Stratification (water)
Encyclopedia
Water stratification occurs when water masses with different properties - salinity
(halocline
), oxygenation
(chemocline
), density
(pycnocline
), temperature
(thermocline
) - form layers that act as barriers to water mixing . These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers.
Water stratification also creates barriers to nutrient mixing between layers. This can affect the primary production
in an area by limiting photosynthetic processes. When nutrients from the benthos cannot travel up into the photic zone
, phytoplankton
may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters .
s of water. Forms of turbulence may include wind-sea surface friction, upwelling
and downwelling
.
Marshall et Al. (2002) suggest that baroclinic eddies (baroclinity
) may be an important factor in maintaining stratification.
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
(halocline
Halocline
In oceanography, a halocline is a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity affects the density of seawater, it can play a role in its vertical stratification...
), oxygenation
Oxygenation (environmental)
Environmental oxygenation can be important to the sustainability of a particular ecosystem. Insufficient oxygen may occur in bodies of water such as ponds and rivers, tending to suppress the presence of aerobic organisms such as fish...
(chemocline
Chemocline
A chemocline is a cline caused by a strong, vertical chemistry gradient within a body of water. A chemocline is analogous to a thermocline, the border at which warmer and cooler waters meet in an ocean, sea, lake, or other body of water...
), density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
(pycnocline
Pycnocline
A pycnocline is the cline or layer where the density gradient is greatest within a body of water. An ocean current is generated by the forces such as breaking waves, terms of temperature and salinity differences, wind, Coriolis effect, and tides caused by the gravitational pull of the Moon and the...
), temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
(thermocline
Thermocline
A thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
) - form layers that act as barriers to water mixing . These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers.
Water stratification also creates barriers to nutrient mixing between layers. This can affect the primary production
Primary production
400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
in an area by limiting photosynthetic processes. When nutrients from the benthos cannot travel up into the photic zone
Photic zone
The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...
, phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters .
Complicating Factors
Stratification may be upset by turbulence. This creates mixed layerMixed layer
The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, cooling, or processes such as evaporation or sea ice formation which result in an increase in salinity...
s of water. Forms of turbulence may include wind-sea surface friction, upwelling
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
and downwelling
Downwelling
Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the sinking limb of a convection cell. Upwelling is the opposite process and together...
.
Marshall et Al. (2002) suggest that baroclinic eddies (baroclinity
Baroclinity
In fluid dynamics, the baroclinity of a stratified fluid is a measure of how misaligned the gradient of pressure is from the gradient of density in a fluid...
) may be an important factor in maintaining stratification.