A density curve of seawater typically shows density...

• A. Density increases with depth
• B. Density decreases with depth
• C. Density stays constant with depth
• D. Density fluctuates randomly with depth

Answer: (A)

Density in seawater rises with depth because the water below tends to be colder and often saltier, and pressure also increases underwater. Cold water is denser, and saltier water is denser, so as you go deeper these properties combine to make density higher. On a density-vs-depth curve this shows up as an upward slope, with a steeper increase in the layer where temperature and salinity change most rapidly (the pycnocline). This creates stable stratification, with lighter, warmer, or fresher water sitting above denser, cooler, saltier water.