Radar Attenuation Characteristics of Low Reflectivity Zones in the Martian South Polar Layered Deposits

Both sets of Martian polar layered deposits (PLDs) display semi-rhythmic reflector stratigraphy in radargrams. The southern PLDs (SPLD), among other peculiarities, also contain widespread, distinctive deposits with few to no reflections that commonly occur at or near the top of the stratigraphic column. Here, we study the low reflectivity zones (LRZs) to determine whether they exhibit radar properties indicative of non-water ice. We find that the previously reported CO2-ice LRZ exhibits a distinct radar signature compared to all other LRZs. We also found behavior that suggests that the other LRZs may contribute to increased radar signal attenuation, which does not support a CO2 ice composition. We observe many instances of LRZs comprising the entire SPLD column and find that the radar attenuation varies across different LRZs, suggesting unique properties within each of these deposits. Variable radar attenuation of LRZs may be connected to differences in bulk compositions, radar-sensitive roughness characteristics, and/or distributions of stratigraphic materials. From orbital data, we know that both of the Martian polar caps contain widespread layers of dusty water ice. However, radar data, in particular, reveal that the southern cap also contains large sections of layer-free material. Previous studies have established that one of these occurrences of layer-free material is composed of carbon dioxide ice. We looked at the remaining occurrences of layer-free zones in the southern cap and found that they do not show the same radar signatures as those used to deduce the composition of the carbon dioxide unit. These other layer-free units are often associated with decreased signal strength compared to regions where layers are present. We also see variations in the signal strength across these layer-free units, suggesting subtle differences in their composition, material distribution, or surface roughness of the polar cap. The large carbon-dioxide ice deposits of Australe Mensa exhibit radar characteristics distinct from other low reflectivity zones The outlying low reflectivity zones show evidence of increased radar attenuation relative to layered regions Variation in attenuation characteristics across low reflectivity zones suggests unique properties across units