Comparative Analysis of Tropospheric Water Isotope Distributions on Mars and Earth: Insights into Ice Cloud Microphysical Processes and Storm Dynamics

Isotopic analysis is a critical tool for understanding planetary water cycles and quantifying the role of distinct atmospheric processes. This study investigates the spatio-temporal distribution and controlling factors of the HDO/H₂O ratio in water vapor within the tropospheres of Earth and Mars, highlighting the similarities and differences in water vapor transport and phase changes on both planets.

We found significant isotopic enrichment from ice sublimation on both planets, with a stronger effect observed on Mars due to longer ice-crystal residence times, lower atmospheric pressures, and substantial temperature fluctuations. In contrast, Earth's near-surface oceans buffer these isotopic variations. Quantifying ice sublimation effects through observational data could help improve the microphysical parameterization in atmospheric models.

Moreover, during Mars's global dust storm, the D/H ratio markedly increased and propagated upward due to reduced condensation and the absence of liquid precipitation. In contrast, Earth-based observations during typhoon events indicate isotopic depletion propagating northward from tropical regions, driven primarily by raindrop evaporation within convective systems. Thus, storm events lead to opposite isotopic responses on Earth (depletion) and Mars (enrichment). Consequently, isotopic signals have considerable potential as proxies for reconstructing storm history and intensity across planetary environments.

This comparative analysis underscores both shared and planet-specific aspects of tropospheric water cycling, supporting a unified conceptual framework that effectively explains isotopic distributions under differing planetary conditions. Our results may enhance climate and weather models by improving representations of cloud microphysics and atmospheric water transport, while offering new tools for interpreting past climate events based on isotopic evidence.