While viral videos have claimed to show boundaries where oceans do not mix, Earth's oceans do mix, though differences in salinity, temperature, and density can cause this process to occur very slowly.

How salt, sunlight, and wind drive ocean currents

The Atlantic Meridional Overturning Circulation plays a critical role in regulating earth's climate, but is threatened by climate change. Explore the effects of temperature, density, and salinity on ocean currents in this 13-minute PBS video.

Just as interconnected landmasses have been divided into distinct nations that have changed throughout history, the world ocean has been divided into multiple oceans for various geographical, practical, and scientific reasons.

Watch a visualization of global ocean currents from NASA's Estimating the Circulation and Climate of the Ocean project, which incorporates hundreds of millions of data points from satellites and floating sensors.

Surface ocean currents are primarily driven by wind, tides, and Earth's rotation, while deep-ocean currents are driven by differences in temperature and salt concentration that create vertical circulation.

Although an estimated 99.999% of the deep ocean has not been explored, techniques such as sonar have been used to identify the deepest known point in each of Earth's five oceans.

The top several meters of the world's oceans can hold as much thermal energy as the entire atmosphere, and their average surface temperature has increased by 0.9 degrees Celsius (1.62 degrees Fahrenheit) since the pre-industrial era.

Visualizing changes in ocean temperatures between 2016 and 2020

How much does the temperature of the sea change in a given year? This visualization helps illustrate the changes by showing sea surface temperature data from January 2016 through March 2020. Sea surface temperature, which refers to water temperature at the sea's surface, plays a significant role in climate and weather.

Ocean salinity comes primarily from eroded rocks, whose salts and minerals are carried into the sea by runoff, and from seawater dissolving salts and minerals from magma at seafloor openings.

When oceanic plates sink beneath tectonic ones, they can generate magma

At converging oceanic-continental plate boundaries, the subduction of the oceanic plate introduces seawater that reduces the melting temperature of the overlying mantle. This causes it to melt into less dense magma, which can rise to fuel more volcanic activity.

The world's oceans, which have an average depth of 3.7 kilometers (2.3 miles), are often vertically divided into five zones based on depth or three zones based on the abundance of light.

A simple pictorial explanation of ocean geography

Visualizing ocean geographical features, such as a coastal zone, continental shelf and abyssal plain. This article from the US Geological Survey also provides several links to diverse ocean facts.

Scientists determined that tectonic plates moved the ocean floor by observing symmetric patterns of magnetic stripes on opposite sides of underwater volcano systems, which could only result from seafloor spreading.

Why the ratios of helium isotopes are analyzed to investigate ocean circulation

Volcanic activity on the seafloor produces high ratios of helium-3 to helium-4, which can be tracked in ocean samples more easily than other elements because helium is nonreactive. Water from deep ocean currents can also be distinguished from air-exposed surface water sources by comparing these ratios, since atmospheric helium ratios are much lower.

Explore the deepest parts of the ocean

The deeps of the Earth's oceans are some of the most extreme environments on the planet. Take a trip 36,000 feet to the deepest parts of the sea in this informative, 10-minute animated video.

As of 2026, the Great Atlantic Sargassum Belt is the world's largest macroalgal bloom, with seaweed stretching from the Caribbean to West Africa.

Records of Earth's magnetic field on the seafloor validated plate tectonics

Matching glacial, fossil, and rock records, mountain ranges, and continental shapes across oceans was insufficient evidence for continental drift. Precise measurements of magnetic minerals on the ocean floor revealed seafloor spreading, which could only be explained by moving landmasses.

Extending from Antarctica to 60 degrees south latitude, the Southern Ocean features the Antarctic Circumpolar Current—the largest ocean current on Earth—which encircles Antarctica and creates a unique biogeographical zone.

How the ocean is the new frontier of innovation

Space has been called the final frontier of innovation and investment for decades. Many innovators say the ocean is the new space, the vast majority of whose hidden depths remain obscure. In this podcast episode, business-minded experts discuss the opportunities founders see in the ocean, including seagrass restoration, underwater cable networks, and more.

Deep-sea trenches form when one tectonic plate subducts another underwater

Oceanic plates sink when colliding with less dense continental plates, bending the seafloor into steep depressions that can be almost 11 kilometers deep. Many of Earth’s strongest earthquakes occur at these plate boundaries, often featuring volcanic activity.

Mapping the route options between the Pacific and Atlantic

This map shows some of the alternative trade route options that are available to shipping companies, from overland routes that rely on railways to transport goods coast-to-coast, to Arctic Ocean passages.

While major oil spills result from accidental pipeline ruptures or damage to transportation vessels or rigs, as much as half the oil that reaches coastlines has naturally leaked from the seafloor.

Most volcanic activity occurs in submarine volcanoes on the seafloor

At divergent plate boundaries in mid-ocean ridges, volcanic activity produces new ocean crust as the seafloor spreads. These areas are home to underwater mountains with extensive biodiversity due to redirecting ocean currents and concentrating food for marine life.

Just as squeezing a grape makes it bulge, the moon's gravity exerts an overall pressure that displaces the oceans toward the opposite sides of Earth's equator, producing tides.

The ocean's ability to store carbon long-term is being hindered by marine heatwaves

More than 4,000 robotic floats with biogeochemical data sensors, including oxygen, pH, nitrate, suspended particles, chlorophyll, temperature, and conductivity, have been deployed as part of the Global Ocean Biogeochemical Array. They have identified changes to ecosystem structure affecting the ocean's ability to transport carbon from surface waters into the deep.

Earth's first oceans may have been as much as 230 degrees Celsius (446 degrees Fahrenheit), with the planet's thick atmosphere exerting sufficient pressure to prevent water from boiling.

Learn about various ocean-atmosphere cycles impacting global weather patterns

Although the El Niño-Southern Oscillation is among the most impactful, the North Atlantic Oscillation strongly influences weather patterns in the Northeast US by periodically changing atmospheric pressure over the Atlantic. The North Pacific Oscillation fluctuates atmospheric pressure and sea-surface temperatures that affect winter temperatures over much of the US.

An interactive of the deep sea

The warmest waters in the ocean are found at hydrothermal vents—hot springs on the seafloor that discharge plumes of mineral-rich water heated by magma to temperatures over 370 degrees Celsius (700 degrees Fahrenheit).

Research suggests that the Antarctic Circumpolar Current—Earth's most powerful ocean current, which carries over 100 times the combined water of all of Earth's rivers—formed about 34 million years ago.

Europa's deep ocean may hold the conditions needed to support alien life

Beneath its frozen crust, Europa hides a salty ocean heated by tidal forces from Jupiter. This environment may resemble Earth's deep-sea hydrothermal vents and have allowed for the development of life over billions of years.