Abstract
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. We
found that populations of polar megaripples and larger TARs are distinct
in terms of their morphology, spatial distribution, and mobility.
Whereas regionally-restricted TARs appeared degraded and static in
long-baseline observations, polar megaripples were not only widespread
but migrating at relatively high rates (0.13± 0.03 m/yr) 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 -
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. Seasonal off-cap sublimation winds and summer-time
polar storms are attributed as the cause for the elevated activity,
rather than cryospheric processes.