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.