Hypolimnion
[1] The word "hypolimnion" is derived from Ancient Greek: λιμνίον, romanized: limníon, lit. 'lake'.
[1] In deep, temperate lakes, the bottom-most waters of the hypolimnion are typically close to 4 °C throughout the year.
Being at depth, it is isolated from surface wind-mixing during summer,[3] and usually receives insufficient irradiance (light) for photosynthesis to occur.
The deepest portions of the hypolimnion often have lower oxygen concentrations than the surface waters (i.e., epilimnion).
In particular, during periods of thermal stratification, gas exchange between the epilimnion and hypolimnion is limited by the density difference between these two layers.
I. The Epilimnion
II. The Metalimnion
III. The Hypolimnion
The scales are used to associate each section of the stratification to their corresponding depths and temperatures. The arrow is used to show the movement of wind over the surface of the water which initiates the turnover in the epilimnion and the hypolimnion.