Haloklinen

Haloklinen, commonly referred to as a halocline, is a distinct vertical zone in a body of water where salinity changes abruptly with depth. It represents a relatively sharp boundary between layers of different salinity and often coincides with a density gradient that reduces vertical mixing.

Haloklines form when bodies of water of different salinities interact but do not mix thoroughly. This occurs in estuaries where freshwater from rivers overlays seawater, in coastal and fjord environments with restricted exchange, and in brackish lakes or seas influenced by evaporation or ice melt. The depth and strength of a haloklinen vary seasonally and geographically, depending on freshwater input, mixing processes, and water exchange with adjacent regions.

The presence of a haloklinen can influence physical and ecological conditions. By limiting vertical mixing, it affects the distribution of oxygen, nutrients, and heat, thereby shaping microbial communities, phytoplankton productivity, and habitats for aquatic organisms. It can also alter chemical processes and the transport of substances between surface and deeper waters.

Measurement and study typically rely on profiles of salinity obtained with CTD instruments (conductivity, temperature, depth) or water sampling across depth. In many systems, haloklines coexist with or lie above thermoclines and pycnoclines, and they may be temporary or persistent depending on hydrological factors.

Related terms include halocline, pycnocline, and chemocline. Haloklinen is the plural form or regional variant used in some languages to describe these salinity transition zones.