Isohalines are lines joining equal :

Isohalines are defined as lines on a map or chart that connect points of equal salinity in bodies of water, such as oceans or lakes [1]. These isolines are essential in oceanography to visualize the distribution of salt concentration, which is typically measured in parts per thousand [1]. Salinity distribution is influenced by factors such as evaporation, precipitation, and freshwater influx from rivers [3]. For comparison, other common isolines include isotherms for equal temperature, isobars for equal atmospheric pressure, and isohyets for equal rainfall. The average salinity of the global ocean is approximately 35 parts per thousand, though this varies significantly in specific regions like the Baltic Sea or Red Sea due to local environmental conditions [2]. Understanding isohalines helps scientists track water mass origins and thermohaline circulation patterns.

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 12: The Oceans > Salinity of the Ocean > p. 107
2. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 33: Ocean temperature and salinity > Vertical Distribution of Salinity > p. 520
3. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 12: Water (Oceans) > HORIZONTAL DISTRIBUTION OF SALINITY > p. 105