holocene lake level trends in the rocky mountains u s a abstract the availability of water shapes life in the western united states and much of the water in the region originates in the rocky mountains few studies however have explicitly examined the history of water levels in the rocky mountains during the holocene here we examine the past levels of three lakes near the continental divide in montana and colorado to reconstruct holocene moisture trends using transects of sediment cores and sub surface geophysical profiles from each lake we find that mid holocene shorelines in the small lakes 4 110 ha were as much as 10 m below the modern lake surfaces our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000 2000 years ago we also discuss evidence for millennial scale moisture variation including an abruptly initiated and terminated wet period in colorado from 4400 to 3700 cal yr bp and find only limited evidence for low lake stands during the past millennium the extent of low water levels during the mid holocene which were most severe and widespread ca 7000 4500 cal yr bp is consistent with the extent of insolation induced aridity in previously published regional climate model simulations like the simulations the lake data provide no evidence for enhanced zonal flow during the mid holocene which has been invoked to explain enhanced mid continent aridity at the time the data including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium confirm the ability of large boundary condition changes to push western water supplies beyond the range of recent natural variability

3d waterflood monitoring at lost hills with crosshole em producing oil and gas at the lost hills field in central california has always been a challenge although the reserves are significant production is hampered by low matrix permeability and unusual mechanical properties in the diatomite marine mudstone siltstone reservoir since 1911 operators have struggled with methods to improve production control local subsidence and well failure and improve recovery that presently is projected to be less than 10

multi method virtual electromagnetic experiments for developing suitable monitoring designs a fictitious co2 sequestration scenario in northern germany we present a numerical study for 3d time lapse electromagnetic monitoring of a fictitious co2 sequestration using the geometry of a real geological site and a suite of suitable electromagnetic methods with different source receiver configurations and different sensitivity patterns all available geological information is processed and directly implemented into the computational domain which is discretized by unstructured tetrahedral grids we thus demonstrate the performance capability of our numerical simulation techniques the scenario considers a co2 injection in approximately 1100 m depth the expected changes in conductivity were inferred from preceding laboratory measurements a resistive anomaly is caused within the conductive brines of the undisturbed reservoir horizon the resistive nature of the anomaly is enhanced by the co2 dissolution regime which prevails in the high salinity environment due to the physicochemical properties of co2 the affected portion of the subsurface is laterally widespread but very thin we combine controlled source electromagnetics borehole transient electromagnetics and the direct current resistivity method to perform a virtual experiment with the aim of scrutinizing a set of source receiver configurations with respect to coverage resolution and detectability of the anomalous co2 plume prior to the field survey our simulation studies are carried out using the 3d codes developed in our working group they are all based on linear and higher order lagrange and n ed elec finite element formulations on unstructured grids providing the necessary flexibility with respect to the complex real world geometry we provide different strategies for addressing the accuracy of numerical simulations in the case of arbitrary structures the presented computations demonstrate the expected great advantage of positioning transmitters or receivers close to the target for direct current geoelectrics 50 change in electric potential may be detected even at the earth s surface monitoring with inductive methods is also promising for a well positioned surface transmitter more than 10 difference in the vertical electric field is predicted for a receiver located 200 m above the target our borehole transient electromagnetics results demonstrate that traditional transient electromagnetics with a vertical magnetic dipole source is not well suited for monitoring a thin horizontal resistive target this is due to the mainly horizontal current system which is induced by a vertical magnetic dipole

borehole to surface electrical resistivity monitoring of a salt water injection experiment a field experiment was conducted at the university of california richmond field station to demonstrate the sensitivity of borehole to surface resistivity measurements in groundwater investigations a quantity of saline water was injected into a fresh water aquifer while the resistivity was monitored using a multichannel borehole to surface system two experiments were conducted using pole pole and pole dipole receiver electrode arrays the data from the pole pole experiment were superimposed to simulate a dipole pole array and the data from the pole dipole array were superimposed to simulate a dipole dipole array this superposition of the data was done to enhance the anomaly and facilitate interpretation a numerical modeling study was performed in conjunction with the field experiment in order to interprete the results a three dimensional modeling program was used to simulate the geological setting of the field experiment and the salt water injection this modeling revealed that an asymmetric displacem

episodes of late holocene aridity recorded by stalagmites from devil s icebox cave central missouri usa two stalagmites from devil s icebox cave central missouri display similar 13 c and 18 o values and trends during the late holocene positive 13 c excursions at 3 5 2 6 ka and 1 2 0 9 ka are interpreted to reflect drier conditions these elevated stalagmite 13 c values could have plausibly been driven by increasing c4 plant abundances over the cave or an increased contribution of bedrock carbon both of which could reflect decreased effective moisture a lack of corresponding oxygen isotopic anomalies during these intervals suggests that neither mean annual temperature nor the seasonality of precipitation changed concomitantly with dryness both of the 13 c excursions identified in our stalagmite record are roughly

assessment of a house affected by ground movement using terrestrial laser scanning and numerical modeling this study analyzed the internal mechanical state of houses disturbed by underground coal mining especially those that are free from damage in subsidence areas traditional surveying and terrestrial laser scanning tls were utilized as the external monitoring methods to obtain the outside displacement of the disturbed houses the results were then used to estimate the internal mechanical state of houses using simulation software three high quality houses in paifang village china were scanned using tls in their pre and post mining stages the magnitude of movement and deformation was highly related to the location of the building in the panel which was enlarged near the center of the subsidence basin ansys was used to compute the internal state of the houses with a focus on the structural columns ring beams and walls of the houses under changing tensile conditions results showed that the structural column and ring beam can resist tensile deformation whereas the window corner was the principal point of stress concentration with potential risk of cracking mastering the internal stress state of undamaged buildings in mining affected areas can help to strengthen the premaintenance of houses and guide the construction of new anti deformation houses the results of this work may benefit the construction of anti deformation buildings in mining regions

casing effects in the sea to borehole electromagnetic method the sea to borehole controlled source electromagnetic csem method has the potential of becoming a useful new exploration and monitoring technique modeling shows that the electromagnetic fields at reservoir depths can be 1 2 orders of magnitude larger than those on the seabed thus opening up the possibility to see deeper or detect and monitor smaller targets in the case of measurements inside metal casing the use of reciprocity to interchange the source and receiver allows the casing conductortobeconsideredasanantenna thisantennaisexcited by a source inside the casing which induces a current flowing along the casing conductor based on the current distribution a casing dipole moment and an equivalent length were derived for thetransversemagnetictmmode inthefrequencyrangeofinterest 0 1 10 hz the increase in field strength resulting from sea to borehole measurements is not lost to the casing attenuation for either the tm or the transverse electric te mode the ratio of the dipole moment of the casing antenna to that of the sourcecurrentcanbeconsideredasthecasingattenuationeffect thisratioisnotfarfromunityforfrequenciessmallerthan1 hz but it decreases rapidly with frequency the equivalent length of the casing antenna can be of the order of a few hundred meters as a consequence the field distribution changes significantly in the presence of casing and the vertical resolution of tm measurementsisdegraded thehorizontalresolutionisnotdegraded significantly measurementofthetmmodehastheadvantageof being sensitive to thin resistive targets and being less affected by sea air interactions in shallow water the te mode measurement having a localized casing effect contributes valuable informationaboutthebackgroundresistivity

understanding lotem data from mountainous terrain long offset transient electromagnetic lotem data from the vesuvius volcano in italy show that the em response of the topography is a potential cause of data distortions a modeling study was carried out to simulate the effect of mountainous terrain on vertical magnetic field time derivatives using a 3 d finite difference code the objectives were to assess the importance of topographic effects and to help identify them in existing field data the total effect of topography on the lotem response can be considered as a combination of four distortions of the corresponding responses for a flat terrain first the receiver is at some height above the flat surface second the mountain acts as a conductive body displacing air third large loop receivers are nonhorizontal and sense a combination of horizontal and vertical magnetic fields finally the electromagnetic coupling between the mountain and deeper lying structure modifies the structure response each of the effects can be identified in field data

a 10 000 year record of dune activity dust storms and severe drought in the central great plains dune fi elds and loess deposits of the great plains of north america contain stratigraphic records of eolian activity that can be used to extend the short observational record of drought we present a 10 000 yr reconstruction of dune activity and dust production in the central great plains region based on 95 optically stimulated luminescence ages the integration of data from both eolian sand and loess is an important new aspect of this record clusters of ages defi ne episodes of extensive eolian activity which we interpret as a response to frequent severe drought at 1 0 0 7 ka and 2 3 4 5 ka with peaks centered on 2 5 and 3 8 ka sustained eolian activity occurred from 9 6 to 6 5 ka parts of this record may be consistent with hypotheses linking holocene drought to sea surface temperature anomalies in the pacifi c or atlantic oceans or to the el nino southern oscillation phenomenon but the record as a whole is diffi cult to reconcile with any of these hypotheses

a diatom record of late holocene climate variation in the northern range of yellowstone national park usa the changes in diatom species composition in a sediment core from crevice lake yellowstone national park spanning the past 2550 yr were used to reconstruct long term limnological and ecological conditions that may be related to late holocene climate variability planktic forms dominate the fossil diatom assemblages throughout this record but changes in species dominance indicate varying nutrient levels over time particularly phosphorus the changes in the nutrient concentrations in the lake were probably driven by changes in temperature and wind strength that affected the duration of water column mixing and thus the extent of nutrient recycling from deep waters prior to 2100 cal before present bp stephanodiscus minutulus and synedra tenera dominated suggesting long cool springs with extensive regeneration of phosphorus from the hypolimnion that resulted from isothermal mixing from 2100 to 800 cal bp these species were replaced by cyclotella michiganiana and cyclotella bodanica these species are characteristic of lower nutrient concentrations and are interpreted here to reflect warm summers with long periods of thermal stratification from 800 to 50 cal bp s minutulus dominated the diatom assemblage suggesting a return to lengthy mixing during spring the most dramatic late holocene changes in the fossil diatom assemblages occurred during the transition from the medieval period to the little ice age approximately 800 cal bp

three dimensional modeling of lacustrine diatom habitat areas improving paleolimnological interpretation of planktic benthic ratios three dimensional modeling of lake morphometry enables the calculation of lake volume planar surface area and basin surface area which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level we have applied three dimensional modeling to foy lake montana and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake the model allows us to produce semiquantitative depth reconstructions and greatly improves lake level reconstruction of this morphometrically complex basin the conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record comparison of the model results with both long and short sedimentary records from foy lake montana suggests that planktic benthic ratios may be a better predictor of mean lake depth than maximum lake depth the model developed here is simple enough to be easily implemented has few requirements can be adapted to suit any lake basin and can be augmented to examine a variety of different lake processes that affect habitat availability

annual precipitation in the yellowstone national park region since ad 1173 cores and cross sections from 133 limber pine pinus flexilis james and douglas fir pseudotsuga menziesii mirbel franco at four sites were used to estimate annual july to june precipitation in the yellowstone national park region for the period from ad 1173 to 1998 examination of the long term record shows that the early 20th century was markedly wet compared to the previous 700 yr extreme wet and dry years within the instrumental period fall within the range of past variability and the magnitude of the worst case droughts of the 20th century ad 1930s and 1950s was likely equaled or exceeded on numerous occasions before ad 1900 spectral analysis showed significant decadal to multidecadal precipitation variability at times this lower frequency variability produces strong regime like behavior in regional precipitation with the potential for rapid high amplitude switching between predominately wet and predominately dry conditions over multiple time scales strong yellowstone region precipitation anomalies were almost always associated with spatially extensive events spanning various combinations of the central and southern u s rockies the northern u s southern canadian rockies and the pacific northwest 2007 university of washington all rights reserved

holocene seasonal variability inferred from multiple proxy records from crevice lake yellowstone national park usa article i nfo a 9400 yr old record from crevice lake a semi closed alkaline lake in northern yellowstone national park was analyzed for pollen charcoal geochemistry mineralogy diatoms and stable isotopes to develop a nu anced understanding of holocene environmental history in a region of northern rocky mountains that re ceives both summer and winter precipitation the limited surface area conical bathymetry and deep water 31 m of crevice lake create oxygen deficient conditions in the hypolimnion and preserve annually laminated sediment varves for much of the record pollen data indicate that the watershed supported a closed pinus dominated forest and low fire frequency prior to 8200 cal yr bp followed by open parkland until 2600 cal yr bp and open mixed conifer forest thereafter fire activity shifted from infrequent stand replacing fires initially to frequent surface fires in the middle holocene and stand replacing events in recent centuries low values of 18 o suggest high winter precipitation in the early holocene followed by steadily drier conditions after 8500 cal yr bp carbonate rich sediments before 5000 cal yr bp imply warmer summer conditions than after 5000 cal yr bp high values of molybdenum mo uranium u and sulfur s indicate anoxic bottom waters before 8000 cal yr bp between 4400 and 3900 cal yr bp and after 2400 cal yr bp the diatom record indicates extensive water column mixing in spring and early summer through much of the holocene but a period between 2200 and 800 cal yr bp had strong summer stratification phosphate limita tion and oxygen deficient bottom waters together the proxy data suggest wet winters protracted springs and warm effectively wet summers in the early holocene and less snowpack cool springs warm dry sum mers in the middle holocene in the late holocene the region and lake experienced extreme changes in win ter spring and summer conditions with particularly short springs and dry summers and winters during the roman warm period 2000 cal yr bp and medieval climate anomaly 1200 800 cal yr bp long springs and mild summers occurred during the little ice age and these conditions persist to the present although the proxy data indicate effectively wet summer conditions in the early holocene and drier conditions in the middle and late holocene none point specifically to changes in summer precipitation as the cause in stead summer conditions were governed by multi seasonal controls on effective moisture that operated over multiple time scales

a 2200 yr record of hydrologic variability from foy lake montana usa inferred from diatom and geochemical data abstract a 2200 yr long high resolution 5 yr record of drought variability in northwest montana is inferred from diatoms and 18o values of bio induced carbonate preserved in a varved lacustrine core from foy lake a previously developed model of the diatom response to lake level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data high frequency decadal fluctuations in the de trended 18o record mirror variations in wet dry cycles inferred from banff tree rings demonstrating the sensitivity of the oxygen isotope values to changes in regional moisture balance low frequency multi centennial isotopic changes may be associated with shifts in the seasonal distribution of precipitation from 200 b c to a d 800 both diatom and isotope records indicate that climate was dry and lake level low with poor diatom preservation and high organic carbon nitrogen ratios subsequently lake level rose slightly although the climate was drier and more stable than modern conditions at a d 1200 lake level increased to approximately 6 m below present elevation after which the lake fluctuated between this elevation and full stage with particularly cool and or wetter conditions after 1700 the hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake s outlet spectral analysis of the 18o data indicates that severe droughts occurred with multi decadal 50 to 70 yr frequency

reservoir characterization using crosswell electromagnetic inversion a feasibility study for the snorre field north sea the spatial resolution of a commercially available crosswell electromagnetic em system is demonstrated using models derived from three time steps from a reservoir simulation of the snorre field in the north sea the numerical simulation of the snorre field waterflood shows that crosswell em field measurements provide high sensitivity to changes in the reservoir over time this sensitivity is achieved by combining the reservoir geometry derived from surface 3 d seismic interpretation reservoir conductivities at well locations and constrained em inversion of the reservoir s electrical conductivity inversions of 2 d and 3 d numerical models show that the changes in electrical conductivity attributable to changes in water saturation can be quantitatively mapped as a function of time the inversions provide smooth estimates of the spatial variation of reservoir electrical conductivity that can discriminate between the level of water saturation at different stages of the waterflood inversions performed on

a land controlled source electromagnetic experiment using a deep vertical electric dipole experimental settings processing and first data interpretation a multichannel borehole to surface controlled source electromagnetic experiment was carried out at the onshore co2 storage site of hontom in spain the electromagnetic source consisted of a vertical electric dipole located 1 5 km deep and the electric field was measured at the surface the subsurface response has been obtained by calculating the transfer function between the transmitted signal and the electric field at the receiver positions the dataset has been processed using a fast processing methodology appropriate to be applied on controlled source electromagnetics csem data with a large signal to noise ratio the dataset has been analysed in terms of data quality and repeatability errors showing data with low experimental errors and good repeatability we evaluate if the induction of current along the casing of the injection well can reproduce the behaviour of the experimental data

optical and radiocarbon ages of stacked paleosols and dune sands in the nebraska sand hills usa abstract optical ages for eolian sands from the nebraska sand hills indicate periods of extensive eolian activity at ca 115 25 840 70 2300 240 and 3560 340 a activity was also noted at single sampling locations at ca 6180 370 8430 510 and 13110 800 a many of these ages are similar to those noted by earlier authors optical ages from samples collected within paleosols indicate shorter and possibly less extensive periods of eolian activity at approximately 1220 150 1590 110 and possibly 1950 150 a during which the paleosol sands accumulated what was originally interpreted as a single 1 2 m thick paleosol is shown by optical dating to consist of three or more welded soils developed within eolian sands with optical ages of ca 3800 240 2740 240 1560 110 and possibly 1930 140 a each of which match eolian pulses recognized elsewhere scatter in some optical ages is attributable to intersection of sand filled rodent burrows extending in outcrop 1 5 m below the contact between paleosol and overlying topset beds a 5310 360 a optical age for one probable intersected burrow provides evidence for upward or lateral transport of older sands

lake sediments record large scale shifts in moisture regimes across the northern prairies of north america during the past two millennia six high resolution climatic reconstructions based on diatom analyses from lake sediment cores from the northern prairies of north america show that shifts in drought conditions on decadal through multicentennial scales have prevailed in this region for at least the last two millennia the predominant broad scale pattern seen at all sites is a major shift in moisture regimes from wet to dry or vice versa depending on location that occurred after a period of relative stability these large scale shifts at the different sites exhibit spatial coherence at regional scales the three canadian sites record this abrupt shift between anno domini 500 and 800 and subsequently conditions become increasingly variable all three u s sites underwent a pronounced change but the timing of this change is between anno domini 1000 and 1300 thus later than in all of the canadian sites the mechanisms behind these patterns are poorly understood but they are likely related to changes in the shape and location of the jet stream and associated storm tracks if the patterns seen at these sites are representative of the region this observed pattern can have huge implications for future water availability in this region

integrated seismic electromagnetic workflow for sub basalt exploration in northwest saudi arabia a project involving magnetotellurics shallow em and gravity acquisition was carried out in northwest saudi arabia to improve the imaging of a basalt covered section of the al jawf graben where seismic is particularly noisy the al jawf graben extends from jordan to saudi arabia mesozoic and paleozoic sections contained within the structure have the potential to host multiple oil reservoirs the lack of reliable seismic data in this area motivated the use of a multi geophysics exploration approach electromagnetic em techniques were identified as the optimal complementary geophysical data set in fact the em signal propagates through the resistive basalt cover with minimal attenuation providing information about the underlying conductive sedimentary section a combination of active source time domain em tdem and broadband magnetotelluric mt techniques imaged the base of the shallow basalt cover and its internal variations as well as larger scale faults that control the graben structure integrati

multidecadal drought and holocene climate instability in the rocky mountains time series analysis of a diatom inferred drought record suggests that holocene hydroclimate of the northern rocky mountains has been characterized by oscillation between two mean climate states the dominant climate state was initiated at the onset of the holocene ca 11 ka under this climate state drought was strongly cyclic recurring at frequencies that are similar to twentieth century multidecadal phase changes of the pacific decadal oscillation this pattern remained consistent throughout much of the midholocene continuing until ca 4 5 ka after this time the mean climate state changed and drought recurrence became unstable periods of cyclic drought alternated with periods of less predictable drought the timing of this shift in climate was coincident with widespread severe drought in the mid continent of north america overall the strongest periodicity in severe drought occurred during the mid holocene when temperatures in the northern rocky mountains were warmer than today

a tree ring based reconstruction of the atlantic multidecadal oscillation since 1567 a d 1 we present a tree ring based reconstruction of the atlantic multidecadal oscillation amo which demonstrates that strong low frequency 60 100 yr variability in basin wide 0 70 n sea surface temperatures ssts has been a consistent feature of north atlantic climate for the past five centuries intervention analysis of reconstructed amo indicates that 20th century modes were similar to those in the preceding 350 yr and wavelet spectra show robust multidecadal oscillations throughout the reconstruction though the exact relationships between low frequency sst modes higher frequency 7 25 yr atmospheric modes e g north atlantic oscillation arctic oscillation and terrestrial climates must still be resolved our results confirm that the amo should be considered in assessments of past and future northern hemisphere climates

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

a borehole to surface electromagnetic survey the results of a limited field trial confirm the usefulness of borehole to surface electromagnetic em measurements for monitoring fluid extraction a vertical em profiling experiment was done at the university of california richmond field station where we simulated a brine spill plume by creating a saline water injection zone at the depth of 30 m the data acquisition mode was analogous to the reverse vertical seismic profiling vsp configuration used for seismic measurements in that the em transmitter traversed the pvc cased borehole used for fluid injection and extraction while the receivers were deployed on the surface the em measurements were made at 9 6 khz with an accuracy of 1 in signal amplitude and 1 in signal phase observations were taken at 5 m intervals along two intersecting profiles that were centered on the injection well and extended for 60 m on either side of it the presence of the injected salt water at the expected 30 m depth was indicated clearly by differences between the p

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

fire and vegetation history during the last 3800 years in northwestern montana abstract foy lake in northwestern montana provides a record of annual to decadal scale landscape change sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years which were then compared to similar records from ad 1880 to 2000 the long term record at foy lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change fire activity inferred from the frequency of charcoal peaks averaged 18 fire episodes 1000 years from 3800 to 2125 cal year bp and increased from 16 fire episodes 1000 years at 2125 cal year bp to 22 episodes 1000 years at 750 cal year bp a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover between 2125 and 750 cal year bp increased forest cover produced more background charcoal than before and after this period when vegetation was dominated by steppe between 750 and 75 cal year bp steppe has expanded and fire episode frequency averaged 33 episodes 1000 years increasing to a maximum of 40 episodes 1000 years at ca 300 cal year bp and then decreasing to present levels since ad 1880 the pollen record indicates an increase in shrubs and grasses from ad 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing no fires have been documented in the foy lake watershed since ad 1880 charcoal from the extralocal fires of ad 1910 burning over 4 111 249 ha in idaho montana and wyoming however is present in foy lake between ad 1970 and 2000 increased arboreal pollen in the record is consistent with observations that the forest has become more closed the activities of euro americans have led to a decline in forest cover between ad 1880 and 1970 followed by a recent increase as trees are now growing in areas previously occupied by steppe euro americans are likely the cause of a reduction in fire activity in watershed since ad 1880

influence of late holocene climate on northern rocky mountain mammals an exceptionally rich paleontological site containing thousands of mammalian fossils and well dated with 18 radiocarbon samples provides evidence of late holocene ecological response to climatic change in northern yellowstone national park wyoming the mammalian fauna composed of 10 597 identified specimens shows surprising affinity to the local habitat with little evidence of long distance transport of faunal elements thus revealing the faithfulness of a fossil site to the community from which it is derived the mammals illustrate ecological sensitivity to a series of mesic to xeric climatic excursions in the sagebrush grassland ecotone during the past 3200 yr from 3200 cal yr b p to a maximum of 1100 cal yr b p the species composition of mammals indicates wetter conditions than today beginning about 1200 cal yr b p the fauna becomes more representative of xeric conditions with maxima in xeric indicator taxa and minima in mesic indicator taxa concordant with the medieval warm period circa 1000 to 650 yr b p cooler wetter conditions which prevailed for most of the little ice age 700 to 100 yr b p in general correspond to a return to a more mesic mammalian fauna a warm period within the little ice age is documented by a xeric fauna these data show that mammalian ecological sensitivity to climatic change over this intermediate time scale holds promise for predictions about the impacts of future global warming

geochemical evidence for hydroclimatic variability over the last 2460 years from crevice lake in yellowstone national park usa abstract a 2460 year long hydroclimatic record for crevice lake yellowstone national park montana was constructed from the 18 o values of endogenic carbonates the 18 o record is compared to the palmer hydrologic drought index phdi and pacific decadal oscillation pdo indices as well as inferred discharge of the yellowstone river during the last century high 18 o values coincide with drought conditions and the warm phase of the pdo index low 18 o values coincide with wet years and a negative pdo index comparison of tree ring inferred discharge of the yellowstone river with the 18 o record over the last 300 years indicates that periods of high discharge i e wet winters with significant snow pack correspond with low 18 o values extrapolating this relationship we infer wet winters and high river discharge for the periods of 1090 1030 970 870 670 620 and 500 430 cal years bp the wet intervals at 670 and 500 cal bp are synchronous with similar events in banff canada and walker lake nevada the wet intervals at 970 and 670 cal bp overlap with wet intervals at walker lake and major drought events identified in the western great basin these results suggest that the northern border of yellowstone national park straddles the boundary between northern rocky mountains and great basin climate regimes

feasibility study for 2d frequency dependent electromagnetic sensing through casing we perform a numerical sensitivity study of various physical phenomena of interest for borehole resistivity logging applications in steel cased wells specifically we analyze the sensitivity of through casing measurements for detecting water invasion shale laminated sands and electrical anisotropy in the formation in addition we study the influence of the frequency of operation on through casing resistivity measurements the sensitivity analysis is performed using a highly accurate and reliable numerical method based on a 2d self adaptive goal oriented high order finite element method fem this method can be applied to simulate all types of resistivity logging measurements including normal laterolog induction and through casing resistivity measurements results quantify the effects of several physical phenomena that can be sensed through casing and that can be measured with accurate sensors we find that water invasion and shale laminated sands behind casing can be detected and accurately qua

widespread drought episodes in the western great lakes region during the past 2000 years geographic extent and potential mechanisms we compared high resolution reconstructions of peatland water table depth at two raised bogs in the western great lakes region separated by 1000 km the sites included minden bog in southeastern michigan and hole in the bog in north central minnesota our objectives were to 1 determine whether large decadal to multidecadal droughts of the past 2000 yrs were spatially and temporally coherent across the region and 2 assess the underlying mechanisms of widespread droughts in the region we found a strong correlation between bog inferred records of moisture variability in the two regions r 0 53 between 2100 and 600 bp extreme drought events centered on 1850 1800 1650 1000 800 and 700 bp are recorded in both regions many of these drought events were contemporaneous with large droughts already documented at sites far to the west in the great plains and rocky mountains to identify potential modern climate analogues we used empirical orthogonal function eof analysis to reveal spatial modes of variability in drought and precipitation records of north america for the past century the first eofs of annual precipitation and palmer drought severity index pdsi were similar to each other and consistent with a pattern of widespread continental drought correlations between these eofs and annual sea surface temperatures ssts indicate strong relationships to ssts in both the atlantic and pacific basins we hypothesize that widespread droughts between 1000 and 700 bp were related to amplification of a spatial mode of moisture variability associated with an anomalously warm north atlantic a warm mid latitude north pacific and an anomalously cold tropical pacific a more extensive network of hydroclimate records developed using a consistent set of methods and proxies could be used in conjunction with high resolution records of past ssts to test this hypothesis

quantifying surface to reservoir electromagnetics for waterflood monitoring in a saudi arabian carbonate reservoir abstractwe modeled surface to borehole controlled source electromagnetics to assess the sensitivity of electromagnetic fields to the detection and evolution of the waterfront position in a saudi arabian carbonate reservoir we studied a test well drilled for research purposes at the edge of the current waterfront the 3d reservoir saturations were obtained by using a black oil simulator and later converted to resistivity using archie s empirical relation the anisotropic overburden model was derived from the upscaling of triaxial resistivity logs acquired from the surface to reservoir depth in the well the modeling study was performed by the combination of 3d finite element time domain and 3d finite difference frequency domain methods using surface galvanic sources in radial and transverse polarization modes with borehole receivers results indicated that the electric field components have the largest sensitivity to static reservoir resistivity distributions and to the time lapse resistivity changes the

the little ice age in the canadian rockies abstract this paper reviews the evidence and history of glacier fluctuations during the little ice age lia in the canadian rockies episodes of synchronous glacier advance occurred in the 12th 13th early 18th and throughout the 19th centuries regional ice cover was probably greatest in the mid 19th century although in places the early 18th century advance was more extensive glaciers have lost over 25 of their area in the 20th century selective preservation of the glacier record furnishes an incomplete chronology of events through the 14th 17th centuries in contrast varve sequences provide continuous annually resolved records of sediments for at least the last millennium in some highly glacierized catchments such records have been used to infer glacier fluctuations evaluation of recent proxy climate reconstructions derived from tree rings provides independent evidence of climate fluctuations over the last millennium most regional glacier advances follow periods of reduced summer temperatures reconstructed from tree rings particularly ca 1190 1250 1280 1340 1690s and the 1800s reconstructed periods of higher precipitation at banff alberta since 1500 are 1515 1550 1585 1610 1660 1680 and the 1880s glacier advances in the early 1700s the late 1800s and in places the 1950 1970s reflect both increased precipitation and reduced summer temperatures negative glacier mass balances from 1976 to 1995 were caused by decreased winter balances the glacier fluctuation record does not contain a simple climate signal it is a complex response to several interacting factors that operate at different timescales evaluation of climate proxies over the last millennium indicates continuous variability at several superimposed timescales dominated by decade century patterns only the 19th century shows a long interval of sustained cold summers this suggests that simplistic concepts of climate over this period should be abandoned and replaced with more realistic records based on continuous proxy data series the use of the term lia should be restricted to describing a period of extended glacier cover rather than being used to define a period with specific climate conditions

direct versus indirect climate controls on holocene diatom assemblages in a sub tropical deep alpine lake lugu hu yunnan sw china the reconstruction of holocene environmental changes in lakes on the plateau region of southwest china provides an understanding of how these ecosystems may respond to climate change fossil diatom assemblages were investigated from an 11 000 year lake sediment core from a deep alpine lake lugu hu in southwest china an area strongly influenced by the southwest or the indian summer monsoon changes in diatom assemblage composition notably the abundance of the two dominant planktonic species cyclotella rhomboideo elliptica and cyclostephanos dubius reflect the effects of climate variability on nutrient dynamics mediated via thermal stratification internal nutrient cycling and catchment vegetation processes statistical analyses of the climate diatom interactions highlight the strong effect of changing orbitally induced solar radiation during the holocene presumably via its effect on the lake s thermal budget in a partial redundancy analysis climate solar insolation and proxies reflecting catchment process pollen percentages c n ratio were the most important drivers of diatom ecological change showing the strong effects of climate catchment vegetation interactions on lake functioning this diatom record reflects long term ontogeny of the lake catchment ecosystem and suggests that climatic changes both temperature and precipitation impact lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports