Water storage capacity of the Martian mantle through time

TL;DR

This study estimates the maximum water storage capacity of the Martian mantle using experimental data and statistical methods, revealing its increase over time and implications for Mars's water history.

Contribution

It provides the first quantitative estimate of the Martian mantle's water capacity considering iron effects, using a bootstrap approach on high-pressure mineral data.

Findings

Estimated current mantle water capacity: ~9 km GEL.

Estimated initial mantle water capacity: ~5 km GEL.

Water capacity increases with planetary cooling.

Abstract

Water has been stored in the Martian mantle since its formation, primarily in nominally anhydrous minerals. The short-lived early hydrosphere and intermittently flowing water on the Martian surface may have been supplied and replenished by magmatic degassing of water from the mantle. Estimating the water storage capacity of the solid Martian mantle places important constraints on its water inventory and helps elucidate the sources, sinks, and temporal variations of water on Mars. In this study, we applied a bootstrap aggregation method to investigate the effects of iron on water storage capacities in olivine, wadsleyite, and ringwoodite, based on high-pressure experimental data compiled from the literature, and we provide a quantitative estimate of the upper bound of the bulk water storage capacity in the FeO-rich solid Martian mantle. Along a series of areotherms at different mantle potential temperatures ($T_{p}$), we estimated a water storage capacity equal to $9.0_{-2.2} ^{+2.8}$ km Global Equivalent Layer (GEL) for the present-day Martian mantle at $T_{p}$ = 1600 K and $4.9_{-1.5}^{+1.7}$ km GEL for the initial Martian mantle at $T_{p}$ = 1900 K. The water storage capacity of the Martian mantle increases with secular cooling through time, but due to the lack of an efficient water recycling mechanism on Mars, its actual mantle water content may be significantly lower than its water storage capacity today.