Ocean Circulation and Its Impact on Climate and Marine Life

1. Chapter 3 Part II

2. Ocean Circulation • The ocean is always moving. • This circulation affects marine organisms, their habitats, and the earth’s climate. • The earth’s climate in turn affects all habitats on land.

3. Surface Circulation • The most intense ocean currents are found at the surface. • Both surface currents and the wind are strongly influenced by what is known as the Coriolis effect.

4. Coriolis Effect • The tendency of objects moving large distances on the earth’s surface to bend to the right in the Northern Hemisphere and the left in the Southern Hemisphere. • In the Northern Hemisphere- winds and ocean currents move to the right. • In the Southern Hemisphere- winds and ocean currents move to the left.

5. Wind Patterns • Winds in our atmosphere are driven by the thermal energy from the sun. • Warmer air rises because it is less dense. Therefore Equatorial air rises and sucks in air from adjacent areas to replace this equatorial air, creating wind.

6. Trade Winds • Steady winds that blow from east to west toward the Equator, replacing the hot air that rises at the Equator.

7. Other Winds • Westerlies- found at the middle latitudes and move opposite to the trade winds. • Polar easterlies- most variable of all winds found at high latitudes.

8. Surface Currents • Are formed by major wind fields pushing the sea surface. • The uppermost layer of surface water beings to move when pushed by the wind. • These currents move off the ocean surface at a 45 degree angle because of the Coriolis effect.

9. Ekman spiral • The spiral change in the movement of water in the water column when the water is pushed by the wind. • The Ekman layer- the part of the water column affected by the wind. • Ekman transport- net movement of water 90 degrees from wind direction.

10. Equatorial Currents • Major ocean currents that move parallel to the equator.

11. Gyres • Huge, less circular systems that are under the influence of the Coriolis effect. • These are wind-driven surface currents. • Fig. 3.18 • Fig. 3.19 • Fig. 3.20

12. Role of Surface Currents • The role of surface currents in transporting heat is reflected in the temperature of the sea surface. • Surface temperature is always higher on the western sides of the oceans. • Because of this, tropical organisms like corals tend to extend into high latitudes on the west sides of oceans. • Fig. 3.21

13. Thermohaline Circulation • Ocean circulation that is driven by differences in water density, due to variations in water temperature and salinity, rather than by the wind or tides.

14. The Three-Layered Ocean • Surface Layer- Usually around 100-200m (330-660 ft) thick. • Much of time this layer is mixed by wind, waves, and currents. • It is also known as the MixedLayer.

15. Thermocline • Sudden changes in water temperature over small depth intervals. • Ex: During spring and summer in polar water, the uppermost water gets heated by the sun. This warm water floats on top. There is a sharp transition between this water and the water below.

16. Intermediate Layer • Lies below the surface layer. • Typically at a depth of 1000-1500m (3300-5000ft). • The MainThermocline, a zone of transition between warm surface water and cold water below is in this layer.

17. Deep and Bottom Layers • Below about 1500m (5000ft). • Typically cold at less than 4C or 39F.

18. Water Column Stability • Most of the time surface water is warm and less dense and floats on top unless it is acted upon by wind or wave energy. • This is referred to as a Stable water column.

19. Water Column Instability • Caused by downwelling. • Downwelling occurs when surface water sinks and displaces and mixes with deeper water. • This process is known as overturn.

20. Because surface water all with the same temperature and density descends through the water column, the temperature and density profiles are vertical straight lines. • Overturn usually occurs in temperate and polar regions during the winter when surface water cools.

21. Oceanographers use this overturn to follow the movement or circulation of water masses over great distances. • Fig. 3.24

22. The Great Ocean Conveyor • The global thermohaline circulation that mixes the oceans every 4000 years. • It is critical in regulating the earth’s climate. • It brings dissolved oxygen to the deep. This effect is enhanced because oxygen dissolves best in cold water.

23. Waves and Tides • Waves- Undulations that form as a disturbance moves along the surface of the water.

24. Parts of a Wave • Crest- highest part of a wave. • Trough- lowest part of a wave. • Wave height- size of an ocean wave. Measured by the vertical distance between the trough and the crest. • Wavelength- the distances between crests or troughs.

25. Period • Time it takes a wave to go by any given point. Did you know? That particles under a wave don’t go anywhere as a wave passes, they just move in a circular motion.

26. Wave size and Wind Speed • Waves begin to form as soon as the wind starts to blow. • The faster and longer the wind blows the larger the waves get. • Fetch- the span of open water over which the wind blows also determines the size of a wave.

27. Types of Waves • Seas- Waves that have a sharp peak and relatively flat trough. Are found in areas where waves are generated by wind. • Swells- A wave with a flatter, rounded wave crest and trough. Are found away from the area where waves are generated by the wind.

28. Surf • Waves that become so high and steep as it approaches the shoreline that it breaks. • Wave reinforcement- when the crests of two waves collide and add together producing a wave that can seem to come from nowhere and can be as tall as a ten-story building.

29. Tides • The periodic, rhythmic rise and fall of the sea surface. • Tides are caused by the gravitational pull of the moon and sun and by the rotations of the earth, moon, and sun.

30. How are tides formed? • The moon’s gravity is strongest on the side of the earth closest to the moon. • Here the moon’s gravity pulls wate in the ocean toward the moon. • On the opposite side of the earth the ocean bulges away from the moon due to centrifugal force. • Fig. 3.32

31. High Tides • Occurs when a given point on the earth is under a bulge. • Because it takes the earth 24 hours to complete a rotation, this point will have two high tides and two low tides every day. • A full tidal cycle takes 24 hours and 50 minutes.

32. The sun’s effect on the tides. • The sun produces tidal bulges, but in a much smaller scale than the moon. • When the sun and moon are in line with each other at the full and new moons their effects on the tide are added together.

33. Tidal range- difference in water level between successive high and low tides. • Spring tides- Tides with a large tidal range. They occur around the time of the full and new moon. • Neap tides-Tides with at small tidal range. They occur around times when the moon is in quarter.

34. Semidiurnal tides- when an area has two high tides and two low tides a day. • Ex: East Coast of North America, most of Europe and Africa. • Mixed semidiurnal tides- areas with successive high tides of different height. • Ex: West Coast of North America, and Canada • Diurnal tides- areas with one high and low tide a day. • Uncommon-but occur in Antarctica, part of the Gulf of Mexico, Caribbean, and Pacific.

35. Tide Tables • Give the predicted time and height of high and low tides in coastal areas.