flow in the upper 1,000 meters of ocean driven by global winds Westerlies & Trade Winds N. and S. hemispheres each have two circulations caused by the Coriolis Effect clockwise in N. hemisphere, opp. in Southern Earths rotation & continents push currents along path of travel Winds Currents cold currents- move towards the Equator Eastern sides of ocean basins warm currents- move towards poles Western sides of ocean basins Gulf Stream N. Atlantic Canary N. Equatorial California Labrador West Wind Drift flow in opposite direction of wind-related currents under current return water taken away from one side of the ocean basin to the opposite side driven by gravity & differences in density Density current= heavier & denser than surrounding water Sink to bottom from surface move very slowly Circulate for years Turbidity currents global circulation of deep ocean currents efficient heat-transport system drives Earths climate Changes in salinity and surface cause water to sink carry oxygen absorbed from surface for deep sea life turbidity currents are an example of VERTICAL density currents! polar water is salty, cold super dense increased evaporation leaves salt behind, which increases the density dense water sinks and is replaced with less dense water Example: Mediterranean vertical density currents that occur when cold deep water comes to the surface can occur anywhere, prevalent along western coasts of continents 1. surface winds push water away from continent 2. denser, salty water suddenly sinks large amounts of nutrients come to surface phytoplankton populations cultivate and provide food for marine life Large-scale fishing areas Examples: California, NW Africa-Morocco, southwestern Africa, Peru, western Australia twice-daily rise and fall of Earths oceans result of gravitational pulls from moon and sun Moon has a greater effect since it is closer Moons effect on the tides: The moon orbits around Earth causes bulges to rotate around the Earth over the lunar month (~29 days). The moon rises about 50 minutes later each days so do the tides. Uniform water level Moon Moons orbit Low tide Direct high tide Indirect high tide sun can enhance or detract from the moons effects Spring Tides occur when the sun and moon are in alignment (enhances tides) High tides are higher and low tides are lower Neap Tides occur when the sun and moon are at right angle (sun detracts from moons pull) High tides are not as high and low tides are not as low Tidal Range is the difference between high and low tides. more noticeable on oceans than lakes Small lakes show no tides at all Great Lakes have tides with ranges of just a few centimeters Ocean tidal ranges can vary greatly closer to the poles the greater the tidal range The shapes of individual shorelines influence the tidal range A narrow bay has a greater tidal range than a wide coastal area. Bay of Fundy, High tide Bay of Fundy, Low tide