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Inferring past climate on Mars through mapping and simulating trough migration paths recorded in polar ice stratigraphy

Presentation #300.05 in the session Martian Ice, Climate, and Habitability (Oral Presentation)

Published onOct 23, 2023
Inferring past climate on Mars through mapping and simulating trough migration paths recorded in polar ice stratigraphy

Mars’ northern polar ice cap has many kilometer long, sub-kilometer deep depressions which spiral around the north pole, called the polar spiral troughs. These troughs have been migrating through time due to sublimation of their equatorial-facing wall and subsequent deposition on the poleward-facing wall. Evidence of this migration is present in the radar observations of the subsurface, which we have mapped across the polar cap in 3D. The shapes of the troughs’ migration paths (TMPs) are likely controlled by the accumulation of ice and the retreat rate of the trough, and can provide information about Mars’ polar paleoclimate and patterns of accumulation in different regions of the polar cap. In this work, we use the phenomenological model developed in Bramson et al. (2019) to compare synthetic TMPs to our mapped TMPs from Laferriere et al. (in prep), and explore regional and localized trends in accumulation and retreat.

We have mapped 33 TMPs across the entire northern polar cap in the 3D Shallow Radar (SHARAD) radar volume, and identified 6 regions based on TMP morphology. These mapped TMPs are inputs for our Markov Chain Monte Carlo (MCMC) approach (Izquierdo et al. in review; this conference), which we can use to explore a large parameter space affecting ice mass balance. We test the dependence of accumulation and retreat (and subsequent horizontal and vertical trough migration) on Mars’ obliquity and solar insolation. We update this approach to treat ice loss as a free variable rather than as an input from a thermal model.

We test this approach on a trough located at 14°E longitude and 86°N, with a generally classical TMP which moved stratigraphically upwards and poleward from the subsurface initiation point. This trough began migrating poleward under an accumulating cap and developed a promontory during the accumulation of the last ~180 m of ice. From our preliminary model runs we find an average accumulation rate ~1 mm/yr for a total of 400 m vertical migration and an ice loss rate of ~1 mm/yr, which results in ~17 km horizontal migration at this site. Applying this method to our mapping of troughs across the polar cap will provide insight into regional variations in accumulation and sublimation of ice.

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