University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USGS Staff -- ubP lished Research US Geological Survey 2002 HIBAL: a hydrologic-isotopic-balance model for application to paleolake systems Larry Benson University of Colorado at Boulder, [email protected] Fred Paillet US Geological Survey Follow this and additional works at: http://digitalcommons.unl.edu/usgsstaffpub Benson, Larry and Paillet, Fred, "HIBAL: a hydrologic-isotopic-balance model for application to paleolake systems" (2002). USGS Staff -- Published Research. 784. http://digitalcommons.unl.edu/usgsstaffpub/784 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. Quaternary Science Reviews 21 (2002) 1521–1539 HIBAL: a hydrologic-isotopic-balance model for application to paleolake systems Larry Bensona,*, FredPaillet b a US Geological Survey, 3215 Marine Street, Boulder, CO 80303, USA b US Geological Survey, MS 403, Denver Federal Center, Lakewood, CO 80225, USA Received18 May 2001; accepted30 August 2001 Abstract A simple hydrologic-isotopic-balance (HIBAL) model for application to paleolake d18O records is presented. Inputs to the model include discharge, on-lake precipitation, evaporation, and the d18O values of these fluidfluxes. Monthly values of climatic parameters that govern the fractionation of 18O and 16O during evaporation have been extracted from historical data sets and held constant in the model. The ability of the model to simulate changes in the hydrologic balance and the d18O evolution of the mixed layer has been demonstrated using measured data from Pyramid Lake, Nevada. Simulations of the response in d18O to step- and periodic-function changes in fluid inputs indicate that the hydrologic balance and d18O values lag climate change. Input of reconstructedriver dischargesandtheir d18O values to PyramidandWalker lakes indicatesthat minima andmaxima in simulated d18O records correspond to minima and maxima in the reconstructed volume records and that the overall shape of the volume and d18O records is similar. The model was also used in a simulation of abrupt oscillations in the d18O values of paleo-Owens Lake, California. Publishedby Elsevier Science Ltd. 1. Introduction can be simulatedin modelruns that invoke step- function changes in the hydrologic state (open or closed) This paper consists of three separate but linked of the lake basin. sections. In this, the first section, we discuss concepts in modeling, previous applications of d18O models, and introduce the hydrologic-isotopic-balance (HIBAL) 1.1. Concepts in modeling model, details of which are provided in Appendix A. The secondsection consists of four parts. First, HIBAL The d18O value of a lake is the sum of its sources and is validated in a simulation of the measured d18O sinks andthe d18O value of water vapor leaving the lake evolution of PyramidLake surface water between 1985 is strongly influencedby its local climate. In the case of and1994. Second,a series of simulations are donethat lakes with watersheds in distant mountains, the climate illustrate the effect of hydrologic closure and overflow of of the watershedalso influences the d18O value of the PyramidLake on its d18O value. Third, simulations of lake through its effect on the d18O value of surface-water the response of lake volume and d18O to periodic input. In such watersheds, the value of precipitation is changes in river discharge are done to assess the degree not constant over time, being a function of the history of to which changes in d18O lag climate forcing. Fourth, the air parcel that carries the precipitation andthe HIBAL is usedin historical simulations of the response temperature at which the precipitation condenses. In of two different lake systems, PyramidandWalker addition, the d18O value of watershedprecipitation may lakes, to nearly identical climate forcings. In the last differ substantially from the d18O value of on-lake section of the paper, we apply the model to paleo-Owens precipitation. Lake, showing that abrupt changes in the d18O record Paleolake records of d18O are storedin carbonate precipitates. Given the fact that d18O records represent a complex integration of the elements of climate change, *Corresponding author. Tel.: +1-303-541-3005; fax: +1-303-447- 18 2505. how do we unravel climate history from the d O E-mail address: [email protected] (L. Benson). record? We must confront the fact that we are dealing 0277-3791/02/$ - see front matter Publishedby Elsevier Science Ltd. PII: S 0277-3791(01)00094-4 1522 L. Benson, F. Paillet / Quaternary Science Reviews 21 (2002) 1521–1539 with a highly underdetermined system, and that to 1.2. Previous applications of d18O models approximate the history of climate change from the d18O recordwe must make a number of assumptions High-resolution d18O records are increasingly being regarding the nature of the climate system. The usedas proxies of change in climate andhydrologic implication of this procedure is that no particular balance of paleo surface-water systems (e.g., Johnson solution will be unique. In some cases, additional et al., 1991; Lister et al., 1991; Fontes et al., 1993; Oviatt information on the climate system may be available et al., 1994; Phillips et al., 1994; Hodell et al., 1995; from other types of climate records, thereby eliminating Benson et al., 1997; Li andKu, 1997; Xia et al., 1997; part of the uncertainty implicit in the modeling exercise. Benson, 1999; Benson et al., 2001). Variation in d18O However, many climate proxies are poorly calibrated values of carbonates precipitatedfrom temperate-region anda multiproxy approach may often introduce as lakes with low-residence times and minimal evaporation many unknowns as solutions into the calibration losses have generally been attributedto variation in the equation set. d18O of precipitation falling in the watershedarea of the A question the modeler must initially address is lake (Stuiver, 1968, 1970; Fritz et al., 1975). Because the whether simulations of the entire d18O recordwill be d18O of precipitation is highly correlatedwith air attemptedor whether simulations will be confinedto temperature (Yurtsever, 1975), changes in the d18O ‘‘interesting’’ parts of the record. The latter strategy value of low-residence-time lakes has, therefore, been has a much higher chance of success in that some associatedwith changes in air temperature (Eicher and climate parameters tendto be relatively stable over Siegenthaler, 1976; Eicher, 1980). In contrast, for lake short time periods, and thus there is justification systems that are hydrologically closed or have long or for holding these parameters constant in the model. intermediate residence times, emphasis has often been Models can also be used to catalog the response of placedon change in the hydrologic balance as the d18O to various hypothetical climatic transitions. In principal process responsible for d18O variability (John- this mode, the model can be run a number of times son et al., 1991; Lister et al., 1991; Fontes et al., 1993; to test the sensitivity of d18O to initial conditions, Oviatt et al., 1994; Phillips et al., 1994; Hodell et al., lake-basin geometry, discharge rates, and overflow 1995; Benson, 1999). rates. Numerical modeling of the behavior of d18Ohas It is of paramount importance that the modeler has a usually been confinedto simulations of the measured thorough understanding of the system that is being d18O variability in lake water (e.g., Gat, 1970; Lewis, simulated. Historic climatic, hydrologic, physical, and 1979; Hostetler andBenson, 1994). Phillips et al. (1994) chemical data sets can be used to determine the have applieda lumped-parametermodel(Phillips et al., variability of various parameters over annual- and 1986, 1992) in an attempt to reproduce a mid-to-late- multi-decadal-time scales and their mutual interdepen- Wisconsin d18O recordfrom the Searles Lake basin, dencies. Historical data are also needed to validate the California. model. The model can be run eliminating or holding Hostetler andBenson (1994) coupledthe isotopic constant parameters that will not be available when derivations later published in Benson and White (1994) simulating paleo-d18O records. In this manner, limita- to a one-dimensional thermal model developed by tions of the model can be exposed. Hostetler andBartlein (1990). The coupledmodelwas One of the great difficulties in the use of HIBAL usedto simulate the d18O structure of PyramidLake for models to estimate past changes in the hydrologic the period 1985–1991. The system was well determined. balance of a lake system is that past values of climatic Inputs to the model included daily values of meteor- parameters must be assignedto the model.For lake ological andlake-thermal data(Hostetler andBenson, systems, we must exactly know the components of past 1993). Daily discharges of the Truckee River were climates that govern lake evaporation, inflow, andon- obtainedfrom US Geological Survey Water-Data lake precipitation in order to reconstruct past changes in Reports (1986–1992) andisotopic datasets were the hydrologic balance. This indicates that all lake- available for Truckee River input andPyramidLake modeling systems are mathematically underdetermined, surface water on a monthly or better frequency (Benson, forcing the modeler to make