What is a halocline?

A halocline refers to a specific layer in a body of water where there is a significant and abrupt change in salinity with increasing depth. This phenomenon occurs because salinity can vary greatly in different layers of water, often influenced by factors such as freshwater input from rivers, evaporation, and water mixing.

In the context of marine environments, a halocline is crucial for understanding the distribution of marine organisms, ocean circulation, and the overall chemistry of the water column. The sharp separation created by the halocline can impact nutrient availability, light penetration, and even the behavior of organisms, as they may prefer certain salinity levels for optimal living conditions.

Other options highlight different characteristics of marine layers but do not accurately define a halocline. For example, a gradual change in temperature with depth refers to a thermocline, while a zone with constant salinity does not convey the idea of abrupt change and is more related to homogeneous layers. A layer of floating organisms does not pertain to salinity changes at all but rather to biological layers in the water column.