Thermal inertia of an ocean water mass is primarily a function of which factors?

• A. Only the depth of the water.
• B. Heat capacity, density, and thermal conductivity.
• C. Salinity alone.
• D. Wind speed.

Answer: (B)

Thermal inertia is the resistance of a water mass to a change in temperature when heat is added or removed. For ocean water, this resistance comes from three material properties: heat capacity, density, and thermal conductivity. Heat capacity (per mass) tells us how much energy is needed to raise the water’s temperature; density tells us how much mass is present per unit volume, so a larger density means more mass to heat; together these give the volumetric heat capacity, which sets how much energy per unit volume is required for a given temperature rise. Thermal conductivity describes how quickly heat can move through the water, influencing how heat is distributed and how rapidly temperature changes propagate. So, the combination of energy required to heat the water and the speed at which heat diffuses through it determines the inertia. Surface conditions like wind speed affect heat exchange at the boundary, not the intrinsic inertia of the water itself.