Chapter 24 Reading Guide The Moving Ocean 24.1 Surface Currents Summarize important ideas about surface currents by completing the organizer. Wind Patterns Such as 2. Westerly Winds 1. Trade Winds Cause 3. Surface Currents Which are 4. Continuous rivers of water flowing at the ocean surface And flow Or Counter-clockwise in 6. The Southern Hemisphere Clockwise in 5. The Northern Hemisphere Describe how monsoon winds affect the behavior of surface currents. Monsoon winds change direction with the seasons, causing surface currents nearby to also change direction. Describe a countercurrent and contrast its flow with the other currents described in this section. A countercurrent flows in the opposite direction as wind-related currents. It develops because wind-related currents push a lot of water to one side of an ocean basic. The countercurrent then pushes it back. 24.2 Currents under the Surface Fill in the chart below, organizing the three major density currents – Antarctic Bottom Water (ABW), North Atlantic Deep Water (NADW), and Antarctic Intermediate Water (ATW) – by salinity, temperature, depth and density. 1. Salinity 2. Temperature 3. Depth 4. Density Greatest ABW NADW ABW ABW Intermediate NADW AIW NADW NADW Least AIW ABW AIW AIW 1. Explain how evaporation affects density currents. Evaporation increases the salinity, and therefore the density, of seawater. Denser water sinks to form currents that flow beneath those formed by less dense water. 2. Describe two types of upwellings and their effect on marine life. One kind of upwelling happens at western continental coasts when surface winds push surface water out to sea and cold water rises from below to fill the void. Another kind happens when opposing winds blow water away from a region and cold water rises to fill the void. Upwelling water brings nutrients with it that support phytoplankton and a rich array of marine life. 24.3 Tides Complete the organizer to explain how each factor affects the tides. 1. Sun 2. Moon Sun’s gravity causes high tides by pulling on water nearest it, and also pulling Earth away from the water on the far side of Earth; low tide results in remaining areas. When in line with the moon, Sun’s gravity enhances moon’s gravity. When at odds, it minimizes the moon’s gravitational effect on tides. Moon’s gravity causes high tides by pulling on water nearest it, and also pulling Earth away from the water on the far side of Earth; low tide results in remaining areas. As moon orbits Earth, tidal changes advance through the day. Tides 3. Shoreline Shape Broad, open shorelines allow high tide waters to spread out, minimizing their height. Narrow, constricted shorelines force high tide waters into confined spaces, maximizing their height. What is the tidal impact of the new moon at perigee? The new moon at perigee causes very high tides because the moon is closest to Earth and sun’s gravity, which enhances the moon’s gravity.