Oceans

The oceans cover more than 360 million square kilometres (139 million square miles) of the Earth’s surface, approximately 71% of its total area. More than 1350 million cubic...

Ocean floor

Much of the ocean seems completely empty: a great expanse of featureless water, dotted with the occasional island. But beneath the waves it is a different picture. Between 4000 and...

Ocean currents

The ocean waters move about the globe in great “rivers” called ocean currents. Surface currents have a big effect on the world’s climates. They make polar regions milder and...

Oceans A-Z

Coral atolls

Layers of lava from eruptions eventually build underwater volcanoes high enough for them to rise above sea level as islands. In tropical waters, coral reefs sometimes form in the...

Polar waters

The North Pole lies not on land but on water: the Arctic Ocean. It is permanently covered by ice, although the size of the ice cap shrinks dramatically in summer months as the ice...

Tides

Sea levels rise and fall twice a day. This pattern is known as the tides. The tidal range is the difference between high and low tide. Seas that are almost surrounded by land, such...

Waves

As wind moves across the surface of the ocean, the water turns over and over in circles, forming waves. The stronger the wind and the wider the expanse of ocean it has blown...

El Niño

El Niño is Spanish for "the child" and refers to the infant Jesus, because the occasional warming in the Pacific Ocean off South America peaks around Christmas time. Every 3-5...

Why is the sea salty?

Most of the salt in the sea comes from the land around us. Rainwater contains some dissolved carbon dioxide from the surrounding air. This makes it a weak acid. Every time it...