23.5 The Restless Oceans
Reading Focus
Key Concepts
How do conditions in the ocean change with depth?- What causes surface currents, density currents, and upwelling?
- How do waves erode rock and deposit sediment?
Vocabulary:
salinity
continental shelf
surface current
density currents
upwelling
hydraulic action
longshore drift
Reading Strategy
Relating Cause and Effect Copy the table below. After you read, complete the table to compare ways that ocean water can move.
Movement Type |
Causes |
Effects |
Surface current |
a. |
b. |
Density current |
c. |
d. |
Upwelling |
e. |
f. |
Longshore drift |
g. |
h. |
Oceans surround all of the continents. Earth's ocean waters are divided into four major oceans: the Pacific Ocean, Atlantic Ocean, Indian Ocean, and Arctic Ocean. These oceans also include smaller bodies of water, such as the Gulf of Mexico and the Mediterranean Sea.
Exploring the Ocean
Most of Earth's water exists as salt water in the oceans. Ocean water is a mixture that includes dissolved salts and gases. Salinity is the proportion of dissolved salts in water. On average, there are about 35 grams of dissolved salts in each kilogram of ocean water. The most abundant salt in ocean water is table salt, sodium chloride (NaCl).
Salt is added to the oceans by rivers and volcanoes. Rain slowly dissolves salts out of surface rocks. These salts are washed into rivers which then carry them to the ocean. In addition, volcanic eruptions send elements such as sulfur and chlorine into the atmosphere and the oceans. At the same time, salt is removed from seawater by animals and plants as they build hard parts and also by deposition as sediment.
Figure 25 Wave action is the primary means of erosion along coastlines. Here, waves are breaking onto rocks at Cape Kiwanda State Park along the Oregon coast.
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