On the origin of perennial water ice at the south pole of Mars: A precession-controlled mechanism

Laboratoire de Météorologie Dynamique, CNRS, UPMC, Paris, IPSL, France
Journal of Geophysical Research Atmospheres (Impact Factor: 3.43). 08/2007; 112(8):8-17. DOI: 10.1029/2007JE002902


1] The poles of Mars are known to have recorded recent (<10 7 years) climatic changes. While the south polar region appears to have preserved its million-year-old environment from major resurfacing events, except for the small portion containing the CO 2 residual cap, the discovery of residual water ice units in areas adjacent to the cap provides compelling evidence for recent glaciological activity. The mapping and characterization of these H 2 O-rich terrains by Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) on board Mars Express, which have supplemented earlier findings by Mars Odyssey and Mars Global Surveyor, have raised a number of questions related to their origin. We propose that these water ice deposits are the relics of Mars' orbit precession cycle and that they were laid down when perihelion was synchronized with northern summer, i.e., more than 10,000 years ago. We favor precession over other possible explanations because (1) as shown by our General Circulation Model (GCM) and previous studies, current climate is not conducive to the accumulation of water at the south pole due to an unfavorable volatile transport and insolation configuration, (2) the residual CO 2 ice cap, which is known to cold trap water molecules on its surface and which probably controls the current extent of the water ice units, is geologically younger, (3) our GCM shows that 21,500 years ago, when perihelion occurred during northern spring, water ice at the north pole was no longer stable and accumulated instead near the south pole with rates as high as 1 mm yr À1 . This could have led to the formation of a meters-thick circumpolar water ice mantle. As perihelion slowly shifted back to the current value, southern summer insolation intensified and the water ice layer became unstable. The layer recessed poleward until the residual CO 2 ice cover eventually formed on top of it and protected water ice from further sublimation. In this polar accumulation process, water ice clouds play a critical role since they regulate the exchange of water between hemispheres. The so-called ''Clancy effect,'' which sequesters water in the spring/summer hemisphere coinciding with aphelion due to cloud sedimentation, is demonstrated to be comparable in magnitude to the circulation bias forced by the north-to-south topographic dichotomy. However, we predict that the response of Mars' water cycle to the precession cycle should be asymmetric between hemispheres not only because of the topographic bias in circulation but also because of an asymmetry in the dust cycle. We predict that under a ''reversed perihelion'' climate, dust activity during northern summer is less pronounced than during southern summer in the opposite perihelion configuration (i.e., today's regime). When averaged over a precession cycle, this reduced potential for dust lifting will force a significantly colder summer in the north and, by virtue of the Clancy effect, will curtail the ability of the northern hemisphere to transfer volatiles to the south. This process may have helped create the observed morphological differences in the layered deposits between the poles and could help explain the large disparity in their resurfacing ages.

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Available from: F. Montmessin, Oct 06, 2015
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    • "Placing limits on the modern day deposition rate of water ice on the SPRC will allow us to better understand the modern-day stability of the southern polar cap (Byrne, 2009) and perhaps even shed light on the formation processes on the south polar cap (Montmessin et al., 2007). Many simulations of the Martian water cycle have investigated the question of cold-trapped water ice on the exposed CO 2 ice (Jakosky, 1983; Haberle and Jakosky, 1990; Houben et al., 1997; Richardson and Wilson, 2002; Montmessin et al., 2004; Montmessin et al., 2007) and we conclude the paper by comparing their predictions with our multiyear CRISM measurements. "
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    ABSTRACT: The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) (Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap (Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a 'minimum apparent' amount of deposition corresponding to a thin H2O ice layer of 0.2mm (with 70 percent porosity). This amount of H2O ice deposition is 0.6-6 percent of the total Martian atmospheric water budget. We compare our 'minimal apparent' quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.
    Earth and Planetary Science Letters 07/2014; 406. DOI:10.1016/j.epsl.2014.08.039 · 4.73 Impact Factor
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    • "The existence of low hygropause conditions in the rising branch of the Hadley cell tends to retain water vapor in the summer hemisphere, a key phenomenon first described in Clancy et al. (1996), and since called ''the Clancy effect " . Its paleoclimatic implications when aphelion occurred during southern summer 25 kyr ago have been studied by Montmessin et al. (2007), who used the LMD/GCM to explain the possible origin of the south residual cap (see Section 2). We will see that the Clancy effect is also key to understanding the northern mid-latitude glaciation. "
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    ABSTRACT: Recent geological observations in the northern mid-latitudes of Mars show evidence for past glacial activity during the late Amazonian, similar to the integrated glacial landsystems in the Dry Valleys of Antarctica. The large accumulation of ice (many hundreds of meters) required to create the observed glacial deposits points to significant atmospheric precipitation, snow and ice accumulation, and glacial flow. In order to understand the climate scenario required for these conditions, we used the LMD (Laboratoire de Météorologie Dynamique) Mars GCM (General Circulation Model), which is able to reproduce the present-day water cycle, and to predict past deposition of ice consistent with geological observations in many cases. Prior to this analysis, however, significant mid-latitude glaciation had not been simulated by the model, run under a range of parameters.In this analysis, we studied the response of the GCM to a wider range of orbital configurations and water ice reservoirs, and show that during periods of moderate obliquity (ϵ = 25–35°) and high dust opacity (τdust = 1.5–2.5), broad-scale glaciation in the northern mid-latitudes occurs if water ice deposited on the flanks of the Tharsis volcanoes at higher obliquity is available for sublimation. We find that high dust contents of the atmosphere increase its water vapor holding capacity, thereby moving the saturation region to the northern mid-latitudes. Precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems, producing surface ice distribution and amounts that are consistent with the geological record. Ice accumulation rates of ∼10 mm yr−1 lead to the formation of a 500–1000 m thick regional ice sheet that will produce glacial flow patterns consistent with the geological observations.
    Icarus 10/2009; 203(2-203):390-405. DOI:10.1016/j.icarus.2009.04.037 · 3.04 Impact Factor
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