1. Astronomie et Systèmes Dynamiques, IMC-CNRS UMR8028, 77 Avenue Denfert-Rochereau, 75014 Paris, France
2. Laboratoire de Météorologie Dynamique, Université Paris VI, 4 Place Jussieu, 75005 Paris, France
3. Space Science Division MS 245-3, NASA/Ames Research Center, Moffett Field, California 94035, USA
4. Present address: Laboratoire de Planétologie et télédétection, UMR 5570, UCBL-ENS Lyon, 43 boulevard du 11 novembre 1918, 69622 Villeurbanne, France

Correspondence to: Benjamin Levrard^1,4 Email: blevrard@imcce.fr

Abstract

Observations from the gamma-ray spectrometer instrument suite on the Mars Odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near-surface ice in high latitudes of both martian hemispheres^{1, 2, 3, 4, 5}. Ice concentrations are estimated to range from 70 per cent at 60° latitude to 100 per cent near the poles, possibly overlain by a few centimetres of ice-free material in most places⁴. This result is supported by morphological evidence of metres-thick layered deposits that are rich in water-ice^{6, 7, 8, 9} and periglacial-like features^{10, 11} found only at high latitudes. Diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution¹², but such a degree of concentration is difficult to accommodate with such processes^{9, 13, 14}. Alternatively, there are suggestions that ice-rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity^{9, 13}, but these results have been difficult to reproduce with other models. Here we propose instead that, during periods of low obliquity (less than 25°), high-latitude ice deposits form in both hemispheres by direct deposition of ice, as a result of sublimation from an equatorial ice reservoir that formed earlier, during a prolonged high-obliquity excursion. Using the ice accumulation rates estimated from global climate model simulations we show that, over the past ten million years, large variations of Mars' obliquity have allowed the formation of such metres-thick, sedimentary layered deposits in high latitude and polar regions.

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