The two main masses of deep water are the Antarctic Lower Water (AABW) and the North Atlantic Deep Water (NADW). The AABW forms on the surface of the Weddell Sea near the Antarctic coast, south of South America. The NADW forms in the Greenland-Iceland-Norway Seas in the North Atlantic Ocean. (Gornitz 944; Garrison 254)Surface ocean 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 around a stationary object is used to measure currents. Eulerian current meters are mounted on buoys attached to cables anchored to the seabed. The direction and drift speed of the 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 floating object to measure surface currents. In this method, floats are left free on the surface to move along with surface currents and are then monitored acoustically or by GPS satellites. (Pinet 197; Garrison 258) The two differences between upwelling and downwelling, both often caused near the coast due to the vertical circulation of water triggered by the wind, can be explained based on their origin and function in the marine ecosystem . In the event of an upwelling, deep water is brought to the ocean surface. This occurs when surface water moves away from the shore due to Ekman transport when the wind blows parallel to the coast. Therefore, surface water is replaced with water from below. In contrast to ascent, descent is the reverse process in which... in the center of the map... objects moving freely in: (a) Northern Hemisphere Objects moving freely north or south in the hemisphere northern they will appear to curve towards the right side. (b) Southern Hemisphere Objects moving freely north or south in the Southern Hemisphere will appear to curve to the left side. (Kershaw 39)Works CitedGarrison, Tom. Oceanography: an invitation to marine science. 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". Network. October 28, 2011. .Pinet, Paul R. Invitation to Oceanography. Ontario: Jones and Bartlett Learning, 2008.