THE LIVING HYDROSPHERE: Ocean Ecosystems

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Chapter Outline

10.1

The Physical Oceans
10.2

Life on the Continental Margins
10.3

Life in Polar Waters
10.4

Life in Open Waters
10.5

Geographic Perspectives: The Problem with Plastic

These islands of green are in the Republic of Palau in the western equatorial Pacific. They are composed of ancient uplifted coral reefs. Coral sands and living coral reefs surround the islands.

(© Reinhard Dirscherl/WaterFrame/Getty Images)

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LIVING PHYSICAL GEOGRAPHY

How deep are the oceans?
Why are the oceans salty?
Why do most deep-sea organisms glow?
What is the Great Pacific Garbage Patch?

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THE BIG PICTURE

Ocean ecosystems range from tropical coral reefs to dark and frigid deep-sea communities. All ocean ecosystems are influenced by people, and plastic pollution in the oceans is a growing problem.

LEARNING GOALS

After reading this chapter, you will be able to:

10.1

Discern the major physical features of the oceans.
10.2

Describe the ecosystems along continental margins and human influences on those ecosystems.
10.3

Explain how polar marine ecosystems function.
10.4

Describe the geographic patterns of life in the open ocean.
10.5

Assess the environmental impact of and remedies for plastic pollution in the oceans.

THE HUMAN SPHERE:

Coastal Dead Zones

COASTAL DEAD ZONES are areas in coastal waters where there is too little dissolved oxygen to support most forms of marine life. Coastal dead zones are a natural phenomenon, but human activity has increased both their numbers and their geographic extent in recent decades. Dead zones are now occurring in areas where they were not found before (Figure 10.1).

Figure 10.1

Coastal dead zones. Red circles show the locations and sizes of coastal dead zones. The largest circles show dead zones 10,000 km² (3,860 mi²) in extent or greater. Dead zones of unknown size are shown with black dots. Note that there are fewer dead zones in the Southern Hemisphere because there is less agricultural activity there.

Anthropogenic dead zones are closely tied to agriculture. Dead zones form or increase in size as fertilizers, applied in excess to agricultural fields, are carried into streams by rainfall runoff. The streams carry the fertilizers to the coastal areas. There they fertilize phytoplankton (see Section 10.3), creating explosive phytoplankton growth. After the phytoplankton die, they settle into deep water, where microbes decompose their remains. The process of decomposition removes dissolved oxygen from the water, creating a dead zone. Most marine life asphyxiates when it enters these anoxic (oxygen-free) dead zones.

This chapter explores the oceans and emphasizes the human influences on them. We first examine the physical characteristics of the world’s oceans. Next, we explore life along the continental margins, in polar waters, and in the open ocean. Finally, we examine the growing problem of plastic debris in the world’s oceans.

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