Climate Forcing of Ripple Migration and Crest Alignment in the Last 400 kyr in Meridiani Planum, Mars

The plains ripples of Meridiani Planum are the first paleo-aeolian bedforms on Mars to have had their last migration episode constrained in time (to similar to 50-200 ka). Here we test how variations in orbital configuration, air pressure, and atmospheric dust loading over the past 400 kyr affect bedform mobility and crest alignment. Using the National Aeronautics and Space Administration Ames Mars Global Climate Model, we ran a series of sensitivity tests under a number of different conditions, seeking changes in wind patterns relative to those modeled for present-day conditions. Results indicate that enhanced sand drift potential in Meridiani Planum correlates with (1) high axial obliquity, (2) a longitude of perihelion (L-p) near southern summer solstice, and (3) a greater air pressure. The last pulse of westward plains ripple migration likely occurred during the most recent obliquity (relative) maximum, from 111 to 86 ka. At L-p coinciding with southern summer solstice, the Mars Global Climate Model produced a westward resultant drift direction, consistent with the observed north-south plains ripple crest alignment. However, smaller superposed ripples, aligned NNE-SSW, are consistent with a strengthened northern summer Hadley return flow, occurring when L-p coincided with northern summer solstice. The superposed NNE-SSW ripples likely formed as the axial obliquity decreased during the last relative maximum and L-p swung toward northern summer, from 86 to 72 ka. The timeline of bedform activity supports the proposed sequence of CO2 sequestration in the south polar residual cap over the past 400 kyr.