Which one of the following is known as a zone of sharp salinity change in the vertical section of ocean?

In the vertical section of the ocean, the halocline is defined as a distinct zone where salinity changes sharply with depth [2]. While salinity generally increases with depth, this variation is subject to latitudinal differences; however, the halocline remains the specific layer of rapid salinity gradient [3]. This stratification occurs because higher salinity water is typically denser and sinks below lower salinity water [3]. In contrast, the thermocline represents a zone of rapid temperature change, and the pycnocline represents a zone of rapid density change [1]. The pycnocline often encompasses both the halocline and thermocline because density is primarily a function of temperature and salinity [1]. The photic zone refers to the upper layer of the ocean that receives sufficient sunlight for photosynthesis and is not defined by salinity gradients [5].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 33: Ocean temperature and salinity > Pycnocline > p. 514
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 33: Ocean temperature and salinity > Vertical Distribution of Salinity > p. 520
3. [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 12: Water (Oceans) > Vertical Distribution of Salinity > p. 106
4. [5] https://www.sciencedirect.com/topics/engineering/halocline