Fraction of world ocean: 20%

 

The Arctic Ocean                                                   

To some people, the waters around the North Pole are a part of the Atlantic, mainly because they are joined to the Atlantic Ocean by a broad stretch of sea between Scandinavia and Greenland. However, most oceanographers call these waters the Arctic Ocean. This is the smallest and shallowest of the four oceans. More than thirteen oceans of its size would fit into the Pacific basin and the Arctic Ocean's average depth is only one quarter that of the Pacific.

Ocean Facts

Fraction of world ocean: 4%

Average depth: 3,407 feet (1,038 m)

The Earth is surrounded by two great oceans: an ocean of air and an ocean of water. Both are in constant motion, driven by the energy of the sun and the gravity of the Earth. Their motions are linked; the winds give energy to the sea surface and ocean currents are the result. The currents carry heat from one location to another, altering the Earth's surface temperature patterns and modifying the air above. Out in the open sea, ocean waters are driven by two great wind systems. Close to the equator the Trade Winds blow the surface waters westward. In the temperate zone, the Westerlies blow the surface waters back toward the east. The result is that in each great ocean basin there is roughly circular movement of the surface waters. In the northern hemisphere these wind driven currents move clockwise and in the southern hemisphere they move counter clockwise. Both surface and deep-water currents affect the world's climate by moving cold water from the poles toward the tropics and vice versa. Ocean waters are always in motion. Currents flow like rivers, waves crash against seashores and tides rise and fall.

 

	From the seashore to the deepest depths, oceans are home to some of the most diverse life on Earth. There are big animals and little ones; long and short ones, multicolored and drab ones, and those that just sit while others that never stop swimming. There are even some organisms that light up. Oceanographers divide the ocean into five broad zones according to how far down sunlight penetrates: the epipelagic, or sunlit, zone: the top layer of the ocean where enough sunlight penetrates for plants to carry on photosynthesis. the mesopelagic, or twilight, zone: a dim zone where some light penetrates, but not enough for plants to grow. the bathypelagic, or midnight, zone: the deep ocean layer where no light penetrates. the abyssal zone: the pitch-black bottom layer of the ocean; the water here is almost freezing and its pressure is immense. the hadal zone: the waters found in the ocean's deepest trenches. Plants are found only in the sunlit zone where there is enough light for photosynthesis, however, animals are found at all depths of the oceans though their numbers are greater near the surface where food is plentiful. Still, over 90 percent of all species dwell on the ocean bottom where a single rock can be home to over ten major groups such as corals, mollusks To the left is a scale model of the ocean zones, from the warm sunlit waters of the surface to the cold dark depths of the Mariana Trench, the deepest point in the oceans at 36,200 feet (11,033 m). Notice how shallow the sunlit zone is compared to the midnight or abyssal zones. Dive deeper into the living sea by continuing your explorations below.
	Life Near the Surface Most of the living things in the ocean are in a very small portion near the surface. Nearly all marine life depends directly or indirectly on microscopic algae found only at the ocean surface. Therefore, most of the animals in the ocean live in the sunlit zone or migrate to it in search of food.	Predators and Prey Some animals eat only plants; they are called herbivores. Animals that eat meat are called carnivores. Omnivores are animals that eat both plants and animals. No matter what animals eat, all their food can be traced back to the ability of plants to produce organic material from the energy of the sun.