Encyclopedia of Environmental Science and Engineering, Volume I and II

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OCEANOGRAPHY

INTRODUCTION

Before beginning a discussion of the origin and structure of

the world’s oceans, one should first reflect on the reasons for

our interest in these bodies of water, which together comprise

approximately seventy percent of the earth’s surface area.

Perhaps one of the more obvious reasons is the enormous

wealth of natural resources hidden in the oceans’ depths,

including vast reserves of food and energy sources. This abun-

dance has of course led to an increased human presence in and

along much of the world’s oceans, prompting considerable

concern for the short and long term consequences of man’s

activities in this fragile environment.

An additional focus of recent oceanographic research has

been the role of the sea in global climate variations, spurred

by the recognition that these variations are driven largely by

fluctuations in the air-sea momentum and heat exchange.

This role was dramatically illustrated in the 1982–1983 El

Nino event, which sparked such wide-ranging weather aber-

rations as flooding in southern California and droughts in

Australia, and is widely believed to have had an oceanic

origin (Rienecker and Mooers, 1986).

In addition to these varied and multi-disciplinary research

activities, the increasing strategic importance of the world’s

oceans has been one of the prime motivations behind recent

advances in underwater communication, depth measure-

ment, and perhaps most significantly, the remote sensing of

ocean physical processes. In the political forum, this strategic

importance, along with the economic benefits of the natural

resources mentioned earlier, continues to provoke interna-

tional debate over such issues as fisheries management, ocean

dumping, and the demarcation of territorial (“exclusive zone”)

boundaries.

Clearly, therefore, the oceans mean many different things

to many different people. The common thread is the need

and desire to learn more about these fascinating and fun-

damentally important bodies of water. In the following, we

shall attempt to provide some insight into the makeup and

behavior of the sea, from its origins to its various modes of

motion. Realizing the short-comings of an overview treatment

of such complex subject matter, the interested reader is urged

to pursue in more detail any of the specific topics addressed

in this article.

ORIGIN AND STRUCTURE OF THE OCEANS

It is generally believed that most of the water now present on

the surface of the earth originated in the earth’s interior. The

prevailing scientific opinion holds that the earth was formed

through the gradual compaction of an accumulation of par-

ticles, primarily silicon compounds, and iron and magnesium

oxides. The heat released as a result of this compaction and

radioactive decay was sufficient to produce a molten mass, the

heaviest material sinking under the action of gravity to form

the earth’s core and the lightest “floating” to the surface to form

the crust. This formative period was characterized by intense

volcanic activity. It is widely accepted that the molten material

introduced to the earth’s surface through this activity served

as the conduit for the release of hydrogen and oxygen into the

atmosphere (primarily in the gaseous form) with some eventu-

ally condensing to form liquid water at the surface. Sediments

discovered in Australia in 1980 appear to be of marine origin

and have been dated at approximately 3.5 billion years old

(Ross, 1982), indicating that surface water has been present

over a significant portion of the earth’s history.

The horizontal movements that produced the present-day

sea-floor are, in geologic terms, a very recent occurrence. In

fact, measurements indicate that the most ancient regions of

the present deep ocean floor are no more than 225 million

years old (Gross, 1977). The oldest dated sediments from the

Atlantic Ocean indicate an age of approximately 165 million

years (Sclater and Tapscott, 1979), while those of the Pacific

reveal a relatively “young” water body at approximately 120

million years old (Heezen and MacGregor, 1973).

The mechanism for the creation and growth of the ocean

basins is commonly referred to as continental drift, or in

more general terms, as plate tectonics. The basic concept can

be explained as follows. The outer shell of the earth (the lith-

osphere) is actually composed of a number of rigid plates.

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