Jarosite formation in deep Antarctic ice provides a window into acidic, water-limited weathering on Mars

Giovanni Baccolo,P B Niles,Dariush Hampai,Christopher Snead,Joseph Michalski,Elena Di Stefano,Barbara Delmonte,Massimo Frezzotti,Valter Maggi,Giannantonio Cibin,Lindsay Keller,Augusto Marcelli

doi:10.1038/s41467-020-20705-z

Abstract

Many interpretations have been proposed to explain the presence of jarosite within Martian surficial sediments, including the possibility that it precipitated within paleo-ice deposits owing to englacial weathering of dust. However, until now a similar geochemical process was not observed on Earth nor in other planetary settings. We report a multi-analytical indication of jarosite formation within deep ice. Below 1000 m depth, jarosite crystals adhering on residual silica-rich particles have been identified in the Talos Dome ice core (East Antarctica) and interpreted as products of weathering involving aeolian dust and acidic atmospheric aerosols. The progressive increase of ice metamorphism and re-crystallization with depth, favours the relocation and concentration of dust and the formation of acidic brines in isolated environments, allowing chemical reactions and mineral neo-formation to occur. This is the first described englacial diagenetic mechanism occurring in deep Antarctic ice and supports the ice-weathering model for jarosite formation on Mars, highlighting the geologic importance of paleo ice-related processes on this planet. Additional implications concern the preservation of dust-related signals in deep ice cores with respect to paleoclimatic reconstructions and the englacial history of meteorites from Antarctic blue ice fields.

Highlights

Many interpretations have been proposed to explain the presence of jarosite within Martian surficial sediments, including the possibility that it precipitated within paleo-ice deposits owing to englacial weathering of dust
The paradox is solved if the interaction occurs in environments isolated from bedrock, where water–rock interaction is limited and low pH is maintained during the diagenesis[14]
Antarctic jarosite has been found in rock varnishes and weathering rinds formed on the surface of erratics[17] and of meteorites collected at blue ice fields[18,19], or in soils developed from sulfide-rich rocks[20], but not in englacial environments

Summary

Introduction

Many interpretations have been proposed to explain the presence of jarosite within Martian surficial sediments, including the possibility that it precipitated within paleo-ice deposits owing to englacial weathering of dust. The progressive increase of ice metamorphism and re-crystallization with depth, favours the relocation and concentration of dust and the formation of acidic brines in isolated environments, allowing chemical reactions and mineral neo-formation to occur. This is the first described englacial diagenetic mechanism occurring in deep Antarctic ice and supports the ice-weathering model for jarosite formation on Mars, highlighting the geologic importance of paleo ice-related processes on this planet. Most of the hypotheses about the formation of Martian jarosite involve the interaction between acidic fluids and weathered sediments in transient lacustrine-evaporative basins similar to Earth playas[3,5,11] or volcanic settings, such as fumaroles[12]. Antarctic jarosite has been found in rock varnishes and weathering rinds formed on the surface of erratics[17] and of meteorites collected at blue ice fields[18,19], or in soils developed from sulfide-rich rocks[20], but not in englacial environments

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