1. NASA Ames Research Center, Space Science Division, Moffett Field, Mountain View, California 94035, USA
2. College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA
3. San José State University Foundation, NASA Ames Research Center, Moffett Field, Mountain View, California 94035, USA
4. US Geological Survey, Astrogeology Team, Flagstaff, Arizona 86001, USA

Correspondence to: Anthony Colaprete¹ Correspondence and requests for materials should be addressed to A.C. (Email: Anthony.Colaprete-1@nasa.gov).

Abstract

The nature of the martian south polar cap has remained enigmatic since the first spacecraft observations^{1, 2, 3, 4, 5, 6}. In particular, the presence of a perennial carbon dioxide ice cap, the formation of a vast area of black 'slab ice' known as the Cryptic region and the asymmetric springtime retreat of the cap have eluded explanation. Here we present observations and climate modelling that indicate the south pole of Mars is characterized by two distinct regional climates that are the result of dynamical forcing by the largest southern impact basins, Argyre and Hellas. The style of surface frost deposition is controlled by these regional climates. In the cold and stormy conditions that exist poleward of 60° S and extend 180° in longitude west from the Mountains of Mitchel ( 30° W), surface frost accumulation is dominated by precipitation. In the opposite hemisphere, the polar atmosphere is relatively warm and clear and frost accumulation is dominated by direct vapour deposition. It is the differences in these deposition styles that determine the cap albedo.

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