THE OCEAN BASINS

I. HYDROLOGY

Hydrology is the study of the waters of the earth in their several states (solid, liquid, and vapor) & the diverse paths that link together the oceans, atmospheric moisture, and surface and groundwater in the continents. (Figure 1)

The earliest recorded ideas on hydrology may be traced to the ancients, particularly the Greeks and the Romans.

The first attempt to place hydrology on a quantitative basis, however, occurred when the French physicists Pierre Perrault & Ede Mariotte made studies of the Seine River and its basins in the 17th century. Perrault measured the rainfall of the Seine’s basins and showed that it equaled six times the total river runoff. Mariotte calculated the discharge of the Seine at Paris from measurement of the channel’s width and depth and the water velocity at its average or level flow.

Hydrologic Sciences

Hydrologic sciences include the several fields of the study concerned with the waters of the Earth, including the occurrence, circulation, distribution, and properties of the waters & their interaction with the environment.

The Hydrosphere

The total volume of the water at or near the Earth’s surface is approximately 1,500,000,000 cubic km (350,000,000 cubic miles)The remaining components of the hydrosphere are, in decreasing order of quantity, glacial ice, fresh water in lakes & rivers, and atmospheric water vapor. Figure 1

II. OCEANOGRAPHY AND ITS MAJOR SUBDIVISIONS

Oceanography involves the application of all sciences in a comprehensive and interrelated study of the oceans.

Oceans cover 72% of the earth’s surface. The average depth of the ocean is 3.8km or about 2 ½ miles; the ocean floor has a thickness of between 5 and 10km.

Major Subdivisions

1. Geological oceanography2. Biological oceanography3. Chemical oceanography4. Physical oceanography

In Northern Hemisphere, there is roughly 61% water and 39% land, while in Southern Hemisphere, 81% is water and 19% is land.

Water resources may be grouped as marine water (coastal and oceanic water), subsurface water (wells, springs, hot springs, geysers, and aquifers), and fresh surface water (rivers, streams, lakes, swamps, and waterfalls.)

Instruments to Explore the Depths

Oceanography draws on all the basic sciences. Oceanographic observations and measurements employ many of the techniques and instruments commonly used in physics, chemistry, and geology. Other instruments may be affected by high humidity, rapid changes in temperatures, and the vibration of the ship’s machinery. For these reasons, specialized instruments have been produced for oceanographic research. Some of these are:

1. Water sampling bottles2. Deep-sea thermometers3. Bottom samplers 4. Current meters5. Sonic depth recorders6. Deep sea cameras

III. THE OCEAN FLOOR

The depressed portions of the earth’s crust containing he waters of the world are called ocean basins. (Figure 2)

The ocean floor is the true surface of the earth. The continents are really great islands raised above the sea floor by the internal forces of the earth.

A more recent theory of the origin of the continents connects them with zones of fracturing in the crust. Millions of years ago, the theory goes, lava poured from volcanoes along great fractures zone. The great masses of rock that are now the continents were built up during this process.

At the present time, there is no sufficient evidence on which to accept or reject any theory of the origin of the continents and ocean basins. It is definitely known that the continents are composed mostly of granite resting on a layer of basalt which is continuous with the sea floor.

Figure 2

Zone of Ocean Depth

The oceans fill and spill over the edges of the continents. At the continental shelf, the sea is very shallow. It is seldom more than 500 or 600 ft deep.

At the edge of the continental shelf, the continent drops off steeply to the depths of the sea floor. This zone is called the continental slope. It is a region where great landslide occurs.

A large amount of sliding materials creates very strong currents. Such currents are called turbidity currents because the water becomes very turbid or muddy. Turbidity currents are probably responsible for cutting deep canyons into the edge of the continental shelf. Such canyons occur on the mouths of many rivers which carry large amounts of sediment into the sea.

Beyond the continental slope is the deep-sea zone which includes the major part of the sea floor. The average depth of the sea beyond the edges of the continents is 2 ½ miles.

The Shape of the Sea Floor

Until a few years ago, it was thought that the sea bottom was a vast plain. This plain was believed to be shaped only by gentles rises and depressions with island here and there.

One of the most unusual features of the sea floor is a series of underwater mountains called mid-ocean ridges, (Figure 3) such as a mountain chain, the Mid-Atlantic Ridge, which averages 200 miles in width and about 10,000 feet in height. It stretches along entire basin of the Atlantic Ocean to the southern tip of the America.

The Indian Ocean ridge in turn joins with several ridges which reach across the Pacific. The peaks of these ridges are higher than those of most continental mountains systems. However, in most cases, their tops are a mile or more below the surface.

Figure 3

The Azores, Ascension Island, and the other scattered island of the Atlantic are the highest peaks. Mount Pico, in the Azores, ascends 7,163 feet above the sea level and its base is 20,000 feet below the surface.

Not all the volcanic activity on the sea floor is connected with the mid-ocean ridges. The most active volcanic regions on the earth are in the vicinity of island arcs. These are chains of island lying close to the edges

of continents. Intense earthquake and volcanic activities are common in island arcs which apparently are located along the major faults of the crust.

Associated with the island arcs are deep gashes in the sea floor which hold trenches. These are formed by faults along places where volcanic eruptions occur.

All the deepest spots in the ocean are located in the trenches. The deepest so far measured is a trench near the Marianas Island in the pacific. It plunges to nearly 7 miles below the sea surface. Other deep trenches are located near the Aleutians, the coast of Japan, the Philippines, Java, and the west coast of Mexico. In the deep sea zone, the bottom is free of any material washed out from the land. All the sediments in the deep sea are formed from the materials that settle from above. These materials build up a heavy collection of extremely fine, slimy sediment called ooze. The rate of the sedimentation in the deep ocean is very slow (approx. 0.4 inch. Per 1,000 years.)

IV. THE OCEANS OF THE WORLD

It is customary to speak of the oceans as if they were separated bodies of water. However, it should be kept in mind that they are really just sections of one great sea covering most of the earth’s surface. There are no natural divisions of the sea floor to separate one ocean from another (Figure 4).

The largest of all oceans is the Pacific. It includes three-eighths of the total area of the earth’s surface. It is the deepest of the oceans; it has an average depth of about 14,000 feet. Next in size is the Atlantic, which takes in one-quarter of the area of the sea. The Atlantic also ranks second in depth with an average of about 13,000 feet.

The Indian Ocean is third in size, with about one-eighth of the total area of the Earth’s surface. It is boarded by Africa and Asia. It extends only a short distance across the equator into the Northern Hemisphere. It has a few islands or adjacent seas and has an average depth of 3,840 meters.

Since Africa and Asia are close to it, conditions in the northern Indian Ocean vary so much during the year around the north pole is the Arctic Ocean, a small ocean with only one-thirtieth of the earth’s surface. The Arctic Ocean is almost completely with ice to a depth of about 10feet. The remaining area of the sea is included in the Antarctic Ocean surrounding the Antarctic continent.

Figure 4V. THE SEAS

Island groups (Japan, Philippines, Aleutian Island, and Kamchatka Peninsula) separate the coastal oceans to form seas. Seas have well-defined boundaries and distinctive water properties due to:

1. Restricted communication with the open ocean.2. Influence of the adjacent continent or variable wind patterns and3. Usually excessive precipitation & river discharge.

Seas are usually shallower, smaller, and closer to the land than oceans, to which they are connected. The world’s seas include:

1. Andaman Sea is the northeastern arm of Indian Ocean2. Baltic Sea is the world’s largest body of brackish water. An area of 1,600 sq. miles (42,000 sq. km)3. Barrents Sea is the outlying portion of the Arctic Ocean.4. Bering Sea is the body of water in the northernmost Pacific Ocean, separating the continents of Asia

(northeastern Siberia) and North America (Alaska). The Bering Sea covers 890,000 sq. miles (2,304,000 sq.km)

5. Caribbean Sea is a sub economic basin part of the Atlantic Ocean, app. 1,020,000sq.miles (2,640,000sq.km) in extent.

6. China Sea is part of the western Pacific Ocean bordering on the South Asian mainland. It covers an area of about 1,340,000sq.miles (3,465,000 sq.km)

7. Hudson Bay is roughly oval-shaped and one of the major continental seas fringing the Arctic Ocean. It is an inland sea indenting East Central Canada with an area of 316,000 sq. miles (819,000 sq. km).

8. Mediterranean Sea is an intercontinental body of water lying between southern Europe (to the north), North Africa (to the south), and the southwestern Asia (to the east). And a total area of 970,000sq. miles.

9. North Sea, one of the most important commercial waterways of the world, is part of the Atlantic Ocean. It occupies a shallow basin between the continent of Europe and the British Isles. The total area of the sea is 220 sq. miles.

10. Red Sea contains the world’s hottest and saltiest sea water. It has an area of 169,000 sq. miles (438,000 sq. km.)

11. Sea of Japan is the marginal Sea of the Pacific Ocean which lies between Japan and the Soviet island of Sakhalin (east) and the Asian mainland of the Soviet Union and Korea (west). It has a surface area of 389,100 sq. miles (1,007,800 sq. km) and a mean depth of 4,429 ft. (1,350 m.)

12. Sea of Okhotsk is the northwestern arm of the Pacific Ocean enclosed by the northeastern Siberia (Russia) coast of Asia from Cape Lazarev to the mouth of the Penzhina River, by the Kamchatka Peninsula and the Kuril Island to the east; and by the Russian island of Sakhalin to the southwest. It has an area of 611,000 sq. miles (1,583,000 sq. km).

Sea Water

Composition of Sea Water

Geologist believes that the Earth in its early stages was without oceans. All of the earth’s water was probably chemically bound within the rocks until volcanism released it. Some of the volcanic actions that originally produce the oceans are still going on. Thus, it is reasonable to suppose that the oceans are still growing today. Volcanic activity is much less now than in the past.

The composition of the sea water today is not the same as that of the water that filled the original oceans. When the water was first released from the original rocks, it was not salty. It only became salty after the rain had washed over the land on its way to the oceans’ basins. As the land was flooded by the downfall of rain, minerals were dissolved and carried into the sea. Since the ocean was formed, the same processes have been going on again and again in an endless hydrologic cycle.

Each year the oceans become more and more salty. On the average, 100 pounds of sea water yields 3 ½ pounds of dissolve minerals. The most abundant are those most soluble in the water. Common table salt (sodium chloride) leads the list.

Dissolved Substances Parts per Million Parts Sea Water

Sodium Chloride (NaCl) Magnesium Chloride (MgCl2) Magnesium Sulfate (MgSO4) Calcium Sulfate (CaSO4) Potassium Sulfate (K2SO4) Calcium Carbonate (CaCO3) Magnesium Bromide (MgBr2)

27,2133,8071,6581,260 86312376

TOTAL 35,000

Minerals from the Sea

The sea is a treasure house of minerals. It contains substances of great value dissolved by its water. However, the richest mineral of all is the water itself. The dissolved minerals in the sea water are useful and valuable. Each cubic mile of sea water contains about 4 million tons of magnesium. These light metals are used in aircraft and many other applications. Almost all of the world’s supply of magnesium is extracted from sea water. The element bromine (used in highest test gasoline and photographic film) and many chemicals are obtained from sea water.

A cubic mile of sea water contains about 90 millions dollars worth of gold. However, no one has yet been able to find an economical way to get gold from the sea.

In many parts of the world, water was once a plentiful but it is now becoming a precious substance. There are only two major ways of insuring an adequate water supply for the future. One is by reducing waste; the other is by increasing the supply of usable water.

The most commonly used method for converting salt water is trough distillation. The water is heated and drawn off as steam, which is pure water when cooled.

The Temperature of Sea Water

The sea water is the greatest storage reservoir for the radiant energy from the sun. Water has much greater capacity to absorb heat than the rest of the land, gases or the atmosphere. The top 30 feet of sea water in all the oceans has as much heat capacity as the entire atmosphere.

The sea accumulates heat from the sun’s radiation during a warm season. In colder periods, this heat is released to the air. This tends to balance the extremes of temperature lost by the earth’s rotation and revolution around the sun. Without the sea, the earth would experience far greatest extremes of temperature than it has now.

Like the land surfaces, the sea receives most heat near the equator. This results in warmer surface temperature in the oceans near the equator. The highest of all the ocean’s surface temperature is found in the Persian Gulf, where readings of 96°F are common. However, most tropical seas have a surface temperature of about 70°F.

In the Arctic Sea, temperatures are low enough to cause the freezing of upper layers of sea water. The freezing temperature of sea water varies with its saltiness, but it is always below 32°F, the freezing point of fresh water.

The slight difference in density is surprisingly effective in preventing mixing of the two zones. In most places in the sea, there is a sharp drop in temperature from 150 to 1,200 feet below the surface where the upper warm water joins the cooler water below. This zone of rapid temperature change, called the thermocline, varies in depth from season to season. Measurable thermoclines are also observed in many lakes.

One effect of thernoclines in oceans is the separation of the current of the warm water above from the current of the cold water beneath.

VI. ECONOMIC ASPECTS OF OCEANS AND SEAS

The sea is generally accepted by scientist as the place where life began on earth. Without the sea, life as it is known today would not exist. It acts as a great reservoir, leveling the temperatures extremes that would otherwise prevail over the earth and expands the dessert areas. The ocean provide the least expensive form of transportation known to man, and the margins of the sea serve as one of the major sites of recreation. The sea is a major source of food and a dumping ground for many wastes. The sea is also a major potential source of protein, minerals, and power, all of which required in ever-increasing quantities by all industrial societies.

The sea is also used as a source of:1. Food and Water

Fishing- man can get 60,000,000 tons of food from the ocean annually by fishing.2. Energy Resources

Power Generation- energy is extracted from the tides of the ocean. Minerals- billions of tons of material can be obtained from the sea. Petroleum- 2,000,000,000 barrels of oil resources can be obtained.

3. Building products- sand, gravel, and lime4. Jewelry- corals and pearls5. Fertilizers- seaweeds and dead organism

KEY CONCEPTS

The study of waters of the earth in their several states and diverse paths that link together the oceans, atmosphere, moisture, and surface and ground water in the continents is referred to as hydrology.

The application of all sciences in a comprehensive and interrelated study of the oceans is known as oceanography.

The depressed portions of the earth’s crust containing the waters of the world are called ocean basins. The largest ocean in the world is the pacific followed by the Atlantic, Indian, and Arctic oceans. Seas are usually shallower, smaller, nearer to the land than oceans to which they are connected. They

have well-defined boundaries due to restricted communication with the open ocean, the influence of the adjacent continent or valuable wind patterns, and excessive precipitation and river discharge.

IMAGE SOURCE: https://books.google.com.phTitle: Earth Science First Edition '97 /Publisher: RBS /Reprinted: April 2004