Recent Climate Shifts Circulation Patterns, and Climate Driven Erosion Recorded in the Morphology of Southern Hemisphere Sand Dunes of Mars
Although Mars is known to have experienced recent climate changes driven by variations in orbital parameters, the impact, timing, and the role of water during these changes is largely unconstrained. Clues to recent climate change are hidden in the morphology of southern hemisphere dunes. A latitudinal shift in dune morphology consistent with stabilized, inactive dunes coincides with the boundary of ground ice inferred from morphology [e.g., Mangold, 2004], Neutron Spectrometer data [Feldman et al., 2004], and a ground ice model [Mellon et al., 2004]. Equatorward of ~60º S, dune slipface crests are crisp, consistent with active dunes. Dunes poleward of this ~60º S boundary display rounded crests and appear coalesced, though deformed in a gravity-driven process.
Sand dunes must form in an environment in which wind energy is great enough to overcome the forces of both gravity and interparticle cohesion. In the high southern latitudes, ground ice is estimated to be present with a water-equivalent mass of greater than 20% (based on a twolayer model) [Feldman et al., 2004] and at a depth of less than ~0.5m [Mellon et al., 2004]. This work seeks to test the following hypothesis: like many terrestrial dune fields, the martian dunes of the southern mid- and high-latitudes formed under different climatic conditions, when sand was more easily mobilized by the wind. Since that time, the dunes have been locked in place by ground ice, and erosive processes have begun to degrade dune crests and slopes. The investigation of this hypothesis will impact the understanding of climate shifts, dune morphology, and climate-dependent atmospheric circulation patterns. Calculating ice table depths and measuring the quantity of sulfate-bearing materials in dune fields will not only provide information on the processes that stabilize dunes, it will also provide an independent test of the impact of such processes on thermal inertial derivations. Predicting ice table depth as a function of varying orbital parameters will be the first attempt to construct the history of sediment availability on another planet, and it is critical to determining the sediment state of dune fields on Mars. The deduction of ancient wind patterns from epochs when the ice table was too deep to restrict dune activity will produce a record of the atmospheric response to known and dated climate changes. Study of the spatial patterns of dune crest rounding and other erosional features will provide an understanding of the extent, forms, and rate of dune degradation since the dunes were last active.