Strata remain level. At active margins the crust is converging and subducting. There is vulcanism and earthquakes. Sediment deposits are contorted by compression and earthquakes. Salinity if the mass of salt ions per unit mass of seawater.
Practical salinity is the salinity estimated by measuring the conductivity of a water sample.
The practical salinity is accurate because the ratio of the various ions is constant throughout the ocean irrespective of the total amount of ions. Since the residence time is long relative to the mixing time, the ions are almost uniformly distributed.