University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USGS Staff -- ubP lished Research US Geological Survey 1989 STABLE ISOTOPES IN PRECIPITATION AND GROUND WATER IN THE YUCCA MOUNTAIN REGION, SOUTHERN NEVADA: PALEOCLIMATIC IMPLICATIONS Larry Benson University of Colorado at Boulder, [email protected] Harold Klieforth Desert Research Institute Follow this and additional works at: http://digitalcommons.unl.edu/usgsstaffpub Benson, Larry and Klieforth, Harold, "STABLE ISOTOPES IN PRECIPITATION AND GROUND WATER IN THE YUCCA MOUNTAIN REGION, SOUTHERN NEVADA: PALEOCLIMATIC IMPLICATIONS" (1989). USGS Staff -- Published Research. 789. http://digitalcommons.unl.edu/usgsstaffpub/789 This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Staff -- ubP lished Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Geophysical Monograph Series Aspects of Climate Variability in the Pacific and the Western Americas Vol. 55 Geophysical Monograph 55 STABLE ISOTOPES IN PRECIPITATION AND GROUND WATER IN THE YUCCA MOUNTAIN REGION, SOUTHERN NEVADA: PALEOCLIMATIC IMPLICATIONS Larry Benson InterdisciplinaryClimate SystemsGroup Room 135, National Center of AtmosphericResearch, Boulder, CO 80307 Harold Klieforth AtmosphericSciences Center Desert Research Institute, Reno, NV 89506 Abstract. Unadjustedages of ground-watersamples indicate that most recordof lake-levelchange in the Lahontanbasin was principallya func- rechargein the Yucca Mountain and AmargosaDesert areasof southern tion of the size and extent of the continental ice sheet. When the ice sheet Nevadamay have occurred between 18,500 and 9000 yearsbefore present. was large (Figure 1), the polar-front jetstream was forced over the Comparisonof thestable-isotope ½180-•5D)concentrations in this water southwesternUnited Statesand provided sufficienteffective moisture,in with stable-isotopeconcentrations in precipitationin the southernNevada terms of increasedprecipitation and cloudiness,for the formationof high- area indicatesthat ground-waterrecharge occurred by infiltrationof cold- standlakes [Bensonand Thompson, 1987a,b; Lao and Benson, 1988]. seasonprecipitation. Infiltration of snowmeltalong the bottom of Fortymile Bensonand Thompson [ 1987b]observed that the maximumextent of Late Canyonseems to be the mostlikely rechargemechanism for YuccaMoun- Wisconsinglacation in the northernpart of the Great Basin precededthe tain groundwater. Ground-water recharge in southernNevada was nearly higheststand of Lake Lahontan[Dorn et al., 1987]. This indicatesincreased synchronouswith the last lake cycle in the Lahontanbasin in northern moistureavailability at a time when glaciersin the upper reachesof water Nevada. This regional-scalechange in the hydrologicbalance occurred shedswere retreating.To explainthis observationBenson and Thompson duringthe transitionfrom maximum-glacialto interglacialconditions and [1987a] hypothesizedthat the seasonalityof precipitationshifted to warmer wasassociated with a changein thelocation of theair-parcel moisture-source regionin the easternPacific Ocean and with a warmingof the climatebe- tween 18,500 and 9000 years before present. In the study area the temperatureof condensationof precipitationthat infiltratedto the watertable a•80planktonic • increasedby about5 øC. The warmingtrend also contributedto the re- foraminifera/• cessionof mountainglaciers in northernNevada. Recent atmospheric global (AtlanticOcean)/ / climatemodel simulations provide an integratingtheory that accountsfor the near synchroneityof ice sheet,lake, and ground-watercycles. In the modelthe positionand persistence of thejetstream, which is associatedwith oll the progressionof maximumeffective precipitation, is substantiallyaffected by the size and shapeof the continentalice sheet. 0 /•---•%%_ Alternate Introduction • • • • '% lakelevels In a recentpaper Benson and Thompson [1987a] suggestedthat the timing foraminifera of the lasthighstand lake in the Lahontanbasin was associatedwith change in the mean positionof the jetstreamduring the Late Wisconsin.Recent (AtlanticOcean) atmosphericglobal climate model (AGCM) results[Kutzbach and Wright, 1985; Manabe and Broccoli, 1985; Kutzbachand Guetter, 1986; Kutzbach, 1987; andRind, 1987] supportthis concept. These studies have shown that between 18,000 and 15,000 years before present(yr B.P.) significant changesoccurred in the glacial age circulation at both the surfaceand jetstreamlevels that primarily were the resultof glacialage lower boundary conditions(ice-sheet size, sea level, sea-iceextent, sea-surface temperature, 0 5 10 15 20 25 30 35 and landalbedo). This widespreadchange indicates the possibilitythat the 103 Year B. P. Fig. 1. Graphcomparing the Lahontanlake-level record and the •5180 This paper is not subjectto U.S. copyright. Publishedin 1989 by recordsfor Atlantic Oceanplanktonic and benthicForaminifera (seetext the American Geophysical Union. for data sources). 41 Geophysical Monograph Series Aspects of Climate Variability in the Pacific and the Western Americas Vol. 55 42 STABLE ISOTOPES SOUTHERN NEVADA 16ø45' 116ø30' monthsor, alternatively, wintersbecame warmer. It is also possiblethat 37ø00' the climatebecame generally warmer, but evaporationover lake basinswas NEVADA reducedby persistentcloud cover. This paperaddresses the question:What typeof climaticchange occurred CarsonCity in the Great Basin between 18,500 and 9000 yr B.P.? It does so by ex- aminingthe Great Basin Late-Wisconsinclimatic and hydrologicchange (lake level, groundwater and glacial cycles)in terms of the isotope(&D and• 80) concentrationsin ground water recharged in theYucca Moun- Approximateboundary tain areaof southernNevada since about 18,500 yr B.P. (Figure 2). Yucca of Yucca Mountain Mountain, which lies about350 km southof the geographiccenter of Lake exploratoryblock Lahontan, is the nearest area where a reasonable amount of data exist on the timing and isotopicchemistry of ground-waterrecharge during the Late Wisconsin.The climaticconditions existing during recharge were inferred usingthe light-isotopicconcentration of present-dayprecipitation known Crater Fiat as a function of four interrelatedvariables (season,air temperature,air- parcel trajectory and altitude). ©VH-1 36ø45' 1350 I I I I I I • I Amargosa • 1300- '-"' • , ', Lake-levelcurve • x forthe western , ahont, / 5m, // • 1200- _•'½/ / I l•0km 1150- -- -6 Fig. 3. Map showinglocation of selectedtest wells in the Yucca Moun- !• Distributionofgroundwater ages forthe Yucca Mountain and z tain area. - sa Desedareas - 5 - -4½ a maximumvalue. In their calculationsWhite andChuma [1987] usedpure water to representthe compositionof rechargewater and allowedcalcium - -3 carbonate(containing 100 percentdead carbon) to dissolveuntil the com- positionof the simulatedground water was the sameas the composition _ _2 • of the actualground water. The quantityof deadcarbon input to the water wasthen used to correct the •4C age of thesample. However, distribution- - -1• of-speciesand saturation-statecalculations using EQ3NR indicate that present-dayfloodwaters (thought to representthe rechargesource for J-12, 0 5 10 15 20 25 30 35 4•¸ J-13 and UE-29a # 2 groundwater [Claassen,1985]) in FortymileWash 10 3 Year B. P. are saturatedwith calciumcarbonate and contain 100 percentmodern car- bon. Input of floodwaterchemical compositions to EQ3NR/EQ6 simula- FiB. 2. Graphcomparin8 the L•ontan lake-levelrecord with the distribu- tionsof the compositionof YuccaMountain ground water, therefore,are tion of unadjusted8round-water abes Jn the •ucca Mountainand Amar8osa expectedto resultin relativelysmall •4C corrections. Desert areas. From August1983 through August 1986, 429 precipitationsamples were collectedat 12 southernNevada stations (Figures 4 and 5). The latitude, longitude,and altitudeof eachstation are listedin Table 2. The sampling Methods intervalof precipitationsamples was halted within 24 hoursafter the cessa- tion of precipitationin order to isolateindividual precipitation events and Ground water from several wells located on or near Yucca Mountain, minimizethe effect of evaporationon the isotopiccontent of the sample. Nevada, (Figure 3) were sampledand analyzedfrom 1971 to 1984 by The dateand approximatetime thatprecipitation began and ended and the membersof the U.S. GeologicalSurvey. Drilling, samplingand analytical volumeand the type of precipitation(rain, snow, or hail) were recorded. proceduresare thosedescribed in Bensonet al. [ 1983]. The isotopiccom- In June1985 CampbellScientific 21X Microloggers(use of brand, firm, positionand unadjustedradiocarbon ages of the water samplesare listed or trade namesin this report is for identificationpurposes only and does in Table la and lb [Bensonand McKinley, 1985]. not constituteendorsement by the U.S. GeologicalSurvey) were installed Age adjustmentof threeground-water samples (J-12, J-13, UE29-a #2) at sevenprecipitation collection stations (Figure 5). Eachmicrologger was have been attemptedpreviously [White and Chuma, 1987] using the connectedto a temperatureprobe and to a tipping-bucketrain gage. The EQ3NR/EQ6software package [Wolery 1979, 1985]. Corrected •4C ages microloggerrecorded Julian date, time, temperature,and rain-gage bucket of eachof the ground-watersamples were about2000 yearsless than unad- tips at 15-minuteintervals. Prior to the installationof microloggers,data