Movements of the Oceans

1. Movements of the Oceans Chapter 21

2. Ocean Currents • Ocean water moves in giant streams called CURRENTS. • Two categories: Surface & Deep Currents

3. Surface Currents • Created as Wind (moving air) pushes the water causing the water to move in the same direction as the air • Made to curve due to the Coriolis Effect - the tendency of a moving object to follow a curved path rather than a straight path because of the Earth’s rotation. • Northern Hemisphere – currents curve to the right, or clockwise • Southern Hemisphere – currents curve to the left, or counterclockwise • Creates GYRES – huge circles of moving water

4. Global Ocean Surface Currents →Warm water currents → Cold water currents

5. Deep Currents • Cold, dense currents far below the surface • Created as cold, dense water of the polar regions sinks and flows beneath warmer ocean water. • Density is affected by temperature • Cold water molecules contract creating denser water that sinks • Warm water molecules are farther apart and less dense causing them to rise above more dense water • Density is affected by salinity • Water with more dissolved solids is more dense and sinks • Arctic Bottom Water is -2˚C and has high salinity making it very dense

6. Antarctic Deep Current

7. Ocean Waves • Periodic up-and-down movement of water created as moving air pushes the water. • Crest – highest part • Trough – lowest part • Wave height – vertical distance between crest and trough • Wavelength – distance from crest to crest • Wave period – time required for 2 consecutive waves to pass a given point

8. Energy is transferred from water molecule to water molecule in the direction of the wave. • Water molecules move in a circular motion • At a depth of about ½ the wavelength there is almost no circular motion of water molecules. • Wave size is determined by 3 factors • Speed of the wind • Length of time the wind blows • Fetch – the distance the wind blows across open water

9. Height of the wave changes as the wave approaches the coast forming breakers • Breaking waves erode sediment from the ocean floor and move sediments along the coastline

10. Refraction – waves bend as they approach the coastline • Longshore current – flow parallel to the shore and carry large quantities of sand • Undertow – irregular current, occurring only near shorelines, created as water carried onto a beach is pulled back into deeper water by gravity. • Rip current – a fast moving current that flows perpendicular to the shore that forms when large breakers return to the ocean through channels that cut through underwater sandbars running parallel to the beach.

11. Tides • Periodic rise and fall in ocean levels caused by the gravitational pulls of the moon and sun. • Occurs every 24hours and 50min. • High tide – when water level is highest in an area • Low tide – when water level is lowest in an area • Tidal range – difference between high and low tides

12. Spring Tides • Sun Earth and Moon are in line (new moon and full moon) • Sun and Moon’s gravitational pull work together to increase the pull of the water and increases the tidal range • Produces higher high tides and lower low tides • Neap Tides • Sun Earth and Moon are at 90˚ angle (first-quarter and third-quarter moon) • Sun and Moon’s gravitation pull work against each other to reduce the pull of the water • Produces lower high tides and higher low tides.