Baroclinic - a stratified fluid where the gradients of pressure and density are misalligned. Instability of broclinicity results in vorticity (eddies).
Barotropic -a stratified fluid where the gradients of pressure and density are alligned ( isobaric surfaces are also isopycnal and isothermal, baroclinic vector is zero and motions of fluid are strongly constrained)
Geostrophy -currents flowing parallel to isobars as a result of the coriolis force balancing the pressure gradient force. A geostrophic flow may be barotropic or baroclinic.
Halocline - the boundary (area of steepest gradient) separating two watermasses of different salinity in a stratified fluid
Internal waves - gravity waves occuring along pycnoclines. Can vary vastly in amplitude and frquency. Can be heightened by the lower water mass interfacing with rough topography.
Kelvin-Helmholtz instability - breaking internal waves, these occur when the Richardson number (the ratio of potential to kinetic energy) of a pycnocline drops below 0.25 (i.e. where the kinetic energy is high enough to break surface tension)
Pycnocline - the boundary (area of steepest gradient) separating two water masses of different density in a stratified fluid (may also be a halocline and/or thermocline)
Permanent Pycnocline - the boundary (area of steepest stable density gradient) which separates the upper waters where surface mixing occurs, and lower waters. This can restrict transport of nutrients between upper and lower layers and can inhibit the vertical migration of plankton. This can be diffused by shear produced turbulence, creating areas of upwelling.
Thermocline - the boundary (area of steepest gradient) separating two water masses of different temperatures in a stratified fluid