what is the term for the colder denser water below the thermocline in a fresh water lake
hypolimnion
title: Thermocline text: Thermocline A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more rapidly with depth than it does in the layers above or below. In the ocean, the thermocline divides the upper mixed layer from the calm deep water below. Depending largely on season, latitude, and turbulent mixing by wind, thermoclines may be a semi-permanent feature of the body of water in which they occur, or they may title: Thermocline text: colder upwelling water runs into a surface layer of warmer water. It gives the water an appearance of wrinkled glass that is often used to obscure bathroom windows and is caused by the altered refractive index of the cold or warm water column. These same schlieren can be observed when hot air rises off the tarmac at airports or desert roads and is the cause of mirages. Thermoclines can also be observed in lakes. In colder climates, this leads to a phenomenon called stratification. During the summer, warm water, which is less dense, will sit on top of colder, denser, title: Thermocline text: of phytoplankton, making these areas productive. As the temperature continues to drop, the water on the surface may get cold enough to freeze and the lake/ocean begins to ice over. A new thermocline develops where the densest water (4 °C) sinks to the bottom, and the less dense water (water that is approaching the freezing point) rises to the top. Once this new stratification establishes itself, it lasts until the water warms enough for the 'spring turnover,' which occurs after the ice melts and the surface water temperature rises to 4 °C. During this transition, a thermal bar may develop. title: Thermocline text: layer. The warmer, less dense air then rises, destroying the stability that characterizes the nightly inversion. This phenomenon was first applied to the field of noise pollution study in the 1960s, contributing to the design of urban highways and noise barriers. Thermocline A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more rapidly with depth than it does in the layers above or below. In the ocean, title: Thermocline text: the upper 100 m (300 ft), depending on wave strength and the existence of surface turbulence caused by currents. Below this mixed layer, the temperature remains relatively stable over day/night cycles. The temperature of the deep ocean drops gradually with depth. As saline water does not freeze until it reaches −2.3 °C (colder as depth and pressure increase) the temperature well below the surface is usually not far from zero degrees. The thermocline varies in depth. It is semi-permanent in the tropics, variable in temperate regions (often deepest during the summer) and shallow to nonexistent in the polar regions, where