The connected bodies of saline water covering most of Earth's surface. Physical oceanography studies their circulation, stratification, waves and heat transport.
The elevation of the ocean surface relative to a specified reference. Global mean, local relative and instantaneous levels answer different questions. Changes of basin capacity, water amount and surface topography can alter flooded continental shelf area and the distribution of marine environments.
The depth and shape of an underwater surface. Its variation affects seismic travel times and the water-column contribution to a marine gravity anomaly.
A tsunami is a train of long surface gravity waves generated by a rapid displacement of water, for example by seabed motion during an earthquake or by a landslide. Its wavelength can be much greater than the ocean depth, so the shallow-water approximation can apply even in a deep ocean.
In that limit the wave speed is . The long wave can cross an ocean while its surface height remains small offshore. Entering shallower water lowers its speed and shortens its wavelength; coastal geometry, focusing and nonlinear flow then control amplification and inundation. Source displacement and bathymetry are therefore needed alongside an earthquake magnitude to predict local effects.[ref]
Tsunami Propagation by National Oceanic and Atmospheric Administration. Propagation description: depth-dependent speed, long wavelength and coastal shoaling
Seawater is water containing dissolved salts and other constituents. Its salinity changes mass density, freezing behaviour and other material properties, so specifying temperature alone does not fix its buoyancy. At a given temperature and pressure, a change in composition can alter whether a parcel rises or sinks relative to neighbouring fluid.
This makes seawater central to ocean circulation and open-ocean convection. Freezing sea ice rejects much of the salt into the surrounding liquid through brine rejection, while melting supplies relatively fresh water. Measuring temperature, salinity and pressure together therefore supplies information that a surface-temperature map alone cannot recover.
Ocean acidification is a sustained decrease in seawater pH, commonly caused by absorption of atmospheric carbon dioxide. Dissolved carbon dioxide shifts chemical equilibrium toward bicarbonate and hydrogen ions. Reactions involving carbonate buffer part of the perturbation while reducing carbonate availability.
The change can affect the conditions for forming or dissolving calcium carbonate, even while the water remains alkaline with a pH above seven. Characterizing the carbonate system requires measurements such as pH, dissolved inorganic carbon, carbon-dioxide partial pressure or alkalinity, together with temperature and salinity. Two suitable independent carbonate-system measurements constrain the others through an equilibrium model.[ref]
What is Ocean Acidification by NOAA Ocean Acidification Program. Seawater chemistry, buffering and monitoring the four carbonate-system parameters
Ocean anoxia is a condition in which dissolved oxygen is absent or nearly exhausted in part of the ocean. Oxygen is supplied by exchange with the atmosphere, biological production and transport of ventilated water. Respiration and oxidation consume it, so weak renewal combined with a large organic-matter supply can deplete a water body.
Density stratification can restrict exchange between oxygenated surface water and deeper water. Measurements of dissolved oxygen and circulation therefore help distinguish low supply from high consumption. Euxinia additionally requires dissolved sulfide; anoxia alone does not specify which reduced chemical species are present.
Anoxic, sulfide-bearing conditions in a water body. Euxinia combines oxygen absence with dissolved sulfide, potentially adding toxicity to the habitat loss caused by ocean anoxia. It is a chemical state rather than a synonym for every low-oxygen environment.
Shallow submerged continental margin extending seaward toward the shelf break.
The temperature of a specified near-surface ocean layer. Skin and bulk measurements refer to different sampling depths. Coupled variations in sea surface temperature, winds and thermocline depth are central to El Niño–Southern Oscillation.
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The term "ocean" typically refers to the vast bodies of saltwater that cover significant portions of the Earth's surface. There are five primary oceans: the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern (or Antarctic) Ocean, and Arctic Ocean. Oceans play a crucial role in regulating the Earth's climate, supporting diverse ecosystems, and facilitating global trade and transportation. Oceans are home to a wide range of marine life, from tiny plankton to massive whales.