It is now well established that isopycnal floats follow density surfaces very 
closely on all time scales, including those for internal waves. Knowledge of 
this can be used to study various processes: isopycnal stirring and mixing from 
in-situ changes in temperature, vorticity conservation from along-track 
variations in Lagrangian stretching vorticity, the internal wave sea state from 
pressure, and biologically important parameters such as oxygen.

Lagrangian temperature and depth along an isopycnal, particularly in fronts and 
eddy fields, reveal pathways of cross-frontal exchange (at various depths) and 
how fluid parcels move laterally and vertically in growing and decaying 
meanders. Changes in temperature signal incursions of water with different 
temperature-salinity properties and thereby indicate lateral stirring and mixing 
processes. These can occur quite suddenly in fronts, a clear indication of 
strong lateral shear that increases the contact area between adjacent water 
masses.

Stretching vorticity or static stability, N2=-g/rho(drho/dz), has been measured 
by numerous floats deployed in the North Atlantic Current (NAC) study. Floats 
usually show the expected changes in layer thickness as they down- or upwell in 
meanders, and in response to flow over topography. One float, caught in an 
anticyclonic lens, indicated a pycnostad with almost zero stratification 
implying recent exposure to the atmosphere. Generally speaking, floats evince 
greater N2 activity in energetic than in quiet regions.

All floats in the ACCE study measured dissolved oxygen along their tracks. 
Floats that surface due to winter time convection show the oxygen levels rapidly 
becoming (super-) saturated. In spring as the seasonal thermocline reestablishes 
itself, a gradual reduction in O2 levels takes places indicative of oxygen 
utilization. The changes in O2 levels can be quite strong and presumably rather 
patchy because they can quickly get erased by mixing events.