Himalayan Permafrost as a Martian Analogue: GPR Insights from the Tsokar Lake Basin of Cold-Arid Ladakh

Technical Summary: Himalayan Permafrost as a Martian Analogue: GPR Insights from the Tsokar Lake Basin of Cold-Arid Ladakh

Problem Statement
High-altitude permafrost in the Himalayas, particularly within the cold-arid regions of Ladakh, remains a critical yet understudied component of the global cryosphere. Unlike the continuous permafrost of polar regions, Himalayan permafrost is heterogeneous and highly sensitive to climate change, yet systematic geophysical characterization of its subsurface architecture is limited compared to Arctic benchmarks. Furthermore, while orbital radar instruments (e.g., SHARAD, MARSIS) have detected widespread subsurface reflectors and ice-rich layers on Mars, a principal challenge remains in reliably interpreting these signatures to reconstruct geological and environmental evolution. The lack of well-characterized terrestrial analogue environments with independently constrained geological frameworks hinders the ability to distinguish between different combinations of sedimentology, ice content, and cryogenic processes that produce similar radar responses. This study addresses the need to characterize the subsurface structure of Ladakh's permafrost using Ground Penetrating Radar (GPR) and to evaluate its suitability as a process-based terrestrial analogue for Martian cryospheric systems.

Methodology
The study was conducted in the Tso-Kar Basin, a topographically closed, hypersaline lake basin located at approximately 4,500 m elevation in the Ladakh region. The basin is characterized by unconsolidated, frozen sediments and a history of lacustrine regression and salinization, providing a robust geological framework for interpreting subsurface data.

• Instrumentation: Data were acquired using a 200 MHz antenna coupled with a SIR-4000 control unit (GSSI).
• Survey Design: Three distinct sites were selected along the eastern margin of the Tso-Kar basin to capture varying geomorphic and sedimentological conditions:
  • Site-1: Southern margin (dry surface, lake-margin sediments).
  • Site-2: Northern margin (vegetated terrain with prominent thermokarst, lithalsas, and frost mounds).
  • Site-3: Intermediate elevation (coarse surface material, paleoshoreline).
• Data Processing: Radar profiles were processed using RADAN 7 software. Processing included 600 MHz low-pass and 50 MHz high-pass Infinite Impulse Rate (IIR) filters, background removal, migration, and scaling. Minimal filtering and gain enhancement were applied to preserve the authenticity of subsurface signatures and reduce processing-induced artifacts.
• Analytical Approach: The study focused on identifying subsurface units based on reflection amplitude, continuity, and dielectric contrasts to delineate the active layer, permafrost table, ice-rich horizons, and taliks (unfrozen zones).

Key Results
The GPR investigations successfully mapped the cryostratigraphy of the Tso-Kar Basin, revealing a permafrost thickness of up to ~12 meters, overlain by buried snow (firn) of up to ~1.5 meters. The permafrost table was identified at depths of up to ~3 meters from the surface, with specific variations across the profiles. The study identified three distinct profiles representing different stages of permafrost stability and degradation:

1. Profile-1 (Stable Permafrost): Characterized by a shallow active layer (1–2.5 m) overlying a well-preserved, frozen subsurface. The profile shows strong, laterally continuous reflectors indicating stable permafrost with distinct ice lenses and segregation structures.
2. Profile-2 (Intermediate Degradation): Represents a transition stage where the active layer has thickened due to seasonal thaw. This profile shows the generation of a transition zone and talik, indicating partial permafrost degradation.
3. Profile-3 (Advanced Degradation): Reflects an advanced stage of degradation, characterized by a debris-rich active layer overlying a discontinuous and irregular permafrost table located at depths of 3.5–4.0 m.

Cryostratigraphic Features:

• Active Layer: Identified as a zone of strong, continuous reflectors subject to annual freeze-thaw cycles.
• Ice-Rich Layers: Sub-horizontal, high-amplitude reflectors indicate the presence of ice lenses and segregation ice.
• Debris Horizons: Heterogeneous, discontinuous reflections correspond to debris layers, colluvium, and freeze-thaw events, acting as stratigraphic markers.
• Deformation: Dipping reflectors and undulating horizons suggest cryoturbation, frost heave, and solifluction, as well as potential influences from active tectonics along the Tso-Kar Fault.
• Talik Zones: Weak, chaotic reflections at greater depths indicate areas of reduced ice content and partially thawed ground, consistent with talik formation.

Significance and Claims
The paper posits that the Tso-Kar Basin serves as a valuable terrestrial analogue for Martian subsurface ice systems, particularly in regions like Utopia Planitia and Arcadia Planitia. The significance of the study is framed around three main contributions:

1. Himalayan Cryosphere Characterization: The study provides one of the few detailed cryostratigraphic investigations of Himalayan permafrost, offering baseline data on spatial distribution, internal structure, and active layer dynamics in a cold-arid environment. It highlights the vulnerability of these systems to climate warming, evidenced by the observed degradation stages and talik formation.
2. Planetary Analogue Calibration: By relating well-constrained geological evolution (lake regression, salinization, tectonics) to specific GPR radar facies, the study establishes a process-based framework for interpreting planetary radar data. The radar signatures of active layers, permafrost tables, and cyclic ice-sediment sequences in Ladakh are presented as analogues for interpreting orbital and rover-based radar observations on Mars.
3. Methodological Validation: The research demonstrates the efficacy of GPR in imaging subsurface ice and sediment layering in high-altitude, cold-desert environments. It suggests that such terrestrial datasets can help reduce uncertainty in interpreting Martian radar signatures, which often suffer from ambiguity regarding sediment composition, ice content, and salinity.

The authors conclude that while extrapolation to Martian conditions requires caution due to differences in gravity, atmospheric pressure, and hydrological cycles, the Ladakh permafrost system offers a critical "natural laboratory" for understanding cryospheric evolution and for calibrating instruments and interpretation models for future Mars exploration missions.