Ocean Currents

Why is Ocean Circulation Important?

• Transport nutrients and organisms

• Influences weather and climate

• Influences commerce

Density of air

• Warm, low density air rises

• Cool, high density air sinks

ITCZ intertropical convergence zone= doldrumsLow pressure, wet climate

High pressure, dry climate

Low pressure, wet climate

30o

30o

60o

60o

90o

90o

0o

High pressure, dry climate

The Coriolis effect• The Coriolis effect

– Is a result of Earth’s rotation– Causes moving objects to follow

curved paths:• In Northern Hemisphere, curvature

is to right• In Southern Hemisphere, curvature

is to left

Surface Currents

The upper 400 meters of the ocean (10%).

Deep Water Currents

Thermal currents (90%)

Ocean Currents

Wind-driven surface currents

Wind-Driven and Density-Driven Currents

• Wind-driven currents occur in the uppermost 100 m or less

Sailors have know about ocean currents for centuries

Sailors have know that “rivers” flow in the seas since ancient times. They used them to shorten voyages, or were delayed by trying to stem them.

If navigators do not correct to deflection by currents, they may be far away from where they think they are and meet disaster.

Ben Franklin and the Gulf Stream

Matthew Fontaine MauryThe first systematic study

of currents was done by Maury based on logbooks in the US Navy’s Depot of Charts and Instruments.

His charts and “Physical Geography of the Sea” assisted navigators worldwide.

http://www.npg.si.edu/exh/brady/gallery/97gal.html

Gyres are large circular-moving loops of waterFive main gyres (one in each ocean

basin):• North Pacific• South Pacific• North Atlantic• South Atlantic• Indian

• Generally 4 currents in each gyre• Centered about 30o north or south

latitude

Current Gyres

Pacific Ocean surface currents

What do Nike shoes, rubber ducks, and hockey gloves have to do with currents?

Lost at Sea

• January 1992 - shipwrecked in the Pacific Ocean, off the coast of China

• November 1992 - half had drifted north to the Bering Sea and Alaska; the other half went south to Indonesia and Australia

• 1995 to 2000 - spent five years in the Arctic ice floes, slowly working their way through the glaciers2001 - the duckies bobbed over the place where the Titanic had sunk

• 2003 - they were predicted to begin washing up onshore in New England, but only one was spotted in Maine

• 2007 - a couple duckies and frogs were found on the beaches of Scotland and southwest England.

Duckie Progress

2004-2007 Barber’s Point

• “Great Pacific Garbage Patch”

• Estimate: 46,000 pieces of floating garbage/mi2.

North Pacific Subtropical Gyre

North Pacific Subtropical Gyre

135° to 155°W and 35° to 42°N

North Pacific Subtropical Gyre

http://marinedebris.noaa.gov/info/patch.html#6

Great Pacific Garbage Patch- Good Morning America 2010 http://www.youtube.com/watch?v=uLrVCI4N67M&feature=player_embedded

Upwelling and downwellingVertical movement of water ()

– Upwelling = movement of deep water to surface• Hoists cold, nutrient-rich water to surface• Produces high productivities and abundant

marine life– Downwelling = movement of surface water

down• Moves warm, nutrient-depleted surface water

down• Not associated with high productivities or

abundant marine life

El Niño

• El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime

El Niño

• Oceanic and atmospheric phenomenon in the Pacific Ocean

• Occurs during December• 2 to 7 year cycle

Sea Surface Temperature

Atmospheric Winds

Upwelling

Normal conditions in the Pacific Ocean

El Niño conditions (ENSO warm phase)

La Niña conditions (ENSO cool phase; opposite of El

Niño)

El NiñoNon El Niño

1997

Non El Niño

El Niño

thermocline

upwelling

Surface and Deep-Sea Current Interactions

Unifying concept: “Global Ocean Conveyor Belt”

http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm

Matter Transport and Surface Currents

• Currents also involved with gas exchanges, especially O2 and CO2

• Nutrient exchanges important within surface waters (including outflow from continents) and deeper waters (upwelling and downwelling)

• Pollution dispersal• Impact on fisheries and other resources

Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.

                                           

                                                                                                             

White sections represent warm surface currents. Purple sections represent deep cold currents

What effect does global warming play in

thermohaline circulation?

http://www.youtube.com/v/MZbsMlr9WRI?version=3

North Atlantic regional cooling

Global climate interconnections

CO2 fossil fuel combustion

Atmospheric and ocean temp

1 2 3 4

6 5

Subtropical evaporation

High latitude precipitation & runoff

Deep water formation & thermohaline circulation

Nordic seas salinity & deep convection

Potential feedback of increased

tropical salinity

1. What is a convection cell?2. Which direction do currents get deflected in

the Southern Hemisphere?3. What depth should the water be for an Ekman

spiral to occur?4. How are surface currents created?5. What is a gyre?6. How can an El Nino impact upwelling?7. Coriolis Effect is strongest near the _____?

Conclusion