Ocean water covers about 71 percent of Earth’s surface. Although maps give the oceans different names, all ocean water is connected. Scientists sometimes refer to this connected body of salt water as the world ocean.
Today, five major ocean regions are commonly recognized: the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. The boundaries between them were created to help people study, map, and describe different parts of the world ocean.
Pacific Ocean
The Pacific Ocean is the largest and deepest of the five oceans. It covers nearly one-third of Earth’s surface and contains more than half of the world ocean’s water. The Pacific lies between Asia and Australia on one side and North and South America on the other. The equator divides it into the North Pacific and South Pacific, but these are connected parts of the same ocean. The Pacific contains the Mariana Trench, the deepest known part of the ocean. It also includes thousands of islands and supports many different marine ecosystems. People throughout the Pacific have used the ocean for travel, trade, fishing, and cultural connections for thousands of years.
Atlantic Ocean
The Atlantic Ocean is the second-largest ocean. It lies between North and South America to the west and Europe and Africa to the east. The Atlantic is connected to the Arctic Ocean in the north and the Southern Ocean in the south. Its shape is sometimes described as resembling the letter S. A long underwater mountain system called the Mid-Atlantic Ridge runs through much of the ocean. New ocean crust forms along parts of this ridge as tectonic plates slowly move apart. For thousands of years, people from Africa, Europe, and the Americas have traveled and traded across parts of the Atlantic. The ocean also became a major route of European colonization and the forced transportation of millions of enslaved Africans. Today, it remains important for shipping, fishing, communication, and travel.
Indian Ocean
The Indian Ocean is the third-largest ocean. It is bordered by Africa to the west, Asia to the north, Australia to the east, and the Southern Ocean to the south. Much of the Indian Ocean lies in warm regions near the equator and the tropics. Its waters support coral reefs, fisheries, mangrove forests, and many kinds of marine life. The Indian Ocean has connected communities in Africa, the Middle East, South Asia, and Southeast Asia for thousands of years. Sailors learned to use seasonal monsoon winds to travel, trade, and exchange goods and ideas. These networks helped spread technologies, languages, foods, and religious traditions across the region. Today, the Indian Ocean remains an important route for international trade. Ships carry oil, manufactured goods, food, and other products through its waters.
Southern Ocean
The Southern Ocean surrounds Antarctica. Its commonly used northern boundary is the line of latitude at 60° south. The Southern Ocean is the fourth-largest ocean. It connects the southern parts of the Pacific, Atlantic, and Indian Oceans. A powerful current called the Antarctic Circumpolar Current flows around Antarctica and helps move water, heat, and nutrients around the planet. The Southern Ocean has extremely cold water, strong winds, and large areas of seasonal sea ice. Even in these difficult conditions, it supports penguins, seals, whales, fish, krill, and other organisms. The name and exact boundaries of the Southern Ocean have changed on maps over time. Today, it is widely recognized as one of the five major oceans.
Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the five oceans. It is located around the North Pole and is almost completely surrounded by North America, Europe, and Asia. Much of the Arctic Ocean is covered by sea ice during at least part of the year. The amount of ice changes with the seasons, but long-term warming has caused Arctic sea ice to shrink. The Arctic is home to fish, seals, whales, walruses, polar bears, seabirds, and many other organisms. Indigenous peoples have lived in Arctic regions for thousands of years and have developed deep knowledge of sea ice, animals, weather, and seasonal change. Changes in the Arctic affect more than the people and wildlife that live there. Melting land ice contributes to rising sea levels, while changes in sea ice can influence ecosystems, weather patterns, travel, and access to resources.
One Connected World Ocean
The five oceans have different names, sizes, climates, and features, but they are all connected. Water, heat, nutrients, animals, ships, and pollution can move from one ocean region to another.
Seas are smaller parts of the world ocean that are usually partly surrounded by land. The Mediterranean Sea, Caribbean Sea, and South China Sea are examples. Scientists who study the ocean are called oceanographers. They investigate ocean water, seafloors, currents, weather, climate, and marine life. Much of the deep ocean has not yet been closely observed, so scientists continue to use ships, satellites, underwater vehicles, and other tools to learn more about it.