oceanographic Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...

water mass is an identifiable

body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such a ...

with a common formation history which has physical properties distinct from surrounding water. Properties include

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...

- isotopic ratios, and other physical quantities which are conservative

flow tracer A flow tracer is any fluid property used to track flow, magnitude, direction, and circulation patterns. Tracers can be chemical properties, such as radioactive material, or chemical compounds, physical properties, such as density, temperature, ...

s. Water mass is also identified by its non-conservative flow tracers such as silicate, nitrate, oxygen, and phosphate. Water masses are generally distinguished not only by their respective tracers but also by their location in the Worlds' oceans. Water masses are also distinguished by their vertical position so that there are surface water masses, intermediate water masses and deep water masses.

Global water masses

Common water masses in the world ocean are: * Antarctic Bottom Water (AABW): Antarctic Bottom Water is a very important water mass. Antarctic Bottom Water is the left over part when sea ice is being made. It is very cold but, not quite freezing so the water moves down and along the ocean floor. *

North Atlantic Deep Water North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the ...

(NADW) * Circumpolar Deep Water (CDW) *

Antarctic Intermediate Water Antarctic Intermediate Water (AAIW) is a cold, relatively low salinity water mass found mostly at intermediate depths in the Southern Ocean. The AAIW is formed at the ocean surface in the Antarctic Convergence zone or more commonly called the Ant ...

(AAIW) *

Subantarctic Mode Water Sub-Antarctic Mode Water (SAMW) is an important water mass in Earth's oceans. It is formed near the Sub-Antarctic Front on the northern flank of the Antarctic Circumpolar Current. The surface density of Sub-Antarctic Mode Water ranges between abo ...

(SAMW) *

Arctic Intermediate Water The Arctic Intermediate Water (AIW) is a water mass found between the top cold, relatively fresh polar water and the bottom deep water in the Arctic domain (bounded by the polar and arctic fronts).Swift, J. H . and Aagaard, K. (1981) Seasonal transi ...

(AIW) *

North Pacific Intermediate Water North Pacific Intermediate Water (NPIW) is cold, moderately low salinity water mass that originates in the mixed water region (MWR) between the Kuroshio and Oyashio waters just east of Japan. Examination of NPIW at stations just east of the MWR i ...

(NPIW) * The central waters of various

oceanic basin In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, ocean basins are large  geologic basins that are below sea level. Most commonly the ocean is divided into basins fol ...

s * Various ocean surface waters.

Characteristics of water masses

Although there are many types of water masses, they all share characteristics. Water Masses are formed from regions of water having different temperatures. When ice is being formed in a cold climate like Antarctica, the cold temperatures separate the molecular bonds of the water causing it to become less dense. However, because water increases its volume by about 9% when frozen, this makes the ice less dense than the water which is why glaciers float. This also in turn causes the salinity of the water to decrease. The salinity of the water makes water freeze at lower temperatures than freshwater. Freshwater freezes at the standard 0°C (32°F), while saltwater freezes at an average of -2°C (28.4°F).

Water mass classification

Temperature and salinity diagram

The best method of classifying a water mass is through using a T-S diagram. In the diagram pictured at the top, it categorises a water mass by the temperature and salinity of the water and is represented by a single point. However, water masses are not constant. Throughout time climates can change, seasons can drag out, or there could be less rainfall meaning that the water masses might change in temperature or salinity. To have a complete water mass classification, it requires the water type of the source and the standard deviations of the temperature and salinity. It can take many years to establish the standard deviations of the water mass and requires constant surveillance. Once all of the necessary measures are completed, the data will now determine what the current density of the water is and help further classify the water mass.

References

* * * Bhutia, T. K. ''Water mass''. https://www.britannica.com/science/water-mass. *Toste Tanhua, Mian Liu. “Characteristics of Water Masses in the Atlantic Ocean Based on GLODAPv2 Data .” ''Characteristics of Water Masses in the Atlantic Ocean Based on GLODAPv2 Data'', 2019, os.copernicus.org/preprints/os-2018-139/os-2018-139.pdf.

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