  In modern geodynamics, isostasy can be viewed either as the static
equilibrium of the crust that minimizes deviatoric stresses, or as a dynamic
process resulting from the viscous relaxation of the non-hydrostatic crustal
shape. Paper~I gave a general formulation of Airy isostasy as a loading problem
solved with Love numbers, and applied it to the case of minimum stress
isostasy. In this sequel, the same framework is used to study Airy isostasy as
the long-time evolution of a viscoelastic shell submitted to surface and
internal loads. Isostatic ratios are defined in terms of time-dependent
deviatoric Love numbers. Dynamic isostasy depends on the loading history, two
flavours of which are the constant load applied at a specific time and the
constant shape maintained by addition or removal of material at the
compensation depth. Whereas the former model has no elastic analog, the latter
is equivalent to elastic isostasy with zero deflection at the surface, which
was shown in Paper~I to be dual to minimum stress isostasy. Viscoelastic and
viscous approaches are completely equivalent. Isostatic models thus belong to
two independent groups: the elastic/stationary approaches and the
time-dependent approaches. If the shell is homogeneous, all models predict a
similar compensation of large-scale gravity perturbations. If the shell
rheology depends on depth, stationary models predict more compensation at long
wavelengths, whereas time-dependent models result in negligible compensation.
Analytical formulas for the isostatic ratios of an incompressible body with
three homogeneous layers are given in complementary software.
