This is still experimental; the colour scale comes out excellently on Macs, quite well on most Unix systems and acceptable on many PCs. We are working on a uniformly acceptable colour scheme.

The quantities are defined as follows: If T denotes temperature, S salinity, the Greek letter rho density and x the horizontal co-ordinate along the transect pointing in the direction of the ship´s progress, the horizontal temperature, salinity and density gradients are given by

To estimate the contribution of the temperature and salinity gradients to the density gradient, all three quantities are normalised by multiplication with the thermal expansion coefficient and haline contraction coefficient as appropriate. This yields three quantities with dimension m^-1:

The images show these three quantities in sequence from top to bottom. If density compensation is perfect, the first two images should be identical and the third image should show no structure.

The thermocline is a region of enhanced vertical gradients. It should in theory not show up in displays of horizontal gradients. In practice the Seasoar data sample so densely that the horizontal scales associated with turbulence and internal waves at the thermocline are very well resolved, and the thermocline is visible in the displays through the effect of enhanced horizontal variability. The features of interest here are, however, large horizontal gradients found above and below the thermocline.