Oceanography

Ocean currents, waves, tides, and thermohaline circulation

What is oceanography?

Oceanography is the study of the ocean — its water, the life within it, the seafloor beneath it, and the currents and waves that move constantly across its surface and depths. Oceans cover more than two-thirds of Earth's surface, making this an enormous field.

Why the ocean is salty

Ocean water contains dissolved salts, mostly sodium chloride, delivered over immense spans of time by rivers carrying dissolved minerals eroded from rock on land. Since water evaporates from the ocean surface but the dissolved salt does not, salt has steadily accumulated in the ocean over hundreds of millions of years, reaching today's roughly stable concentration.

Ocean currents

Water in the ocean is in constant motion, driven by wind blowing across the surface, differences in water temperature and salt content, and the same Coriolis effect covered in the Meteorology article. These currents move enormous volumes of water around the globe, carrying heat from warmer regions toward colder ones and playing a major role in shaping regional climates — the Gulf Stream, for example, carries warm water from the tropics up along the eastern coast of North America and across to Western Europe.

Waves and tides

Ocean waves are mostly generated by wind blowing across the water's surface, transferring energy that travels outward as waves without the water itself traveling far. Tides are different: they're caused by the gravitational pull of the Moon (and, to a lesser extent, the Sun) on Earth's oceans, producing the regular rise and fall of sea level observed along coastlines roughly twice a day.

Why oceanography matters

Oceanography supports fisheries and food security, helps predict and understand hurricanes and coastal flooding, guides the study of marine ecosystems, and plays a central role in understanding Earth's climate, since the ocean stores and moves enormous amounts of heat and absorbs a large share of the carbon dioxide released into the atmosphere.