This is a global ocean climatological dataset of 17 thermohaline parameters such as isothermal layer (ITL) depth (hT), mixed layer (ML) depth (hD), thermocline gradient (GT), pycnocline gradient (GD) determined from temperature (T) and salinity (S) profiles of the National Centers for Environmental Information (NCEI) world ocean atlas 2018 (WOA18) using the double gradient method along with the identity-index (i-index) showing the quality of the determination. With the identified (hT,hD) and (GT,GD), other parameters such as ITL heat content (HITL), mixed layer fresh-water content (FML), maximum thermocline gradient (GTmax), thermocline depth (hth), temperature at thermocline depth (Tth), maximum density gradientGDmax), pycnocline depth (hpyc), density at pycnocline depth (ρpyc), and (hT−hD) (barrier layer if positive or compensated layer if negative). The dataset is located at the NOAA/NCEI website (10.25921/j3v2-jy50). It provides useful background information for ocean mixed layer dynamics, air-sea interaction, climatological studies. This paper is the only document for the dataset.