Spin effects in the tunneling regime of strong field ionization of hydrogenlike highly charged ions in linearly as well as circularly polarized laser fields are investigated. The impact of the polarization of a laser field on the spin effects are analyzed. Spin-resolved differential ionization rates are calculated employing the relativistic Coulomb-corrected strong-field approximation (SFA) developed in the previous paper of the series. Analytical expressions for spin asymmetries and spin flip probability, depending on the laser's polarization, are obtained for the photoelectron momentum corresponding to the maximum of tunneling probability. A simpleman model is developed for the description of spin dynamics in tunnel-ionization, which provides an intuitive explanation for the spin effects. The spin flip is shown to be experimentally observable by using moderate highly charged ions with a charge of the order of 20 and a laser field with an intensity of I ~ 1022 W / cm2</sup
