Ocean Currents, Waves, and TidesChapter 11 & 12

(Highways in the Sea; Waves and Tides)

Oceanography 2014

Ch 11 Key Vocabulary1. Ocean Current

continuous, directed movement

of seawater generated by the

forces acting upon it

2. Sea Level

3. Pressure Gradient Force

4. Gyre

5. Ekman Transport

6. Friction Depth

7. Geostrophic Current

8. Countercurrents

9. Upwelling

10. Downwelling

11. El Nino p11-22

12. La Nina p11-24

13. Deep Circulation

14. Contour Currents

15. Ocean Conveyor Belt

16. Doppler Shift

Ch 12 Key Vocabulary1. Wavelength

2. Crest

3. Trough

4. Period

5. Wave Speed

6. Fully Developed Sea

7. Internal Ocean Waves

8. Storm Surge

9. Seiche

10. Tsunami

Background Vocabulary (Chapter 10)1. Coriolis Effect2. Trade Winds

prevailing pattern of easterly surface winds found in the tropics

3. Westerliesprevailing winds in the middle latitudes between 30 and 60 degrees latitude

4. Easterlieswinds with an easterly component at the surface near theEarth's poles, usually at latitudes more than 60 degrees

5. Doldrums6. Horse Latitudes7. SCUBA

Self Contained Underwater Breathing Apparatus

Chapter 11Currents: Highways in

the Sea

Surface CurrentsCurrents that are 0-400 meters deep

Tend to flow right in the N hemisphere and left in the S hemisphere (Coriolis Effect)

Caused by:Wind

Cause changes in sea level across horizontal distancesDifferences in density

Also causes change across horizontal distances More dense water sinks below less dense water

GyresCombination of

currents creating a circular flow

Example: North Atlantic GyreWesterlies pushing

water eastward along the upper latitudes of the Atlantic

Trade winds pushing westward near the equator

Coriolis effect

The 5 Major Ocean Gyres

Ekman TransportMotion of the water column

down to friction depth (90o right in N hemisphere and 90o left in S hemisphere)

Currents due to friction with the wind shift to right or left

Result of the Coriolis Effect

Ekman Spiral: thin layers of water flowing in a direction caused by the layer above down to friction depth (deepest point friction from wind affects water movement)

Boundary CurrentsCurrents with

characteristics determined by the presence of a coastlineWestern boundary

currents (occur along the eastern continental coasts) Gulf Stream

Eastern boundary currents (occur along the western continental coasts) Canary Current

Characteristic Western Eastern

Temperature Warm Cold

Width Narrow Wide

Depth Deep Shallow

Volume High Low

Speed Fast Slow

Direction Toward Poles Toward Equator

Special Current TypesCounter-currents: current that flows

in a direction opposite of the adjacent current

UpwellingUpward vertical current bringing

deep water to the surfaceOccurs when wind blowing parallel to

the shore pushes surface water out to sea (due to Ekman transport)

Downwelling: Occurs when surface water is forced

downward at the shorelineOccurs when Ekman transport causes

surface water to flow toward the shore

Deep CurrentsWater motion caused by mixing water of different

densities

Ocean is stratified into different layers

Five Primary Water Masses

1. Surface Water-0-200 meters deep

2. Central Water-Extends into the thermocline-Depth Varies with latitude

3. Intermediate Water-To about 1500 meters deep

4. Deep Water-Below Intermediate, but does not contact ocean bottom

5. Bottom Water-In contact with sea floor

Ocean Conveyor BeltConstant motion in the ocean = global ocean

conveyor beltDue to thermohaline currents:

Cold, salty water is dense and sinks to the bottom of the ocean

Warm water is less dense and rises to the surface It takes almost 1,000 years for the conveyor belt

to complete one “cycle.”

Process of the Ocean Conveyor Belt1. “Starts” in the Norwegian Sea

-Warm water from the Gulf Stream heats the atmosphere in the cold northern latitudes -This loss of heat to the atmosphere makes the water cooler and denser, causing it to sink to the bottom of the ocean

2. As more warm water is transported north, cooler water sinks and moves south to make room for the incoming warm water

3. This cold bottom water flows south of the equator all the way down to Antarctica

4. Eventually, the cold bottom waters are able to warm and rise to the surface, continuing the conveyor belt that encircles the globe

Chapter 12Waves & Tides

TidesDaily variations in the ocean’s sea level

Vary by locationCauses:

Result of the gravitational pull of the moon (and to some degree, also the Sun)

Pulls the ocean into a huge wave with a wavelength the size of the entire ocean basin

Equilibrium TheoryIsaac Newton: the Sun and moon create

two opposite bulges on each side of the Earth – each rotate around the Earth as the Sun and moon change position As bulge moves toward coast, tides rise As bulge moves away from coast, tides fall

Dynamic Theory of TidesPierre-Simon Laplace modified

Newton’s theory because it was too simple to explain everything about tides on Earth

More than 2 tidal bulges

Tides occur in a pinwheel-shaped, standing-wave pattern

In addition to lunar and solar gravity, this theory accounts for:Imperfect shape of EarthSeasonsShape of Ocean BasinsCoriolis Effect

Extreme TidesBay of FundyDiffer in volume by as

much as 100 km3 (that is more than 4x the volume of all the rivers in the world combined)

Demonstrates that tides are much more complex that Newton’s simple model.

WavesWave: transmission of energy through matterThree types of waves in all matter:

LongitudinalTransverseOrbital

Ocean Waves Only in fluid – energy moves a fluid in a circular motion as it

passes

Causes and CharacteristicsCreated by “disturbing forces”Intensity and duration of forces determine wave characteristics

Disturbing forces includeWindChanges in gravitySeismic Activity

Movement of water is resisted by “restoring forces”GravityCoriolis EffectSurface Tension

Wave ClassificationDeep-water WavesTransitional WavesShallow-Water

Waves

Internal WavesOccur within different density layersMove slowly compared to surface waves

Destructive WavesStorm Surge

Forms when high winds push water into shore

Seiche (pronounced SAY-sh)Motion of water in lake

or bay rocking back and forth due to earthquake or very strong wind

TsunamiSudden movement of

water caused by a landslide, iceberg falling into the sea, or Earthquake

Oceanography Feb 6, 2014Waves/Currents/Tides

1. What do you think causes tides?

2. List 2-3 facts you already know about waves.

Oceanography Feb 11, 2014Gyres

1. What is a gyre? 2. Name the 5 major ocean gyres.

Oceanography Feb 18, 2014Vocab Review

1. What is the Ocean Conveyor Belt?2. The average level of the ocean

between high and low tide is called what?

3. What type of circulation is caused by mixing water masses of differing densities?

4. What is Ekman Transport?5. What is El Nino?

Oceanography Feb 18, 2014Vocab Review Answers

1. What is the Ocean Conveyor Belt?-Constant motion of the ocean due to connected currents worldwide

2. The average level of the ocean between high and low tide is called what?-Sea Level

3. What type of circulation is caused by mixing water masses of differing densities?-Deep Circulation

4. What is Ekman Transport?-Motion of water due to wind motion that causes spiraling motion down to friction depth

5. What is El Nino?-Rearrangement of high and low pressure systems