The two main deep water bodies are the Antarctic Bottom Water (AABW) and the North Atlantic Deep Water (NADW). AABW forms on the surface of the Weddell Sea near the Antarctic coast in southern South America. NADW forms in the Greenland-Iceland-Norway seas of the North Atlantic Ocean. (Gornitz 944; Garrison 254) Ocean surface currents are largely caused by wind movements. Surface currents can be measured by several methods, two of which, namely the Eulerian method and the Lagrangian method, are discussed as follows: The Eulerian method is also called the flow method. In this method, the flow of water past a fixed object is used to measure currents. Eulerian current meters are mounted on buoys attached to cables anchored to the sea floor. The direction and drift speed of surface currents are then measured and the data is stored on a computer chip. The Lagrangian method, also known as the float method, uses a freely floating object to measure surface currents. In this method, floats are released to the surface to move with surface currents, then are tracked acoustically or by GPS satellites. (Pinet 197; Garrison 258) The two differences between upwelling and downwelling, both of which are often caused near coastlines due to the vertical circulation of water triggered by wind, can be explained by their origin as well as by their function in the marine ecosystem. In upwelling, deep water is brought to the surface of the ocean. This occurs when surface water moves away from the shore due to Ekman transport when the wind blows parallel to the coast. Thus, surface water is replaced by water from below. Unlike upwelling, downwelling is the reverse process in which...... middle of paper ...... actually moving objects in: (a) Northern Hemisphere Freely moving objects moving northward or south in the Northern Hemisphere will appear curved towards the right side. (b) Southern Hemisphere Freely moving objects moving north or south in the Southern Hemisphere will appear to curve toward the left side. (Kershaw 39)Works CitedGarrison, Tom. Oceanography: an invitation to marine sciences. California: Cengage Learning, 2009. Gornitz, Vivien. Encyclopedia of paleoclimatology and ancient environments. Netherlands: Springer, 2009. Kershaw, Steve. Oceanography: an Earth science perspective. Cheltenham: Stanley Thornes, 2000.Montereyinstitute.org. "Currents and marine life". Internet. October 28, 2011. Pinet, Paul R. Invitation to oceanography. Ontario: Jones and Bartlett Apprenticeship, 2008.