1. Ocean Circulation
Vol 1: Surface Currents

2. Preview I. Causes of Global Currents II. Surface Currents
III. Coastal Currents
IV. Gravitational Currents
V. Thermohaline Circulation

3. I. Causes of Global Currents
Ocean circulation- the total movement of all ocean currents.
Currents are caused by different things, including
Wind direction
Coastline shape
Differences in the density of masses of water

4. II. Surface Currents
Global wind patterns (trade winds, prevailing westerlies, and polar easterlies) drive surface currents.
1. Surface (drift) currents extend up to 100 meters below the ocean surface.
2. Ekman transport estimates that currents flow 900 to the right of the wind in the northern hemisphere, and 900 to the left in the southern hemisphere.
3. Currents circulate clockwise in the northern hemisphere, and counterclockwise in the south.

5. III. Coastal Currents
A. Longshore current is when a wave hits the beach at an angle, the front end slows and the rest of the wave bends and flows along the coast.
1. This can cause longshore drift- serious beach erosion and the movement of coastal features like inlets, points, and peninsulas.

6. III. Coastal Currents
B. In addition to longshore currents, barrier islands, sandbars and reefs create small gaps or channels along the coast through which water must funnel.
As the tide flows out (ebbs) or in (floods) it can create currents perpendicular to the shore, called rip current or rip tides.

7. III. Coastal Currents
C. Upwelling- as winds blow along the shore, pushing water by the shore out to sea, deeper ocean water rises up to fill the “gap.”
1. This cold, deep water is nutrient rich and can be important to humans as it supports fisheries- areas where fish gather to feed and breed. Half of the world’s catch comes from upwelling areas.

8. III. Coastal Currents Knowledge check:
For Ekman transport to move water away from the shore and cause upwelling in the northern hemisphere, the wind must be blowing:
a. To the south
b. To the north
c. away from the shore

9. III. Coastal Currents
D. Downwelling- as winds blow and Ekman transport pushes ocean water in to the shore, some of it gets pushed down along the coastline, bringing warmer, oxygen-rich and nutrient-poor water to the depths.