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