Ocean CirculationI. Surface Currentsa. About 10% of the ocean’s water is in surface currents, water flowing horizontally in the uppermost 400 mi. Driven mostly by wind frictionii. Most wind energy comes from the trade winds (easterlies) and westerliesiii. The moving water will ‘pile up’ in the direction the wind is blowing1. gravity will pull water down this slope, in the direction from which it came2. However, the Coriolis effect causes surface currents in the N.Hemisphere to be deflected to the right and to the left in the S. Hemisphere.3. Continents block the flow of the water, causing the currentsto flow in large circular patterns called gyres.b. Gyresi. Example: N. Atlanticii. Water flows clockwise around the N. Atlanticiii. The East/West winds flow to the right of the prevailing winds.iv. When driven by the wind, the topmost layer of the ocean in the N. Hemisphere flows at about 45° to the right of the wind direction. 1. Layers below the top layer respond by being deflected in a similar manner.2. This trend continues to a depth of about 100 m below the surface3. This results in an Ekman Spirala. Ekman spirals transport water 90° to the right of wind in the N. Hemisphere and to the left in the S. Hemisphere b. They are about 100 m deep. 4. This causes a build up of water in the center of the ocean, which is really a hill of water about 2 m higher than the restof the ocean.5. This hill is maintained by wind energy, friction with the surrounding continents, and the coriolis effect. 6. Pressure gradients, from gravity, propel the currents of the gyre and hold them along the outside edges of the ocean basins.v. Geostrophic Gyres1. Gyres in balance between the pressure gradient and the Coriolis effect are called geostrophic gyres (Geo=earth; strophe= turning), and their currents are called geostrophiccurrents. a. Geostrophic gyres are largely independent of each other.2. There are six great current circuits in the world ocean.a. Two in the S. Hemisphere and four in the S. Hemisphereb. Five are Geostrophic gyresi. N. Atlanticii. S. Atlanticiii. N. Pacificiv. S. Pacificv. Indianc. The sixth and largest current system is the Antarctic Circumpolar Current and because it flows around the entire world it is not considered geostrophic.vi. Currents within Gyres1. Western Boundary Currentsa. Located on the gyre’s western endb. Ex: Gulf Stream (G.S.), Kuroshio, Brazil, Agulhas, East Australianc. G.S. moves about 2 m/s (5 miles/h) off Miamii. That’s >160km/day ii. >450 m deepiii. Width about 70 kmd. They transport warm water away from the equatore. Lots of water gets transportedi. G.S. is at least 55 Sverdrups (sv), one sverdrup is 1 million cubic meters/second (about ½ the size of the Louisiana Superdome), about 300 times the flow of theAmazonf. Really looks like a river in the sea. i. The water is distinctly different.1. Warmer2. Clearer3. Bluerii. Often eddies, turbulent rings, form in the current and trap cold or warm water in the centers and then separate from the main stream2. Eastern Boundary Currentsa. There are five Eastern Boundary Currentsi. Canary Current, ii. Benguela Currentiii. California currentiv. West Australian Currentv. Humboldt or Peru currentb. On the Eastern edge of the gyre.c. They carry cold water toward the equatord. They are shallow and broade. They carry less water then W.B.C.’si. Canary current only carries about 16 sv’s3. Transverse Currentsa. These are currents that connect the E.B.C.’s and W.B.C.’s and are driven by windsb. The N. and S. Equatorial Currents in the Talantic and Pacific are formed by the push of the trade winds.c. These currents are usually impeded by continents. d. However, in the S. Ocean there are no continents in the way and the transverse current forms the Antarctic Circumpolar Current.4. Countercurrents and Undercurrentsa. Equitorial Currents are usually accompanied by countercurrents flowing on the surface in opposite direction of the main flow.b. This backward flow is a reaction to the build up of water on one side of the ocean.c. Countercurrents also exist beneath surface currentsi. Called undercurrents, they are 100 to 200 m below the surface and can carry as much water as the surface currents.5. Effect of currents on climatea. When you have warm water moving into colder regions it heats the atmospherei. England is much warmer than Labrador, even though they are at comparable latitudesb. When you have cold water moving into warmer regions it cools the atmospherei. Summers in Seattle are not as hot as summers in New Yorkc. Upwelling and Downwellingi. In the Equatorial Pacific the trade winds cause the formation of the North and South Equitorial Currents1. These currents move warm water across the pacific from the East to the West. a. In the East, along the coasts of Peru and Chile, the water removal of water causes coastal upwelling and the lowering of the sea surface heighti. Upwelling: process by which deep, cold, nutrient-rich water is brought from depths tothe surfaceii. Coastal Upwelling: the movement of surface water away from a coast line causesdeeper water to be brought up in order to replace it.iii. This deeper water is colder, because it is farther from the sun.iv. The sea surface is lower because 1. Water that removed2. The water the replaces it is colder, denser and therefore has a smaller volumeb. In the West, along the coasts of SE Asia and Micronesia, there is a build up of warm water.ii. During an El Niño the trade winds weaken, stop all together, or even reverse direction.1. This change in the winds causes that pile of warm water in the Western Pacific to slosh back along the equator until it hits the South Americaa. The presence of that warm water creates a cap on the water column and effectively shuts down upwelling. b. Without the upwelling of nutrients, the productivity of the sea shuts down, thus destroying the fishery inPeru and Chile2. During a strong El Niño, the wave of warm equatorial water can be pushed along the coasts of North and South America, even as far north as Oregon.iii. When water is driven toward a coastline it will be forced downward returning seaward along the continental shelf1. This downwelling supplies deeper ocean water with dissolved gases and nutrientsd. Vertical Motion and the Three-Layered Oceani. The oceans are a three dimensional habitat and vary horizontally and vertically. 1. Many of the changes in habitat are due to changes with depth.2. The