Fig. 1. A point of the –s plane with the scales chosen so that the isopycnal is at with the axes. The spiciness isopleth at that point is constructed so that ; it is orthogonal to the isopycnal with this choice of scales. A vertical profile unstable to salt fingering is drawn, with =-71.6°(R=2); the arrow indicates the downward direction. The sectors corresponding to profiles diffusely stable, unstable to salt fingering and layering, and gravitationally unstable are also shown. Positive angles are counter-clockwise.