a spatially explicit model of runoff evaporation and lake extent application to modern and late pleistocene lakes in the great basin region western united states 1 a spatially explicit hydrological model was applied to the great basin in the western united states to predict runoff magnitude and lake distributions under modern and late pleistocene conditions the model iteratively routes runoff through depression to find a steady state solution and was calibrated with mean annual precipitation pan evaporation temperature and stream runoff data the predicted lake distribution provides a close match to present day lakes for the late pleistocene the sizes of lakes bonneville and lahontan are well predicted by linear combinations of 0 2 5 8 c decreases in temperature and corresponding increases in precipitation from 2 0 to 1 0 times modern values this corresponds to runoff depths ranging from 1 7 to 4 1 times the present values and yearly evaporation from 0 4 to 1 times modern values to reproduce lake manly however combinations of temperature decreases up to 9 c or precipitation up to 2 8 times the present values were required

carbonate deposition pyramid lake subbasin nevada 2 lake levels and polar jet stream positions reconstructed from radiocarbon ages and elevations of carbonates tufas deposited in the lahontan basin most of the tufas in the pyramid lake subbasin were deposited within the last 35 000 yr including most of the mound tufas that border the existing lake many of the older tufas 21 000 yr b p contained in the mounds were formed in association with ground water discharge the radiocarbon 14c ages of the older tufas represent maximum estimates of the time of their formation lake lahontan experienced large and abrupt rises in level at 22 000 15 000 and 11 000 yr b p and three abrupt recessions in level at 16 000 13 600 and 10 000 yr b p the lake level rises that were initiated at 23 500 and 15 500 yr b p are believed to indicate the passage of the polar jet stream over the lahontan basin during expansion of the laurentide ice sheet the jet stream moved south across the basin and during the contraction of the ice sheet the jet stream moved north across the basin the bulk of the carbonate contained in the mound tufas was deposited during the last major lake cycle 23 500 12 000 yr b p indicating that ground and surface water discharges increased at 23 500 and decreased at 12 000 yr b p a lake level oscillation that occurred between 11 000 and 10 000 yr b p is represented by a 2 cm thick layer of dense laminated tufa that occurs at and below 1180 m in the low elevation tufa mounds and at 1205 m in the winnemucca lake subbasin

annually resolved late holocene paleohydrology of the southern sierra nevada and tulare lake california here we present 2000 year long annually resolved records of streamflow for the kings kaweah tule and kern rivers in the southwestern sierra nevada of california and consequent lake level fluctuations at tulare lake in the southern san joaquin valley the integrated approach of using moisture sensitive tree ring records from the living blended drought atlas to reconstruct annual discharge and then routing this discharge to an annual tulare lake water balance model highlights the differences between these two types of paleoclimate records even when subject to the same forcing factors the reconstructed streamflow in the southern sierra responded to yearly changes in precipitation and expressed a strong periodicity in the 2 8 year range over most of the reconstruction the storage capacity of tulare lake caused it to fluctuate more slowly masking the 2 8 year streamflow periodicity and instead expressing a strong periodicity in the 32 64 year range over much of the record although there have been longer droughts the 2015 water year represents the driest in the last 2015 years and the 2012 2015 drought represents the driest 4 year period in the record under natural conditions simulated tulare lake levels would now be at about 60 m which is not as low as what occurred multiple times over the last 2000 years this long term perspective of fluctuations in climate and water supply suggests that different drought scenarios that vary in terms of severity and duration can produce similar lake level responses in closed lake basins

rise and fall of late pleistocene pluvial lakes in response to reduced evaporation and precipitation evidence from lake surprise california widespread late pleistocene lake systems of the basin and range province indicate substantially greater moisture availability during glacial periods relative to modern times but the climatic factors that drive changes in lake levels are poorly constrained to better constrain these climatic forcing factors we present a new lacustrine paleoclimate record and precipitation estimates for lake surprise a closed basin lake in northeastern california we combine a detailed analysis of lake hydrography and constitutive relationships describing the water balance to determine the influence of precipitation evaporation temperature and seasonal insolation on past lake levels at its maximum extent during the last deglaciation lake surprise covered 1366 km 2 36 of the terminally draining surprise valley watershed using paired radiocarbon and 230 th u analyses we dated shoreline tufa deposits from wave cut lake terraces in surprise valley california to determine the hydrography of the most recent lake cycle this new lake hydrograph places the highest lake level 176 m above the present day playa at 15 19 0 18 calibrated ka 14 c age this significantly postdates the last glacial maximum lgm when lake surprise stood at only moderate levels 65 99 m above modern playa similar to nearby lake lahontan to evaluate the climatic factors associated with lake level changes we use an oxygen isotope mass balance model combined with an analysis of predictions from the paleoclimate model intercomparison project 3 pmip3 climate model ensemble our isotope mass balance model predicts minimal precipitation increases of only 2 18 during the lgm relative to modern compared to an 75 increase in precipitation during the 15 19 ka highstand lgm pmip3 climate model simulations corroborate these findings simulating an average precipitation increase of only 6 5 relative to modern accompanied by a 28 decrease in total evaporation driven by a 7 c decrease in mean annual temperature lgm pmip3 climate model simulations also suggest a seasonal decoupling of runoff and precipitation with peak runoff shifting to the late spring early summer from the late winter early spring our coupled analyses suggest that moderate lake levels during the lgm were a result of reduced evaporation driven by reduced summer insolation and temperatures not by increased precipitation reduced evaporation primed basin and range lake systems particularly smaller isolated basins such as surprise valley to respond rapidly to increased precipitation during late heinrich stadial 1 hs1 post lgm highstands were potentially driven by increased rainfall during hs1 brought by latitudinally extensive and strengthened midlatitude westerly storm tracks the effects of which are recorded in the region9s lacustrine and glacial records these results suggest that seasonal insolation and reduced temperatures have been underinvestigated as long term drivers of moisture availability in the western united states

late holocene hydroclimate inferences for the northern great basin from little lake elko county nevada usa abstract prominent lunette dunes 500 800 m long 50 80 m wide and up to 5 m tall are present on the floor of the independence valley in northeast nevada usa these dunes border the downwind margins of circular playas at the end of a drainage descending from the east humboldt mountains which terminates in an ephemeral water body named little lake gastropod shells from the little lake playa yield radiocarbon ages of 400 cal yr bp after correction for a hard water effect a similar age was obtained for shells from the crest of one of the lunettes deeper sediment in this lunette yielded shell ages clustering around 600 cal yr bp this pattern suggests two intervals of relatively persistent water at little lake both of which ended with lake desiccation and deflation of sediment and shells to the adjacent lunette shells from the crest of another lunette yielded radiocarbon ages between 3800 and 1750 cal yr bp this dune therefore is considerably older and accumulated over a much longer stretch of time using the global surface water explorer years between 1984 and 2018 were identified in which little lake contained water in most of the available summer imagery these years form three clusters 1984 1987 1997 2000 and 2017 2018 snow water equivalent swe is greater in the mountains snow makes up a greater percent of total annual precipitation and palmer drought severity index is more positive in this region in years when water is present in little lake compared with those in which the lake remains dry values of the pdo are also higher in years when little lake holds water although the hydrology of little lake may be influenced to an unknown degree by upstream water diversions this overall pattern implies that the lake and its associated lunettes are a sensitive recorder of late holocene hydroclimate variability in the northern great basin

carbonate deposition pyramid lake subbasin nevada 1 sequence of formation and elevational distribution of carbonate deposits tufas abstract during the late quarternary the elevation of terrace cutting and carbonate deposition in the pyramid lake subbasin were controlled by constancy of lake level imposed by spill to adjoining subbasins sill elevations are 1177 1183 m mud lake slough sill 1207 m emerson pass sill and 1265 m darwin pass sill carbonate deposition was favored by 1 hydrologic closure 2 proximity to a source of calcium 3 elevated water temperature and 4 a solid substrate the thickness and aspect of tufa are a function oflake level dynamics relatively thin sheets and pendant sheets were deposited during a rising or falling lake the upper parts of thick reef form tufas have a horizontal aspect and were deposited in a lake which was stabilized by spill to the carson desert subbasin the lower parts of the reef form tufas are thinner and their outer surface has a vertical aspect indicating that the lower part formed in a receding lake the thickest and most complete sequences of tufa are mounds that border the pyramid lake shore the tops of the tallest mounds reach the elevation of the darwin pass sill and many mounds have been eroded to the elevations of the mud lake slough sill of the emerson pass sill the sequence of tufa formation from oldest to youngest displayed in these mounds is 1 a beachrock containing carbonate cemented volcanic cobbles 2 broken and eroded old spheroids that contain thinolitic tufa and an outer rind of dense laminated tufa 3 large cylindrical tubular tufas capped by 4 coatings of old dense tufas and 5 several generations of old branching tufa commonly associated with thin platy tufas and coatings of thinolitic tufa 6 young spheroids that contain poorly oriented young thinolitic tufa in the center and several generations of radially oriented young thinolitic tufas near the outer edge 7 a transitional thinolite to branching tufa 8 two or more layers of young branching tufa 9 a 0 5 cm thick layer of fine grained dolomite 10 a 2 cm thick layer of young dense laminated tufa 11 a 0 1 cm thick layer of encrusting tufa that was covered by a beach deposit and 12 a 1 0 cm thick layer of porous encrusting tufa that coated the beach deposit and the sides of tufa mounds the elevational ranges of the principal varieties of tufa are not related to terrace or spill elevations it seems likely that the distribution of tufa varieties is related to variation in the thermal structure or chemistry of lake lahontan it is hypothesized that the thinolitic tufa ikaite formed in the near freezing hypolimnion and the braching tufa calcite formed in the seasonally warmer epiliminion of the lake

new 230th u and 14c ages from lake lahontan carbonates nevada usa and a discussion of the origin of initial thorium five sets of coeval lacustrine carbonate samples from pleistocene lake lahontan in western nevada were dated by both the ams 14c and 230th u isochron methods all five groups of samples were analyzed for u th isotopes by alpha spectrometry and one of the groups was additionally measured by thermal and secondary ionization mass spectrometry tims and sims for comparison the 14c ages were corrected to calendar years using the calibration curve recommended by bard et al 1992 without local reservoir correction on the 14c ages mean 230th u isochron ages of some sets are apparently older than their calendar corrected 14c ages by up to 2300 years modern carbon contamination of these carbonate samples through recrystallization or deposition of secondary calcite is likely to be responsible for part of the age discrepancies we explored additional biases associated with the isochron ages maybe produced by the presence of initial th coprecipitated from the lake water it can be shown that if dissolved hydrogenous th is directly incorporated into the pure carbonates then the three component mixing among 1 detrital th 2 hydrogenous th adsorbed on detritus and 3 hydrogenous th incorporated by the carbonate can introduce a positive age bias we have developed an approach to estimate the magnitude of this bias of the lake lahontan carbonates the preliminary estimates suggest a positive age bias of 1000 to 2000 years for two sets of the samples

assessing the extent of carbonate deposition in early rift settings select lacustrine and marine depositional settings show a spectrum of styles of carbonate deposition and illustrate the types of carbonates with an emphasis on microbialites and tufa to be expected in early rift settings early rift lake examples examined in this review article are all from east africa lakes turkana bogoria natron and magadi manyara and tanganyika other lake examples include four from the western united states great salt lake and high lake level lake bonneville mono lake and high lake level russell lake pyramid lake and high lake level lake lahontan and searles lake and two from australia lakes clifton and thetis marine basin examples are the hamelin pool part of shark bay from australia marginal marine and the red sea marine rift landsat images and digital elevation models for each example are used to delineate present and past lake basin margins based on published lake level elevations and for some examples the shorelines representing different lake levels can be compared to evaluate how changes in size shape and lake configuration might have impacted carbonate development the early rift lakes show a range of characteristics to be expected in lacustrine settings during the earliest stages of continental extension and rifting whereas the red sea shows well advanced rifting with marine incursion and reef skeletal sand development collectively the lacustrine examples show a wide range of sizes with several of them being large enough that they could produce carbonate deposits of potential economic interest three of the areas great salt lake and high lake level lake bonneville pyramid lake and high lake level lake lahontan and the red sea are exceedingly complex in that they illustrate a large degree of potential depositional facies heterogeneity because of their size irregular pattern and connectivity of subbasins within the overall basin outline

evaluating the size and extent of paleolakes in central tibet during the late pleistocene subhorizontal lake shorelines allow a geodynamic test of the size and extent of a hypothesized paleo lake in central tibet the east qiangtang lake eql during the last interglacial period marine isotope stage mis 5e reconstructions based on relict lake deposits suggest that the eql would have been 400 m deep and over 66 000 km2 models of flexural rebound driven by lake recession predict that shorelines near the eql center at the present day location of siling co would have rebounded 60 90 m above their initial elevation new 36cl chronology of the highest relict shorelines around siling co indicates that they reflect lake levels between 110 190 ka these shorelines however are presently 300 m below their predicted elevations implying a substantially smaller water load our results reveal that the expansion of tibetan lakes during mis 5e was relatively limited instead individual lakes were supplied by river networks much as they are today

the influence of basin morphometry on the regional coherence of patterns of diatom inferred salinity in lakes of the northern great plains usa sedimentary diatom profiles from saline lakes are frequently used to reconstruct lakewater salinity as an indicator of drought however diatom inferred salinity di salinity reconstructions from geographically proximal sites in the great plains usa have yielded disparate results this study explores how physical changes in lake habitat resulting from drought may affect climate inferences from salinity reconstructions differences in relationships among drought lake level change and diatom community structure over the last century were examined for three saline lakes in the northern great plains with dissimilar di salinity records at each site models were developed relating available planktic benthic p b habitat area to lake level change and models were compared with instrumental drought records and fossil diatoms to understand how drought conditions were recorded in sedimentary diatom assemblages the degree to which di salinity tracked drought variation was affected by site specific physical characteristics that influenced the relationship between lake level change and p b habitat zonation within each lake moon lake showed the strongest correlation between drought and disalinity although this relationship was weaker during wetter conditions as highstands resulted in a larger influx of benthic diatoms at coldwater lake a dual basin system p b varied depending on lake level which apparently reduced the correlation between di salinity and drought at lake cochrane the simplest and freshest of the three basins the p b of fossil diatoms was a better proxy for drought than di salinity the integration of additional ecological characteristics into interpretations of paleoclimate records particularly for biologically based proxies may improve reconstructions of regional patterns of climate variation

lake level reconstruction for 12 8 2 3 ka of the ngangla ring tso closed basin lake system southwest tibetan plateau article i nfo we present a shoreline based millennial scale record of lake level changes spanning 12 8 2 3 ka for a large closed basin lake system on the southwestern tibetan plateau fifty three radiocarbon and eight u th series ages of tufa and beach cement provide age control on paleoshorelines ringing the basin supplemented by nineteen ages from shell and aquatic plant material from natural exposures generally recording lake regressions our results show that paleo ngangla ring tso exceeded modern lake level 4727 m asl continuously between 12 8 and 2 3 ka the lake was at its highstand 135 m 4862 m asl above the modern lake from 10 3 ka to 8 6 ka this is similar to other closed basin lakes in western tibet and coincides with peak northern hemisphere summer insolation and peak indian summer monsoon intensity the lake experienced a series of millennial scale oscillations centered on 11 5 10 8 8 3 5 9 and 3 6 ka consistent with weak monsoon events in proxy records of the indian summer mon soon it is unclear whether these events were forced by north atlantic or indian ocean conditions but based on the abrupt lake level regressions recorded for ngangla ring tso they resulted in significant periodic reductions in rainfall over the western tibetan plateau throughout the holocene

revisiting growth and decline of late quaternary mega lakes across the south central tibetan plateau abstract lake basins record critical interactions between the hydrosphere cryosphere and atmosphere their sediments and shoreline landforms archive timing duration and intensity of past climatic variability and environmental impacts over a variety of timescales thousands of lake systems spread across the internally drained tibetan plateau today of which many are only the salty remains of much more expansive paleolakes in the past this study presents new shoreline ages integrated with quantitative digital topographic analysis and regional geomorphic evidence to reconstruct the sizes and extents of late quaternary rift lake systems for the south central tibetan plateau this study presents optically stimulated luminescence osl and the first k feldspar post infrared infrared pirir stimulated luminescence ages for zabuye caka and dawa tso and tests if these lakes were once part of a singular pleistocene mega lake established across four n s rift systems our new results show that two large but separate paleolake systems developed in the latest pleistocene earliest holocene and no lake larger than 6460 km2 has existed since at least 41 ka in the lunggar region early holocene paleolakes expanded up to 7 modern 220 335 km3 with two to four fold asymmetric lake expansion in the west compared to the east findings corroborate earlier investigations implying that dramatic runoff increase and or evapotranspiration reduction prompted rapid earliest holocene lake expansion precipitation variability in combination with permafrost degradation temperature and wind strength governed paleolake moisture balance open system lake behavior and evolving drainage configurations across complex topography explain delayed onsets of lake regression and punctuated lake decline this suggests abrupt holocene climate shifts are not necessarily required for punctuated lake decline lastly unique geomorphological and paleoclimatic similarities between tibetan and east african rift lakes highlight the potential for some tibetan paleolakes to function as natural climate amplifiers over both short and geologic timescales

quantifying closed basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in earth history such as carbon cycle perturbations and glacial interglacial cycles geochemical measurements of biogenic carbonate for example 18o 13c 87sr 86sr li u sr and mg are indicators of hydrologic variability in lake systems throughout the geologic record in this study we present a new closed basin lake modeling approach hybim the hydrologic balance inverse model that employs a system of total differential equations and uses the measured 18o sr ca and mg ca of biogenic carbonate to determine changes in temperature runoff and lake evaporation using equally spaced time steps these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate we use a monte carlo approach to account for uncertainty in the input parameters such as 18o temperature relationships partition coefficient uncertainty and watershed solute chemistry for illustrative purposes we apply the model to two ostracod valve datasets covering different timescales 1 the cretaceous songliao basin northeast china and 2 holocene lake miragoane haiti modern water measurements of water isotopes and cation concentrations from each location are required as model inputs we compare our modeling results with author interpretations and geologic observations the modeling approach presented in this study can be applied to other closed basin lake records can be modified for other calcifying species for example gastropods or mollusks or with calibration to inorganic lacustrine carbonate in addition this approach holds promise for extension with additional proxy measurements that is d u ca or li ca and changing source area on tectonic timescales using proxies that reflect changing source lithology that is sr and pb isotopes future incorporation of age model uncertainty in the monte carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments

the shoreline preservation index as a relative age dating tool for late pleistocene shorelines an example from the bonneville basin u s a this paper evaluates the utility of the shoreline preservation index s p i for estimating the age of late pleistocene palaeolake shorelines the relative influence of various factors on shoreline preservation and whether shoreline preservation varies significantly with shoreline aspect sampled shorelines from the 3300 km2 study area which includes the skull tule and puddle valley portions of the lake bonneville basin range in age from approximately 26 to 12 ka their total s p i values range from 23 to 69 per cent average 46 per cent and do not vary significantly with shoreline aspect the data from skull and tule valleys where studied shorelines are of known age are analysed first in order to determine if there are statistically significant associations between variables representing shoreline preservation age degree of geomorphic development and duration of subaerial exposure pairwise correlation is then repeated using observations from all three valleys in order to determine how data from the puddle valley shorelines whose hypothesized ages are not supported by radiocarbon analyses affect the results results show that s p i is useful as a relative age dating tool that the postulated ages of the puddle valley shorelines are ordinally correct and that geomorphic development is not an important influence on the preservation of these late pleistocene shorelines the relative importance of shoreline age and the relative unimportance of duration of subaerial exposure with respect to shoreline preservation suggest that subaqueous processes play a more substantial role in shoreline obliteration than is generally suggested

geochronology and stratigraphy of late pleistocene lake cycles on the southern bolivian altiplano implications for causes of tropical climate change large paleolakes 33 000 60 000 km2 that once occupied the high altitude poopo coipasa and uyuni basins in southern bolivia 18 22 s provide evidence of major changes in low latitude moisture in these now dry or oligosaline basins extensive natural exposure reveals evidence for two deep lake and several minor lake cycles over the past 120 k y fifty three new u th and 87 new 14c dates provide a chronologic framework for changes in lake level deposits from the ouki deep lake cycle are extensively exposed in the poopo basin but no deep lakes are apparent in the record between 98 and 18 1 ka the ouki lake cycle was 80 m deep and nineteen u th dates place this deep lake cycle between 120 and 98 ka shallow lakes were present in the terminal uyuni basin between 95 and 80 ka salinas lake cycle at ca 46 inca huasi lake cycle and between 24 and 20 5 ka sajsi lake cycle the tauca deep lake cycle occurred between 18 1 and 14 1 ka resulting in the deepest 140 m and largest lake in the basin over the past 120 ka multiple 14c and u th dates constrain the highest stand of lake tauca along a topographically conspicuous shoreline between 16 4 and 14 1 ka a probable post tauca lake cycle the coipasa produced a 55 m deep lake that is tentatively dated between 13 and 11 ka we suggest that paleolakes on the bolivian altiplano expanded in response to increased moisture in the amazon and enhanced transport of that moisture onto the altiplano by strengthened trade winds or southward displacement of the intertropical convergence zone itcz pole to equator sea surface temperature sst and atmospheric gradients may have influenced the position of the itcz affecting moisture balance over the altiplano and at other locations in the amazon basin links between the position of the itcz and the ca 23 ka precessional solar cycle have been postulated march insolation over the altiplano is a relatively good fit to our lake record but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire amazon basin temperature may influence altiplano lake levels indirectly as potentially dry glacial periods in the amazon basin are linked to dry conditions on the altiplano intensification of the trade winds associated with la nina like conditions currently brings increased precipitation on the altiplano and deep lake development during the tauca lake cycle coincided with apparently intense and persistent la nina like conditions in the central pacific this suggests that sst gradients in the pacific are also a major influence on deep lake development on the altiplano

hurricane maximum intensity past and present hurricane intensity forecasting has lagged far behind the forecasting of hurricane track in an effort to improve the understanding of the hurricane intensity dilemma several attempts have been made to compute an upper bound on the intensity of tropical cyclones this paper investigates the strides made into determining the maximum intensity of hurricanes concentrating on the most recent attempts to understand the maximum intensity problem the theories of holland and emanuel are reviewed with the objective of assessing their validity in real tropical cyclones each theory is then tested using both observations and the axisymmetric hurricane numerical models of ooyama and emanuel it is found that ambient convective instability plays a minor role in the determination of the maximum intensity and that the emanuel model is the closest to providing a useful calculation of maximum intensity several shortcomings are revealed in emanuel s theory however showing the need for more basic research on the axisymmetric and asymmetric dynamics of hurricanes as an illustration of the importance of asymmetric vorticity dynamics in the determination of a hurricane s maximum intensity it is shown using ooyama s hurricane model that the maximum intensity of a tropical cyclone may be diminished by convectively generated vorticity anomolies excited outside the primary eyewall the vorticity anomolies are parameterized by adding a concentric ring of vorticity outside the primary eyewall that acts to cut off its supply of angular momentum and moist enthalpy it is suggested that the generation of vorticity rings or bands outside the primary eyewall is a major reason why tropical cyclones fail to attain their maximum intensity even in an otherwise favorable environment the upshot of this work points to the need for obtaining a more complete understanding of asymmetric vorticity processes in hurricanes and their coupling to the boundary layer and convection

the use of total lake surface area as an indicator of climatic change examples from the lahontan basin abstract variation in the size of lakes in the lahontan basin is topographically constrained river diversion also has played a major role in regulating lake size in lahontan subbasins the proper gage of lake response to change in the hydrologic balance is neither lake depth level nor lake volume but instead lake surface area normalization of surface area is necessary when comparing surface areas of lakes in basins having different topographies to a first approximation normalization can be accomplished by dividing the paleosurface area of a lake by its mean historical reconstructed surface area

u series chronology of lacustrine deposits in death valley california uranium series dating on a 186 m core dv93 1 drilled from badwater basin in death valley california and on calcareous tufas from nearby strandlines shows that lake manly the lake that periodically flooded death valley during the late pleistocene experienced large fluctuations in depth and chemistry over the last 200 000 yr death valley has been occupied by a long standing deep lake perennial shallow saline lakes and a desiccated salt pan similar to the modern valley floor the average sedimentation rate of about 1 mm yr for core dv93 1 was punctuated by episodes of more rapid accumulation of halite arid conditions similar to the modern conditions prevailed during the entire holocene and between 120 000 and 60 000 yr b p from 35 000 yr b p to the beginning of the holocene a perennial saline lake existed over 70 m at its deepest a much deeper and longer lasting perennial lake manly existed from about 185 000 to 128 000 yr b p with water depths reaching about 175 m if not 330 m this lake had two significant dry excursions of 102 103yr duration about 166 000 and 146 000 yr b p and it began to shrink to the point of halite precipitation between 128 000 and 120 000 yr b p the two perennial lake periods correspond to marine oxygen isotopic stages ois 2 and 6 based on the shoreline tufa ages we do not rule out the possible existence 200 000 yr ago of yet a third perennial lake comparable in size to the ois 6 lake the234u 238u data suggest that u in tufa owes its origin mainly to ca rich springs fed by groundwater that emanated along lake shorelines in southern death valley and that an increase of this spring water input relative to the river water input apparently occurred during ois 6

reconstructing palaeoclimate and hydrological fluctuations in the fezzan basin southern libya since 130 ka a catchment based approach abstract we propose a novel method to evaluate regional palaeoclimate that can be used to alleviate the problems caused by the discontinuous nature of palaeoenvironmental data found in deserts the technique involves processing satellite imagery and dem s to map past rivers catchments and evaluate the areas and volumes of palaeolakes this information is used to determine the new lake evaluation index lei that allows a qualitative estimate of the amount of sediment received by lakes and how long lived those lakes are lakes with considerable longevity and large sediment stores are selected for study validation is performed using image interpretation of remote sensing data ultragpr surveys and fieldwork these techniques are also used to identify and study spring deposits and fluvial landforms that provide valuable palaeoclimate information the method is applied to the fezzan basin in southern libya focusing on the wadi ash shati and wadi el agial catchments results indicate that the palaeohydrology is accurately mapped except within dune fields we analysed the sedimentology of the key deposits identified by this methodology developing a chronology using optically stimulated luminescence osl and radiocarbon dating we find evidence for relatively humid conditions during mis 5c d and e as well as during the early to middle holocene larger lakes and more extensive river systems were present during mis 5 than are found during the holocene suggestive of greater humidity the holocene humid period started at 11 ka and continued until 5 ka being interrupted by abrupt periods of aridity at 8 2 ka and 6 ka that coincide with north atlantic cooling after each of these arid events the climate was less humid than previously suggesting that they were superimposed upon an overall drying trend the termination of the holocene humid period in the sahara has received much scrutiny in recent years and sediments of palaeolake shati provide a continuous record of this we do not find evidence to support the hypothesis of either sudden or gradual aridification of the sahara at 5 ka instead we find that that aridity started to develop at 6 5 ka whereupon the lake levels oscillated until finally drying up by 5 3 ka most of the other lakes in the fezzan also dried up at 5ka we suggest that thousands of years of aridification prior to 5 ka shrunk these lakes so that additional aridity at this time led to their final desiccation because lakes are prodigious dust sources this mechanism potentially explains the rapid rise in dust flux to the atlantic at 5 ka with this final drying being the culmination of longer term aridity albeit overprinted with considerable climate variability

water level changes and their effect on deepwater sand accumulation in a lacustrine system a case study from the late miocene of western pannonian basin hungary major deepwater sand accumulations are known to be connected to sea level lowstands in marine basins due to the relative lack of accommodation space on the shelf this model was tested for the late miocene lake pannon a large endorheic lake depositing a sedimentary succession up to 3 4 km thick the progradation of the shelf between 9 7 and 6 ma was tracked along a 2d seismic network the shelf edge trajectory indicates continuous moderate lake level rise between 9 7 and 9 ma this is followed by alternating intervals of quasi steady and rapidly rising relative lake level with a period of ca 250 ky however due to the lack of significant lake level drops no third order sequence boundary was identified in the studied time span 9 7 6 ma the sand ratio of the deepwater deposits does not show strong correlation with these lake level changes moreover the units deposited under rising lake level conditions generally contain slightly larger proportion of sand these features can be explained by the climatic origin of water level rises increasing precipitation enhances not only water inflow but also sediment influx which can overwhelm the well known effect of accommodation space on the sand transport toward the deep water the results suggest that shelf margin trajectory might not be an efficient tool for predicting deepwater accumulations of sand in endorheic lacustrine basins

beachrock as sea level indicator a case study at the coastline of oman indian ocean abstract future sea level changes are a threat to coastal communities worldwide therefore reliable methods for the reconstruction of past relative sea level variations are essential to make predictions of future developments beachrocks are a widely distributed indicator of quaternary paleo coastlines with a high potential for preservation nevertheless their use as sea level indicator faces challenges in the determination of the exact elevation of beachrock formation with respect to paleo sea level this information is crucial to the establishment of a sea level index point our study area on the northeastern coastline of oman shows a set of twelve marine terraces that reach a height of 500 m above mean sea level while the upper terraces are erosional the lowest three are depositional on the erosional terraces beachrocks are the only sediment cover that withstood erosion on the depositional terraces however beachrocks occur alongside other sediments which can be fluvial alluvial or marine in origin the coastal development of the area is of high interest as uplift and tectonic activity are ongoing fieldwork and petrographic methods on eight outcrops on three terrace levels led to the identification of eight lithofacies in six facies associations we used facies analysis to improve the information on paleo sea level as derived by the sole use of geomorphological indicators here we demonstrate that facies analysis so far applied exclusively on sandy deposits is applicable also to gravel dominated systems the results contribute to knowledge on local changes in the depositional environment and help to reconstruct uplift rates

high resolution saline lake sediments as enhanced tools for relating proxy paleolake records to recent climatic data series abstract lake level in an endorheic saline lake in southern europe has been inferred for the last 105 years 1889 1994 at an annual level of resolution using two independent methods first ordination analyses factor analysis fa correspondence analysis ca and detrended correspondence analysis dca have been used to point out the mineral successions of the sedimentary record these successions are evidenced by the arch disposition of both samples and mineral phases in the plane defined by the first two eigenvectors calculated by these analyses these temporal evolutions are the same as those obtained during the drying and refilling phases of saline lakes relay indices ri were obtained from distances to the first two eigenvectors which accurately reconstructed the lake level evolution during this period second an inferred lake level series was obtained using a multivariate time series model from the average maximum temperatures and total rainfall six main drought periods were found which coincided with known droughts in the area a high level of agreement was found between the two reconstructions which offered the possibility of directly extending the instrumental record back into the past therefore climatic changes could be reconstructed from saline lakes provided that an accurate chronological control of sedimentary processes is available

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

lake level variation in the lahontan basin for the past 50 000 years selected radiocarbon data on surficial materials from the lahontan basin nevada and california provide a chronology of lake level variation for the past 50 000 yr a moderate sized lake connected three western lahontan subbasins the smoke creek black rock desert subbasin the pyramid lake subbasin and the winnemucca dry lake subbasin from about 45 000 to 16 500 yr b p between 50 000 and 45 000 yr b p walker lake rose to its sill level in adrian valley and spilled to the carson desert subbasin by 20 000 yr b p lake level in the western lahontan subbasins had risen to about 1265 m above sea level where it remained for 3500 yr by 16 000 yr b p lake level in the western lahontan subbasins had fallen to 1240 m this recession appears synchronous with a desiccation of walker lake however whether the walker lake desiccation resulted from climate change or from diversion of the walker river is not known from about 15 000 to 13 500 yr b p lake level rapidly rose so that lake lahontan was a single body of water by 14 000 yr b p the lake appears to have reached a maximum highstand altitude of 1330 m by 13 500 yr b p a condition that persisted until about 12 500 yr b p at which time lake level fell 100 m no data exist that indicate the level of lakes in the various subbasins between 12 000 and 10 000 yr b p during the holocene the lahontan basin was the site of shallow lakes with many subbasins being the site of one or more periods of desiccation the shape of the lake level curve for the three western subbasins indicates that past changes in the hydrologic balance and hence climate of the lahontan basin were large in magnitude and took place in a rapid step like manner the rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream as it was forced north or south by the changing size and shape of the continental ice sheet

late pleistocene to early holocene lake level and paleoclimate insights from stansbury island bonneville basin utah abstract this paper reports on recent multiproxy research conducted to determine the chronology of lake level fluctuations recorded in sediments from a natural exposure at a classic bonneville basin site grain size carbonate percentage magnetic susceptibility amount of charcoal and diatom community composition data were collected from the 16 lacustrine units that compose the 122 cm stratigraphic column in stansbury gulch trends observed in the measured proxies reveal several significant changes in lake level and thereby effective moisture over the approximately 14 500 yr time span represented by the sediments results 1 verify the effectiveness of the multiproxy approach in bonneville basin studies which has been underutilized in this region 2 reaffirm the double nature of lake bonneville s stansbury oscillation 3 suggest a previously undocumented post gilbert highstand of great salt lake and 4 identify possible teleconnections between climate events in the bonneville basin and events in the north atlantic at about 20 500 and 7500 14c yr bp

change in the size of walker lake during the past 5000 years benson l v meyers p a and spencer r j 1991 change in the size of walker lake during the past 5000 years palaeogeogr palaeoclimatol palaeoecol 81 189 214 in 1984 a 12 m sediment core wlc84 8 was taken from the deepest part of walker lake samples of the core were analysed for diatoms pollen carbonate mineralogy magnesium content 6180 and 613c values of the total inorganic fraction 6180 and 613c values of limnocythere ceriotuberosa 613c values of the total organic fraction grain size and magnetic susceptibility the data indicate that walker lake became shallow and probably desiccated between i 5300 4800 and 27002100 yr b p each of the organic and inorganic proxy indicators of lake size discussed in this paper was useful in determining the presence of the shallow lake intervals however none of the indicators was useful in determining the cause of the shallowlake intervals instead the types of fish living in walker lake prior to 1940 were used to demonstrate that shallow lake intervals resulted from diversion of the walker river and not from climatic aridity major changes in mineralogy and magnesium content of carbonates and major changes in diatom populations with time were found to be a function of the chemical evolution of walker lake combined with changing lake size the stable isotopes of oxygen and carbon were found to be good indicators of lake volume changes a lake level record for walker lake constructed from stable isotope data was found to be similar to a lake level record constructed using tufa and tree stump data both records indicate relatively high lake levels between 4800 2700 yr b p at 1250 yr b p and within the last 300 yr substantial declines in lake level occurred 2000 and 1000 yr b p

a groundwater model to explain past lake levels at parkers prairie minnesota usa the response of a lake level to a shift in climate depends on characteristics of surficial and groundwater hydrology that are unique to that lake determination of the past levels of several lakes rather than just one can help provide a more precise determination of past hydrology and climate for a given region the levels of several closed basin lakes in the parkers prairie sandplain in west central minnesota were lowest about 7 ka a steady state analytic element groundwater model was used to quantify the effect of changing regional groundwater recharge n on the altitude of the water table surrounding these lakes because overland flow on the sandplain is limited the surficial hydrology of the lakes can be simplified to the net quantity lake evaporation minus precipitation e p both n and e p were manipulated to force the model water table to coincide with the palaeolake levels model results indicate that lake levels at 7 ka can be explained primarily by reducing n to about 50 60 mm yr 1 40 5

carbonate deposition pyramid lake subbasin nevada 3 the use of 87sr values in carbonate deposits tufas to determine the hydrologic state of paleolake systems abstract sierran rivers that discharge to the lahontan basin have much lower 4 5 87sr values than the humboldt river which drains northeastern nevada the 87sr values of tufas deposited during the last lake cycle were used to determine when humboldt derived sr entered the pyramid lake subbasin prior to 15 000 yr b p the humboldt river flowed to the smoke creek black rock desert subbasin during the recession of lake lahontan the humboldt river diverted to the carson desert subbasin this study has demonstrated that 87sr can be used to determine drainage histories of multi basin lake systems if the 87sr values of rivers that discharge to the basins are sufficiently different

late holocene paleohydrology of walker lake and the carson sink in the western great basin nevada usa the late holocene histories of walker lake and the carson sink were reconstructed by synthesizing existing data in both basins along with new age constraints from key sites supplemented with paleohydrologic modeling the repeated diversions of the walker river to the carson sink and then back to walker lake caused walker lake level fluctuations spanning 50 m low lake levels at about 1000 750 and 300 cal yr bp are time correlative to the ages of fluvial deposits along the walker river paleochannel when flow was directed toward the carson sink the timing and duration of large lakes in the carson sink were further refined using moisture sensitive tree ring chronologies the largest lakes required a fourfold to fivefold increase in discharge spanning decades addition of walker river flow to the carson sink by itself is inadequate to account for the required discharge instead increases in the runoff coefficient and larger areas of the drainage basin contributing surface runoff may explain the enhanced discharge required to create these large lakes

pluvial lakes in the great basin of the western united states a view from the outcrop abstract paleo lakes in the western united states provide geomorphic and hydrologic records of climate and drainage basin change at multiple time scales extending back to the miocene recent reviews and studies of paleo lake records have focused on interpretations of proxies in lake sediment cores from the northern and central parts of the great basin in this review emphasis is placed on equally important studies of lake history during the past 30 years that were derived from outcrop exposures and geomorphology in some cases combined with cores outcrop and core records have different strengths and weaknesses that must be recognized and exploited in the interpretation of paleohydrology and paleoclimate outcrops and landforms can yield direct evidence of lake level facies changes that record details of lake level fluctuations and geologic events such as catastrophic floods drainage basin changes and isostatic rebound cores can potentially yield continuous records when sampled in stable parts of lake basins and can provide proxies for changes in lake level water temperature and chemistry and ecological conditions in the surrounding landscape however proxies such as stable isotopes may be influenced by several competing factors the relative effects of which may be difficult to assess and interpretations may be confounded by geologic events within the drainage basin that were unrecorded or not recognized in a core the best evidence for documenting absolute lake level changes lies within the shore nearshore and deltaic sediments that were deposited across piedmonts and at the mouths of streams as lake level rose and fell we review the different shorezone environments and resulting deposits used in such reconstructions and discuss potential estimation errors lake level studies based on deposits and landforms have provided paleohydrologic records ranging from general changes during the past million years to centennial scale details of fluctuations during the late pleistocene and holocene outcrop studies have documented the integration histories of several important drainage basins including the humboldt amargosa owens and mojave river systems that have evolved since the miocene within the active tectonic setting of the great basin these histories have influenced lake levels in terminal basins many pre late pleistocene lakes in the western great basin were significantly larger and record wetter conditions than the youngest lakes outcrop based lake level data provide important checks on core based proxy interpretations we discuss four such comparisons in some cases such as for lakes owens and manix outcrop and core data synthesis yields stronger and more complete records in other cases such as for bonneville and lahontan conflicts point toward reconsideration of confounding factors in interpretation of core based proxies