51st Lunar and Planetary Science Conference (2020) 1777.pdf

THE MCMURDO DRY VALLEYS OF ANTARCTICA AS AN ANALOG FOR PAST AND PRESENT MARTIAN SURFACE PROCESSES. M. R. Salvatore1, J. S. Levy2, J. W. Head3, and J. L. Dickson4, 1Department of Astronomy and Planetary Science, Northern Arizona University, [email protected], 2Dept. of Geology, Colgate University, 3Dept. of Earth, Environmental, and Planetary Sciences, Brown University, 4Division of Geological and Planetary Sciences, Caltech.

Introduction: The McMurdo Dry Valleys (MDV) of observed on Mars. We also highlight where additional Antarctica have been considered a valuable martian work in the MDV is necessary to address outstanding analog since the Viking era of Mars exploration [1]. Over questions in martian science. the past two decades, our understanding of martian Cold and Icy Early Mars?: The apparent environmental and geologic evolution has significantly disagreement between observed fluvial and lacustrine improved thanks to the plethora of orbital and landed landforms and the inability for global climate models to missions. New observations have raised many new produce mean annual temperatures greater than 0º C enigmatic questions about how cold and dry geological suggest that the martian surface was possibly never systems evolve, which has revitalized the MDV as an clement from a terrestrial perspective. Instead of a long- important terrestrial analog for Mars, from its earliest lived and continuously active hydrological system on recorded geologic history [2] to the present [3]. early Mars, is it possible that hydrological activity was Global martian climate models struggle to produce more episodic through punctuated climatic excursions on consistently warm and wet conditions at the martian an otherwise cold and icy early Mars? The fluvial and surface early in its history, even with the aid of additional lacustrine systems of the MDV are one possible analog greenhouse gases to offset the distance between Mars and where localized climatic optima drive local hydrological the faint young Sun [4]. Together with studies suggesting systems that can cease once conditions are unfavorable that snowmelt can satisfy the known distribution of [2,12]. The MDV provide compelling evidence for valley networks in parts of the southern highlands [e.g., comparable landforms found in ancient martian 5], these lines of evidence suggest that early Mars may landscapes. It is therefore possible that hydrological have been dominated by relatively cold and dry conditions as opposed to more clement conditions. The hyper-arid and hypo-thermal conditions that dominate the MDV today are some of the most comparable terrestrial conditions to those on modern (cold and dry) Mars [3,6,7] (Fig. 1). Shallow buried ice, glacial processes, and anhydrous oxidative weathering processes are pervasive across both landscapes. More recent work, however, has helped to appreciate the role of locally optimized conditions in driving many surface processes that generate habitable conditions, even in the extremely arid, cold, and radiative environment of the MDV [2]. For example, localized salt concentrations are able to facilitate deliquescence [8], melting of snowpacks and glaciers are facilitated by topographically controlled insolation [9] and, at least in the MDV, microbial ecosystems are able to suspend biological activity indefinitely until conditions are optimal [10]. These cold and dry conditions operate at one end of a hydrological continuum [11] in the MDV--the other end of which is the “cold and wet” endmember--where glacial melt, Fig. 1. Cold desert hydrological landforms on Earth and snow-fed streams, and ice-covered lakes persist, despite Mars. (a) Streams in the MDV. A portion of Quickbird only ~2 months of melting [3,12]. The hydrological and image 101001000AF37000. North is up. (b) Gullies in habitability gradients operating in the MDV make them Wright Valley, Antarctica. Gully fans are ~150 m across. the ideal environment for exploring Mars-like surface (c) Water track in Taylor Valley, Antarctica. Water track processes that have shaped both planets under both is ~2-3 m wide and flows downstream towards image ancient and modern climate conditions [2,3]. bottom. (d) Amazonian valley with flat-topped terminal fan. Portion of HiRISE image PSP_005950_1401. In this work, we highlight the recent developments in North is up. (e) Gullies on Mars. Portion of HiRISE comparative planetology between the martian surface image ESP_021584_1440. North is up. (f) Recurring and the MDV. This work has helped to decipher many slope lineae (RSL) on Mars. Portion of HiRISE image enigmatic climatological and geological features PSP_005787_1475. North is up. 51st Lunar and Planetary Science Conference (2020) 1777.pdf

systems present in the MDV, where mean annual A912-A928. [2] Head, J. W., & Marchant, D. R. (2014), temperatures are less than -20º C, can be analogous to Ant. Sci. 26, 774-800. [3] Marchant, D. R., & Head, J. W. those hypothesized to have formed on early Mars. (2007), Icarus 192, 187-222. [4] Wordsworth, R. D. Locally Optimized Conditions at Present: Local (2016), Ann. Rev. Earth Planet. Sci. 44, 381-408. [5] influences of topography, geologic resurfacing, Scanlon, K. E. et al. (2013), GRL 40, 4182-4187. [6] proximity to open water, and the distribution of snow and Doran, P. T. et al. (2002), JGR 107, glaciers play a major role in controlling local doi:10.1029/2001JD002045. [7] Heldmann, J. L. et al. environmental conditions in polar deserts that lack (2013), PSS 85, 53-58. [8] Levy, J. S. et al. (2012), GRL vegetation or other modulating influences [13]. For 39, doi:10.1029/2012GL050898. [9] Dickson, J. L., & example, direct insolation on glacial surfaces can result Head, J. W. (2009), Icarus 204, 63-86. [10] McKnight, in local melting, cascading off of the sides of the glaciers, D. M. et al. (1999), BioSci. 49, 985-995. [11] Levy, J. S. and runoff in ephemeral stream channels along the valley (2015), Geomorph. 240, 70-82. [12] Wlostowski, A. N. walls into the melted margins of perennially frozen lakes et al. (2016), Hydr. Proc. 30, 2958-2975. [13] Lyons, W. [14]. At finer scales, where topographic obstacles result et al. (2000), Fresh. Bio. 43, 355-367. [14] Dickson, J. L. in snow drift formation and subsequent melt et al. (2017), GSL Spec. Pub. 467, doi:10.1144/SP467.4. enhancement, saturated groundwater flow can occur atop [15] Levy, J. S. et al. (2011), GSA Bull. 123, 2295-2311. the permafrost ice table [15]. Finally, local [16] Gough, R. V. et al. (2017), EPSL 476, 189-198. [17] concentrations of salts in soils can deliquesce when Doran, P. T. et al. (2010), relative humidity increases [8,16], resulting in doi:10.1017/CBO9780511712258. hydrological linkages in the absence of well-developed stream channels. In tandem, these hydrological systems that form in seemingly unsuitable geographic and environmental regimes demonstrate how it is possible for local extrema can dominate over global norms. Biological Consequences of Cold Polar Conditions: Biologically simple yet metabolically complex ecosystems are present in the MDV and are dominated by microbial communities, mosses, algae, and microinvertebrates. These ecosystems are fueled by ephemeral glacial and snow melt, ions leached from rocks and soils through chemical weathering, and abundant sunlight during the warmer austral summer. Challenges to the growth and development of these ecosystems include long stretches of dark, subfreezing, and dry conditions centered around the austral winter (e.g., Fig. 2). The fact that biological communities were able to form, live, and adapt to the harsh Antarctic environment provides wishful thinking for life on both ancient and modern Mars as well as a useful guide for looking at the metabolic adaptations of such extreme communities [17]. Implications and Conclusions: The MDV are a unique geological, hydrological, and ecological environment on their own. It is one of the few locations on Earth where a plethora of important variables can be isolated, minimized, or even removed when considering the growth and development of ecosystems. For these reasons, in addition to the cold temperatures and limited availability of liquid water, the MDV are a valuable planetary analog environment. Specifically, the MDV demonstrate how and why locally optimized Fig. 2. An active (a) and inactive dry (b) stream channel environmental conditions can dominate important with orange and black mats within the channel thalweg and along the margins, respectively. Inactive mats geological and ecological processes in Antarctica and brighten and become flaky when desiccated. Both (a) suggests that similar optimized conditions may play and (b) are ~2 m wide. (c) A piece of dry black microbial important roles in the evolution of Mars. mat showing the texture of desiccated mat materials. References: [1] Gibson, E. K. et al. (1983), JGR 88, Image is ~5 cm wide.