Oceans

More than a habitat — an interconnected living system spanning the planet.

The largest connected habitat on Earth, from sunlit surface waters to the dark deep sea.

Overview

The ocean is one continuous body of water divided into basins, currents and depth zones. Sunlight only reaches the upper layer, where microscopic algae produce food and much of the oxygen we breathe. Below it, life adapts to cold, darkness and enormous pressure. Currents connect the whole system, carrying heat, nutrients and migrating animals between the poles and the tropics.

Climate

Water temperature ranges from below freezing in polar seas to warm tropical surface waters, and the ocean buffers the planet’s climate by storing and moving heat.

Where it is found

Global — every ocean basin, from the Arctic to the Southern Ocean.

Vegetation

Most production comes from phytoplankton. Near the coast, kelp forests and seagrass meadows form underwater “forests”.

Living conditions

Light: Sunlight fades quickly with depth; below roughly 200 m there is too little light for photosynthesis.
Pressure: Pressure increases with every metre of depth, so deep-sea life has special adaptations.
Currents: Surface and deep currents move heat, nutrients and larvae around the globe.

Key facts

Area: ≈ 71% of Earth’s surface (NOAA)
Average depth: ≈ 3,700 m (NOAA)
Deepest point: ≈ 11,000 m (Challenger Deep, Mariana Trench)
Salinity: ≈ 35 g of salt per kg of water (Average seawater)
Temperature: About −2 °C to 30 °C+ (Polar seas to tropical surface water)

How the ecosystem works

Primary producers: Phytoplankton form the base of almost every marine food web.
Migration: Whales, turtles and fish travel thousands of kilometres between feeding and breeding areas.
Nutrient cycling: Large animals help move nutrients up and down the water column.

Food web

Producers: Phytoplankton, Kelp & seagrass
Grazers: Zooplankton, Krill, Green sea turtle
Predators: Blue whale, Orca
Decomposers: Marine bacteria, Deep-sea scavengers

Biodiversity

Marine life ranges from microscopic plankton to the largest animal that has ever lived. Much of the deep ocean is still unexplored, so new species are described every year.

Threats

Ocean warming — Warmer water holds less oxygen and pushes species toward the poles.
Acidification — Absorbed carbon dioxide makes seawater more acidic, which harms shell-building animals.
Overfishing — Removing too many fish disrupts food webs and the animals that depend on them.
Pollution — Plastics, chemicals and noise reach even remote parts of the ocean.

Conservation

A healthy ocean regulates climate, produces oxygen and feeds billions of people. Protecting it means protecting the systems every coast depends on.

Marine protected areas give populations room to recover.
Sustainable fishing keeps food webs intact.
Cutting pollution at its source protects remote waters too.