Study Guide Oceanography: Chapter 8


Ocean Circulation

• Know your currents (names, cold or warm) • Equatorial currents are driven by the trade winds. • Surface ocean circulation is driven primarily by wind and modified by the Coriolis Effect and land. • Convection cells driven by the relatively weak winds near the center of gyres are called langmuir circulation. • Surface water circulation near Antarctica is dominated by two circumpolar currents, one current that moves water to the east and one current that moves water to the west. • When a meander from the Gulf Stream pinches off and isolates a body of water within the center of the North Atlantic gyre, the body of water is called a cold core ring. • During winter months, monsoon winds over the Indian Ocean flow from land to sea and are dry. • Compared to an eastern boundary current in a gyre, a western boundary current is deeper, faster, narrow, and has intensification in subtropical latitudes. • Westward intensification causes a steeper slope of surface water in the western section of the gyre as compared to the eastern section of the gyre, equatorial counter currents, the center of the gyre to be shiftred to the west, and causes very swift western boundary currents. • Surface waters are pushed away from land and replaced by nutrient-rich bottom water through upwelling. • Strong upwelling occurs between the North and South Equatorial Currents, in areas of surface current divergence, near the Galapagos Islands, and where water is constantly pushed away from the shoreline. • Deep ocean water generally has high amounts of nutrients and oxygen. • The worldwide effect of El Niño includes coral reef deaths in the Pacific, crop failure in the Philippines, increased Pacific cyclone activity, and water shortages in Sri Lanka. • The El Niño Southern Oscillation can best be described as the relationship between sea surface temperature and high altitude pressure. • The El Niño weather pattern is associated with drought and fires in Australia. • The Ekman spiral is driven by wind. • In the southern hemisphere, the direction of Ekman transport is to the left of the wind direction. • Geostrophic circulation works in opposition to Ekman transport in a gyre. • Thermohaline circulation is driven by density. • Compared to Antarctic Bottom Water, North Atlantic Deep Water is lower on oxygen. • The location where water flow is uninterrupted between the Pacific, the Atlantic, and the Indian Oceans is in the Southern Ocean. • The arrangement of water masses in the southern Atlantic Ocean from the surface to the bottom is Antarctic Intermediate Water, North Atlantic Deep Water, Antarctic Bottom Water. • The deep Pacific Ocean water is old due to its low oxygen levels. • Deep water circulation in the Pacific Ocean is influenced by hydrothermal vents from the East Pacific Rise. Deep ocean water in the Indian Ocean includes Red Sea water which has high salinity and low oxygen. • The largest current by volume in the oceans is the Antarctic Circumpolar Current (West Wind Drift). • The circular pattern of surface water currents is called a gyre. • Downwelling may be the result of winds blowing parallel to a coastline. • Deep ocean currents often move cold, dense water away from the poles. • The source of some deep ocean water masses can be identified by the amount of dissolved oxygen in the water mass. • Deep ocean water masses have characteristic temperatures and salinities. • All deep water in ocean basins originates in the Atlantic Ocean. • A geostrophic current is one that (ideally) flows parallel to the center of a gyre. • Ekman transport is an average path of motion which, under ideal conditions, is at 90 degrees to the wind’s direction. • One of the first indications that an El Niño event may be occurring is when warm water from near Australia migrates toward South America. • The circulation cell in the equatorial South Pacific created by the movement of air between high- and low- pressure regions is called the Walker Cell. • Western intensification is due to a gyre’s apex being located west of the ocean basin’s geographic center.

Know Figure 8-4, p.235, Figure 8-11, p. 242, Figure 8-16, p.246, Figure 8-18, p.249, and Figure 8-25, p.259. These figures will be matching questions.

Essay : You are to pick two. The answers must be typed. Three Paragraphs for each (beginning, middle, end).

1. Describe the location of the warm current and the cold current within a gyre. How is the direction of the current related to heat distribution in the Earth's oceans? 2. Compare and contrast eastern and western boundary currents. 3. Differentiate between upwelling and downwelling. Describe the impact of coastal geography and latitude on these processes. 4. Discuss the biological impact of upwelling and downwelling on marine ecosystems. Provide examples of marine systems that are impacted by these processes in your answer. 5. Describe the El Niño Southern Oscillation. What global environmental effects characterize an El Niño event? What global environmental effects characterize a La Niña event?