Sublimation of terrestrial permafrost and the implications for ice-loss processes on Mars

Thomas A Douglas,Michael T Mellon

doi:10.1038/s41467-019-09410-8

Abstract

Sublimation of ice is rate-controlled by vapor transport away from its outer surface and may have generated landforms on Mars. In ice-cemented ground (permafrost), the lag of soil particles remaining after ice loss decreases subsequent sublimation. Varying soil-ice ratios lead to differential lag development. Here we report 52 years of sublimation measurements from a permafrost tunnel near Fairbanks, Alaska, and constrain models of sublimation, diffusion through porous soil, and lag formation. We derive the first long-term in situ effective diffusion coefficient of ice-free loess, a Mars analog soil, of 9.05 × 10−6 m2 s−1, ~5× larger than past theoretical studies. Exposed ice-wedge sublimation proceeds ~4× faster than predicted from analogy to heat loss by buoyant convection, a theory frequently employed in Mars studies. Our results can be used to map near-surface ice-content differences, identify surface processes controlling landform formation and morphology, and identify target landing sites for human exploration of Mars.

Highlights

Sublimation of ice is rate-controlled by vapor transport away from its outer surface and may have generated landforms on Mars
Sublimation tills have been found to protect glacial deposits from ice loss[2] while scalloped and dissected mantle terrains, and thermokarst-like pits and scarps, all may have formed by subsurface ice sublimation[3,7]
Complex valley terrains resembling the folded curvilinear ridge-and-trough texture of brain coral may have formed from a combination of ice flow and distortion and the differential sublimation of glacial ice beneath patterned soils[2,8]

Summary

Introduction

We report 52 years of sublimation measurements from a permafrost tunnel near Fairbanks, Alaska, and constrain models of sublimation, diffusion through porous soil, and lag formation. Sublimation tills may coat or hide residual snowpack, glacial ice, frozen ancient lakes, or ocean deposits[7] These features may indicate the presence of persistent water ice and, as such, they provide potential target landing sites for human exploration. Multiple periods of Tunnel excavation provide access to exposed surfaces where sublimation can be accurately quantified over a variety of exposure times. From these observations we are able to quantify water-vapor diffusion through undisturbed loess (a Mars analog soil16), and sublimation of clean ice by free convection

Methods

Results

Conclusion