  The adiabatic decay of different types of internal wave solitons caused by
the Earth rotation is studied within the framework of the Gardner-Ostrovsky
equation. The governing equation describing such processes includes quadratic
and cubic nonlinear terms, as well as the Boussinesq and Coriolis dispersions.
It is shown that at the early stage of evolution solitons gradually decay under
the influence of weak Earth rotation. The characteristic decay time is derived
for different types of solitons for positive and negative coefficient of cubic
nonlinearity (both signs of that parameter may occur in the oceans). The
coefficient of quadratic nonlinearity determines only a polarity of solitary
wave. It is found that the adiabatic theory describes well the decay of
solitons having bell-shaped profiles. In contrast to that, large amplitude
table-top solitons, which can exist when the cubic nonlinear term is negative,
are structurally unstable. Under the influence of Earth rotation they transfer
first to the bell-shaped solitons, which decay then adiabatically. Estimates of
the characteristic decay time of internal solitons are presented for the real
oceanographic conditions.
