Widespread Megaripple Activity Across the North Polar Ergs of Mars

The most expansive dune fields on Mars surround the northern polar cap where various aeolian bedform classes are modified by wind and ice. The morphology and dynamics of these ripples, intermediate-scale bedforms (termed megaripples and transverse aeolian ridges (TARs)), and sand dunes reflect information regarding regional boundary conditions (e.g., wind regime, grain size distribution, seasonal ice influence). We found that populations of polar megaripples (5-40 m spacing, ~1-2 m tall) and larger TARs (10-100 m spacing and 1-14 m tall) are distinct in terms of their morphology, spatial distribution, and mobility. Polar TARs were found to be regionally-restricted, showed degraded morphology (possibly ice-cemented), and were static in long-baseline HiRISE observations. In contrast, polar megaripples were noted to be widespread, migrating at relatively high rates (0.13± 0.03 m/Earth year), and possibly more active than other regions on Mars. This high level of activity is somewhat surprising since there is limited seasonality for aeolian transport due to surficial frost and ice during the latter half of the martian year. A comprehensive analysis of an Olympia Cavi dune field estimated that the advancement of megaripples, ripples, and dunes avalanches accounted for ~1%, ~10%, and ~100%, respectively, of the total aeolian system’s sand fluxes. This included dark-toned ripples that migrated the average equivalent of 9.6±6 m/yr over just 22 days in northern summer (L_s 94.96-105.08°) - unprecedented rates for Mars. While bedform transport rates are some of the highest yet reported on Mars, the sand flux contribution between the different bedforms does not substantially vary from equatorial sites with lower rates [1]. Whereas seasonal ice contributes to some bedform movements, such as dune slip face alcoves, no evidence was found that cryospheric processes directly promoted megaripple migration. However, late spring-summer off-cap katabatic ‘sublimation winds’ along with polar storm induced winds are deemed major factors for the high levels of observed bedform activity.

For full details see [2].

[1] Silvestro, S., Chojnacki, M., Vaz, D.A., Cardinale, M., Yizhaq, H., Esposito, F., 2020. Megaripple Migration on Mars. J. Geophys. Res. Planets. https://doi.org/10.1029/2020JE006446

[2] Chojnacki, M., Vaz, D.A., Silvestro, S., Silva, D.C.A., 2021. Widespread Megaripple Activity Across the North Polar Ergs of Mars. J Geophys Res Planets 126. https://doi.org/10.1029/2021JE006970