A pycnocline is a layer in a body of water where there is a rapid change in density with depth. This phenomenon typically occurs in oceans and large lakes, where warmer, lighter water sits above colder, denser water. The pycnocline acts as a barrier, preventing mixing between these layers, which can affect marine life and nutrient distribution. The presence of a pycnocline is influenced by factors such as temperature and salinity, which are key components of the thermocline and halocline. Understanding the pycnocline is essential for studying oceanography and the behavior of aquatic ecosystems.