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From Martian dunes to Martian sand flux


Campus Paris-Rive-Gauche


Séminaires Planétologie et Sciences Spatiales

522, bât. Lamarck

Laura Fernandez


Dunes provide a unique set of information about local wind regimes on planetary bodies where in-situ meteorological measurements are scarce. Wind directional variability and sediment availability are known to control the dune growth mechanism and the subsequent dune shape and orientation. In zones of high sediment availability (i.e., mobilizable sediment in the inter-dune areas), dunes grow in height perpendicularly to the maximum gross bedform-normal transport. This dune growth mechanism is henceforth referred as BI, the “bed instability mode”. In contrast, in zones of low sand availability (i.e., non-mobilizable bed in the inter-dune areas), dunes elongate in the direction of the resultant sand flux by deposition at the dune tip of the sediment, which is transported along the crest. This dune growth mechanism is henceforth referred as F, the “fingering mode”. On Mars, dunes cover an area estimated around 975,000 km2 of which 86% belong to the North Polar Region. Fifty years of Martian surface observation show that dunes are still active on Mars. In Polar Regions, because of the seasonal CO2 cap, sediment transport may only occur from late spring to early autumn, hence during approximately 30% of a Martian year. Modern winds on Mars are therefore supposed to contribute to shape sand seas. Nevertheless, wind regimes on Mars are still under debate. Actually, they essentially rely on the predictions of Global Circulation Models (GCM). Here, we show that both dune growth mechanisms coexist on Mars and that there is a strong dependence of dune orientation on sediment availability. We use this dependence at two different sites at the border of the largest sand sea to infer new constraints on the local multidirectional wind regimes.