Ocean Circulation

Ocean Circulation• Key Points:

– I can discuss the importance of ocean circulation.

– I can describe the circulation of wind in a non-rotating vs. a rotating Earth.

– I can discuss the physical properties of the atmosphere.

– I can begin to understand the Coriolis effect.

Why is Ocean Circulation Important?

• Transport ~ 20% of latitudinal heat– Equator to poles

• Transport nutrients and organisms

• Influences weather and climate

• Influences commerce

Convection cell model

Non-rotating Earth

Add rotation and add landmasses unequal heating and cooling of the Earth You Tube LinkYouTube Link #2

Physical properties of the atmosphere: Density

• Warm, low density air rises

• Cool, high density air sinks

• Creates circular- moving loop of air (convection cell)

Physical properties of the atmosphere: Water vapor

• Cool air cannot hold much water vapor, so is typically dry

• Warm air can hold more water vapor, so is typically moist

• Water vapor decreases the density of air

Physical properties of the atmosphere: Pressure

The Coriolis effecthttp://www.youtube.com/watch?v=Wda7azMvabEhttp://www.youtube.com/watch?v=i2mec3vgeaIhttp://www.youtube.com/watch?v=XiYs4QBWTOo

• 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

– Changes with latitude:• No Coriolis effect at Equator• Maximum Coriolis effect at poles

The Coriolis effect on Earth

• As Earth rotates, different latitudes travel at different speeds

• The change in speed with latitude causes the Coriolis effect

Ocean Currents• Recap Key Points:

– I can discuss the importance of ocean circulation.

– I can describe the circulation of wind in a non-rotating vs. a rotating Earth.

– I can discuss the physical properties of the atmosphere.

– I can begin to understand the Coriolis effect.

Ocean Currents• Key Points:

– I can describe how the Coriolis effect influences surface winds.

– I can explain the difference between factors affecting surface circulation vs. deep ocean circulation.

– I can describe oceanic gyres & their rotations.

A) Idealized winds generated by pressure gradient and Coriolis Force.  B) Actual wind patterns owing to land mass distribution..

http://www.youtube.com/watch?v=aeY9tY9vKgs&feature=youtube_gdata_player

Surface Currents

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

Deep Water Currents

Thermal currents (90%)

Ocean Currents

Surface Currents

Forces

1. Solar Heating (temp, density)

2. Winds

3. Coriolis

Wind-driven surface currents

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 GyresCurrent Gyres

Surface and Deep-Sea Current Interactions

Unifying concept: “Global Ocean Conveyor Belt”

http://www.youtube.com/watch?v=6vgvTeuoDWY

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

Heat Transport by Currents

• Surface currents transport heat energy from equator towards the poles

• 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

Ocean Currents• Recap the Key Points:

– I can describe how the Coriolis effect influences surface winds.

– I can explain the difference between factors affecting surface circulation vs. deep ocean circulation.

– I can describe oceanic gyres & their rotations.

Ocean Currents• Key Points:

Upwelling and downwelling

Vertical 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

upwelling

downwelling

Satellite Observations

• TOPEX/Poseidon, Jason 1, and other satellites have observed patterns of change over the past few years

• Animation of seasonal and climatically-influence shifts available at

http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/MOVIES/Topex_Dynamic_Ocean_Topography.mpg

El Niño-Southern Oscillation (ENSO)

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

• Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño

• ENSO describes a combined oceanic-atmospheric disturbance

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

El Niño events over the last 55 years

El Niño warmings (red) and La Niña coolings (blue) since 1950. Source: NOAA Climate Diagnostics Center

http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html

El Nino Animation

World Wide Effects of El Niño

• Weather patterns

• Marine Life

• Economic resources

Effects of severe El Niños

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 _____?

Inquiry