I propose that the source for the sulfuric acid may have formerly been volcanic on the large scale of these ancient collapsed underground streams, but that current dissolution features are produced by sulfuric acid as the waste product of lithotrophic bacteria or "lichens". I believe that those can be seen in the micro images, as well as bacteria in the soil dissolving or eating the spherules.

At the upper center of this image dark looping putative "lichens"

Near the center, a bit left in this next image are some small eroded spheres. The soil near to, and overlapping them has many looping structures. There is an appearance that they may be dissolving (eating?) these spheres. These looping structures are unusual. One would think them to be very frail, thus of recent origin. An alternative hypotheses, recent crystalization of brines, is the best alternative explanation, I believe. This would require liquid phases and ongoing crystalization. Perhaps current climate cycles could drive that, but I am thinking more top down here, not bottom up.

As to your question about frozen water, I am uncertain what you meant, but what I mean is that the freezing point depression can be so much for brines or acid solutions, that they will be liquids under current Martian surface conditions. While the freezing point for pure sulfuric acid is 10.4C, for its solutions it is substantially below 0C (haven't found the data yet). For 15% MgCl2 it is -15.6C. For 15% NaCl it is -10.9C, and -21C for 23%. While thes two salt solutions would rapidly dry out, Sulfuric acid is very highly hygroscopic, so it could form solutions even with the very low atmospheric partial pressure of water at Mars, I suspect. Another substance in this category is the deliquescent (water absorbing, or hygroscopic) Sodium Sulfate, a compound likely present in Opportunity Ledge.

I didn't understand the question about moving fluids uphill, but capillary wicking might be able to do that. I thought that was part of the tentative Nasa theory about brines wicking to the surface.