World Climate and Climate Change | Class 11 Geography Notes

Salinity of Ocean Waters

Salinity refers to the total concentration of dissolved mineral salts in seawater, usually expressed in parts per thousand (‰ or ppt). It is calculated as the grams of salt dissolved in 1,000 grams of seawater. Salinity varies horizontally and vertically in oceans due to factors such as evaporation, precipitation, river inflow, freezing and thawing of ice, wind, and ocean currents. High evaporation increases salinity, while freshwater inflow from rivers or melting ice decreases it. Surface salinity ranges typically between 33‰ and 37‰ in open oceans but can be as high as 41‰ in landlocked seas like the Red Sea or as low as near zero in estuaries and polar regions. Vertically, salinity generally increases with depth, with a distinct halocline zone where salinity rises sharply. Salinity influences seawater density, which affects ocean circulation and stratification. Some of the highest salinity water bodies include Lake Van (330‰), the Dead Sea (238‰), and the Great Salt Lake (220‰).

📊 Diagram: Figure 12.5: Surface salinity of the World's Oceans

🧪 Activity: Analyze salinity data from different ocean regions and relate to climatic and geographic factors.

🔗 Connection: The chapter concludes with exercises and project work to reinforce understanding of oceanic features and processes.