1777.PDF

THE MCMURDO DRY VALLEYS OF ANTARCTICA AS AN ANALOG FOR PAST AND PRESENT

MARTIAN SURFACE PROCESSES. M. R. Salvatore

, J. S. Levy

, J. W. Head

, and J. L. Dickson

Department

of Astronomy and Planetary Science, Northern Arizona University, mark.salvatore@nau.edu,

Dept. of Geology,

Colgate University,

Dept. of Earth, Environmental, and Planetary Sciences, Brown University,

Division of

Geological and Planetary Sciences, Caltech.

Introduction: The McMurdo Dry Valleys (MDV) of

Antarctica have been considered a valuable martian

analog since the Viking era of Mars exploration [1]. Over

the past two decades, our understanding of martian

environmental and geologic evolution has significantly

improved thanks to the plethora of orbital and landed

missions. New observations have raised many new

enigmatic questions about how cold and dry geological

systems evolve, which has revitalized the MDV as an

important terrestrial analog for Mars, from its earliest

recorded geologic history [2] to the present [3].

Global martian climate models struggle to produce

consistently warm and wet conditions at the martian

surface early in its history, even with the aid of additional

greenhouse gases to offset the distance between Mars and

the faint young Sun [4]. Together with studies suggesting

that snowmelt can satisfy the known distribution of

valley networks in parts of the southern highlands [e.g.,

5], these lines of evidence suggest that early Mars may

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,

snow-fed streams, and ice-covered lakes persist, despite

only ~2 months of melting [3,12]. The hydrological and

habitability gradients operating in the MDV make them

the ideal environment for exploring Mars-like surface

processes that have shaped both planets under both

ancient and modern climate conditions [2,3].

In this work, we highlight the recent developments in

comparative planetology between the martian surface

and the MDV. This work has helped to decipher many

enigmatic climatological and geological features

observed on Mars. We also highlight where additional

work in the MDV is necessary to address outstanding

questions in martian science.

Cold and Icy Early Mars?: The apparent

disagreement between observed fluvial and lacustrine

landforms and the inability for global climate models to

produce mean annual temperatures greater than 0º C

suggest that the martian surface was possibly never

clement from a terrestrial perspective. Instead of a long-

lived and continuously active hydrological system on

early Mars, is it possible that hydrological activity was

more episodic through punctuated climatic excursions on

an otherwise cold and icy early Mars? The fluvial and

lacustrine systems of the MDV are one possible analog

where localized climatic optima drive local hydrological

systems that can cease once conditions are unfavorable

[2,12]. The MDV provide compelling evidence for

comparable landforms found in ancient martian

landscapes. It is therefore possible that hydrological

Fig. 1. Cold desert hydrological landforms on Earth and

Mars. (a) Streams in the MDV. A portion of Quickbird

image 101001000AF37000. North is up. (b) Gullies in

Wright Valley, Antarctica. Gully fans are ~150 m across.

is ~2-3 m wide and flows downstream towards image

bottom. (d) Amazonian valley with flat-topped terminal

fan. Portion of HiRISE image PSP_005950_1401.

North is up. (e) Gullies on Mars. Portion of HiRISE

image ESP_021584_1440. North is up. (f) Recurring

slope lineae (RSL) on Mars. Portion of HiRISE image

PSP_005787_1475. North is up.

1777.pdf51st Lunar and Planetary Science Conference (2020)

systems present in the MDV, where mean annual

temperatures are less than -20º C, can be analogous to

those hypothesized to have formed on early Mars.

Locally Optimized Conditions at Present: Local

influences of topography, geologic resurfacing,

proximity to open water, and the distribution of snow and

glaciers play a major role in controlling local

environmental conditions in polar deserts that lack

vegetation or other modulating influences [13]. For

example, direct insolation on glacial surfaces can result

in local melting, cascading off of the sides of the glaciers,

and runoff in ephemeral stream channels along the valley

walls into the melted margins of perennially frozen lakes

[14]. At finer scales, where topographic obstacles result

in snow drift formation and subsequent melt

enhancement, saturated groundwater flow can occur atop

the permafrost ice table [15]. Finally, local

concentrations of salts in soils can deliquesce when

relative humidity increases [8,16], resulting in

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

environmental conditions can dominate important

geological and ecological processes in Antarctica and

suggests that similar optimized conditions may play

important roles in the evolution of Mars.

References: [1] Gibson, E. K. et al. (1983), JGR 88,

A912-A928. [2] Head, J. W., & Marchant, D. R. (2014),

Ant. Sci. 26, 774-800. [3] Marchant, D. R., & Head, J. W.

(2007), Icarus 192, 187-222. [4] Wordsworth, R. D.

(2016), Ann. Rev. Earth Planet. Sci. 44, 381-408. [5]

Scanlon, K. E. et al. (2013), GRL 40, 4182-4187. [6]

Doran, P. T. et al. (2002), JGR 107,

doi:10.1029/2001JD002045. [7] Heldmann, J. L. et al.

(2013), PSS 85, 53-58. [8] Levy, J. S. et al. (2012), GRL

39, doi:10.1029/2012GL050898. [9] Dickson, J. L., &

Head, J. W. (2009), Icarus 204, 63-86. [10] McKnight,

D. M. et al. (1999), BioSci. 49, 985-995. [11] Levy, J. S.

(2015), Geomorph. 240, 70-82. [12] Wlostowski, A. N.

et al. (2016), Hydr. Proc. 30, 2958-2975. [13] Lyons, W.

et al. (2000), Fresh. Bio. 43, 355-367. [14] Dickson, J. L.

et al. (2017), GSL Spec. Pub. 467, doi:10.1144/SP467.4.

[15] Levy, J. S. et al. (2011), GSA Bull. 123, 2295-2311.

[16] Gough, R. V. et al. (2017), EPSL 476, 189-198. [17]

Doran, P. T. et al. (2010),

doi:10.1017/CBO9780511712258.

Fig. 2. An active (a) and inactive dry (b) stream channel

with orange and black mats within the channel thalweg

and along the margins, respectively. Inactive mats

brighten and become flaky when desiccated. Both (a)

and (b) are ~2 m wide. (c) A piece of dry black microbial

mat showing the texture of desiccated mat materials.

Image is ~5 cm wide.

1777.pdf51st Lunar and Planetary Science Conference (2020)