warm pool stays in western
Pacific Increased upwelling in eastern
Pacific Shift in precipitation patterns Shift in atmospheric pressure
ENSO data collection TOGA Tropical Ocean Global
Atmosphere TAO Tropical Atmosphere Ocean
Monitor ocean and atmosphere Data indicate what phase ENSO
Pacific Decadal Oscillation Decades-long cycles of warming and cooling in Pacific Ocean
Indian Ocean Circulation North and South Equatorial
Currents Equatorial Counter Current Agulhas Current Antarctic Circumpolar Current West Australian Seasonal shifts (monsoons) of
winds and currents
Thermohaline circulation 90% of world
ocean Below pycnocline Large volumes of
seawater Extremely slow
speed Each ocean basin
is similar in deep-ocean circulation
Sources of deep water
Densest seawater is cold Most deep water masses
from polar oceans Sink to density level and
move horizontally
Antarctic Bottom Water Densest deep
water (coldest) Sinks around
Antarctica Most widespread
deep-water mass Found as far as
40o N Carries O2 into
deep ocean Fig. 8-25
North Atlantic Deep Water Complex mixture
of cold seawater from Norwegian sea mixing with Gulf Stream Mediterranean
Intermediate Water
Other NA water masses
Extends from North Atlantic to about 40o south
Intermediate Water Masses
Antarctic Intermediate Water Sinks at Antarctic Convergence Cold Salinity less than average
Mediterranean Intermediate Water Warm Very salty
Conveyor Belt Circulation Mixture of
surface ocean circulation and deep-ocean circulation
Mixes surface and deep
Mixes waters in different oceans
Fig. 8-26
Langmuir Circulation Alternately converging and diverging
convection cells Wind blowing over calm ocean Alternate rows of upwelling and downwelling
End of Chapter 8: Ocean Circulation