Photograph by Paul Chesley
Why the Ocean Matters
The ocean makes our planet a wonderful place to live. It gives us more than half of the oxygen we breathe. It regulates the climate, absorbs a quarter of the carbon that we put into the atmosphere every year, provides livelihoods for hundreds of millions of people, and contributes hundreds of billions of dollars to the global economy.—Marine ecologist Enric Sala
These vast bodies of water surrounding the continents are critical to humankind. But overfishing and global warming threaten to leave this vital habitat barren.
The ocean is a continuous body of saltwater that covers more than 70 percent of the Earth's surface. Ocean currents govern the world's weather and churn a kaleidoscope of life. Humans depend on these teeming waters for comfort and survival, but global warming and overfishing threaten to leave the ocean agitated and empty.
Geographers divide the ocean into four major sections: the Pacific, Atlantic, Indian, and Arctic. Smaller ocean regions are called seas, gulfs, and bays, such as the Mediterranean Sea, Gulf of Mexico, and the Bay of Bengal. Stand-alone bodies of saltwater like the Caspian Sea and the Great Salt Lake are distinct from the world's oceans.
The oceans hold about 320 million cubic miles (1.35 billion cubic kilometers) of water, which is roughly 97 percent of Earth's water supply. The water is about 3.5 percent salt and contains traces of all chemical elements found on Earth. The oceans absorb the sun's heat, transferring it to the atmosphere and distributing it around the world via the ever-moving ocean currents. This drives global weather patterns and acts as a heater in the winter and an air conditioner in the summer.
Life began in the ocean, and the ocean remains home to the majority of Earth's plants and animals—from tiny single-celled organisms to the blue whale, the planet's largest living animal.
Most of the ocean's plant life consists of microscopic algae called phytoplankton that float at the surface and through photosynthesis produce about half of the oxygen that humans and all other terrestrial creatures breathe. Seaweed and kelp are big algae easily visible to the naked eye. Marine plants with roots, like seagrasses, can only survive as deep as the sun’s rays can support photosynthesis—about 650 feet (200 meters). Nearly half of the ocean is more than 9,800 feet (3,000 meters) deep.
The deepest reaches of the ocean are largely devoid of life, but biological hotspots appear around places like hydrothermal vents. These chimney-like structures spew gases and mineral-rich water from beneath the Earth's crust. Tube worms, clams, and mussels gather around the vents to feed on heat-loving bacteria. Bizarre fish with sensitive eyes, translucent fangs, and bioluminescent lures lurk about in nearby waters.
Other fish, octopuses, squid, eels, dolphins, and whales ply the open waters while crabs, lobsters, starfish, oysters, and snails crawl and scoot along the ocean bottom. Creatures like jellyfish lack their own way to get around and are mostly left to the whim of the wind and currents. Mammals like otters, walruses, and even polar bears also depend on the ocean for their survival and dip in and out as their biology requires.
Colonies of polyps form coral reefs as they die. The reefs are mostly found in shallow tropical waters and are home to a brilliant mosaic of polyps, plants, and fish. Coral reefs are also visible victims of human activity. Global warming, siltation, pollution, and other phenomena are stressing the corals to death, and overzealous fishers net more food than the reefs can restore.
Human activities impact nearly all parts of the ocean. Lost and discarded nets continue to lethally snare fish, seabirds, and marine mammals as they drift. Ships spill oil and garbage and transport critters to alien habitats unprepared for their arrival. Mangrove forests are cleared for homes and industry. More than half of the U.S. population lives in coastal areas, spilling garbage and sewage into the ocean. Fertilizer runoff from farms turns vast swaths of the ocean into dead zones, including a New Jersey-size area in the Gulf of Mexico. The greenhouse gas carbon dioxide is turning ocean waters acidic, and an influx of freshwater from melting glaciers threatens to alter the weather-driving currents.
Conservationists urge international protections to protect and replenish dwindling ocean fish stocks and reductions in greenhouse gases to curb global warming.
More About Oceans
The oceans are facing threats from many sides. Learn about the issues—pollution, overfishing, and global warming chief among them—and the possible solutions.
Biggest, deepest, smallest, saltiest—do you know these marine standouts? Put your sea smarts to the test.
Learn about current and upcoming projects led by National Geographic explorers and grantees who are using cutting-edge technology to explore the oceans.
Pristine Seas is an exploration, research, and conservation project that aims to find, survey, and help protect the last healthy, undisturbed places in the ocean.
The sea is so vast that a million or more as yet unknown species may live in its waters, and most of these aquatic species are tied together through the food web.
Find out how we can balance our tastes with what's right for the oceans.
Are you concerned about the health of our ocean? Learn ten things you can do to help save it.
- Ballard, Robert
- Bowermaster, Jon
- De Rothschild, David
- Doubilet, David
- Earle, Sylvia
- Frozen Seafood Benefits
- Goodman, Beverly
- Habitat Destruction
- Invasive Species
- Kristof, Emory
- Marine Food Chain
- Marine Pollution
- Nicklen, Paul
- Norman, Brad
- Ocean Overview
- Pristine Seas Expeditions
- Sala, Enric
- Seafood Decision Guide
- Seafood Substitutions
- Sea Level Rise
- Sea Temperature Rise
- Seaver, Barton
- Sustainable Seafood
- Thys, Tierney
- Tips to Save the Ocean
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Support the Ocean
Help protect the last healthy, undisturbed places in the ocean so we can learn how to help healthy reefs thrive, help unhealthy reefs recover, and better preserve the ocean.
Explore the Ocean
Order ocean books, DVDs, maps, and more from the National Geographic online store.
Explore the world's oceans, from their prehistoric beginnings to modern-day efforts to preserve their natural wonder.
Immerse yourself in the wonders of the deep through colorful maps, photos, and satellite images.
Engage, Conserve, Restore
The National Geographic Society’s freshwater initiative is a multi-year global effort to inspire and empower individuals and communities to conserve freshwater and preserve the extraordinary diversity of life that rivers, lakes, and wetlands sustain.