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A Bayesian modeling approach applied to migrating polar troughs to infer ice deposition rates on Mars

Presentation #300.04 in the session Martian Ice, Climate, and Habitability (Oral Presentation)

Published onOct 23, 2023
A Bayesian modeling approach applied to migrating polar troughs to infer ice deposition rates on Mars

The north polar cap of Mars is the second largest water-ice reservoir on the planet. Understanding the rate that ice in the polar cap has been deposited and sublimated is of key importance to understanding Mars’ past climate. One way to infer the depositional environment of the cap is by relating observed discontinuities in the subsurface ice stratigraphy (e.g. Smith & Holt, 2010; Laferriere et al. this conference), observed in SHARAD radar data (Seu et al., 2007), to past locations of surface depressions called polar spiral troughs. These observations show that the troughs have moved upwards stratigraphically as ice has accumulated while migrating towards the north pole due to preferential sublimation of their equator facing wall. We use the model developed in Bramson et al. (2019) to link the speed of vertical and horizontal migration of the troughs to obliquity and insolation induced changes in the climate. Additionally, we use a thermal model to calculate the expected retreat of the ice at the equator facing wall of the trough, including the effects of a surficial layer of dust which protects the ice from sublimation. In this work, we have additionally implemented a Monte Carlo approach to sample the ice accumulation and sublimation values of the past 5 Myr that are consistent with the 2D profile of the migration of two troughs. The two troughs are adjacent to each other and are currently located between 86°–87° N and 16°–20° E. Our preliminary results show that, assuming our nominal retreat rates, the local accumulation of the ice is between 0.11–0.18 mm/yr, lower than the 0.5 mm/yr previously proposed for the whole cap (Hvidberg et al., 2012; Laskar et al., 2002). Our results therefore suggest the polar cap might be older than the previously proposed 4 Myr. As future work, we will assess the sensitivity of the inferred migration speeds to differences in the number of input migration data points used, which might cause artificial variations in speed between adjacent features. Additionally, we will update our algorithm to use several 2D profiles of the migration of each trough as input, which will more fully capture the range of migration speeds and behavior of each trough over time.

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