hypolimnion is the term for the colder denser water below the thermocline in a fresh water lake.
hypolimnion is the term for the colder denser water below the thermocline in a fresh water lake.
what is the term for the colder denser water below the thermocline in a fresh water lake?
hypolimnion
temperature regimes are very different in large lakes (fig. 2). in temperate regions, for example, as air temperatures increase, the icy layer formed on the surface of the lake breaks up, leaving the water at approximately 4 °c. this is the temperature at which water has the highest density. as the season progresses, the warmer air temperatures heat the surface waters, making them less dense. the deeper waters remain cool and dense due to reduced light penetration. as the summer begins, two distinct layers become established, with such a large temperature difference between them that they remain stratified. the lowest zone in the lake is the coldest and is called the hypolimnion. the upper warm zone is called the epilimnion. between these zones is a band of rapid temperature change called the thermocline. during the colder fall season, heat is lost at the surface and the epilimnion cools. when the temperatures of the two zones are close enough, the waters begin to mix again to create a uniform temperature, an event termed lake turnover. in the winter, inverse stratification occurs as water near the surface cools freezes, while warmer, but denser water remains near the bottom. a thermocline is established, and the cycle repeats.
lake ecosystem
for the western pacific, the mechanism for barrier layer formation is different. along the equator, the eastern edge of the warm pool (typically 28c isotherm - see sst plot in the western pacific) is a demarcation region between warm fresh water to the west and cold, salty, upwelled water in the central pacific. a barrier layer is formed in the isothermal layer when salty water is subducted (i.e. a denser water mass moves below another) from the east into the warm pool due to local convergence or warm fresh water overrides denser water to the east. here, weak winds, heavy precipitation, eastward advection of low salinity water, westward subduction of salty water and downwelling equatorial kelvin or rossby waves are factors that contribute to deep blt formation.
mixed layer