Top 500m of water are saltier in warmer than polar water since it evaporates faster leaving behind salt at surface

• A. Temperature
• B. Salinity
• C. Density
• D. Pressure

Answer: (B)

Salinity is the key idea here—the amount of dissolved salts in seawater. When surface waters heat up, evaporation happens more quickly, and this process removes water but leaves the dissolved salts behind. The result is a higher concentration of salt in the surface layer, so the top 500 meters become saltier in warmer regions than in polar regions. Temperature describes how hot the water is, not how much salt is dissolved. Density is influenced by both salinity and temperature, so while higher salinity can raise density, the question is about what changes in the salt content itself. Pressure changes with depth, but near the surface they don’t drive this difference in salinity.