> The present thinking is that the oxygen will come from ice in deep pockets in crater walls at the Lunar South Pole

Based on this related article from NASA, my understanding is that the oxygen will be extracted directly from the regolith.

Given that they're already going to be processing the stuff to obtain the metals in the first place, that makes more sense than drawing O2 from the ice, and can be done at any old site on Luna, which is not the case if you're dependent on polar ice.