How does ocean salinity affect density and circulation?

• A. Higher salinity increases density and promotes sinking, driving thermohaline circulation and influencing climate and nutrient distribution
• B. Higher salinity decreases density
• C. Salinity has no effect on density
• D. Salinity only affects surface current speed

Answer: (A)

Salinity changes the density of seawater: when salinity increases, density rises because the dissolved salt adds mass without a comparable increase in volume. This makes water parcels heavier and more prone to sinking when they are also cold, which sets up vertical movement in the ocean. That sinking part of the water column drives the thermohaline circulation, the global pattern that moves water between basins, carrying heat and nutrients and thus shaping climate and ecological distribution. Surface currents are largely driven by winds, but salinity-induced density differences enable deep currents and upwelling that link different regions. So the correct idea is that higher salinity increases density and promotes sinking, fueling large-scale circulation and influencing climate and nutrient transport.