  We investigate strongly correlated spin-1 ultracold bosons with
antiferromagnetic interactions in a cubic optical lattice, based on bosonic
dynamical mean-field theory. Rich phase diagrams of the system are mapped out
at both zero and finite temperature, and in particular the existence of a
spin-singlet condensate is established. Interestingly, at finite temperature,
we find that the superfluid can be heated into a Mott insulator with even (odd)
filling via a first- (second-) order phase transition, analogous to the
Pomeranchuk effect in $^{3}$He. Moreover, for typical experimental setups, we
estimate the critical temperatures for different ordered phases and our results
suggest that direct experimental observation of these phases is promising.
