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McMurdo Dry Valleys snow and ice microenvironments illustrating the multiple sources of snow and ice concentrations available for seasonal melting.

McMurdo Dry Valleys snow and ice microenvironments illustrating the multiple sources of snow and ice concentrations available for seasonal melting.

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The early climate of Mars (Noachian Period, the first ~20% of its history) is thought to differ significantly from that of its more recent history (Amazonian Period, the last ~66%) which is characterized by hyperarid, hypothermal conditions that result in mean annual air temperatures (MAAT) well below 0°C, a global cryosphere, minimal melting on th...

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... summary, the MDV hydrologic cycle is horizontally stratified rather than vertically integrated (Fig. 4b). A permafrost layer, caused by MAAT well below 0°C, creates a barrier between any surface meltwater and the groundwater zone below. The top of the ice-cemented soil is in diffusive equilibrium with the atmosphere. Any seasonal meltwater (Fig. 5) soaks into the dry active layer, wets the adjacent soil (see Fig. 8a & b widespread, perennial liquid water, weathering and erosion rates are lower by several orders of magnitude ( Summerfield et al. 1998) and can vary considerably depending on local conditions and seasonal abundances of liquid water in ...
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... wet coastal thaw zone (Marchant & Head 2007) averaged ~1%, and increased steadily with depth to about 10% just above top of the ice table, and much higher in the permafrost layer below. In spite of this dryness, there are numerous local microenvironments in which water sources exist, typically in the form of localized deposits of snow and ice ( Fig. ...
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... inland mixed zone (Marchant & Head 2007) so that local melting of snow and ice patches can occur. Although snow patches insulate underlying soils from elevated temperatures, top-down heating of the patches causes meltwater to form, flow, and ultimately soak into the upper dry part of the permafrost adjacent to the snow and ice patches ( Fig. 5), typically in the downslope direction. Campbell et al. (1998) measured the time-dependent behaviour of one of these snow patches and showed that the upper 5 cm of the adjacent wetted soil had a GWC of 15% at the edge of the thawing and subliming snow patch, 12% at 1.5 m distance, and 2.5% at 4 m distance. Following the retreat and ...
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... underline the importance of two timescales of hydrologic and biogeochemical exchange in Antarctic streams: 1) near- stream zones of rapid exchange, and 2) extended zones in which slower water fraction and biogeochemical reaction rates occur and can influence stream water chemistry on longer timescales. These various snow and ice microenvironments (Fig. 5 (Figs 4d & ...
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... traps the limited surface water produced by melting of surface snow and ice, and restricts groundwater flow to the active layer (in the largely dry layer lying above the ice table). Liquid water travels on and in the perched aquifer (Figs 4b & d, 5 & 8) and may be wicked up through capillary action (Fig. 6b & c). Recognizable geomorphic features (Fig. 5) range from local dark fringes around melting snow patches, to dark slope streaks on slopes below larger accumulations of melting snow and ice (Fig. 6b & c), to surface channelization (streams) where additional snowmelt and glacial meltwater flows (Fig. 7) and soaks into the regions adjacent to the streams (Fig. 7b & c) (hyporheic ...
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... hyperarid, hypothermal MDV ( Fig. 4b & d). Delivery of water to the surface is by direct snowfall in very small amounts (3-50 mm a -1 water equivalent in the MDV; Fountain et al. 2009) and from snow transported off the polar plateau by drainage winds (Speirs et al. 2010). Snowfall can drift and be sequestered in topographic traps and wind shadows (Fig. 5). Long-term snow and ice accumulation results in the formation of perennial snowbanks and glaciers, and their seasonal melting represents the major source of liquid water for fluvial activity (Fig. 5). Drainage basins are limited to the zones of snow and ice accumulation (alcoves, depressions, lee of obstacles, and glacier surfaces; ...
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... off the polar plateau by drainage winds (Speirs et al. 2010). Snowfall can drift and be sequestered in topographic traps and wind shadows (Fig. 5). Long-term snow and ice accumulation results in the formation of perennial snowbanks and glaciers, and their seasonal melting represents the major source of liquid water for fluvial activity (Fig. 5). Drainage basins are limited to the zones of snow and ice accumulation (alcoves, depressions, lee of obstacles, and glacier surfaces; Fig. 5) and are therefore insignificant in area compared to highly integrated basins in temperate climates. Although regional topography is inherited from earlier times (Sugden et al. 1995), due to ...
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... (Fig. 5). Long-term snow and ice accumulation results in the formation of perennial snowbanks and glaciers, and their seasonal melting represents the major source of liquid water for fluvial activity (Fig. 5). Drainage basins are limited to the zones of snow and ice accumulation (alcoves, depressions, lee of obstacles, and glacier surfaces; Fig. 5) and are therefore insignificant in area compared to highly integrated basins in temperate climates. Although regional topography is inherited from earlier times (Sugden et al. 1995), due to localized water sources, short stream lengths, and the locally immature topography of the MDV, stream order is very low (Fig. 9a & c), and streams ...
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... of the ice table (20 cm depth) until mid-December and hovers there until mid-February, where it rapidly descends to temperatures well below 0°C. These data suggest that melting of the top of the permafrost aquiclude (the ice table) provides a small contribution to meltwater and stream flow compared to melting of surface snow and ice reservoirs (Fig. 5). These records illustrate the two phases of meltwater production for the gully in the South Fork of upper Wright Valley ( Figs 7 & 10). Early PDTs (late October-mid-November) melt snow sequestered in the gully channel (Figs 7c & d, 10a-g), causing low-flux pulses of meltwater (Fig. 10d), and annual development of the wetted hyporheic ...
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... do the MDV lakes differ from typical temperate lakes? First, the MDV lakes lie on top of a 200-300 m thick permafrost layer (Fig. 5) and thus should freeze solid due to the underlying permafrost and the mean annual surface air temperature of ~ -20°C. However, very finely tuned conditions lead to the present characteristics of MDV wet-based lakes. Key to the heat balance and survival of the liquid water is the input of summer meltwater to the lake and the presence of ...
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... of water feeding lakes and relation to climate history: Where does the water come from and under what conditions is excess meltwater produced to form these lakes (Fig. 5) and cause modifications in their levels (Fig. 13)? The dominant means of supply (meltwater) and loss (ablation) are clearly seasonally and climatically controlled in the MDV. It is clear that small perturbations to the climate system can result in large changes in lake systems, often in non-intuitive ways (Chinn 1993, Hall et al. ...
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... The configuration of water sources are predominantly local (Fig. 5) and their behaviour has different consequences for geomorphic features (gullies, lakes, etc.) and amounts/fluxes of ...
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... Sources of meltwater (Fig. 5) include isolated snow patches, snow and ice patches in polygon troughs, alcoves and channels, glacial ice, frozen meltwater, and, in places, subsurface ice (Fig. ...
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... Melting of ice and snow (Fig. 5), and flow of liquid water (Fig. 10) occur annually in association with peak southern summer seasonal and daytime temperatures, which in low-lying regions can approach and sometimes exceed the melting point of water. At higher elevations, low-albedo surface rocks can be heated to temperatures well above 0°C and assist in localized ...
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... 12). Top-down melting of snow and ice during this period could generate significant meltwater, whose fate would be to drain off the top of the upland regional ice deposit into surrounding low areas and form gully channels, streams and rivers draining toward lower elevations, ponding in lows and craters to form closed- and open-basin lakes (e.g. Fig. 5). These repeated seasonal diurnal periods of melting would cause warming of the cryosphere but the melting geotherm would be unlikely to penetrate deep into or through the kilometres-thick cryosphere (Figs 1a & 12). Thus, meltwater streams would be perched above the ice table (Figs 4b, 4d & 5), influent, poorly integrated, and tend to ...

Citations

... A particularly promising solution is the possibility that glaciofluvial processes could have played a key role in sculpting the VN we see today. While this is not a new proposition (e.g., [Kargel and Strom, 1992;Lucchitta et al., 1981]) our understanding of terrestrial subglacial dynamics is evolving, providing new insights when applied to the Martian environment [Head and Marchant, 2014;Hewitt, 2011;Werder et al., 2013]. A promising feature of the glaciofluvial driven VN formation mechanism theory is that it addresses several of the characteristics of VN that are unresolved by precipitation/groundwater driven formation processes (Supplementary Fig. S1). ...
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Although the nature of the early Martian climate is a matter of considerable debate, the presence of valley networks (VN) provides unambiguous evidence for the presence of liquid water on Mars' surface. A subaerial fluvial origin of VN is at odds with the expected phase instability of near-surface water in the cold, dry Late Noachian climate. Furthermore, many geomorphic properties of VN (e.g., deep U-shaped valleys with constant widths; longitudinal profile reversals) are inconsistent with surface water flow. Conversely, subglacial channels exhibit many of these characteristics and could have persisted beneath ice sheets even in a cold climate. Here we model basal melting beneath a Late Noachian Icy Highlands ice sheet and map subglacial hydrological flow paths to investigate the distribution and geomorphometry of subglacial channels. We show that subglacial processes produce enough melt water to carve Mars' VN; that predicted channel distribution is consistent with observations; and corroborate reversed channel gradient measurements of VN consistent with subglacial formation mechanisms. We suggest that, given a sufficient historical global water inventory and Late Noachian geothermal heat flux, subglacial hydrology may have played a significant role in the surface modification of Mars. Plain language summary. Thousands of valley networks on Mars appear to have been carved by flowing water, and exhibit branching characteristics akin to river networks on Earth. Their origins, however, remain enigmatic for two primary reasons. First, ancient Mars was potentially cold, dry, and unable to support liquid water on its surface. Second, many physical characteristics of the valleys are inconsistent with features formed by precipitation and runoff. On Earth, water flowing beneath ice sheets produces channels with similar characteristics to Mars' valley networks. Here we model the deposition and evolution of Martian ice sheets and show that melting at the ice sheet base is likely even under cold and dry surface conditions. The volume, regional distribution, and flow patterns of melt are consistent with the volume and dynamics needed to carve the observed valley networks. A subglacial origin for Mars' valley networks accounts for their formation in a cold, dry climate and produces valley characteristics that match observations.
... The subsurface brine flows into one of the coldest and driest places on Earth (Keys, 1980;Doran et al., 2002;Obryk et al., 2020), the McMurdo Dry Valleys, long considered a Martian analog (Doran et al., 2010). In this polar desert, myriad geochemical processes that depend on moisture and temperature, such as weathering, deliquescence, precipitation, deaquation, and species mobility, proceed differently than anywhere else this planet (i.e., Keys and Williams 1981;Gibson et al., 1983, Campbell andClaridge, 1987;Hall et al., 2002, Head andMarchant, 2014). Cold, dry, and salt-rich environments are prime geochemical and microbiological analogue sites for planetary exploration (Murray et al., 2012;Rutishauser et al., 2018). ...
Article
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Aperiodic discharge of brine at Blood Falls forms a red-tinged fan at the terminus of Taylor Glacier, Antarctica. Samples from this discharge provide an opportunity for mineralogical study at a Martian analogue study site. Environmental samples were collected in the field and analyzed in the laboratory using Fourier transform infrared, Raman, visible to near-infrared, and Mössbauer spectroscopies. Samples were further characterized using microprobe and inductively coupled plasma optical emission spectroscopy for chemistry, and x-ray diffraction, scanning electron microscopy, and transmission electron microscopy for mineralogy, crystallography, and chemistry. The mineralogy of these samples is dominated by the carbonate minerals calcite and aragonite, accompanied by quartz, feldspar, halide, and clay minerals. There is no strong evidence for crystalline iron oxide/hydroxide phases, but compositionally and morphologically diverse iron- and chlorine-rich amorphous nanospheres are found in many of the samples. These results showcase the strengths and weaknesses of different analytical methods and underscore the need for multiple complementary techniques to inform the complicated mineralogy at this locale. These analyses suggest that the red color at Blood Falls arises from oxidation of dissolved Fe ²⁺ in the subglacial fluid that transforms upon exposure to air to form nanospheres of amorphous hydroxylated mixed-valent iron-containing material, with color also influenced by other ions in those structures. Finally, the results provide a comprehensive mineralogical analysis previously missing from the literature for an analogue site with a well-studied sub-ice microbial community. Thus, this mineral assemblage could indicate a habitable environment if found elsewhere in the Solar System.
... If life existed or had been transferred in the past to other celestial bodies, such as shadowed craters on the Moon, it may be potentially detectable via nucleic acids, which have, on Earth, an estimated half-life at À25 C in the order of 10 7 years (Millar and Lambert, 2013). For example, conditions persisting during the Amazonian period on Mars could have permitted the preservation of DNA beyond 10 million years (Head and Marchant, 2014). The lunar surface is exposed to 570 mSv of galactic cosmic rays in a year, calculated in the period between the solar maximum and minimum (Hayatsu et al., 2008), and DNA persistence times under these conditions are not known. ...
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The Moon is characterised by extremely harsh conditions due to ultraviolet irradiation, wide temperature extremes, vacuum resulting from the absence of an atmosphere, and high ionising radiation. Therefore, its surface may provide a unique platform to investigate the effects of such conditions. For lunar exploration with the Lunar Gateway platform, exposure experiments in Low Earth Orbit are useful testbeds to prepare for lunar space experiments and to understand how and if potential biomarkers are influenced by extra‐terrestrial conditions. During the BIOMEX (BIOlogy and Mars EXperiment) project, dried colonies of the fungus Cryomyces antarcticus grown on Lunar Regolith Analogue (LRA) were exposed to space conditions for 16 months aboard the EXPOSE‐R2 payload outside the International Space Station. In this study, we investigated the stability/degradation of fungal biomarkers in LRA after exposure to i) simulated space and ii) real space conditions, using Raman spectroscopy, gas chromatography‐mass spectrometry, and DNA amplification. The results demonstrated that fungal biomarkers were detectable after 16 months of real space exposure. This work will contribute to the interpretation of data from future biological experiments in the Cislunar orbit with the Lunar Gateway platform and/or on the lunar surface, in preparation for the next step of human exploration. This article is protected by copyright. All rights reserved.
... Estimates of a Noachian surface/near-surface water inventory of ∼34 m global equivalent layer (GEL; Carr & Head 2015) would restrict Noachian glaciation to a scenario where the extent and thickness of glacial ice is constrained to a finite volume (Fastook & Head 2015). Likewise, the predicted ranges of surface temperatures and geothermal heat flux in the Noachian require supply-limited glaciation to have been coldbased rather than wet-based (Wordsworth et al. , 2015Head & Marchant 2014), with basal melting expected only in extreme cases of ice thicknesses greater than ∼1 km (Fastook & Head 2015). Geomorphic signatures of cold-based glaciation are distinct from the wet-based features commonly observed on Earth (e.g., eskers, drumlins, moraines) and are often more difficult to detect (Marchant & Head 2007;Head & Marchant 2014). ...
... Likewise, the predicted ranges of surface temperatures and geothermal heat flux in the Noachian require supply-limited glaciation to have been coldbased rather than wet-based (Wordsworth et al. , 2015Head & Marchant 2014), with basal melting expected only in extreme cases of ice thicknesses greater than ∼1 km (Fastook & Head 2015). Geomorphic signatures of cold-based glaciation are distinct from the wet-based features commonly observed on Earth (e.g., eskers, drumlins, moraines) and are often more difficult to detect (Marchant & Head 2007;Head & Marchant 2014). These factors complicate the search for geomorphic evidence of cold-based glaciation that might otherwise support a cold and icy early Mars highlands hypothesis. ...
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A body of geologic evidence suggests that Noachian-aged craters on Mars were modified primarily by runoff from rainfall in a warm and wet early Mars climate. Although melting and runoff of frozen water ice have been suggested as plausible alternatives, supporting geomorphic evidence of Noachian glaciation on Mars has been elusive. We previously identified a Noachian-aged crater in the southern highlands that contained evidence of glacially derived fluvial and lacustrine features but was hydrologically disconnected from its surroundings. This closed-source drainage basin (CSDB) crater and proglacial paleolake provided the first candidate evidence of Noachian cold-based glaciation on Mars. Here, we describe a second nearby CSDB crater that contains similar evidence of glacial melting leading to the formation of proglacial fluvial channels and paleolakes on the crater floor. This new evidence suggests that CSDB formation was occurring episodically at regional scales throughout the Late Noachian and into the Early Hesperian. Recurrent episodes of glacial melting are consistent with climate model predictions of a cold and icy early Mars highlands with limited melting of glacial ice during periods of punctuated warming.
... Their water ecosystems are entirely microscopic, with no fauna larger than nematodes. The lakes and their ecosystems are studied as models for ancient Mars (16) and as indicators of climate change (17). ...
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The Antarctic Taylor Valley Lakes Fryxell and Bonney harbor oligotrophic microbial communities that are separated geographically from other aquatic systems. Their microbiomes include planktonic as well as lift-off mat communities that float to the underside of the perennial ice cover and eventually emerge at the surface. We investigated the antibiotic resistance genes (ARGs) from metagenomes of lift-off mats emerging from ice, from filtered water samples of Lake Fryxell, and from filtered water samples of Lake Bonney. ARG sequence markers were designed by ShortBRED-Identify using the Comprehensive Antibiotic Resistance Database (CARD). The overall proportion of ARG hits in the metagenomes was found to be similar to that found in temperate-zone rural water bodies with moderate human inputs (0.0002-0.0007%). The specific ARGs found showed distinct distributions for the two lakes, and for mat versus planktonic sources. An enrichment culture of Rhodoferax antarcticus from a Lake Fryxell mat sample showed a mat-forming phenotype not previously reported for this species. Its genome showed no ARGs associated with Betaproteobacteria, but had ARGs consistent with a Pseudomonas minor component. The Antarctic lake mats and water showed specific ARGs distinctive to the mat and water sources, but overall ARG levels were similar to those of temperate water bodies.
... This recently developed approach to investigating Martian glaciology, complements the geomorphological studies of hydrological features and periglacial phenomena, where the McMurdo Dry Valley region in Antarctica is considered to be an appropriate analog (Head & Marchant, 2014). ...
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The aims of this review are to: (i) describe and interpret structures in valley glaciers in relation to strain history; and (ii) to explore how these structures inform our understanding of the kinematics of large ice masses, and a wide range of other aspects of glaciology. Structures in glaciers give insight as to how ice deforms at the macroscopic and larger scale. Structures also provide information concerning the deformation history of ice masses over centuries and millennia. From a geological perspective, glaciers can be considered to be models of rock deformation, but with rates of change that are measurable on a human time-scale. However, structural assemblages in glaciers are commonly complex, and unravelling them to determine the deformation history is challenging; it thus requires the approach of the structural geologist. A wide range of structures are present in valley glaciers: (i) primary structures include sedimentary stratification and various veins; (ii) secondary structures that are the result of brittle and ductile deformation include crevasses, faults, crevasse traces, foliation, folds, and boudinage structures. Some of these structures, notably crevasses, relate well to measured strain-rates, but to explain ductile structures analysis of cumulative strain is required. Some structures occur in all glaciers irrespective of size, and they are therefore recognizable in ice streams and ice shelves. Structural approaches have wide (but as yet under-developed potential) application to other sub-disciplines of glaciology, notably glacier hydrology, debris entrainment and transfer, landform development, microbiological investigations, and in the interpretation of glacier-like features on Mars.
... In line with Hobbs et al. (2016), we cannot discriminate among the potential liquid water sources (pro-or subglacial meltwater, precipitation, groundwater sapping) due to the progressed degradation of the furrows and their superposition by unit HNcfs and sub-map-scale mantling deposits. Nevertheless, a glaciated highlands scenario as part of a mostly cold and icy early Mars model (e.g., Fairén, 2010;Head and Marchant, 2014;Wordsworth et al., 2015) could have provided the implied ice and meltwater. In any case, unit Nf potentially represents the oldest (prewrinkle-ridged plains, i.e., pre-Npr) remnant of (glacio-)fluvial activity in our mapping area and possibly of entire Noachis Terra. ...
... While Rogers and Nazarian (2013) interpreted the IR-dark areas as outcrops of widespread flood volcanics sourced by Hellas ring fractures, this might not be applicable to the inter-and intra-crater plains in central Noachis Terra that are beyond the detectable Hellas ring system (Bernhardt et al., 2016a(Bernhardt et al., , 2016b(Bernhardt et al., , 2018. Although we cannot rule out that gradation due to planation (as implied by the ubiquitous, highly degraded, small craters) by wind and/or possibly by past highland glaciation(s) (e.g., Head and Marchant, 2014) accounts for the generally low density of sinuous valleys, there is no extant indication for significant fluvial sedimentation. Furthermore, most of Noachis and Promethei Terra should have been covered by kilometers-thick ejecta by the Hellas and Argyre impact events (e.g., Edgett, 1989;Morrison and Frey, 2007), which might therefore comprise the majority of unit Nh. ...
... We therefore submit that Barnard's ridges are the youngest unambiguous (glacio-)fluvial landforms in the Malea Planum region, suggesting a ~mid-Hesperian, relatively short-lived supply of liquid water that likely was locally constrained. For the ridges in the Noachian craters of Terra Sabaea and elsewhere, localized meltwater streams from extensive ice sheets on the southern highlands were brought forward as sources by Boatwright and Head (2019) based on Noachian glaciation models (e.g., Head and Marchant, 2014;Fastook and Head, 2015). While obliquity-forced ice accumulation in certain areas around the Hellas basin was also suggested for the Hesperian and Amazonian (Forget et al., 2006), a meltwater scenario raises the Table 2; symbology is explained in Fig. 3 and 4. C) Blended HRSC images H2525_0000_ND and H2503_0000_ND showing the northern rim of Barnard crater (location indicated in (B)). ...
Article
Characterized by large paterae and late Noachian wrinkle-ridged plains, the ~1.2 million km² Malea Planum region (MPR) has been grouped into a circum-Hellas volcanic province and likely represents the oldest of the large volcanic areas on Mars. Being key to Mars’ early volcanic, tectonic, and climate evolution, we conducted a comprehensive and in-depth photogeological investigation of the MPR using multiple datasets including THEMIS-IR as a basemap. We identified 26 geomorphologic units and derived apparent model ages based on crater size-frequency distribution measurements for six of them. Along with stratigraphic, morphologic, hyperspectral, and gravimetric analyses, as well as findings by previous works in the surrounding regions, our chronostratigraphy resulted in a complete landscape formation model of the mapping area. At 3.9–3.8 Ga, Malea and Pityusa Paterae form, probably as volcanic collapse calderas geographically controlled by Hellas-concentric faults. Pityusa Patera hosts folded, layered deposits, possibly pyroclastics emplaced and shortened during patera formation as a piston-type caldera. Around 3.8–3.7 Ga, i.e., during the same time the ridged plains of the Hellas basin are formed, up to ~3.9 million km³ of volcanic and clastic/ballistic deposits partially sourced by Pityusa/Malea Patera activity and/or by now-obscured vents are emplaced and superpose Pityusa and Malea Paterae, thus covering any potential features associated with them. Simplistically assuming the wrinkle-ridged plains to entirely consist of basaltic deposits with ~2 wt% H2O, outgassing might have produced ~0.8 m Global Equivalence Layer of water and/or 3.9 hPa of H2, which could have temporarily increased ambient temperatures, potentially enabling fluvial and lacustrine processes across the Malea-Hellas regions. After plains emplacement, doming above a shallow magma chamber and its subsequent partial evacuation forms Amphitrites Patera as a caldera on a ~1.5 km high, broad rise collocated with a positive ~2.6 x 10⁻³ m/s² free-air, but no significant Bouguer gravity anomaly. Smooth crater fills throughout the area that often show high thermal inertias as well as enrichments of plagioclase and clay minerals (probably from leaching) might represent pyroclastic deposits resulting from this patera formation. Between 3.7 and 3.6 Ga, the northern slope of Amphitrites Patera is heavily dissected by low-viscosity flow processes that drain towards the Hellas basin floor and leave behind the Axius Valles amongst others, forming one of the densest martian valley networks with a drainage density of ~0.08 km⁻¹. 1,777 km long Mad Vallis and other smaller channels traversing the entire MPR and connecting the South Pole area with the Hellas basin are also formed around this time. Based on the geologic context and feasibility studies, we favor glacial meltwater/mud or alternatively low-viscosity lavas sourced from Amphitrites’ summit over a catastrophic sapping event as causes for the Axius Valles. Following this, the Barnard impact event deposits ejecta on the surrounding flow features southeast of Amphitrites Patera. Relatively shortly after its formation, sinuous valleys and ridges are formed in Barnard crater, likely by meltwater from ice sheets that might also have occupied Amphitrites Patera. Around 3.5 Ga, approximately 80-140 m (i.e., up to ~140,000 km³) of layered, friable materials are emplaced across large parts of the MPR as far north as 60°S. These materials are an extension of the circum-south polar Dorsa Argentea Formation (DAF) and possibly originate as lag deposits from wet-based glaciation. Entrained within these deposits are dark, fine-grained materials, likely pyroclastics potentially sourced from volcanic activity at Peneus Patera, which might have formed around the same time, with bounding faults penetrating the wrinkle-ridged plains but without completely resurfacing its interior floor. Combining structural analyses of radial wrinkle ridges within Peneus Patera with a piston-type caldera model similar to Pityusa Patera (Bernhardt and Williams, 2021) would imply the collapse of a magma chamber at 19.5 to 26 km depth, i.e., potentially in the mid-crust. Another, distinct set of up to ~210,000 km³ of friable airfall deposits, possibly sourced by ongoing/recurring Peneus activity, then cover the entire MPR but are relatively quickly eroded except where they are armored by superposing impact ejecta, thus forming numerous pedestal craters. In the Amazonian, these pedestals are themselves covered by up to few 10s of 1000s of km³ of atmosphere-derived volatiles and fines, which are then also sculpted into a second, distinctly younger pedestal crater population. Observable ongoing erosion of pyroclastic materials entrained in DAF deposits across the MPR and elsewhere provide mafic fines that potentially supply the formation of vast, mostly transversal and barchanoid dune fields in local depressions, e.g., within Pityusa Patera and on the floors of larger impact craters throughout the MPR and Noachis Terra to the northwest, which is contrary to previous theories of more local supplies. In conclusion, our in-depth investigation of the MPR, which included a comprehensive map and chronostratigraphic as well as morphometric analyses, shows that the area experienced a complex volcanic, tectonic, eolian as well as most likely (glacio-)fluvial history and acted as corridor between the south polar area and the Hellas basin. In total, ~294,000 km³ of material were eroded from the MPR in multiple episodes, i.e., not just in in one catastrophic event. This might have contributed close to a third of the originally one million km³ of hummocky materials residing on the Hellas basin floor (Bernhardt et al., 2016a). Unlike Olympus Mons in the Tharsis region (Zuber and Mouginis-Mark, 1992) but similar to Pityusa Patera, Peneus Patera formed as relatively deep-seated caldera. Activity related to Amphitrites and Peneus Paterae likely contributed to ridged plains formation and the associated volatile release as well as mobilization had significant environmental effects on the southern hemisphere.
... This would favor a colder, potentially subfreezing Noachian climate with only transient warming. Some global climate modeling studies support ambient Noachian temperatures well below freezing Wordsworth et al. 2013Wordsworth et al. , 2015 with cold-based glaciation occurring in the southern highlands (Head & Marchant 2014;Fastook & Head 2015). Thus, the nature of the ambient Noachian martian climate is currently debated. ...
... Instead, top-down (supraglacial) melting of a cold-based glacier could occur in cases where air temperatures locally exceeded 273 K (e.g., Head & Marchant 2014). In the more recent Amazonian, cold-based glaciation in crater interiors has produced a variety of distinctive morphological features. ...
... Additional top-down melting at the glacial front would then result in proglacial fluvial erosion of sediments derived either directly from glacial debris deposition (e.g., Head et al. 2017; or from preexisting aeolian mantles (Fassett & Head 2007). Proglacial meltwater channels are also observed in conjunction with seasonal top-down melting processes in the Antarctic McMurdo Dry Valleys (e.g., Atkins & Dickinson 2007;Atkins 2013;Head & Marchant 2014). In some cases, ridges may form between active channels (Atkins & Dickinson 2007;Atkins 2013) as the result of stranded icecored ground exposed by glacial retreat; this process is distinct from the topographic inversion that we interpret for the formation of the ridges in crater B. ...
Article
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A 54 km diameter Noachian-aged crater in the southern highlands of Mars contains unusually well preserved inverted fluvial channel networks and lacustrine deposits, all of which formed completely inside the crater. This “closed-source drainage basin” (CSDB) crater is distinct from previously documented fluvially breached or groundwater-fed crater basin lakes on Mars. We compare our observations to previously established models of crater degradation, fluvial incision, and topographic inversion on Mars to assess the most likely origins of the water that formed the fluvial and lacustrine features. We favor top-down melting of a cold-based glacier as the source of water in the CSDB crater, which would represent the first examples of proglacial fluvial channels and lakes found on Noachian Mars.
... Instead, these models suggest a "cold and icy" early Mars climate (Head & Marchant, 2014) in which snow and ice were deposited ...
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Advances in origins of life research and prebiotic chemistry suggest that life as we know it may have emerged from an earlier RNA World. However, it has been difficult to reconcile the conditions used in laboratory experiments with real-world geochemical environments that may have existed on the early Earth and hosted the origin(s) of life. This challenge is due to geologic resurfacing and recycling that have erased the overwhelming majority of the Earth's prebiotic history. We therefore propose that Mars, a planet frozen in time, comprised of many surfaces that have remained relatively unchanged since their formation > 4 Gya, is the best alternative to search for environments consistent with geochemical requirements imposed by the RNA world. In this study, we synthesize in situ and orbital observations of Mars and modeling of its early atmosphere into solutions containing a range of pHs and concentrations of prebiotically relevant metals (Fe2+ , Mg2+ , and Mn2+ ) spanning various candidate aqueous environments. We then experimentally determine RNA degradation kinetics due to metal-catalyzed hydrolysis (cleavage) and evaluate whether early Mars could have been permissive toward the accumulation of long-lived RNA polymers. Our results indicate that a Mg2+ -rich basalt sourcing metals to a slightly acidic (pH 5.4) environment mediates the slowest rates of RNA cleavage, though geologic evidence and basalt weathering models suggest aquifers on Mars would be near neutral (pH ~ 7). Moreover, the early onset of oxidizing conditions on Mars has major consequences regarding the availability of oxygen-sensitive metals (i.e., Fe2+ and Mn2+ ) due to increased RNA degradation rates and precipitation. Overall, (a) low pH decreases RNA cleavage at high metal concentrations; (b) acidic to neutral pH environments with Fe2+ or Mn2+ cleave more RNA than Mg2+ ; and (c) alkaline environments with Mg2+ dramatically cleaves more RNA while precipitates were observed for Fe2+ and Mn2+ .
... Whether the southern highlands have ever experienced a regional glaciation event remains a subject of intense debate. It has been proposed that the region was covered by an ice sheet at or before the Late Noachian (~3.8 Ga) Wordsworth et al., 2013;Head and Marchant, 2014;Cassanelli et al., 2015;Fastook and Head, 2015;Wordsworth, 2016). In contrast, a warm-wet Mars climate in the Late Noachian was also proposed (see review by Ramirez and Craddock, 2018), which may explain the widely occurring gully networks that formed before the end of the Noachian (Fassett and Head III, 2008) in the southern highlands. ...
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In this study we address the question of whether the Tharsis rise on Mars was once covered by an ice cap, and the ice melting was responsible for the development of the Late Hesperian (3.6-3.5 Ga) circum-Tharsis giant (>1000s km in length) outflow channels. To achieve this goal we conducted geomorphologic mapping across Oudemans crater and its bounding plateau plains in north-central Tharsis. Our work shows that the Oudemans-impact-induced landforms were superposed by a suite of younger landform assemblages, which we interpret to consist of horn-like peaks, arête-like ridges, cirque-like depressions, hanging-valley-like features, trim-line-like escarpments, lobate ridges, striated, pitted and hummocky terrains, and features resembling drumlins, crag-and-tails and roches moutonnées. A plateau-plain striated terrain exhibits streamlined linear ridges that are 400-2000 m wide and up to ~17 km long. The length-width ratio, shape, and morphology of the striated features are comparable to mega-scale glacial lineations (MSGLs) on Earth. Using well-understood Earth analogues as a guide, we interpret the younger assemblages to have formed during regional glaciation. We further suggest the striated terrain to have been generated by an ice stream in a regional ice sheet that filled 4-km deep Oudemans crater and covered the crater-bounding plateau plains. The shape of the glacier-induced landforms and their cross-cutting relationships require early northward-flowing northward-advancing glaciation, followed by southward-flowing northward-retreating glaciation. The size-frequency distribution of the craters superposed on top of the interpreted glaciated landforms in the mapped area yields a glaciation age of ca. 3.5 Ga, coeval with the estimated age of the interpreted glacial landforms along Valles Marineris. The inferred glaciation age is also coeval with the development of the circum-Tharsis outflow channels. Although our work supports the Tharsis ice-cap hypothesis, the extent of the ice cap and the required rapid ice-melting mechanism remain unconstrained.