Task: Class Definition Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes 'pycnocline'?

A. A the concept is a layer across which there is a rapid change in water density with depth. In freshwater environments such as lakes this density change is primarily caused by water temperature, while in seawater environments such as oceans the density change may be caused by changes in water temperature and/or salinity
B. In oceanography, a the concept is a strong, vertical salinity gradient. Because salinity (in concert with temperature) affects the density of seawater, it can play a role in its vertical stratification.
C. The the concept or euphotic zone is the depth of the water whether in a lake or an ocean, that is exposed to sufficient sunlight for photosynthesis to occur. The depth of the euphotic zone can be greatly affected by seasonal turbidity.
D. The the concept is a deep zone of a body of water, such as an ocean or a lake, located below the range of effective light penetration. This is typically below the thermocline, the vertical zone in the water through which temperature drops rapidly. The lack of light in the the concept determines the type of biological community that can live in this region, which is distinctly different from the community in the overlying waters. The the concept is part of the aphotic zone.

Answer: A the concept is a layer across which there is a rapid change in water density with depth. In freshwater environments such as lakes this density change is primarily caused by water temperature, while in seawater environments such as oceans the density change may be caused by changes in water temperature and/or salinity