When conductivity does not mean saltier water

A conductivity change is not a direct measurement of changing salt content because temperature, pressure, units, and seawater composition affect its interpretation. This methods note follows the documented TEOS-10 calculation chain from conductivity to Practical Salinity and Absolute Salinity, then to thermodynamic interpretation. A published Gibbs SeaWater demonstration supplies two nearly equal conductivities with substantially different calculated salinities, making the importance of context explicit. Hypothetical archive and mooring cases show how a convention change can create an artificial step and why validated freshening does not uniquely identify its source. No field deployment or calibration is analysed. The note identifies the variable definitions, original inputs, processing versions, and quality information needed before a profile can support claims about water masses, density, or freshwater pathways.