"Can anyone with access tell us what the oxidative chemical is?
see ya"

Sorry, I can't tell you as they apparently aren't certain.

The redox potential (Eh) of several Atacama Desert samples was oxidizing with values ranging from 365 to 635 mV. We performed chemical assays for superoxides and hydrogen peroxide, because these are the most plausible oxidants and are those suggested as explanations for the reactivity observed by the Viking landers. Our results rule out these oxidants as the cause of the reactivity seen at the Yungay area, because the concentrations are too low (0.05 to 0.14 ppm) to explain our results and because the variation with latitude does not follow the variation seen in the organic or microbial concentrations. Nitrates are present in the soil in high levels (10 to 140 ppm), but they alone are not oxidizing enough to account for the reactivity seen in our samples. Nitrates may lead to the formation of peroxonitrite (NOO2–), and this has been suggested as a possible martian oxidant (13). However, the nitrate concentrations needed are in the percent level (10), much higher than in the Atacama. Thus, although our results show the presence of a strong oxidant in the soils in the Yungay area, the nature of the oxidant remains unexplained. Photochemical reactions initiated by sunlight continually produce oxidants in the lower atmosphere and surface. However, in most soils, biological production of reduced organic material completely dominates the net redox state of soils. When biological production is less than the photochemical production of oxidation, then the soil will become oxidizing. The transition from biologically dominated soils to photochemically dominated soils appears to be abrupt. Whichever process dominates will shift the redox state in one direction or another. In the Atacama, there is a gradual decline in biological activity as conditions became drier, yet near the extreme arid region there is an abrupt transition to very low bacterial levels and low organic content.

It is unlikely that the oxidizing conditions are due to high ultraviolet flux, because the site is only 1 km above sea level. Instead, the dry conditions in the Atacama must inhibit biological production of reductants and possibly enhance the survival of photochemically produced oxidants. Our results suggest that in the extreme arid core of the Atacama, we have crossed the dry limit of microbial survival in extreme environments. The net result is that photochemical processes dominate. Thus, in the Atacama Desert, we find almost no microorganisms and low levels of organic material, and the organic material present appears to have been oxidized. The LR experiments confirm the presence of as-yet-unidentified oxidants in the Atacama soil. In many respects, these soils are similar to the Mars soils investigated by the Viking Biology Experiment and may provide a valuable testing ground for instruments and experiments designed for future Mars missions.