Interannual variability of sand dune fluxes and the influence of dust storms across Mars

Diverse aeolian bedforms, including dunes, megaripples, and ripples, are migrating across the surface of Mars today, as driven by seasonally variable winds. While long-term sand flux and their regional boundary conditions have been well constrained for many dune fields, an understanding of annual sand transport variability (or consistency) is lacking. Here we provide a decadal-scale analysis of migration patterns for Martian aeolian dune systems and test the hypothesis that global dust storm (GDS)-related winds can influence bedform sediment fluxes.

Annual migration was assessed at select sites in High Resolution Imaging Science Experiment (HiRISE) orthoimages (0.25–1-m/pix) and digital terrain models. Displacements were recorded by manually mapping polylines along the dune crests in GIS over 3-8 Mars years’ worth of images. Sand fluxes were computed using slipface heights from the HiRISE topography, along with dune migration estimates – see Urso et al. 2017; Chojnacki et al. 2024. A total of 20 dune fields were analyzed from 85°N-45°S for Mars years (MY) 28-36, where sites were chosen based on data availability and long-term migration trends.

Migration rates for dunes ranged between 0.3-1.2-m/Earth year, with dune median heights of 6-17-m. Whereas median sand fluxes for sites ranged between 1-10-m³/m/yr over decadal-scale time periods, annual measurements may vary by an order of magnitude. The north polar erg dunes yield the highest rates despite being largely frozen and immobile during the northern autumn, winter, and spring. Here, the seasonal cap thickness and springtime defrost timing dictate how long winds can transport sand. There were notable sand flux maxima over the MY28-29 timestep and minima in MY34-35. The most notable events during these periods were the MY28 and MY34 global dust storms, which impacted the polar vortex, temperatures, and CO₂ ice deposition. MARCI and HiRISE image mapping demonstrated that MY29 (early defrost) and MY35 (late) were endmembers in terms of spring defrosting. These events were attributed to the observed sand flux heterogeneity for some polar dune fields - see Chojnacki et al., 2024.

Equatorial or tropical latitude sites also showed significant deviations of sand transport rates, including during GDS years. Five dune fields showed reduced sand fluxes (33-49%) during the 2018/MY34 (~L_s 180-240°) GDS, relative to the prior year’s measurements. This reduction of nominal sand transport may be due to the depressed daytime surface temperatures or misaligned storm track directions (relative to nominal dune-forming winds) during the 2018 GDS, which were reported in the literature. In contrast, four dune fields were observed with increased fluxes (16-39%) in that GDS year. Elevated transport rates may relate to the alignment of dunes with dust storm corridors that experienced elevated wind shear or more localized factors. Finally, three sites showed no significant deviations in annual measurements, suggesting some bedforms may be in steady state in terms of sand transport. Climate factors such as global dust storms, seasonal ice cycles, and temperature variability appear to have a crucial role in sand availability and transport for Martian dunes; these factors demonstrate the complex interplay of boundary conditions on Mars.