© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Ekman Spiral and Transport The motion of the water at the surface is driven by the wind. Each subsequent layer below is driven by the movement of the water above, and slowed down by friction. This is termed the Ekman spiral, although the water itself does not spiral.

Figure 8.2

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Uneven Solar Heating and Latitude Earth as a whole is in thermal equilibrium, but different latitudes are not. Moving masses of air and ocean currents transport energy from locations with a surplus to those with a deficit.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. The Coriolis Effect Air moves in cells, influenced by the Coriolis effect.

Ekman spiral & transport

Figure 8.3

Figure 8.4

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Flow Within a Gyre The surface of the North Atlantic is raised through wind motion and Ekman transport to form a low hill. Can you determine why the center of the hill is offset to the west? Note, there’s more to this than meets the eye...a parameter called vorticity is very important.

Western Boundary Currents result from a change in vorticity necessary to balance difference in latitude of the flowing ocean. This change in “planetary” vorticity comes from the fact that the Coriolis effect is zero at the equator and maximum at the poles. Basic equations are*: Western ocean: wind stress (  ) + planetary vorticity (  ) = friction (  ) Eastern ocean: wind stress (  ) = planetary vorticity (  ) + friction (  ) So, the western side must flow narrower and stronger to balance the wide and slow eastern side. *from Knauss, J.A., “Introduction to Physical Oceanography, Second Edition”, 1997, Prentice-Hall Inc.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Geostrophic Gyres Geostrophic gyres are gyres in balance between the pressure gradient and the Coriolis effect. Of the six great currents in the world’s ocean, five are geostrophic gyres.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Gyres can be further subdivided into distinct currents. The four interconnected currents in the North Atlantic Gyre have different flow characteristics and temperatures. Flow Within a Gyre

Gulf Stream rings are large-scale vortices from instbilities in the flow. They play a significant roll in spreading energy and water properties around the Atlantic.

Figure 8.8

Divergent zones bring deep water to surface which is very important for primary production.