Martian dunes indicative of wind regime shift in line with end of ice age

The study addresses the lack of in situ, lower- to mid-latitude observations that can validate a hypothesized recent Martian glacial–interglacial transition inferred from orbital data and obliquity models. While forward modeling from the ancient record is hindered by missing key elements, inverse modeling using known recent conditions and predictable orbital parameters over the last ~20 Myr suggests a recent ice age, deposition of a latitude-dependent ice-dust mantle (LDM), and a shift to an interglacial period as obliquity amplitude decreased ~0.4 Ma. To test these hypotheses, detailed rover-scale observations in the dynamic southern LDM margin (25–35° latitude) are needed to link surface morphology and stratigraphy with mesoscale and global atmospheric circulation models. The Zhurong rover landed at ~25.066° N in Utopia Planitia, traversed 1,921 m across the LDM transition region, and observed abundant aeolian features to infer recent wind regimes and climate history.

Prior work has identified a latitude-dependent ice-dust mantle and proposed a recent Martian ice age based on orbital geology and predictable obliquity cycles over the past ~20 Myr. Polar cap stratigraphy provides corroborative evidence for climate cycling. Aeolian landforms, notably bright transverse aeolian ridges (TARs) and barchans, are among the youngest geomorphic features and encode wind directions and atmospheric processes, but their ages, compositions, distributions, and roles in the sediment cycle remain incompletely understood. Previous rover investigations (largely at <20° latitude) advanced understanding of aeolian processes but lacked concurrent in situ meteorology, humidity, temperature, and geochemistry with stratigraphic context. General circulation models (GCMs) have struggled to reconcile observed TAR orientations with modeled wind fields, underscoring the need for improved boundary-condition constraints from rover-scale studies in key LDM transition regions. Reported TAR ages span ~3.0 to 0.1 Myr, indicating very recent aeolian activity on Mars.

• Study area and traverse: Zhurong rover traversed 1,921 m southward across the southern LDM transition zone in Utopia Planitia (~25.066° N) on a relatively flat surface (average slope ~2.5°).
• Target selection: Five bright barchan dunes (decameter-scale) and associated dark sediment accumulations were examined along the traverse.
• Imaging and morphology: High-resolution panoramic imaging by NaTeCam and MSCam characterized dune morphology, surface textures (cracks, crusts), and superposition relationships. 3D scenes were derived from NaTeCam stereo for local topography. Orbital images (HiRISE/HiRIC) provided regional context, orientations, and consistency checks with in situ measurements.
• Wind direction inference: Dune morphologies (barchan orientations, horn asymmetries) and superposed dark longitudinal dunes were used to infer predominant wind directions. Orientations of wind-erosion traces, linear ridges, and ventifacts were measured to corroborate wind regimes. Azimuths were quantified for specific features and compared with orbital measurements.
• Grain-scale analysis: MarSCoDe LIBS laser shots on coarse grains assessed whether larger clasts were agglomerates of finer particles by observing laser-induced fragmentation to 100–300 µm powders. Micro-imaging before/after LIBS documented textural changes.
• Composition and mineralogy: LIBS spectra characterized bulk chemistry of bright and dark sands (near-basaltic compositions), with minor Mg differences. Short-wave infrared (SWIR) spectroscopy detected hydration-related absorptions consistent with sulfates and chlorides.
• Surface roughness and albedo: MSCam-derived roughness parameters compared bright barchans vs dark dunes (dark dune roughness ~2× higher). Consideration of fine dust coatings and cemented crusts provided a basis for albedo contrasts.
• Age dating: Impact crater size-frequency distribution (CSFD) on 2,262 bright barchans identified 38 superposed craters. Absolute model ages (AMA) were derived for the bright barchan population, acknowledging caveats of small count areas.
• Climate and modeling context: Results were compared to Mars Climate Station (MCS) observations and LMD Mars GCM simulations (various scenarios including control and high dust) to assess seasonal wind fields (e.g., Ls 120–150°) and obliquity-dependent circulation changes. Obliquity/insolation histories and North polar layered deposit (NPLD) brightness profiles were used to correlate climatic transitions with dune stratigraphy.

• Two distinct wind regimes recorded: Earlier regime formed isolated bright barchans under a predominant north-easterly wind (azimuth ~12.5°), followed by a later regime with north-westerly winds (azimuth ~300°) that eroded barchans and produced superposed dark longitudinal dunes. The shift represents a >70° change in predominant wind direction.
• Morphology and stratigraphy: Bright barchans are encrusted and smooth with abundant centimeter-scale cracks (polygonal or parallel to contours), indicative of desiccation and surface evaporation. Dune horns show asymmetry: sharp, narrow eastern horns and shorter, wider western horns bearing dark longitudinal dunes oriented ~NW (e.g., mean azimuths 283.9° and 290.4° on dunes 2 and 5). Dark dunes are smaller than regional large dark dunes, implying limited sand sources and/or short duration.
• Multiple wind indicators: Wind-erosion traces, linear ridges, and ventifacts indicate two wind directions, NE (azimuth ~11.6°–29.8°) and NW (azimuth ~292.7°–295.8°), consistent with dune-derived orientations.
• Grain-scale evidence for cementation/agglomeration: Abundant coarse grains (3–15 mm) on dark dune surfaces and ridges disaggregated under LIBS into 100–300 µm powders similar to bright dune sands, indicating agglomerated particles formed by cementation. Bright barchans exhibit cemented crusts.
• Composition/mineralogy: Both bright and dark sands have near-basaltic compositions typical of average Martian soils; bright sands contain slightly more Mg. SWIR spectra reveal hydrated sulfates and chlorides associated with dunes, implicating salts and brines in induration and agglomeration.
• Surface properties: Dark dunes exhibit roughness parameters nearly twice those of bright barchans; albedo differences likely reflect finer dust in cemented crusts and thin dust coatings.
• Ages: CSFD on 2,262 bright barchans (38 superposed craters) yields absolute model ages between ~2 and 0.4 Myr, consistent with activity during the recent ice age and cessation near its end. Superposed dark dunes indicate subsequent, more modern activity during the interglacial.
• Climate linkage: The wind-regime transition aligns with obliquity amplitude decrease ~0.4 Ma and with increased brightness in upper NPLD cycles, suggesting synchronous global climate change. GCMs show annual mean NE winds but allow seasonal NW winds (Ls 120–150°), particularly under high dust scenarios, providing a mechanism for the younger NW regime.

The Zhurong rover’s in situ observations directly address the research question by providing stratigraphic and geomorphic evidence of a recent shift in wind regime at the southern LDM margin. The earlier NE winds produced bright, cemented barchans during high-obliquity conditions conducive to enhanced water cycle activity and dust deposition. As obliquity amplitude decreased (~0.4 Ma), climatic conditions favored dune surface cementation and crust formation, and a later regime of seasonally strengthened NW winds eroded the bright dunes and formed dark longitudinal dunes. The ~70° change in inferred predominant wind direction signifies a reorganization of atmospheric circulation at low–mid latitudes, consistent with a global transition from glacial to interglacial conditions. These findings dovetail with independent evidence: polar cap stratigraphy shows an abrupt increase in brightness around ~0.4 Ma, and obliquity/insolation models indicate a shift to lower, more stable obliquity amplitudes thereafter. While most GCMs do not predict a change in annual mean predominant wind direction, Zhurong’s data highlight significant seasonal variations (e.g., NW winds at Ls 120–150°) and the role of dust loading that can reconcile observed dune orientations with climate dynamics. The compositional and spectral evidence for sulfates and chlorides, together with observed agglomerated grains and crusts, point to transient brine activity facilitating cementation and surface induration under contemporary Martian conditions. Collectively, the Zhurong results improve linkage between rover-scale stratigraphy and global climate models and provide a coherent narrative for recent Martian climate evolution.

This study provides the first rover-scale stratigraphic evidence in the southern LDM margin of a recent wind-regime shift on Mars that aligns with the end of a geologically recent ice age. Bright barchans formed under NE winds (high obliquity) became cemented and later were eroded by seasonally strong NW winds that generated dark longitudinal dunes in the interglacial period. Crater-count ages (2–0.4 Myr) and polar cap brightness transitions around ~0.4 Ma corroborate a synchronous, global climate shift. The detection of hydrated sulfates and chlorides, agglomerated grains, and crusts indicates brine-involved cementation under present-day environmental cycles. These findings complement GCMs by emphasizing seasonal wind variability and provide essential constraints for refining climate models. Future research should: (1) extend in situ investigations to additional LDM margins and other latitudes to test regional vs global applicability; (2) obtain concurrent meteorology, humidity, temperature, and surface geochemistry to quantify active processes; (3) improve age constraints via expanded crater counts and dating of aeolian deposits; and (4) advance GCMs with higher spatial/temporal resolution and dust-variability scenarios to capture seasonal wind regimes driving aeolian reworking.

• Age uncertainties: CSFD ages are derived from a small count area (38 craters over 2,262 barchans), introducing uncertainties typical of limited-area crater statistics.
• Temporal correlation limits: Lack of precise absolute age control hinders exact synchronization between dune activity phases and individual polar layered deposit brightness cycles.
• Modeling constraints: GCM annual means do not capture observed seasonal wind variability; reliance on seasonal windows and dust scenarios introduces modeling uncertainties.
• Sediment supply and preservation biases: Small size of dark longitudinal dunes suggests limited sediment availability and potentially short-duration events, complicating interpretation of wind strength/duration.
• Spatial representativeness: Observations are confined to a single traverse at ~25° N; extrapolation to global conditions assumes broader applicability that requires further validation.