The Ocean

Looking at our Earth from space, it is obvious that we live on a water planet. Ocean covers over 70 percent of Earth's surface and contains about 97 percent of Earth's surface water. How much do you know about our ocean?



Most of the Earth's water is found in:

Most of Earth's water (96.5 percent) is saline, or salty, ocean seawater. Most of the fresh water is tied up in glaciers and ice sheets, which means that only a relatively small portion is available to sustain human, plant and animal life.


Which of these has a greater effect on global sea level?

Sea level rise is caused primarily by two factors related to global warming: the added water from melting land ice and the expansion of seawater as it warms. Melting sea ice does not contribute nearly as much to ocean water volume because floating ice displaces water in an amount equal to its volume. Some coastal regions and island nations have begun to experience the consequences of sea level rise. Rising seas not only affect dwellings and infrastructure, but fresh water is also affected as rising saltwater begins to contaminate it through "saltwater intrusion."


Measurements of Earth’s gravitational field permit topographic, or surface, mapping of the ocean floor.

Undersea mountain ranges like the the Mid-Atlantic Ridge, chains of islands and sea mounts like the strand from Hawai’i Island past Midway to the Aleutian Islands chain, and deep sea trenches like the Japan Trench can be identified in data collected by the GRACE (Gravity Recovery and Climate Experiment) spacecraft. The additional mass of rock that composes the undersea mountains and the lack of rock in trenches provide gravitational telltales that GRACE can detect.


What is sea surface salinity?

NASA's Aquarius satellite measures sea surface salinity from space. The concentration of salt on the ocean's surface — the part of the ocean that actively exchanges water and heat with Earth's atmosphere — is a critical driver of ocean processes and climate variability. To better understand the regional and global processes that link variations in ocean salinity to changes in the global water cycle — and how these variations influence ocean circulation and climate — NASA built and launched Aquarius, the primary instrument aboard the international Aquarius/Satélite de Aplicaciones Científicas (SAC)-D observatory.


The ocean affects the climate on our planet.

Water evaporates from the ocean, cools and turns into clouds made of water molecules or ice particles. As the atmosphere moves the water vapor around the planet, those droplets come down to Earth's surface, forming rivers, feeding lakes and streams, and so on, and then returning to the ocean. This is called the "hydrological cycle."


The only current that makes an uninterrupted circle around the entire Earth without hitting land is the:

Ocean currents are driven by ocean winds and influenced by the "Coriolis effect." Water flows along the current until it encounters land, where the Coriolis effect causes the current to rotate clockwise in the northern hemisphere and counterclockwise in the south. Most currents form "gyres," or large systems of rotating ocean currents. The gyre’s rotational patterns draw in debris from across the ocean, while wind patterns push the trash toward the center, trapping it there. In the Southern Ocean around Antarctica, there is no land, which allows the Antarctic Circumpolar Current to travel around the globe uninterrupted.


Sea level isn’t level at all. The ocean has hills and valleys similar to what we see on the land's surface. Ocean surface highs and lows are known as:

"Topography" is the shape of a surface, including its relief. Sea surface topography is influenced by both gravity and ocean circulation. Accurate gravity data are critical for determining large- and medium-scale ocean circulation patterns.


Tides are caused by:

Both the sun and the moon influence tide rise and fall, which are caused by the gravitational attraction between the ocean and the moon as well as the ocean and the sun. "Centrifugal force" — the same force that pulls you backward on the teacup ride at Disneyland – is generated from Earth’s spin and is another factor that influences Earth's tides.


NASA has been measuring sea surface height from space since 1993. Over that period, average global sea level has:

Sea level is a global climate change indicator. Through continuous long-term measurements of global sea level, scientists can see the ocean’s role in climate and the effects of a changing climate on the ocean. Since 1993, global mean sea level has risen by about 4 inches (10 centimeters).