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Ocean Currents What makes that River Flow? What’s the role of wind? 1st: High heat capacity of water (and ocean currents) buffer ocean temperatures 2nd: Land temperatures fluctuate more, especially in higher latitudes 3rd: These differences in surface energy create prevailing winds. 4th: These prevailing winds drive surface currents. winds and currents Which way do currents flow? Northern Hemisphere: surface currents rotate clockwise (Coriolis aids in this, wind driven mostly) Southern Hemisphere: currents rotate counterclockwise Gyres 1. Circular current flow due to coriolis effect 2. Currents tend to “hug” the coasts as they move CW in the N. Hemis. Global Conveyer Belt •Ocean currents move 40% of “excess heat” from equator to poles •Driven by circulation of deep ocean waters (cold, salty water) (density) and surface winds •Warm currents (east coast) away for equator; cold (west coast) toward equator Our Closest Currents East coast: Influence of Gulf Stream & N. Atlantic Notice how the Arctic Ice is pushed back by the warm water. For the area located at higher latitudes, average temperatures are significantly warmer than other areas at the same latitude. (England, Norway, etc) The Labrador Current (cold): Bringer of Death!! Icebergs from Greenland calve off and enter the N. Atlantic via the Labrador Current. Ex. Titanic East Coast Currents • Cold- Labrador (Canada) • Warm- Gulf Stream (FL to Canada) & N. Atlantic (Canada to England) Surface Currents West Coast Currents • Cold – California Currentsouth along west coast from OR toward Baja penisula – North Pacific Currenttoward Washington state, British Columbia (really between cold and warm) • Warm – Alaska-north to Alaska As bottom currents reach landforms, upwelling occurs. The cold water reaches the surface and warms (keeps the process going). So how do the following influence ocean currents? 1) Winds? Answer: Surface winds tends to push water along in the same direction as the wind 2) Temperature? Answer: Colder water will sink and warmer water rises (Convection). 3) Salinity (density)? Answer: The more salt dissolved in the water the more dense the water, thus the greater the salinity, the more likely the water is going to sink. So putting the three together Fresh warm water (such as runoff from rivers) or fresh cool water (from melting ice) will most often be found near the surface. Cold, salty water is very dense and is most likely to be near the bottom of the ocean. Together, a circulation is created as cold, salty water (from polar regions) sinks towards/moves along the bottom of the ocean and warm, salty (usually less salty than the bottom) moves along the surface (from the equator).