Chapter 14 Page 364 387 Currents Imagine that you are stranded on a desert island You stuff a distress message into a bottle amp throw it into the ocean hoping it will find its way to someone who will send help ID: 1025567
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1. The MovementofOcean WaterChapter 14Page 364 – 387
2. CurrentsImagine that you are stranded on a desert island. You stuff a distress message into a bottle & throw it into the ocean, hoping it will find its way to someone who will send help. What are the forces that would send your bottle across the ocean, bobbing up & down as it traveled? Is there any way to predict where your bottle may land?Page 366
3. Surface CurrentsSurface currents = streamlike movements of water that occur at or near the surface of the ocean.Some surface currents are several thousand kilometers in length, traveling across entire oceans.Surface currents are controlled by three factors: global winds, the Coriolis effect, & continental deflections.Page 367
4. Global WindsWind has the power to move large quantities of water. Different winds cause currents to flow in different directions. Near the equator, the wind blow ocean water east to west, but closer to the poles, ocean water is blown west to east.Merchant ships often use these currents to travel more quickly back & forth across the oceans.Page 367
5. The Coriolis EffectCoriolis effect = The turning of moving objects, such as ocean currents, by the Earth’s rotationThe Earth’s rotation cause surface currents to move in curved paths rather than in straight lines. Ocean currents in the Northern Hemisphere turn clockwise, while ocean currents in the Southern Hemisphere turn counterclockwise.Continental DeflectionsWhen surface currents meet continents, they deflect, or change direction.Page 368
6. Taking TemperaturesAlong with the previous three factors temperatures play a role in the pattern of surface currents on Earth.Warm-water currents begin near the equator & carry warm water to other parts of the ocean. Cold-water currents begin near begin closer to the poles & carry cold water to other parts of the ocean.All oceans are connected, & both warm-water & cold-water currents travel from one ocean to another.Page 369
7. Deep CurrentsDeep currents = streamlike movements of ocean water far below the surface.Decreasing temperature in the Earth’s polar regions, cold air chills the water molecules slow down & move closer together.Increasing Salinity Through Freezing. If the polar winds chill ocean water enough, it may freeze at the surface.Increasing Salinity Through Evaporation.Page 370
8. Movement of Deep CurrentsThe movement of deep currents as they travel along the ocean floor is very complex. Differences in temperature & salinity, & therefore in density, cause variations in deep currents.The main thermocline is a barrier that keeps warm surface waters from mixing efficiently with cold deep currents. It takes about 1,000 years for water from cold regions to cycle through warm regions.Currents Trading PlacesCheck out the currents on page 371Page 371
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10. Surface Current & ClimatesSurface currents affect the climate in many parts of the world. Some surface currents warm or cool coastal areas year-round. Other surface currents sometimes change their circulation pattern. This causes changes in the atmosphere that disrupt the climate in parts of the worldCurrents That Stabilize ClimateGulf Stream carries warm water from the tropics to the North Atlantic Ocean; flows to the British Isles which creates a relatively mild climate.California Current carries cold water from the north southward all the way to Mexico. This keeps the climate along the West Coast fairly cool all year. Page 372
11. Current Variations – El NiñoUpwelling = a near-shore process in which cold, nutrient-rich water from the deep ocean rises to the surface to replace warm surface water that is blown farther out to sea by prevailing winds.El Niño = periodic change in location of warm & cool surface waters in the Pacific OceanEffects of El NiñoAreas that receive little to no rain can flood & areas that depend on lots of rain for crop growth suffer drought during El Niño.Page 373
12. WavesAnatomy of a WaveWaves of made up of two main components – crest & troughs.Crest = the highest point of a waveTrough = the lowest point of a waveWavelength = the distance between two adjacent wave crests or wave troughsWave height = the vertical distance between a wave’s crest & its troughPage 374
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14. Wave Formation & MovementMost waves form as wind blows across the water’s surface, transferring energy to the water. As the energy moves through the water, so do the waves. But the water itself stays behind, rising & falling in circular movements.Youtube – “Circular motion in wind generated waves”Notice the deeper circles are smaller because as depth increases wave energy decreasesWave energy only reaches a certain depthPage 374
15. Specifics of Wave MovementWaves not only come in different sizes but also travel at different speeds. To calculate wave speed you have to know wavelength & wave period.Wave period = the time between the passage of two wave crests (or troughs) at a fixed pointDividing wavelength by wave period gives you wave speedPage 375Wavelength (m)Wave period (s)=Wave speed (m/s)
16. Types of WavesWind driven waves (most common)Underwater earthquakes form wavesLandslides form wavesImpacts by cosmic bodies form wavesThe size of the different types of waves can vary, but most move the same way.Page 375
17. Deep-Water Waves & Shallow-Water WavesDeep-water waves – waves that move in water that is deeper than one-half of their wavelength.Shallow-water waves – waves that reach that are shallower than one-half of their wavelength, they begin to interact with the ocean floor.Breaker zone = near-shore area where waves first begin to tumble downward or breakSurf = the area between the breaker zone & the shorePage 376
18. Deep-Water Waves & Shallow-Water Waves (Cont’d)Undertow – receding movement of water, which carries sand, rock particles, & plankton away from the shoreLongshore current – when waves hit the shore at an angle, they cause water to move along the shore in a currentPage 377
19. Open-Ocean WavesWhitecaps = white, foaming waves with very steep crests that break in the open ocean before the waves get close to shore. These waves usually form during stormy weather, & they are usually short-lived.Swells = rolling waves that move in a steady procession across the ocean. Swells have longer wavelengths than whitecaps & can travel for thousands of kilometers.Page 377
20. TsunamisTsunamis = waves that form when a large volume of ocean water is suddenly moved up or downThis movement can be caused by underwater earthquake, volcanic eruptions, landslides, underwater explosions, or the impact of a cosmic body.The majority of tsunamis occur in the Pacific Ocean because of the greater number of earthquakes in that region.Page 378
21. Storm SurgesStrom surge = a local rise in sea level near the shore that is caused by strong winds from a storm, such as a hurricane.Winds form a storm surge surge by blowing water into a big pile under the storm. As the storm moves onto shore, so does the giant mass of water beneath it.Storm surges contain a lot of energy & can reach about 8 m in height. This often makes them the most destructive part of hurricanes.Page 379
22. TidesTides = daily movements of ocean water that change the level of the ocean’s surface.Tides are influenced by the sun & the moon, & they occur in a variety of cycles.The Lure of the MoonThe moon’s influence on the tides were first discovered more than 2,000 years ago by a Greek explore Pytheas.A scientific explanation was given in 1687 by Sir Isaac NewtonPage 380
23. High Tide & Low TideHow high tides get & how often they occur depend on the position of the moon as it revolves around the Earth.The moon’s pull is strongest on the part of the Earth directly facing the moon. high tides – water that bulges toward the moonPages 380 – 381
24. Tidal VariationsThe sun also affects tides but less so than the moon.Tidal range = the difference between levels of ocean water at high tide & low tide.Spring TidesSpring tides = tides with maximum daily tidal range that occur during the new & full moons.Neap TidesNeap tides = tides with minimum daily tidal range that occur during the 1st & 3rd quarters of the moon.Page 382
25. Tides & TopographyTides can be accurately predicted once the tidal range has been measured at a certain point over a period of time.Tidal bore = a body of water that rushes up through a narrow bay, estuary, or river channel during the rise of high tide, causing a very sudden tidal rise.Tidal bores occur in coastal areas of China, the British Isles, France, & Canada.Page 383