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Ocean Currents, Waves, and Tides Chapter 11 & 12 (Highways in the Sea; Waves and Tides). Oceanography 2014. Ch 11 Key Vocabulary. Ocean Current continuous, directed movement of seawater generated by the forces acting upon it Sea Level Pressure Gradient Force Gyre Ekman Transport
Ocean Currents, Waves, and TidesChapter 11 & 12 (Highways in the Sea; Waves and Tides) Oceanography 2014
Ch 11 Key Vocabulary • Ocean Currentcontinuous, directed movement of seawater generated by the forces acting upon it • Sea Level • Pressure Gradient Force • Gyre • Ekman Transport • Friction Depth • Geostrophic Current • Countercurrents • Upwelling • Downwelling • El Nino p11-22 • La Nina p11-24 • Deep Circulation • Contour Currents • Ocean Conveyor Belt • Doppler Shift
Ch 12 Key Vocabulary • Wavelength • Crest • Trough • Period • Wave Speed • Fully Developed Sea • Internal Ocean Waves • Storm Surge • Seiche • Tsunami Background Vocabulary (Chapter 10) • Coriolis Effect • Trade Windsprevailing pattern of easterly surface winds found in the tropics • Westerliesprevailing winds in the middle latitudes between 30 and 60 degrees latitude • Easterlieswinds with an easterly component at the surface near theEarth's poles, usually at latitudes more than 60 degrees • Doldrums • Horse Latitudes • SCUBASelf Contained UnderwaterBreathing Apparatus
Chapter 11 Currents: Highways in the Sea
Surface Currents • Currents 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 distances • Differences in density • Also causes change across horizontal distances • More dense water sinks below less dense water
Gyres • Combination of currents creating a circular flow • Example: North Atlantic Gyre • Westerlies pushing water eastward along the upper latitudes of the Atlantic • Trade winds pushing westward near the equator • Coriolis effect
Ekman Transport • Motion 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 Currents • Currents with characteristics determined by the presence of a coastline • Western boundary currents (occur along the eastern continental coasts) • Gulf Stream • Eastern boundary currents (occur along the western continental coasts) • Canary Current
Special Current Types • Counter-currents: current that flows in a direction opposite of the adjacent current • Upwelling • Upward vertical current bringing deep water to the surface • Occurs 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 shoreline • Occurs when Ekman transport causes surface water to flow toward the shore
Deep Currents • Water motion caused by mixing water of different densities • Ocean is stratified into different layers
Five Primary Water Masses • Surface Water • -0-200 meters deep • Central Water • -Extends into the thermocline • -Depth Varies with latitude • Intermediate Water • -To about 1500 meters deep • Deep Water • -Below Intermediate, but does not contact ocean bottom • Bottom Water • -In contact with sea floor
Ocean Conveyor Belt • Constant motion in the ocean = global ocean conveyor belt • Due to thermohalinecurrents: • 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 Belt • “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 • As more warm water is transported north, cooler water sinks and moves south to make room for the incoming warm water • This cold bottom water flows south of the equator all the way down to Antarctica • Eventually, the cold bottom waters are able to warm and rise to the surface, continuing the conveyor belt that encircles the globe
Chapter 12 Waves & Tides
Tides • Daily variations in the ocean’s sea level • Vary by location • Causes: • 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 Theory • Isaac 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 Tides • Pierre-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 Earth • Seasons • Shape of Ocean Basins • Coriolis Effect
Extreme Tides Bay of Fundy • Differ 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.
Waves • Wave: transmission of energy through matter • Three types of waves in all matter: • Longitudinal • Transverse • Orbital • Ocean Waves • Only in fluid – energy moves a fluid in a circular motion as it passes
Causes and Characteristics • Created by “disturbing forces” • Intensity and duration of forces determine wave characteristics • Disturbing forces include • Wind • Changes in gravity • Seismic Activity • Movement of water is resisted by “restoring forces” • Gravity • Coriolis Effect • Surface Tension
Wave Classification • Deep-water Waves • Transitional Waves • Shallow-Water Waves
Internal Waves • Occur within different density layers • Move slowly compared to surface waves
Destructive Waves • Storm 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 • Tsunami • Sudden movement of water caused by a landslide, iceberg falling into the sea, or Earthquake
Oceanography Feb 6, 2014 Waves/Currents/Tides • What do you think causes tides? • List 2-3 facts you already know about waves.
Oceanography Feb 11, 2014 Gyres • What is a gyre? • Name the 5 major ocean gyres.
Oceanography Feb 18, 2014 Vocab Review • What is the Ocean Conveyor Belt? • The average level of the ocean between high and low tide is called what? • What type of circulation is caused by mixing water masses of differing densities? • What is Ekman Transport? • What is El Nino?
Oceanography Feb 18, 2014 Vocab Review Answers • What is the Ocean Conveyor Belt?-Constant motion of the ocean due to connected currents worldwide • The average level of the ocean between high and low tide is called what?-Sea Level • What type of circulation is caused by mixing water masses of differing densities?-Deep Circulation • What is Ekman Transport?-Motion of water due to wind motion that causes spiraling motion down to friction depth • What is El Nino?-Rearrangement of high and low pressure systems