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