Earth Science: Water – Oceans
More than two-thirds of the Earth’s surface is covered in water. The ocean is the largest and oldest habitat on our planet and plays a central role in shaping the climate.
It provides energy, natural resources, and one of the major food sources for humans. Nevertheless, large parts of the oceans still remain undiscovered.
The World’s Oceans
Globally there are 332 million cubic miles (1.384 billion km3) of water reserves, of which 97 percent makes up the world’s oceans. Water is distributed more heavily toward the Earth’s Southern Hemisphere.
The interconnected world’s oceans are the Atlantic Ocean, the Indian Ocean, and the Pacific Ocean. The oceans of the Northern Hemisphere are divided by continents and offshore islands. The Southern Hemisphere lacks such natural barriers. In order to geographically structure the ocean of the Southern Hemisphere, meridians running through the southern tips of the three large landmasses were defined as boundaries. Hence, the meridian running through Cape Agulhas at 20° east longitude separates the Atlantic Ocean from the Indian Ocean.
The meridian running through the South East Cape of Tasmania at 147° eastern longitude is the boundary between the Indian Ocean and the Pacific Ocean. The southern boundary between the Pacific and the Atlantic Oceans passes through Cape Horn at 68° west longitude to the Bering Strait, which defines the northern boundary. Bering Strait is the channel between the Russian Cape Dezhnev, the easternmost point of the Asian continent, and Cape Prince of Wales, Alaska, which is the westernmost point of North America.
The Pacific Ocean is not only the oldest, but also the largest of the three main oceans and the one with the most islands. Its average depth is 12,926 feet (3,940 m). The greatest depth recorded to date is in the Mariana Trench at 36,200 feet (11,034 m) deep, whereas the deepest point recorded in the Atlantic Ocean is the Milwaukee Deep in the Puerto Rico Trench at 30,246 feet (9,219 m). With 29 million square miles (75 million km2), the Indian Ocean is the smallest of the three major oceans. The Sunda Trench is the deepest point of the Indian Ocean, and reaches 24,458 feet (7,455 m).
Adjacent and semienclosed seas
Several adjacent seas are separate from the oceans and are located adjacent to land, hence their name. Examples include the North Sea, the Bering Sea, the Gulf of Saint Lawrence, the Irish Sea, the Gulf of California, the Sea of Japan, and the East China Sea. The so-called semienclosed seas are in fact almost entirely enclosed by landmasses, leaving only a narrow connection with the oceans.
The European Mediterranean, the American Mediterranean Sea, the Baltic Sea, Hudson Bay, the Red Sea, and the Persian Gulf are all semienclosed seas. The Arctic Ocean is an adjacent sea of the Atlantic Ocean. The ocean surrounding the continent Antarctica is called the Southern Ocean, or the Antarctic Ocean. From the Antarctic, it expands to 55° south latitude.
BASICS
SHELF SEAS The continents are sur- rounded by a zone of shallow waters These vast areas rarely reach a depth greater than 656 feet (200 m) and are known as shelf seas. The name refers to the continental shelves, which are those parts of the continental plates covered by ocean water.
Continental shelves vary in size from a few miles to more than 620 miles (1,000 km)—for example, in the Bering Sea.