thermocline marine pelagic feature marine thermocline 2010-03-16T12:16:11Z ENVO ENVO:01000075 ORCID:0000-0002-4366-3088 The marine thermocline describes a sharp change in the temperature of seawater (in relation to the temperature gradients of the water mass surrounding it) in the marine water column, which is usually associated with rapid changes in water density and salinity.