Reconstructing the past climate at Gale crater, Mars, from hydrological modeling of late-stage lakes Item Type Article Authors Horvath, David G.; Andrews-Hanna, Jeffrey C. Citation Reconstructing the past climate at Gale crater, Mars, from hydrological modeling of late-stage lakes 2017, 44 (16):8196 Geophysical Research Letters DOI 10.1002/2017GL074654 Publisher AMER GEOPHYSICAL UNION Journal Geophysical Research Letters Rights © 2017. American Geophysical Union. All Rights Reserved. Download date 23/09/2021 17:52:57 Item License http://rightsstatements.org/vocab/InC/1.0/ Version Final published version Link to Item http://hdl.handle.net/10150/625822 PUBLICATIONS Geophysical Research Letters RESEARCH LETTER Reconstructing the past climate at Gale crater, Mars, 10.1002/2017GL074654 from hydrological modeling of late-stage lakes Key Points: David G. Horvath1,2 and Jeffrey C. Andrews-Hanna3 • Hydrological modeling and observational constraints at Gale 1Planetary Science Directorate, Southwest Research Institute, Boulder, Colorado, USA, 2Department of Geophysics and crater are used to reconstruct the 3 past climate of post-Noachian Mars Center for Space Resources, Colorado School of Mines, Golden, Colorado, USA, Lunar and Planetary Laboratory, University • Late-stage lake levels in Gale crater of Arizona, Tucson, Arizona, USA require semiarid climates • Subsurface flow may contribute up to half of the water flux into lakes at the Abstract The sedimentary deposits in Gale crater may preserve one of the best records of the early dichotomy boundary Martian climate during the Late Noachian and Early Hesperian. Surface and orbital observations support the presence of two periods of lake stability in Gale crater—prior to the formation of the sedimentary mound Supporting Information: during the Late Noachian and after the formation and erosion of the mound to its present state in the Early • Supporting Information S1 Hesperian. Here we use hydrological models and late-stage lake levels at Gale, to reconstruct the climate of Correspondence to: Mars after mound formation and erosion to its present state. Using Earth analog climates, we show that the D. G. Horvath, late-stage lakes require wetter interludes characterized by semiarid climates after the transition to arid [email protected] conditions in the Hesperian. These climates are much wetter than is thought to characterize much of the Hesperian and are more similar to estimates of the Late Noachian climate. Citation: Horvath, D. G., and J. C. Andrews-Hanna (2017), Reconstructing the past 1. Introduction climate at Gale crater, Mars, from hydrological modeling of late-stage The broad distribution of dendritic valley networks [Craddock et al., 1997; Craddock and Howard, 2002; Hynek lakes, Geophys.Res.Lett., 44, 8196–8204, doi:10.1002/2017GL074654. and Phillips, 2003; Irwin et al., 2005b; Howard et al., 2005; Hynek et al., 2010] and abundant clay bearing units exposed in Noachian-aged terrain [e.g., Pollack et al., 1987; Bibring et al., 2006; Mustard et al., 2008; Murchie Received 19 JUN 2017 et al., 2009; Ehlmann et al., 2011; Carter et al., 2013] led to the idea that early Mars was warmer and wetter Accepted 9 AUG 2017 and likely experienced a hydrologic cycle that included precipitation-induced runoff and stable surface water. Accepted article online 15 AUG 2017 Published online 31 AUG 2017 Morphological studies [Howard, 2007; Barnhart et al., 2009] and discharge estimates [Hoke et al., 2011] of Martian channels supported semiarid to arid climate conditions during the Late Noachian, although other studies argued that the morphology and immaturity of the fluvial systems are more consistent with arid to hyperarid environments on Earth [Stepinski and Stepinski, 2005; Irwin et al., 2011]. An investigation of the sur- face hydrology using open-basin lakes and valley networks in the southern highlands [Matsubara et al., 2011, 2013] suggested a climate similar to the Pleistocene Great Basin region when conditions were wetter and colder during the Last Glacial Maximum. Hydrated clay minerals [Mustard et al., 2008], fan deposits, and fluvial channels discharging into impact basins indicate that water existed on the surface as crater lakes [Forsythe and Blackwelder, 1998; Cabrol and Grin, 1999; Fassett and Head, 2008; Goudge et al., 2012, 2015] over time- scales necessary to deposit and aqueously alter rocks in a lacustrine environment. This early wet period was followed by a transition in the Late Noachian and Early Hesperian to sulfate deposi- tion [Bibring et al., 2006] and potentially subsurface-dominated hydrology [Andrews-Hanna et al., 2007, 2010]. These sulfate-rich sedimentary deposits appear to have been more widespread in the past [Zabrusky et al., 2012], having undergone extensive erosion requiring a period defined by a deeper water table and a cessa- tion of hydrological activity [Andrews-Hanna and Lewis, 2011]. This progression from clay alteration and lake and valley network formation to sulfate deposition and finally to erosion of those deposits indicates an increasingly arid climate beginning in the Late Noachian to Early Hesperian. However, evidence for fluvial activity into the Hesperian and possibly as late as the Amazonian [e.g., Irwin et al., 2005a; Mangold et al., 2008; Hynek et al., 2010; Goudge et al., 2016] indicates that wetter climate conditions than those of the present day may have existed later than previously thought during short-lived episodes. Gale crater, first identified as containing a potential closed-basin lake by Forsythe and Blackwelder [1998], is a Late Noachian to Early Hesperian crater located on the dichotomy boundary and is currently the location of the Mars Science Laboratory (MSL) on the Curiosity rover. In addition to the extensive aeolian erosion, geo- ©2017. American Geophysical Union. morphic observations of Gale crater noted layered deposits in a central crater mound (Aeolis Mons) that All Rights Reserved. had been fluvially eroded, fan deposits on the crater floor, and fluvial dissection of the crater rim [Cabrol HORVATH AND ANDREWS-HANNA LAKE HYDROLOGY AT GALE CRATER 8196 Geophysical Research Letters 10.1002/2017GL074654 and Grin, 1999; Irwin et al., 2005b; Anderson and Bell, 2010; Le Deit et al., 2013; Grotzinger et al., 2015; Palucis et al., 2014, 2016]. Spectral analyses of the Gale crater mound deposit noted the presence of clays at the base of the deposit, mixed with sulfates at higher levels, together making up the lower ~250 m of the mound [Milliken et al., 2010; Thomson et al., 2011]. Recent observations by MSL revealed further evidence for a past wet environment in Gale [e.g., Palucis et al., 2014; Grotzinger et al., 2014; Stack et al., 2014; Siebach et al., 2014]. Mudstone layers forming the basal unit of Aeolis Mons on the crater floor, deltaic deposits extending from the crater rim, and millimeter-scale varves provide evidence for stable lakes in Gale crater and lake sediments forming the basal unit of Aeolis Mons early during the evolution of Gale crater [Grotzinger et al., 2014, 2015; Ehlmann and Buz, 2015; Hurowitz et al., 2017]. In the lower mound, there is evidence for a change in the aqueous environment, from a more neutral lacustrine environment under wetter climates indicated by clay deposits to a more acidic environment under drier conditions indicated by sulfate-bearing aeolian deposits [Milliken et al., 2010; Thomson et al., 2011]. The sulfate deposits are in turn overlain by aeolian deposits with no evidence for aqueous alteration, likely repre- senting ash or dust [Milliken et al., 2010]. The mound deposits were likely more laterally extensive during their deposition, possibly forming a continuous crater-filling deposit [Siebach and Grotzinger, 2014; Grotzinger et al., 2015; Watkins et al., 2017]. This deposit then must have been eroded into its current mound shape. Alternatively, it has been argued that the mound could have formed in its current configuration through aeo- lian processes [Kite et al., 2013]. Evidence for later stage hydrology, after mound formation and erosion, has been identified from fan deposits on the Gale crater floor [Le Deit et al., 2013; Palucis et al., 2016]. Palucis et al. [2016] identified three distinct lake stands based on several Gilbert-style deltaic deposits, similar to those found in lakes on Earth, and other immature fans breaking at roughly the same elevation within Gale crater. Based on the observed elevations of deltas and fans, these lake stands were estimated to fluctuate between À3280 m elevation (followed by a desiccation period), À3980 m, and À3780 m. These lakes were likely active during the Hesperian, though an Amazonian age cannot be ruled out [Palucis et al., 2016]. The large extent of these fan deposits suggests that these lakes persisted for 10,000 to 100,000 years depending on assumed discharge rates in the surrounding catchments and a rock to water ratio of 0.0001 [Palucis et al., 2016]. Although the existence of persistent liquid water ponded within Gale crater both before and after the forma- tion of Aeolis Mons is clearly demonstrated by the orbital and MSL observations, the aridity of the past cli- mate cannot be constrained from the observations alone. Lake levels are a product of the complicated interplay of the surface and subsurface components of the hydrological cycle, which in turn are driven by the climate and the topography of a basin and its watershed. Here we focus on the climate during the wet interludes responsible for the late-stage lakes. We use hydrological models of Gale crater lake to constrain a range of post-Aeolis Mons climates compatible with the lake stands inferred by Palucis et al. [2016] and open- and closed-basin lakes outside of Gale crater [Cabrol and Grin, 1999; Fassett and Head, 2008; Goudge et al., 2012, 2015]. The models assume an average annual temperature above the freezing point of water, a surface hydrology similar to semiarid and arid terrestrial regions, the presence of a porous and permeable aquifer to enable subsurface hydrology, and a range of climates based on scaled terrestrial climates.