Paleo‐Evolution of Martian Subsurface Ice and Its Role in the Polar Physical and Isotopic Layering.
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| Title: | Paleo‐Evolution of Martian Subsurface Ice and Its Role in the Polar Physical and Isotopic Layering. |
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| Authors: | Vos, E.1 (AUTHOR) eran.vos@weizmann.ac.il, Aharonson, O.1,2 (AUTHOR), Schörghofer, N.2 (AUTHOR), Forget, F.3 (AUTHOR), Lange, L.3 (AUTHOR), Millour, E.3 (AUTHOR) |
| Source: | Journal of Geophysical Research. Planets. Oct2023, Vol. 128 Issue 10, p1-16. 16p. |
| Subject Terms: | *Climate change models, *Ice, *Hydrologic cycle, Energy budget (Geophysics), Milankovitch cycles |
| Abstract: | Mars harbors ice deposits in several forms, on the surface and in the subsurface, which exchange with each other on various timescales. We seek to study the pore ice evolution over millennial time scales and how it contributes to and affects the Polar cap's evolution. We calculate the evolution of SubSurface Ice (SSI) pore filling by coupling two models, the Mars LMD Global Climate Model, which calculates the atmospheric and surface evolution on an annual timescale, and the dynamical version of the Mars Subsurface Ice Model, which calculates the evolution of the SSI on a millennial timescale. The SSI latitudinal boundary fluctuates over more than 25° in one obliquity cycle, overall extending equatorward of latitude ±35° at high obliquity, and receding to about ±60° at low obliquity. In locations where the SSI is stable continuously over orbital cycles, the simulations predict layering caused by a sublimation front at the SSI top boundary. Between 5 and 2.5 Myr ago, the subsurface lost at least ∼95 m of polar equivalent layer ice. The SSI flux routinely reaches ∼1 mm/Mars year. In addition to the direct contribution to the growth of the North Polar Layered Deposits (NPLD), the SSI causes variations in the NPLD accumulation rate due to the changes in the SSI distribution that affect the seasonal energy budget. These variations are comparable to the change in rate due to variations in orbital elements. When running paleo‐climate simulations, particularly to reconstruct the NPLD profile, changes in the SSI distribution should be considered. Plain Language Summary: Ice on Mars is abundant and can be found on the surface and in the subsurface. In this work, we model the evolution of subsurface ice by diffusion. We examine how the evolution of the subsurface affects the North Polar cap stratigraphy. We use humidity calculated by a Global Climate Model and a thermal diffusion model to calculate the growth and retreat of ice in the subsurface. We calculate the depth and the fraction of pore‐filling ice at present. The subsurface can contribute ∼95 m (of the overall ∼2,000 m) of the North Polar Cap column. Subsurface ice indirectly affects the accumulation rate and isotopic ratio of the North Polar Cap growth by changing the seasonal energy budget. This occurs because when ice extends in the subsurface, it changes the thermal properties of the ground. These results emphasize the importance of the subsurface ice in the Martian water cycle, and it needs to be considered when reconstructing the North Polar Cap profile. Key Points: Subsurface‐atmosphere vapor (ice) exchange is modeled over Milankovitch cycles using Mars climate and subsurface modelsIn regions where subsurface ice periodically forms and disappears due to vapor diffusion, ice concentrations are expected to be smallThe pore‐ice volume lost between 5 and 2.5 Myr ago is equivalent to a layer of max‐imum thickness 95 m distributed over the North Polar Layered Deposits [ABSTRACT FROM AUTHOR] |
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| Database: | GreenFILE |
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