Don Juan Pond, Antarctica: Near-surface CaCl -brine feeding Earth’s most saline 2 SUBJECTAREAS: lake and implications for Mars INNERPLANETS ENVIRONMENTALSCIENCES JamesL.Dickson1,JamesW.Head1,JosephS.Levy2&DavidR.Marchant3 CLIMATESCIENCES PLANETARYSCIENCE 1DepartmentofGeologicalSciences,BrownUniversity,Providence,RhodeIsland02912,USA,2CollegeofEarth,Ocean,and AtmosphericSciences,OregonStateUniversity,Corvallis,Oregon97331,USA,3DepartmentofEarthandEnvironment,Boston Received University,Boston,Massachusetts02215,USA. 25October2012 Accepted ThediscoveryonMarsofrecurringslopelineae(RSL),thoughttorepresentseasonalbrines,hassparked 19December2012 interestinanalogousenvironmentsonEarth.WereportonnewstudiesofDonJuanPond(DJP),which existsattheupperlimitofephemeralwaterintheMcMurdoDryValleys(MDV)ofAntarctica,andis Published adjacenttoseveralsteep-slopedwatertracks,theclosestanalogforRSL.ThesourceofDJPhasbeen 30January2013 interpretedtobedeepgroundwater.Wepresenttime-lapsedataandmeteorologicalmeasurementsthat confirmdeliquescencewithintheDJPwatershedandshowthatthis,togetherwithsmallamountsof meltwater,arecapableofgeneratingbrinesthatcontrolsummertimewaterlevels.Groundwaterinputwas notobserved.InadditiontoprovidingananalogforRSLformation,CaCl brinesandchloridedepositsin Correspondenceand 2 basinsmayprovidecluestotheoriginofancientchloridedepositsonMarsdatingfromthetransitionperiod requestsformaterials from‘‘warm/wet’’to‘‘cold/dry’’climates. shouldbeaddressedto J.L.D.(jdickson@ brown.edu) DonJuanPond(DJP),foundatthelowestpoint intheSouthForkofUpperWrightValley,Antarctica (Figure1a),isthemostsalinenaturalbodyofwaterintheworld1.Asaconsequence,itrarelyfreezes,even whenthesurfacetemperaturedescendsto250uCduringAustralwinteranditisauniquesiteforthestudy ofhabitabilityinextremeenvironmentsonEarth2–4,andpotentiallyforlifeonMars2,3.Unlikelarger,ice-covered lakesintheMcMurdoDryValleys(MDV),DJPisisolatedfromfresh,glacialrunoffasitisboundedtothenorth andsouthbysteepinclinesthatexposeoutcropsofgraniticbasementmaterialandJurassic-ageddoleritesills5,to thewestbyachannel-incisedandice-cementedsedimentlobe(alsomappedasaninactiverockglacier)6,7,andto theeast byashallow slope characterized by,20 cm ofcolluvium above an impermeable, ice-cemented per- mafrostlayer8.Multiplewatertracks8areobservedwithinthecolluviumtotheeastofDJP7,asisastream-channel systemattheeasternmostextentoftheDonJuanbasin(Figure1b). Inadditiontothehyper-salinityofDJP(,40%bymass)1,2,10–14,thecompositionofthebrineisunlikeanyother bodyofwaterintheworld,as,90%ofthesaltisCaCl 1,2,10–14.Thus,anymodelthatcansuccessfullyexplainhow 2 saltsaretransportedtoDJPmustalsoexplainhowtheCaCl isisolated.Previousstudieshaveproposedbothdeep 2 groundwater13andnear-surfaceactivelayertransportfortheDJPbrine14,withthemajorityofstudiesfavoring upwellingfromaweathered-doleriteaquifer2,3,13,15.Wesoughttodocumentinputintothepondbymonitoring DJP during Austral spring/summer with high-resolution, long-duration, high-frequency time-lapse pho- tography.Theseobservations,synchronizedwithasuiteofmeteorologicalmeasurementsandviewedincon- junctionwithpreviousstudiesofthegeochemistryofDonJuanbasin,permitareassessmentofthemostlikely contributorstotheunprecedentedsalinityofDonJuanPond. Results SourcesofWaterinDonJuanbasin.SeveralpotentialsourcesforwaterareavailablewithinDonJuanbasin12,14 (Figure 1): (1) direct precipitation (snow); (2) stream input from the western lobe; (3) upwelling of a deep groundwateraquifer;and(4)activelayertransportatopthepermafrosttablewithinthecolluviumeastofDJP. First, while the pond is subject to direct snow precipitation, this produces only between 5 and 10 g/cm2 annually12, most of which is lost via sublimation12,16. Further, while direct snowfall inputs salt into the pond, thereisnoreasonforsnow-depositedsaltstoproduceafractionationinfavorofCaCl 17.Thus,directsnowfallis 2 notconsideredasignificantsourceofwaterand/orCaCl withinDJP. 2 SCIENTIFICREPORTS |3:1166|DOI:10.1038/srep01166 1 www.nature.com/scientificreports Figure1| (A)DonJuanbasinintheSouthForkofUpperWrightValley,McMurdoDryValleys,Antarctica.DonJuanPondisfoundatthelowestpointof thebasin.Thepondisboundedbysteep(,30u)slopestothenorthandsouth,adebris-coveredlobetothewest,andcolluvium-mantledterrainto theeast,wherethemostprominentwatertracksareobserved.IKONOSorbitalcolorimage,acquiredonFebruary1,2009.(B)Theeastern-mostchannels withinDonJuanbasin.Whenactive,thesechannelsproducewatertracksattheirterminithatconnecttothewatertrackonthethalwegeastofDonJuan Pond(Figure2).IKONOSorbitalpan-chromaticimage,acquiredonJanuary31,2003.(C)InsetofDonJuanPondonFebruary1,2009. Second,theviscouslobetothewestofDJP6,7isincisedbyasmall DJP,inwhichupwellingfromaweathereddoleriteaquiferat,60 m network of 1–2 m-wide channels (Figure 1a) that drain into DJP depththroughanunfrozenstratumoflakesedimentsfeedsthepond. during peaksummer conditions through distributaries adjacent to Finally,multiplestudieshaveshownthatwaterflowsacrossthe thewesternedgeofthepond(Figure1c).Severalinvestigations10,12,13 top of the permafrost table east of DJP8,13,18. At the surface, this involvingmajorionanalysisofwaterinthisstreamhaveshownthat processismanifestedaswatertracks8,9,21,22,zonesofhighsoilmois- itislowsalinity(TDS,500 ppm)12andisdepletedinCa21andCl2 ture that act as downslope paths for saline liquids on top of the relative to Na1 and SO 22, respectively13, suggesting a snowmelt permafrost table (,10 cm depth) that wick up to the surface in 4 origin for the water and salt ratios that preclude it from being a low-slope,fine-grainedsoils,creatinglinearpatternsofseasonalsur- candidate for the source of CaCl in DJP. This corroborates our facedarkening8,9(Figure1a,b).Geochemicalmeasurements14ofthis 2 ownfieldobservationsthatthiswaterissourcedbychannel-trapped liquidtotheeastofDJPshowedthat,likeDJP,itisenrichedinCa21 snowonthesurfaceofthewesternlobe. relativetoNa1andhaslowNa1/Cl2ratios,consistentwithrecent Third, previous studies have attributed the extreme salinity to measurements of water tracks in the Lake Hoare basin in Taylor upwellingofarelativelydeep(tensofmeters)bedrockaquifer2,13,15. Valley6.ThisCa21andCl2enrichmentledWilson14toproposethat Electricaldepthsoundings19,20andseismicprofiles20providedcon- salts left by sublimated snow at the surface are separated when sistentfindingsthattheterrainbeneathDJPisunfrozentodepthsof humidityfrontspassthroughDonJuanbasin.Saltsthatdeliquesce tensofmeters.Abruptshiftsinbothseismicvelocityandresistivity at lower relative humidity (like CaCl ) are more mobile. During 2 wereobservedat,30 mdepthontheeasternmarginofthepond, humidity optima, they preferentially deliquesce and percolate andthisinterfaceslopedto,60 mdepthbelowthewesternmargin through the colluvium until they encounter the impermeable per- ofDJP.Thegeophysicalpropertiesofeachmediumwereinterpreted mafrosttable.Oncethere,humidity-separatedbrinescanbetrans- as unfrozen basement rock superposed by wet lacustrine deposits portedtoDJPviaflushingbyseasonalsnowmelt8from(1)astream immediatelyunderlyingthepond20.Samplesofwatercollecteddur- channelattheeasternmostextentofDonJuanbasin(Figure1b)or ingtheDryValleyDrillingProject(DVDP)showedthatsubsurface (2) alcove-trapped snowpacks that accumulate above steep-sloped waterbeneaththepondwasenrichedinCaCl ,thoughtherewasa watertracks(Figure1a)8. 2 contrastinweightpercentofthetotalsolutionbetweensamplesat Time-lapseobservationsandmeasurementsofrelativehumidity thesurfaceandsamplesatdepth:17%and18%CaCl concentration thatweobtainedofthethalwegeastofDonJuanPond(Figure1a)in 2 forsamplesfrom15 mand58 mdepth,respectively,versus34%for December,2010,showthatwatertracksrapidlyrespondtomoistair surfacewaters13.Giventhatevaporationatthesurfacecouldconcen- byhydratinganddarkening(Figure2),demonstratingthatdeliques- tratethesalts,thisledtotheprevailingmodelfortransportofsaltsto cence and brine hydration is an active process within the DJP SCIENTIFICREPORTS |3:1166|DOI:10.1038/srep01166 2 www.nature.com/scientificreports Figure2|Framesfromatime-lapsesequenceofwatertrackdarkeningonthethalwegofSouthFork(locationinFigure1a). Fullsequencecanbe accessedviasupplementaryinformation.DarkeningoccurswhiletheentiresceneisundertheshadowoftheAsgardRangetothesouth,ensuringthat darkeningisnotaphotometriceffectfromvariablesolarincidenceangle.Thedarkeningdirectlycorrelateswithasteepincreaseinrelativehumidity,such thatsaltsinthewatertrackareabsorbingwaterfromtheatmosphere(deliquescence),andthathydrationofthesebrinesmoistensthesurface. RelativehumiditymeasurementisfromameteorologicalstationontheedgeofDJP,,975mupvalley/downslopefromtheobservation(Figure1c).This samesteepincreaseinrelativehumiditywasobserved15minutesearlieratanothermetstation1.1kmdownvalley/upslopefromthissite.Thisis consistentwithamassofmoistairmovinginlandfromthecoasttowardstheicecap. watershed. Since the water track on the thalweg east of DJP was proxy for volume) from (1) deep groundwater upwelling from the alreadyrelativelydampcomparedtothesurroundingterrainatthe centralandsouthernportionofthepond,(2)watertrackdischarge outset due to drainage from snowmelt channels found upslope fromtheeast,wherewatertracksareobserved,and(3)freshsnow-fed (Figure1b),thisprocessappearstoconcentrateatmospheric-derived stream discharge from the west. This imaging campaign was per- moistureinhighsalinitysoils,ratherthanuniformlydampeningall formed in concert with soil moisture measurements on one of the soils23. steep-slopewatertracksabovethepondtotheeast(Figure1a),aswell Here, we evaluate the relative importance of these hydrological asasuiteofmeteorologicalobservationsacquiredfromtheeastern- processesbyexamininginteractionsamongwatertracks,snow-fed mostportionofthesaltpansurroundingthepond(Figure1c). steams,andputativegroundwaterdischarge.Sinceitisnotrecharged Ourtime-lapseobservationsofDJPshowthatdischargeintothe by glacial meltwater, DJP is very shallow (generally , 10 cm1,10 pondiscontrolledbydiurnalsurfacetemperaturecycles,whicharea thoughitcandeepento,23 cm20).Thus,detailedmonitoringdur- functionofinsolation(Figure3).Whilethesundoesnotastronom- ing a relatively low precipitation year provides the opportunity to icallysetduringthistimeperiodintheMDV,thesteepsouthernwall detect inputs into the pond. During the 2009–2010 summer field ofUpperWrightValleycreatesadiurnalshadowingofthefloorof season, we imaged the pond at 5-minute intervals from late theDonJuanbasin(Figure1a),suchthatsurfaceconditionspermit November 2009 through January 2010 from the southern end of meltingofnear-surface/surfaceiceduringthedaybutnotatnight, the Dais, a mesa perched ,750 m above DJP (see Figure 1a for when the sun is behind the Asgard Range to the south (approxi- vantage point). From the 16,280 acquired images during this mately22:00to06:15thenextmorningatsummersolstice). timespan,wemappedallevidenceforinputintothepondinorder Usingpondsurfaceareaasaproxyforvolume,time-lapseimage to evaluate the magnitude of contributions to lake surface area (a datarevealthatthemostsignificantinputofliquidintoDJPcomes Figure3|Time-lapseimagepairofdischargeintoDonJuanPondonDecember11,2009,withdischargeobservedfromboththewestandtheeast.Full time-lapsesequenceshowingactivitythroughoutlate-spring/early-summercanbeaccessedviasupplementaryinformation.Imageswereacquiredat5- minuteintervalsfromthesouthernmarginoftheDais(seeFigure1aforvantagepoint).Dailypulsesoffreshwaterinputfromstreamactivityatopthe adjacentdebris-coveredlobeareobservedtocomefromthewest,whilesmallswarmsofdischargeareobservedtocomefromtheeasternmarginofthe pond.TheseseepsareinterpretedtobedischargeofCaCl -richbrinesthataretransportedthroughthedryactivelayereastofthepondonthetopofthe 2 permafrosttable.Pulsescorrelatewithdiurnalincreasesinsurfacetemperature(measurementsacquiredfromameteorologicalstationonthe easternmostedgeoftheDJPsaltpan–seeFigure1cforlocation). SCIENTIFICREPORTS |3:1166|DOI:10.1038/srep01166 3 www.nature.com/scientificreports Figure4|ThesurfacetemperaturerecordfromthesaltpansurroundingDonJuanPondwithdischargeeventsfromtheeasternmarginofDJP (reddashedlines).Dischargefromtheeasternmarginofthepondisdirectlycorrelatedwithsteepincreasesinsurfacetemperature,whichiscontrolledby diurnalcyclesinpeakinsolation. from the freshwater stream that incises the lobe adjacent to the The other observed input to DJP is discharge from the eastern westernmarginofthepond(Figure3).Snowandicetrappedwithin marginofthepond(Figure 3),observable on30ofthe52days of the channel melt and produce surface area-expanding pulses that thestudy(Figure4).Insteadofonemajorpulse,asisobservedfrom extend nearly across the entire pond on particularly warm days the freshwater stream to the west of the pond, this discharge is (Figure 3). These pulses occur at the same time of day as sudden characterized by smallswarms ofindividual pulses that startfrom spikesinthehydrographmeasurementsofHarrisandCartwright13 large boulders embedded in the lake sediments (Figure 5) and fromearlyDecember1975thattheyinterpretedasseiches.Thewater migratetowards thecenterofthepond. Likethelarger freshwater pulsessoakintotheunderlyinglacustrinesedimentsonthefloorof pulsesfromthewest,thesepulsesarestronglycorrelatedwithsteep thepond,fillingporespacesinthepondshorezone.Samplesfrom increases in surface temperature (,8–10uC over ,5–7 hours), as previousstudieshaveshownthatthiswaterisfresh10,12,13andhasan activity is always observed during peak insolation conditions ionic ratio that precludes it from being the primary driver of DJP (Figure 4). There is little to no lag between peak temperature and chemistry. discharge, suggesting that warming is not propagating into a deep aquifer.In16,280images,thesesmallpulsesareonlyobservedonthe easternmarginofthepond,whichisaboveandoutsideofthepoten- tialgroundwaterdischargezoneidentifiedbyHarris&Cartwright13. Detailedobservationsofthebouldersontheeasternmarginofthe saltpanofDJP(Figure5)showthattheyfrequentlyhostpondliquid intheirannularmoats,whileothershostbrighthalosofevaporites, relationshipsnotcommonlyobservedaroundotherportionsofthe pond. In some cases, the pond liquids overtop their moats in the direction of the center of the pond and flow downslope (Figure5d).BouldersgeneratebreaksinslopeinotherDryValley watertracks,wheretheyactasspringsthatdischargeattheground surface9,24,25,asobservedelsewhereinSouthFork26. In order to determine if liquids were flowingthrough thewater trackseastofDJP(Figure1a)atthetimethatdischargewasobserved on the eastern margin of DJP (Figure 3), we instrumented one of thesteep-sloped watertracks8withDecagonECH Osoilmoisture 2 probesonandoffofthetrackstartingonDecember10,2009(loca- tion in Figure 1a). Soil moisture onthe water track is consistently greater than soil moisture 1 m off the track’s eastern margin (Figure 6). A noticeable increase in soil moisture on the track Figure5|(A)DischargelocationsontheeasternmarginofDonJuanPond occurredcloseto1January,whichfollowedaweek-longperiodof (seeFigure1cforlocation).(B)Multiplenearbybouldersareobservedto extremelywarmconditionswhensurfacetemperatureswerenever haveliquiddischargedatthesurface,consistentwithbouldersdepressing below 0uC and peak surface temperatures approached 20uC. This thenear-surfacepermafrosttable.(C)Alargeboulderhostsliquidinthe ,1-weeklagbetweenincreasedsurfacetemperatureandwatertrack downslopeportionofitsannularmoat.(D)Aboulderisnearlyburiedby moistureincreasesisrepeatedseveraltimesthroughourthree-year dischargedliquidthatisflowingdownslope,inthedirectionofDJP.Image temperature/soil-moisture record of this site (austral spring 2009 wasacquiredonDecember8,2009,whentime-lapseobservationsshow through austral summer 2012), which favors a scenario by which dischargefromthisportionofthepond(Figure4). fresh meltwater from (1) seasonal snow trapped in alcoves at SCIENTIFICREPORTS |3:1166|DOI:10.1038/srep01166 4 www.nature.com/scientificreports Figure6|Soilmoisturerecordedonandoffofoneofthemajorsteep-slopedwatertracksonthesouthern(equator-facing)wallaboveDonJuanPond (seeFigure1aforlocation). Sensorswereplaced1-meteronthetrackand1-meteroffthetrack.Valueswererecordedevery15minutes,andplottedas 24-houraverages.Activityisclearlyconcentratedentirelywithinthetrack.Increasedsoil-moistureactivityduringthemiddleofJanuarycorrespondsto themostconcentratedactivityofdischargeintoDJPfromitseasternmargin. the heads of the steep-sloped water tracks8 and (2) perennial readings14,includingthosewithwatertrackswithintheirwatershed9. snowbanksatthebaseoftheneighboringAsgardRange27percolates Water tracks that drain into larger fresh-water lakes contribute downslope and flushes the deliquescence-derived CaCl2 brine CaCl -rich brines that are denser than the more-abundant 2 downslope towards DJP, using the channel system at the eastern- freshwater9.Therefore,thebrinesshouldbeconcentratedatthebase, mostextentofDonJuanbasinasaconduit(Figure1b).Soilmoisture a trend that is observed14. Furthermore, water circulation in the on the track also remained elevated from January 7 through the absence of a deep groundwater connection makes this a plausible end of the month (Figure 6). On the eastern margin of DJP, modelforahydrologicsystemonpresent-dayMars,whereextremely pulses from the east were observed on 13 of the 15 days from low temperatures (255uC annual average, 127uC maximum, January7untilJanuary22,whendatacollectionceasedfortheseason 2143uC minimum; in comparison with an annual average of (Figure4). 220uC,monthlyaveragemaximumof11uC,andmonthlyaverage minimumof254uC)atalllatitudes and aglobalpermafrostlayer Discussion shouldlargelyprecludedeepaquiferinteractionwiththesurface,and OurobservationsindicatethatdischargeofCaCl -richbrinesthatflow forancientMars,whensurfacewatersweremoreabundant. 2 across the top of the permafrost table are the likely source for the ThefeaturesthatfeedCaCl toDJP,watertracks(Figure1a,b),are 2 extremesalinitymeasuredinDJP.EvidenceforinternalfillingofDJP similar in planform morphology to recently discovered Recurring fromupwellingofadeepaquiferwasnotfoundduringourimaging Slope Lineae (RSL) in the southern mid-latitudes of Mars: low- campaign. The only two liquid sources that provided measurable albedostreaksofsoilonsteep(,30u)slopesthatadvanceandrecede changes to DJP surface area from November 27, 2009 to January each martian year, initiating when surface temperatures approach 22,2010werefreshwaterstreamdischargefromthewestand active the melting point of H O28. Downslope propagation rates for RSL 2 water track transport fromthe east. Evaporative mixtures ofstream andAntarcticwatertracksareconsistentwitheachbeingformedby waterandwatertrackfluidscanaccountforthechemistryofDJPand brineflowthroughashallowregolith,basedonremotelymeasured produce the observed filling and hydrograph patterns reported by averagepermeabilityvaluesof1028to1029 cm2forRSLand1026to HarrisandCartwright13.Asthistransportmechanismmoreeffectively 1027 cm2, which are consistent with fluid flow through sandy, explainstheabundanceofCaCl comparedtoothersalts11,itreadily unconsolidatedsediments29. 2 accountsforallofthegeochemicalmeasurements11–14inadditionto CouldaDJP-likehydrologicalsystembeactiveonmodernMars? theflow-directionobservationsdocumentedinthisstudy(Figure3). Chloride-bearingsaltshavebeendocumentedonMarsfrombothin- Theseresultsalsoprovideamodelinwhichitispossibletomain- situ30andremote31observations,andpeakdailytemperaturesonthe tain ecosystem-sustaining hydrological systems in Earth’s coldest warm,equator-facingslopeswhereRSLareobservedfrequentlysur- and driest environments entirely through atmospheric interaction pass 0uC28. Seasonal water frost is observed on the surface in with the surface, without invoking deep groundwater resources. hyperspectraldataatlatitudesaslowas12uinthesouthernhemi- Therefore, this model may have broad implications, explaining sphere32,33,suchthatsufficientatmosphericwatervaporisavailable whylarger,ice-coveredMDVlakestendtohavehighbasalsalinity to initiate relative deliquescence at mid-latitudes, where RSL are SCIENTIFICREPORTS |3:1166|DOI:10.1038/srep01166 5 www.nature.com/scientificreports found.Therefore,theessentialconditionsforaDJP-likehydrological 6. Hassinger,J.M.&Mayewski,P.A.Morphologyanddynamicsoftherockglaciers systemmaybetransientlyachievableoncontemporaryMarsatRSL- inSouthernVictoriaLand,Antarctica.ArcticAlpineRes.15,351–368(1983). 7. Morgan,G.A.,Head,J.W.,Marchant,D.R.,Dickson,J.L.&Levy,J.S.Interaction bearinglocations. betweengulliesandlobatedebristonguesonMarsandintheAntarcticDry Chloride-bearing units exposed within topographic basin floors Valleys.LunarPlanet.Sci.Conf.39,2303(2008). have also been mapped from orbit in the southern hemisphere of 8. Head,J.W.,Marchant,D.R.,Dickson,J.L.,Levy,J.S.&Morgan,G.A.Slope Mars31.UnlikeRSL,whichareactivetoday,theseunitsareprimarily streaksintheAntarcticDryValleys:Characteristics,candidateformation mechanisms,andimplicationsforslopestreakformationintheMartian found within ,4 Gyr old Noachian terrain, suggesting that they environment.OnlineProc.ofthe10thISAES#177(2007). were deposited early in Mars’ history when conditions were more 9. Levy,J.S.,Fountain,A.G.,Gooseff,M.N.,Welch,K.A.&Lyons,W.B.Water conducivetoliquidwaterstabilitythantoday.Thechemicalsepara- tracksandpermafrostinTaylorValley,Antarctica:Extensiveandshallow groundwaterconnectivityinacolddesertecosystem.GSABulletin123, tion and transport mechanisms that produced these units are 2295–2311(2011). notwellunderstood,butthecold-desertmodelprovidedbyDJPof 10.Yamagata,N.,Torii,T.&Murata,S.Chemicalcompositionoflakewaters.Report humidity-induced relative deliquescence may be applicable, pro- oftheJapaneseSummerPartiesinDryValleys,VictoriaLand,1963–19655, videdthattheywereformedintheabsenceofpluvialactivity14. 53–75(1967). 11.Torii,T.,Yamagata,N.,Ossaka,J.&Murata,S.SaltbalanceintheDonJuanbasin. While the volumes of freshwater available to these hydrologic AntarcticRecord(NIPR)58,116–130. systems on Mars is unknown, recent work in the Atacama desert 12.Harris,H.J.H.,Cartwright,K.&Torii,T.Dynamicchemicalequilibriumina hasprovidedin-situdocumentationofcyanobacteriathatarecap- polardesertpond:Asensitiveindexofmeteorologicalcycles.Science204, ableofsubsistingentirelyonthebrinescreatedfromdeliquescencein 301–303(1979). haliterocks34,averylocalizedecological modelthat hasbeenpro- 13.Harris,H.J.H.&Cartwright,K.HydrologyoftheDonJuanBasin,WrightValley, Antarctica.InDryValleyDrillingProject,Ant.Res.Ser.33,ed.McGinnis,L.D. posed for Mars in the past35. Furthermore, work in the MDV has AmericanGeophysicalUnion,Washington,D.C.,161–184(1981). shown that certain organisms are capable of being preserved in a 14.Wilson,A.T.GeochemicalproblemsoftheAntarcticdryareas.Nature280, cryptobioticstatefordecades,thenflourishonceexposedtostream 205–208(1979). waters36.Thus,ifRSLandchloride-bearingbasinfloorunitsonMars 15.Carlson,C.A.,Phillips,F.M.,Elmore,D.&Bentley,H.W.Chlorine-36tracingof salinitysourcesintheDryValleysofVictoriaLand,Antarctica.Geochim. dorepresentDJP-likehydrologicsystems,theymayhavesignificant Cosmochim.Acta54,311–318(1990). potential for hosting resilient microbiota, and the most habitable 16.Fountain,A.G.,Nylen,T.H.,Monaghan,A.,Basagic,H.J.&Bromwich,D.Snow placesonMarsmaymimictheleasthabitableplacesonEarth. intheMcMurdoDryValleys,Antarctica.Int.J.Climatol.30,633–642(2010). 17.Lyons,W.B.,Welch,K.A.,Fountain,A.G.,Dana,G.L.,Vaughn,B.H.& McKnight,D.M.SurfaceglaciochemistryofTaylorValley,southernVictoria Methods Land,Antarcticaanditsrelationshiptostreamchemistry.HydrologicalProcesses ThecolorimageinFigure1aand1cwasacquiredonFebruary1,2009andis 17,115–130(2003). composedof4m/pixelIKONOSmulti-spectraldata(Blue:0.445–0.516mm;Green: 18.Levy,J.S.,Head,J.W.&Marchant,D.R.Theroleofthermalcontractioncrack 0.506–0.595mm;Red:0.632–0.698mm),pan-sharpenedinENVIto1m/pixelusing polygonsincold-desertfluvialsystems.AntarcticScience20,565–579(2008). 1m/pixelpanchromaticimagery(0.45–0.90mm).ThegrayscaleimageinFigure1b 19.McGinnis,L.D.&Jensen,T.E.Permafrost-hydrogeologicregimenintwoice-free wasacquiredonJanuary31,2003andconsistsof1m/pxpanchromaticimagery valleys,Antarctica,fromelectricaldepthsounding.QuaternaryResearch1, (0.45–0.90mm).BothimageswereorthorectifiedinENVIusing200m/pixel 389–409(1971). RADARSATtopographydataandrenderedinArcMapinLambertConformalConic 20.McGinnis,L.D.,Nakao,K.&Clark,C.C.Geophysicalidentificationoffrozenand projection(centralmeridian:162uE;StandardParallel1:76.66667uS;Standard unfrozenground,Antarctica.2ndInt.Conf.onPermafrost(N.A.Contribution), Parallel2:79.33333uS;LatitudeofOrigin:78.0uS). 136–146(1973). 21.Hastings,S.J.,Luchessa,S.A.,Oechel,W.C.&Tenhunen,J.D.Standingbiomass Thetime-lapseimageryfromDecember2010(Figure2)wasacquiredat2-minute andproductioninwaterdrainagesofthefoothillsofthePhilipSmithMountains, intervalswithafirmware-modifiedCanonPowerShotSX1digitalcamera,locatedat Alaska.HolarcticEcology12,304–311(1989). 77.563uS,161.256uE.RelativeHumiditywasmeasuredusinganOnset12-bit 22.McNamara,J.P.,Kane,D.L.&Hinzman,L.D.Ananalysisofanarcticchannel Temperature/RHprobe(S-THB-M002)insideasolarradiationshield,sampling networkusingadigitalelevationmodel.Geomorphology29,339–353(1999). every3minutes(averagedforonereadingevery15minutes)2mabovethesurfaceon 23.Levy,J.S.,Fountain,A.G.,Welch,K.A.&Lyons,W.B.Hypersaline‘‘wetpatches’’ theeasternmostedgeofthesaltpansurroundingDonJuanPond(77.563uS, inTaylorValley,Antarctica.Geophys.Res.Lett.39,L05402(2012). 161.208uE).Dataandtime-lapseimageryweresynchronizedusingproprietary 24.Lyons,W.B.,Welch,K.A.,Carey,A.E.,Doran,P.T.,Wall,D.H.,Virginia,R.A., softwarewrittenbytheauthorsthatcorrelatestimestampsonimageswith Fountain,A.G.,Tremper,C.M.&Csatho,B.M.GroundwaterseepsinTaylor meteorologicaldatatables,suchthateachimageisnomorethan7.5minutesbefore/ ValleyAntarctica:anexampleofasubsurfacemeltevent.AnnalsofGlaciology40, afterthecorrelatedmeasurement(whichisloggedevery15minutesinanOnset 200–206(2005). HOBOMicrostation). 25.Harris,K.J.,Carey,A.E.,Lyons,W.B.,Welch,K.A.&Fountain,A.G.Soluteand Thetime-lapseimageryfromJanuary2010(Figure3)wasacquiredat5-minute isotopegeochemistryofsubsurfaceicemeltseepsinTaylorValley,Antarctica. intervalswithafirmware-modifiedCanonPowershota590ISdigitalcamera,located GSABulletin119,548–555(2007). onthesouthernmarginoftheDais(77.551uS,161.176uE).Groundsurface 26.Levy,J.S.,Head,J.W.,Marchant,D.R.,Morgan,G.A.&Dickson,J.L.Gully temperaturewasrecordedatthesurfaceoftheeasternmostedgeofthesaltpan surfaceandshallowsubsurfacestructureintheSouthForkofWrightValley, surroundingDonJuanPond(77.563uS,161.208uE)withanOnset12-bit AntarcticDryValleys:ImplicationsforgullyactivityonMars.Lun.Planet.Sci. Temperatureprobe(S-TMB-M002)located,2cmbelowthesurfaceloggedbyan Conf.38,1728(2007). 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Additionalinformation Acknowledgments Competingfinancialinterests:Theauthorsdeclarenocompetingfinancialinterests. InvaluableengineeringassistancewasprovidedbyBrendanHermalynandJohnHuffman. License:ThisworkislicensedunderaCreativeCommons WeappreciatefieldassistancefromMikeWyatt,MarkSalvatore,LauraKerber,Sylvain Attribution-NonCommercial-NoDerivs3.0UnportedLicense.Toviewacopyofthis Piqueux,J.R.Skok,andDavidHollibaugh-Baker.InfrastructuresupportfromRaytheon license,visithttp://creativecommons.org/licenses/by-nc-nd/3.0/ PolarServicesatMcMurdoStationandhelicoptersupportfromPetroleumHelicopters Howtocitethisarticle:Dickson,J.L.,Head,J.W.,Levy,J.S.&Marchant,D.R.DonJuan International(PHI)arealsogratefullyacknowledged.SoftwaresupportfromCalebFassett Pond,Antarctica:Near-surfaceCaCl2-brinefeedingEarth’smostsalinelakeand expeditedtheanalysisportionofthispaper. implicationsforMars.Sci.Rep.3,1166;DOI:10.1038/srep01166(2013). SCIENTIFICREPORTS |3:1166|DOI:10.1038/srep01166 7