Part 5: Motion of the Ocean 1. Three Types of Motion 1. Waves 2. Currents 3. Tides 2.

Earths Oceans

Earths OceansPart 5: Motion of the Ocean1Three Types of MotionWavesCurrentsTides2WavesPulses of energy that move through waterSet in motion by:Wind (most commonly)EarthquakesThe gravitational pull of the moon

3WavesView the following lesson on waves:http://oceanexplorer.noaa.gov/edu/learning/player/lesson09.html

Photo credit: NOAA4Waves Caused by WindCalled surface wavesWind transfers energy to the water as it moves over the ocean surfaceThe energy then moves through the water as a waveThe water moves up and down in a circular motion but does not move horizontally along the surface.

Height of these waves depends upon:Wind speedLength of time the wind blowsDistance the wind blows over the water

Animation from http://www.onr.navy.mil/focus/ocean/motion/waves1.htm5Characteristics of WavesCrest highest pointTrough lowest pointWavelength horizontal distance between wavesWave height vertical distance between crest and trough (amplitude)Wave period time it take for one wavelength to pass a give pointWave frequency number of waves per unit of time

Diagram from: http://www.onr.navy.mil/focus/ocean/motion/waves1.htm6Wave ActionSwells long, wide waves in the open ocean that are not very highNear the shore, wavelength decreases, wave height increases and crests become more peakedThe slope of the shore determines how the waves break Surf: the surging of the ocean waves on to the shoreUndertow: water flowing back to the ocean View animation:http://oceanexplorer.noaa.gov/edu/learning/player/lesson09/l9la1_a.html7TsunamisCaused by sudden displacements in the sea floor (earthquakes), landslides, or volcanic activityResulting waves can be very tall (up to 35 m when they strike)Can cause great damage and loss of life along the coast

Animation from: http://www.tsunami.noaa.gov/tsunami_story.html The 12/26/2004 tsunami in the Indian Ocean killed over 230,000 people.8CurrentsMovement of ocean water in streams or riversCan flow for great distancesCan play a dominant role in determining the climate of a regionCaused by two factors:Wind patternsDifferences in water density9Surface CurrentsCaused mainly by wind patternsTo depths of ~400 mVideo: http://svs.gsfc.nasa.gov/vis/a000000/a003800/a003827/prepetual_ocean_1080p30.mp4

Circular motionClockwise in the Northern HemisphereCounterclockwise in the Southern Hemisphere (as with winds)May be warm or cold, depending on where they originate10Long Distance Surface Currents

Generally west coasts have cold currents & east coasts have warm currents11Long Distance Surface CurrentsGulf StreamAbout 150 km wide, up to 1,000 m deep, speed averages 6.4 km/h (4 mph)Carries warm water from the southern tip of Florida north along the east coast of the USVideo http://www.teachersdomain.org/resource/ess05.sci.ess.watcyc.drifters/Interactive diagram of 25 major ocean currents http://www.srh.noaa.gov/jetstream/ocean/currents_max.htm12Short Distance Surface CurrentsFound near shorelines where waves hit at an angleLongshore currents move parallel to the shorelinePick up sand and other materials and then deposit them in the water close to the shoreline forming a sandbar

Sandbar off Long Island CoastPhoto credit: David Shankbone, August 2006.13Short Distance Surface CurrentsIf the current cuts through a sandbar, the resulting powerful, narrow, outflow back to the ocean is a rip current.A rip current is a type of undertow.As the sandbar is often underwater, rip currents are difficult to see and dangerous.

14Deep CurrentsCaused by difference in density of waterDensity affected by:TemperatureSalinityColder, saltier water at the poles sinks to the depths of the ocean and then moves away from the poles.Most flow in directions opposite that of surface currents

Global Ocean Conveyor Belt. This collection of currents is responsible for the large-scale exchange of water masses in the ocean, including providing oxygen to the deep ocean. The entire circulation pattern takes ~2000 years.15UpwellingThe rising of deep cold currents to the ocean surfaceOccurs when winds blow parallel to the coastlineCarries nutrient rich waters to the surface to support high levels of seaweed and plankton growth.These areas are the best fisheries.

Areas of coastal upwelling in red.16TidesRegular rise and fall of ocean water caused by gravitational attraction between the Earth, moon, and sun.Most coastal locations experience two high tides and two low tides per day.

Reference: http://csep10.phys.utk.edu/astr161/lect/time/tides.htmlLow TideLow TideHigh TideHigh Tide17