reliable late pleistocene stratigraphic ages and shorter groundwater travel times from14c in fossil snails from the southern great basin both aquatic and land snails are common in the geologic record but their utility in dating is greatly restricted by their well documented tendency to yield14c dates inconsistent with true14c ages in this study we examine the use of14c ages from 1 small previously unstudied terrestrial snails to date hosting spring deposits and from 2 cooccuring aquatic snails to constrain groundwater travel times during the last glacial period our study area in the southern great basin encompasses yucca mountain site of the proposed high level nuclear waste repository where information on the age and extent of past high water tables and on groundwater flow times is crucial to several licensing issues our results show that shells of small terrestrial snails belonging tovalloniasp yield14c dates consistent with14c ages of associated carbonized wood these results imply that these taxa can provide reliable14c age control on the broadly distributed deposits in which they have been described in contrast cooccurring aquatic snails from fossil spring deposits yield14c ages generally greater than the control age this is because the aquatic shells often formed in spring waters that had an initial14c deficiency however the magnitude of the deficiency is much less than that observed in nearby modern springs arguing for much higher average14c contents in late pleistocene groundwaters in these basins if representative this implies shorter groundwater travel times through aquifers in southern nevada during late glacial time

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

age characteristics in a multidecadal arctic sea ice simulation 1 results from adding a tracer for age of sea ice to a sophisticated sea ice model that is widely used for climate studies are presented the consistent simulation of ice age dynamics and thermodynamics in the model shows explicitly that the loss of arctic perennial ice has accelerated in the past three decades as has been seen in satellite derived observations our model shows that the september ice age average across the northern hemisphere varies from about 5 to 8 years and the ice is much younger about 2 3 years in late winter because of the expansion of first year ice we find seasonal ice on average comprises about 5 of the total ice area in september but as much as 1 34 106 km2 survives in some years our simulated ice age in the late 1980s and early 1990s declined markedly in agreement with other studies after this period of decline the ice age began to recover but in the final years of the simulation very little young ice remains after the melt season a strong indication that the age of the pack will again decline in the future as older ice classes fail to be replenished the arctic ice pack has fluctuated between older and younger ice types over the past 30 years while ice area thickness and volume all declined over the same period with an apparent acceleration in the last decade

carbon and isotopic mass balance models of oasis valley fortymile canyon groundwater basin southern nevada environmental isotopes and carbon chemistry provide means of differentiating various recharge areas flow paths and ages of ground water in portions of the nevada test site and vicinity regional delta d delta sup 18 o trends are offset from the present day meteoric line by a deuterium depletion of 5 per thousandth suggesting paleoclimatic changes partial pressures of co sub 2 and the sup 18 o and sup 13 c data indicate solubility and isotopic equilibrium between the gas and water in the soil zone with progressive exchange with underlying ground water in the shallow alluvium of oasis valley application of a closed system co sub 2 model using the eq3nr eq6 reaction path simulator successfully reproduces chemical compositions observed in the alluvium in the amargosa desert and in the deep tuff aquifer beneath pahute mesa and yucca mountain initial p sub co sub 2 input to the soil zone during recharge was calculated to range from 0 03 to 0 10 atm which is comparable to measured soil co sub 2 pressures in oasis valley results are compared for sup 14 c ages using the delta sup 13 c dilution correction and a mass action correction term relating predicted and calculated ionic activity products of caco sub 3 results are generally comparable with discrepancies attributed to anomalous delta supmore 13 c values less

conservative behavior of arsenic and other oxyanion forming trace elements in an oxic groundwater flow system summary groundwater samples were collected along a flow path in a shallow fractured tuffaceous aquifer from the oasis valley beatty wash region of southern nevada usa and analyzed for a number of oxyanion forming trace elements including arsenic as antimony sb selenium se molybdenum mo and tungsten w in addition ancillary geochemical parameters including ph major solute compositions dissolved silica dissolved oxygen and iron and manganese concentrations were quantified in the groundwaters arsenic concentrations range from 70 nmol kg up to 316 nmol kg in groundwaters of the oasis valley beatty wash flow system and generally exhibit increasing concentrations with flow down gradient along the flow path antimony w and to a lesser extent mo exhibit similar increasing concentration trends with flow down gradient in the aquifer albeit at lower concentrations levels e g mean sd for sb w and mo are 2 3 0 9 nmol kg 7 4 3 7 nmol kg and 101 19 nmol kg respectively selenium concentration which range between 4 and 11 nmol kg generally decrease in groundwaters with flow down gradients in the oasis valley beatty wash groundwater flow systems inverse modeling of groundwater chemistry evolution from the lower reaches of the oasis valley flow path using phreeqc indicate that the groundwater composition is consistent with mixing of nearly equal proportions of groundwater from upper reaches of oasis valley and beatty wash groundwater along with dissolution of volcanic glass potassium feldspar and gypsum followed by calcite precipitation and formation of secondary zeolites analcime clay minerals ca montmorillonite and cristobalite the geochemical modeling indicates that the concentrations of as and the other oxyanion forming trace elements are controlled by dissolution of volcanic glass water rock interaction with mineralized zones within the aquifer i e sulfide oxidation desorption from aquifer surface sites and mixing of oasis valley and beatty wash groundwaters

large scale ice thickness distribution of first year sea ice in spring and summer north of svalbard the large scale thickness distribution of sea ice was measured during several campaigns in the european arctic north of svalbard from 2007 using an airborne electromagnetic induction device in august 2010 and april may 2011 this was complemented by extensive on ice work including measurements of snow thickness and freeboard ice thicknesses show a clear difference between the seasons with thicker ice during spring than in summer in spring 2011 negative freeboard and flooding were observed as a result of the extensive snow cover we find that the characteristics of the first year sea ice allow combining observations from different years the ice thickness in the marginal ice zone increases with increasing latitude and increasing distance to the ice edge however in the inner ice pack from 100 km from the ice edge the thickness remains almost constant modal ice thickness in spring reaches 2 4 m whereas in summer it is 1 0 1 4 m our study provides new insight into ice thickness distributions of a typical ice cover consisting of mainly first and second year ice which may become the dominant ice type in the arctic in the future

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

geochemical and isotopic evidence of a groundwater source in the corral canyon meadow complex central nevada usa major inorganic ions and stable carbon and oxygen isotopes in stream water groundwater groundwater seeps and springs were measured in the corral canyon meadow complex and watershed in the toquima mountains of central nevada usa the purpose of the study was to determine whether stream water or groundwater was the source of water that supports vegetation in the meadow complex water samples from the watershed and meadow complex were mixed cation hco3 type stream water sampled at different locations in the meadow complex showed variations in temperature ph and specific conductance the cation anion proportions for stream water were similar to groundwater groundwater seeps and runoff from the meadow complex stable oxygen isotope ratios for stream water 17 1 to 17 6 versus vsmow and groundwater and groundwater seeps in the meadow site 17 0 to 17 7 versus vsmow were similar and consistent with a local meteoric origin dissolved inorganic carbon dic and the 13cdic for stream water 12 1 to 15 0 versus vpdb were different from that of groundwater from the meadow complex 15 3 to 19 9 versus vpdb suggesting different carbon evolution pathways however a simple model based on cation 13cdic suggests that stream water was being recharged by shallow groundwater groundwater seeps and runoff from the meadow complex this leads to the conclusion that the source of water that supports vegetation in the meadow complex was primarily groundwater the results of this study suggest that multiple chemical and stable carbon isotope tracers are useful in determining the source of water that supports vegetation in meadow complexes in small alpine watersheds copyright 2004 john wiley sons ltd

thickness and density of snow covered sea ice and hydrostatic equilibrium assumption from in situ measurements in fram strait the barents sea and the svalbard coast modern satellite measurements of sea ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface for retrieval of sea ice thickness it is assumed that the ice is in hydrostatic equilibrium and that the snow load on the ice and the density of the sea ice and sea water are known this study presents data from in situ sea ice thickness drillings and snow and ice density measurements from fram strait the barents sea and the svalbard coast in the european arctic the error in the altimetry ice thickness products is assessed based on the spatial variability of snow and ice density and snow thickness data ice thickness uncertainty related to snow depth was found to be 40 cm radar altimeter and 90 cm laser altimeter while uncertainty related to ice density is 25 cm for both techniques the assumption of hydrostatic equilibrium at the scales of the measurements 10 100 m was found to hold better in the case of level landfast ice near svalbard than for fram strait drift ice which consists of mixed ice types where the deviation between the calculated and measured ice thicknesses was on average 0 5 m

isotopic and trace element constraints on the origin and evolution of saline groundwaters from central missouri na ca cl groundwaters with salinities of 1 to 30 discharge from natural springs and artesian wells in mississippian carbonates and ordovician sandstones and carbonates in central missouri carbonate saturation and quartz supersaturation are maintained throughout the salinity range major and trace element and isotopic variations in the waters are used to place constraints on models for rock water interaction and regional hydrology the groundwaters have d values that range from 108 to 45 and 18 o values that range from 14 7 to 6 5 smow these data lie approximately along the meteoric water line ranging from values similar to local recharge in missouri to significantly lower values that are similar to 18 o and d for meteoric recharge in high altitude and high latitude regions of north america the more saline samples have the lowest 18 o and d contents a trend that is opposite to that observed in most other studies of saline waters the h o isotopic correlation and the range in salinity and several major and trace element concentrations in central missouri groundwaters are readily explained by a saline dilute water mixing model 87sr 86sr ratios for the groundwaters range from 0 7155 to 0 7161 these values are significantly higher than previously published values for 1 estimates of 87 sr 86 sr in phanerozoic seawater 0 7068 0 7092 and 2 carbonates of the mississippian burlington keokuk fm 0 7075 0 7105 through which some of the waters migrate as they pass to the surface nd 0 values in the groundwaters range from 10 9 to 8 1 and 147 sm 144 nd ratios range from 0 108 to 0 128 these values are similar to or lower than previously published analyses of carbonates and other authigenic phases from the burlington keokuk fm mean nd 0 7 8 0 8 1 mean 147 sm 144 nd 0 141 the h o sr and nd isotopic data and the results of model calculations preclude 1 models involving the modification of ancient seawater for the origin of the saline waters and 2 extensive interaction between the groundwaters and their host carbonates the waters apparently acquired their 18 o and d values as meteoric recharge and their 87sr 86sr and rare earth element signatures from extraformational crustal sources high 87 sr 86 sr low nd 0 low 147sm 144nd and largely preserved these isotopic signatures during subsequent migration through the carbonates chemical exchange via rock water interaction is required for isotopic exchange to occur therefore the present state of chemical equilibrium between the groundwaters and carbonate aquifer minerals may serve to limit rock water interaction and hence preserve the extraformational isotopic signatures in the waters the integration of geochemical isotopic and hydrologic data on a local and regional scale suggests a history for the central missouri groundwaters involving 1 meteoric recharge in the front range of colorado 2 dissolution of permian halite in the subsurface of kansas 3 interaction with predominantly silicate mineral assemblages in paleozoic strata and possibly precambrian basement with aquisition of crustal sr and ree signatures 4 dilution and migration to shallow aquifer levels in central missouri and 5 mixing with local meteoric recharge through mississippian carbonates with no significant change of the isotopic signatures acquired in stage 3

crustal structure of a proterozoic craton boundary east albany fraser orogen western australia imaged with passive seismic and gravity anomaly data abstract we use passive seismic and gravity data to characterize the crustal structure and the crust mantle boundary of the east albany fraser orogen in western australia a proterozoic orogen that reworked the southern and southeastern margin of the archean yilgarn craton the crustal thickness pattern retrieved from receiver functions shows a belt of substantially thickened crust that follows the trend of the orogen but narrows to the southwest common conversion point profiles show a clear transition from a wide symmetric moho trough in the northeast to a one sided northwestern moho dip in the southwest where the moho appears to underthrust the craton towards its interior this change appears to coincide with the inferred trace of the ida fault a major terrane boundary within the yilgarn craton forward modelling of gravity anomaly data using the retrieved moho geometry as a geometric constraint shows that a conspicuous elongated gravity low on the northwestern side of the east albany fraser orogen is almost certainly caused by thickened archean crust to obtain a model that resembles the regional gravity pattern the following assumptions are necessary high density rocks occur in the upper crust of the fraser zone at depth inside the moho trough and in parts of the eastern nornalup zone east of the moho trough although our gravity models do not constrain at which crustal level these high density rocks occur active deep seismic surveys suggest that large extents of the east albany fraser orogen s lower crust include a mesoproterozoic magmatic underplate known as the gunnadorrah seismic province the simplest interpretation of the imaged crustal structure is that the gunnadorrah seismic province is underthrust beneath the yilgarn craton likely as a consequence of crustal shortening during accretion further east the imaged geometry overall appears to show a wedge of archean lower crust that was driven between the exhumed fraser zone and the gunnadorrah seismic province effectively splitting the paleo to mesoproterozoic crust of the east albany fraser orogen the vertical splitting of proterozoic crust by a cratonic crustal wedge comparable to what we image in this study may be a process that contributed to forming many craton margins around the world

snow depth observations by adventurers traveling on arctic sea ice snow depth is a key parameter for assessing the sea ice mass budget in the arctic and for the surface energy balance at the atmosphere snow ice ocean interfaces however scientific expeditions to the high arctic ocean are rare and for large parts of the year no snow and ice data are collected in situ in most regions therefore any additional in situ observations of snow depth are of interest to the scientific community arctic adventurers and tourists are among the most frequent visitors to the arctic ocean and north pole if properly trained and carefully adhering to standard protocols they could collect valuable snow depth data from large regions here we analyse such data from four arctic basin ski traverses carried out between 1994 and 2007 individual datasets show characteristic regional differences of snow thickness which provide invaluable information for the validation of models and satellite data the observations were made applying a continuously upgraded observation guideline scheme earlier observations were based on a relatively broad view of easily observable snow and ice parameters improvements included requirements of more detailed snow thickness surveys in order to observe the spatial variability over varying sea ice surfaces in a better way possibilities for and limitations of ice thickness estimates and measurements are also discussed often assessment of ice thickness is more problematic since measurements are either time consuming or biased meaning that possibilities for collecting large datasets are limited

exploration of groundwater flowpaths and effective recharge in the amargosa desert nevada using multivariate statistical analysis and elevation dependent chloride mass balance method estimation of groundwater flowpaths and effective recharge was performed in the vicinity of amargosa desert nevada usa using multivariate statistical methods msms and a simple elevation dependent chloride mass balance method modified by estimating a minimum effective recharge elevation mere msms were applied to major ion data to explain the relationships among different groundwater chemical species define hydrochemical facies needed to determine groundwater flowpaths and evolution and identify the influence of surface and geologic features on groundwater for each defined watershed an average groundwater chloride concentration is used and the chloride deposition rate is assessed in the subject watersheds over all land elevations above the estimated mere by assuming two constant spatial and temporal concentrations of chloride in precipitation which is a function of elevation the mere for the amargosa desert was appraised as 1200 m above mean sea level m amsl based upon the elevation of the orifice of cane spring 1237 m amsl one of the lowest elevation permanent springs on the nevada national security site this minimum elevation is the cutoff altitude for our calculations at which precipitation is considered to make a significant contribution to recharge elevation dependent precipitation was evaluated relating elevation data from the online mapping software acme labs mapper 2 1 and precipitation data from the prism climate group s prism these analyses provide further insight into the hydrology of the region and demonstrate the strong impact surface and geologic features can have on surface water infiltration and groundwater in arid regions specifically evidence is presented of past focused recharge around the ephemeral fortymile wash and interaction between geologic faults and groundwater infiltration and flowpaths in addition groundwater flow based upon water chemistry appears to be segmented by major faults groundwater recharge in the vicinity of the amargosa desert has been estimated around 15 280 acre ft year

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

vanadium geochemistry along groundwater flow paths in contrasting aquifers of the united states carrizo sand texas and oasis valley nevada aquifers abstract vanadium v concentrations were measured along the flow paths in two contrasting aquifer systems to study how changing solution composition and redox conditions affect v cycling and transport in groundwater flow systems the oasis valley groundwater system in nevada is an unconfined system where groundwaters generally remain oxic along the flow path whereas the carrizo sand aquifer is a deep confined coastal plain aquifer in texas that contains well defined fe iii and so 4 2 reduction zones along the flow path speciation modeling predicts that in groundwaters from the oasis valley v chiefly occurs as the vanadate oxyanion e g h 2 vo 4 hvo 4 2 which is mobile along the entire flow path because of vanadate s solubility in oxic and alkaline waters furthermore the data indicate that v concentrations increase in groundwaters along the flow path suggesting that mineral dissolution and or desorption reactions progressively contribute v to groundwaters of the oasis valley system geochemical modeling is consistent with dissolution of mafic phenocrysts that are common in the local tuffaceous aquifer rocks as a probable source of v to oasis valley groundwaters within the carrizo sand aquifer groundwater v concentrations decrease with flow beyond the recharge zone and into the confined portion of the aquifer thereafter total v concentrations remain low and relatively constant along the remainder of the studied flow path exhibiting no systematic variations across the fe iii and so 4 2 reduction zones groundwaters from the carrizo sand aquifer are generally reducing and as such geochemical modeling suggests that both v v and v iv species occur in carrizo sand groundwaters and furthermore that the proportion of v iv species increases concurrent with the decrease in total v concentrations along the flow path results from sequential extraction experiments on carrizo sand aquifer sediment samples suggest that v adsorption onto fe iii mn iv oxides oxyhydroxides acts to decrease the aqueous v concentrations in carrizo sand groundwater furthermore geochemical modeling is consistent with complexation of v iv with dissolved organic matter dom within the carrizo sand aquifer groundwaters which owing to the low dom concentrations appears to buffer v at low but relatively constant concentrations within the confined and reducing carrizo sand groundwaters these results support previous reports of v iv dom binding and imply that aquifer material maintains an essential role in not only determining the availability of v to enter aqueous solution but also in influencing partitioning between solid and aqueous phases

solute and isotopic geochemistry and ground water flow in the central wasatch range utah ground water flow systems in the rugged central wasatch range utah were investigated by solute and isotopic methods six types of ground water systems were identified on the basis of rock type and structure the systems are broadly grouped into four categories 1 granitic systems 2 non granitic systems a unconsolidated alluvial systems b consolidated sedimentary rock systems and c fault controlled systems 3 thermal systems 4 mine drainage systems these ground water systems have distinctive solute and isotopic chemistries based on an analysis of 3h and 14c data all of the ground waters have a component of post 1952 recharge water and most of the ground waters are composed almost entirely of post 1952 recharge water a few of the ground water systems contain some water which is hundreds to perhaps thousands of years old the 18o and 2h data plot on a local meteoric water line and none of the data exhibit a positive 18o shift the absence of a positive 18o shift suggests maximum aquifer temperatures are approximately 100 c granitic terrains are dominated by fracture controlled local ground water flow systems which respond rapidly to recharge events the granitic ground water systems have estimated maximum circulation depths of about 160 m below land surface all the alluvial most of the consolidated sedimentary bedrock and some of the fault controlled ground water systems are shallow circulating local flow systems with short travel times ground water circulation of most of the local flow systems is within 200 m of land surface and is bedding plane controlled some of the consolidated bedrock and many of the fault controlled ground water systems are of the intermediate type and have circulation depths to 500 m four thermal ground water systems have been identified the thermal systems are heated by the geothermal gradient and have not circulated deeper than 2 2 5 km the thermal systems are of the intermediate and regional type the solute chemistry of most of the non granitic ground waters may be attributed to the dissolution of carbonate minerals and minor amounts of gypsum contributions of external co2 g to some of the thermal systems from either metamorphic or silicate hydrolysis processes is suspected

geochemical and statistical evidence of deep carbonate groundwater within overlying volcanic rock aquifers aquitards of southern nevada usa abstract samples collected from springs and wells in southern nevada were analyzed for major solutes and trace elements as part of a larger study to characterize the geochemical signatures of these groundwaters in this study principal component analysis pca was used to reduce the large data sets including the four major cations ca mg na k and 27 trace elements analyzed in these groundwater samples principal components analysis of the major cation data indicates that groundwaters from cenozoic felsic volcanic rock aquifers aquitards of southern nevada exhibit strong chemical associations to each other but weak relationships to groundwaters from the regional carbonate aquifer which were instead chemically similar to each other however pca of the trace element data demonstrates that some groundwaters from the volcanic aquifers aquitards are chemically similar to those of the underlying regional carbonate aquifer the pca also reveals that these groundwaters from the volcanic aquifers aquitards have significantly different trace element compositions than perched groundwaters contained within similar felsic volcanic rocks moreover rare earth element ree data from groundwaters collected from wells finished in the volcanic aquifers aquitards of southern nevada have similar concentrations and similar shale normalized patterns to the carbonate aquifer groundwaters as well as local carbonate rocks these same southern nevada well waters do not exhibit ree concentrations or shale normalized signatures that resemble the perched volcanic groundwaters or the tuffs of southern nevada the ree data and trace element pca along with previous carbon isotope analyses water temperature data hydraulic head relations and results of a recent pump test of a well near yucca mountain suggest close contact of the regional carbonate groundwaters and groundwaters from the overlying volcanic rocks of southern nevada and possible upwelling of the carbonate groundwaters into the overlying volcanic rock units in the vicinity of yucca mountain

thickness and surface properties of different sea ice regimes within the arctic trans polar drift data from summers 2001 2004 and 2007 1 large scale sea ice thickness and surface property data were obtained in three summers and in three different sea ice regimes in the arctic trans polar drift tpd by means of helicopter electromagnetic sounding distribution functions p of sea ice thickness and of the height spacing and density of sails were analyzed to characterize ice regimes of different ages and deformations results suggest that modal ice thickness is affected by the age of a sea ice regime and that the degree of deformation is represented by the shape of p mean thickness changes with both age and deformation standard error calculations showed that representative mean and modal thickness could be obtained with transect lengths of 15 km and 50 km respectively in less deformed ice regimes such as those around the north pole in heavier deformed ice regimes closer to greenland 100 km transects were necessary for mean thickness determination and a representative modal thickness could not be obtained at all mean sail height did not differ between ice regimes whereas sail density increased with the degree of deformation furthermore the fraction of level ice open melt ponds and open water along the transects were determined although overall ice thickness in the central tpd was 50 thinner in 2007 than in 2001 first year ice fyi was not significantly thinner in 2007 than fyi in 2001 with a decrease of only 0 3 m thinner fyi in 2007 only occurred close to the sea ice edge where open water covered more than 10 of the surface melt pond coverage retrieved from laser measurements was 15 in both the 2004 myi regime and the 2007 fyi regime

interannual variability of summer sea ice thickness in the siberian and central arctic under different atmospheric circulation regimes extensive drill hole and electromagnetic induction measurements of sea ice thickness in the siberian and central arctic seas in the summers of 1993 1995 and 1996 reveal significant interannual variability in the laptev sea minimum and maximum modal first year ice thicknesses amounted to 1 25 and 1 85 m in 1995 and 1996 respectively ice thickness correlates with ice extent which reached a record minimum in august 1995 and was well above average in 1996 these differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt from drifting buoys deployed in 1995 and satellite radar backscatter data first and second year ice regimes are delineated differences in first year ice backscatter coefficients between 1993 1995 and 1996 are explained by differences in level ice surface roughness the lagrangian evolution of ice thickness between 1995 and 1996 is studied while the shape of the thickness distribution does not change significantly the mean modal ice thickness of the ice field increases from 1 80 m 1 25 m in 1995 to 2 86 m 2 25 m in 1996 the thickness distribution of second year ice in 1996 closely agrees with that of level multiyear ice downstream in the transpolar drift obtained in 1991 in 1996 mean level ice thickness increases at 0 23 and 0 16 m deg 1 with latitude in the kara and laptev sea sectors of the arctic ocean respectively

hydrochemical and 14c constraints on groundwater recharge and interbasin flow in an arid watershed tule desert nevada summary geochemical data deduced from groundwater and vein calcite were used to quantify groundwater recharge and interbasin flow rates in the tule desert southeastern nevada 14 c age gradients below the water table suggest recharge rates of 1 2 mm yr which correspond to a sustainable yield of 5 10 4 km 3 yr to 1 10 3 km 3 yr uncertainties in the applied effective porosity value and increasing horizontal interbasin flow components at greater depths may bias these estimates low compared to those previously reported using the water budget method the deviation of the groundwater 18 o time series pattern for the pleistocene holocene transition from that of the devils hole vein calcite which is considered a proxy for local climate change allows interbasin flow rates of northerly derived groundwater to be estimated the constrained rates 75 0 120 m yr are slightly higher than those previously calculated using darcy s law but translate into hydraulic conductivity values strikingly similar to those obtained from pump tests data further indicate that production wells located closer to the western mountainous margin will be producing mainly from locally derived mountain system recharge whereas wells located closer to the eastern margin are more influenced by older regionally derived carbonate groundwater

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

indirect measurements of the mass balance of summer arctic sea ice with an electromagnetic induction technique abstract in the framework of the surface heat budget of the arctic ocean sheba study indirect non invasive icemass balance measurements were carried out at a drifting station in the northern chukchi sea between mayand august of 1998 ice thickness was derived from electromagnetic induction em measurements ofapparent conductivity along 13 profiles 60 to 900 m long as shown through sensitivity studies with a 1 d model the apparent conductivity data from individual points can be inverted to yield estimates of icethickness and ablation with an accuracy of approximately 0 05 m for 2 m thick level ice ablation ratesranged between 8 and 18 mm d 1 with total ablation amounting to roughly 0 9 to 1 2 m measurements ofthickness and melt rates along different profiles in undeformed multi year ice corresponded closely indicating that the sampling statistics are adequate the roughness of undeformed ice has been found toincrease during the summer due to deepening of melt ponds and enhanced bottom melt ice under melt pondswas disproportionately thinner most likely a result of thicker snow cover reducing winter accretion

sources and fractionation processes influencing the isotopic distribution of h o and c in the long valley hydrothermal system california u s a abstract the isotopic ratios of h o and c in water within the long valley caldera california reflect input from sources external to the hydrothermal reservoir a decrease in d in precipitation of 0 5 km 1 from west to east across long valley is caused by the introduction of less fractionated marine moisture through a low elevation embayment in the sierra nevada mountain range relative to seasonal fluctuations in precipitation 158 to 35 d ranges in hot and cold surface and groundwaters are much less variable 135 to 105 only winter and spring moisture reflecting higher precipitation rates with lighter isotopic signatures recharge the hydrological system the hydrothermal fluids are mixtures of isotopically heavy recharge d 115 18 o 15 derived from the mammoth embayment and isotopically lighter cold water d 135 18 o 18 this cold water is not representative of current local recharge the 13 c values for dissolved carbon in hot water are significantly heavier 7 to 3 than in cold water 18 to 10 denoting a separate hydrothermal origin these 13 c values overlie the range generally attributed to magmatic degassing of co 2 however 13 c values of metamorphosed paleozoic basement carbonates surrounding long valley fall in a similar range indicating that hydrothermal decarbonization reactions are a probable source of co 2 the 13 c and 18 o values of secondary travertime and vein calcite indicate respective fractionation with co 2 and h 2 o at temperatures approximating current hydrothermal conditions

rare earth element fractionation and concentration variations along a groundwater flow path within a shallow basin fill aquifer southern nevada usa abstract rare earth element ree concentrations were measured in 5 well water samples and 3 springs located along a groundwater flow path in a shallow tuffaceous alluvial aquifer from southern nevada usa the ree concentrations in these groundwaters decrease in the direction of groundwater flow a previous investigation demonstrated that ree solid liquid phase partitioning coefficients i e kd s for groundwaters from tuffaceous alluvial aquifers in southern nevada are relatively high mean kd 102 6 our groundwater ree data in conjunction with these kd s support strong sorption of aqueous rees to aquifer surface sites as the primary removal mechanism of rees from these groundwaters in addition relatively high aqueous ree concentrations occur at distinct locations along the groundwater flow path the elevated ree concentrations are explained by addition of deeper groundwaters influx of geothermal waters from a hot spring system differences in solution complexation and or mixtures of regional and local recharge sources solution complexation modelling of rees in the groundwaters indicate that carbonate complexes account for more than 99 of each rees in solution moreover groundwater yb nd ratios a measure of ree fractionation are associated with alkalinity hco3 co32 r 0 71 the data and speciation model results indicate that ree fractionation i e the observed heavy ree hree enrichments compared to rock sources is controlled by formation of progressively stronger carbonate complexes in solution with increasing atomic number which inhibits hree sorption compared to light rees lree and a greater affinity for the lrees to sorb to surface sites in the local tuffaceous alluvial aquifers compared to the hrees

multivariate statistical analysis of arsenic and selenium concentrations in groundwaters from south central nevada and death valley california abstract arsenic and selenium concentrations along with the major solutes were measured in ground waters sampled from springs in pahranagat valley and ash meadows nevada death valley california and from wells from the nevada test site and yucca mountain nevada the multivariate statistical technique correspondence analysis was applied to the data to determine relationships between the groundwaters from these areas the aquifer materials and the as and se concentrations and to examine the relationships between as and se and the other chemical parameters included in the statistical analysis the correspondence analysis indicates that a strong relationship exists between chloride and se in the groundwaters and that as is not associated with chloride the strong association between chloride and se suggests that se behaves more conservatively than as in these oxygenated circumneutral ph groundwaters no strong association was observed between the as and or se concentrations of the groundwaters and the aquifer material with which these waters interact i e regional paleozoic carbonate aquifer tertiary tuffaceous volcanic rocks and or basin fill deposits however it is likely that sampling of groundwaters from the various aquifers was insufficient to determine relationships between the aquifer materials and groundwater chemistry associations were observed between the groundwaters of the nevada test site and yucca mountain regions and the groundwaters of the regional carbonate aquifer that discharge at ash meadows and death valley suggesting mixing of these waters ground water from the regional carbonate aquifer in pahranagat valley which is upgradient from the nevada test site yucca mountain ash meadows and death valley exhibited no association with groundwaters from these regions

using multivariate statistical analysis of groundwater major cation and trace element concentrations to evaluate groundwater flow in a regional aquifer groundwater samples were collected from 11 springs in ash meadows national wildlife refuge in southern nevada and seven springs from death valley national park in eastern california concentrations of the major cations ca mg na and k and 45 trace elements were determined in these groundwater samples the resultant data were subjected to evaluation via the multivariate statistical technique principal components analysis pca to investigate the chemical relationships between the ash meadows and death valley spring waters to evaluate whether the results of the pca support those of previous hydrogeological and isotopic studies and to determine if pca can be used to help delineate potential groundwater flow patterns based on the chemical compositions of groundwaters the results of the pca indicated that groundwaters from the regional paleozoic carbonate aquifers all of the ash meadows springs and four springs from the furnace creek region of death valley exhibited strong statistical associations whereas other death valley groundwaters were chemically different the results of the pca support earlier studies where potentiometric head levels 18o and d geological relationships and rare earth element data were used to evaluate groundwater flow which suggest groundwater flows from ash meadows to the furnace creek springs in death valley the pca suggests that furnace creek groundwaters are moderately concentrated ash meadows groundwater reflecting longer aquifer residence times for the furnace creek groundwaters moreover pca indicates that groundwater may flow from springs in the region surrounding scotty s castle in death valley national park to a spring discharging on the valley floor the study indicates that pca may provide rapid and relatively cost effective methods to assess possible groundwater flow regimes in systems that have not been previously investigated copyright 1999 john wiley sons ltd

provenance and fate of arsenic and other solutes in the chaco pampean plain of the andean foreland argentina from perspectives of hydrogeochemical modeling and regional tectonic setting extensive arsenic as enriched groundwater is known to occur in the aquifers of the chaco pampean plain of argentina previous studies speculated that the as mobilization in these groundwaters was a direct result of their elevated ph and oxidative conditions the volcanic glass layers present in the aquifer matrix were hypothesized as one of the possible sources of as to the groundwaters here we examine the groundwater chemistry of the santiago del estero province of chaco pampean plains of argentina and test these hypotheses by using hydrogeochemical modeling within the framework of the regional geologic tectonic setting the study area is located in the active foreland of the andean orogenic belt which forms a continental arc setting and is dotted with several hot springs rhyolitic volcanic glass fragments derived from arc volcanism are abundant within the aeolian fluvial aquifer sediments and are related to the paleo igneous extrusion in the vicinity hydrogeochemical analyses show that the groundwater is in predominantly oxidative condition in addition some of the groundwaters exhibit very high na cl and so42 concentrations it is hypothesized in this study that the groundwater chemistry has largely evolved by dissolution of rhyolitic volcanic glass fragments contained within the aquifer sediments along with mixing with saline surface waters from adjoining salinas which are thought to be partially evaporated remnants of a paleo inland sea flow path modeling stability diagrams and thermodynamic analyses undertaken in this study indicate that the dominant evolutionary processes include ion exchange reactions chemical weathering of silicate and evaporites in monosialitization dominated weathering geochemical modeling predicts that plagioclase feldspar and volcanic glass are the major solids phases that contribute metal cations and dissolved silica to the local groundwaters co influxed oxyanions with similar ionic radii and structure e g mo si v po43 compete with as for mineral surface site leading to as mobilization to the groundwaters without considering the influence of microbial activities further the transition of the ca rich groundwater to na rich groundwater by mixing with water from the salinas and or evaporative concentration might also have led to counter ion effects a type of ion exchange reactions and hence further enrichment of groundwater by as some of the as may also have been contributed from mixing of meteoric water with magmatic sourced water in the geothermal springs

regional groundwater flow in structurally complex extended terranes an evaluation of the sources of discharge at ash meadows nevada summary ash meadows nevada usa is a site of major groundwater discharge 38 000 l min in the arid mojave desert and hosts a number of endemic and threatened wetland species in addition to these resources ash meadows may also represent the future discharge location of radionuclide laden waters from nuclear weapons testing at the nevada test site more importantly however ash meadows provides the opportunity to understand the controls on water transfer between basins through fractured bedrock 4000 solute analyses were assembled from the literature into a single database the data were screened for spatial distribution completeness charge balance and elevated temperatures 20 c and within regional flow systems with 246 candidate up gradient water remaining distributed among six potential source areas in addition to and ash meadows itself these potential sources include both carbonate volcanic and perhaps valley fill aquifer systems these waters were characterized by cluster analysis in order to sort similar waters in an objective fashion into potential flow paths and to establish representative endmember waters for inverse geochemical models and other modes of analysis isotopic tracers both conservative and those reflecting water rock interaction all suggest that waters at ash meadows are derived by southward flow from volcanic terranes parallel to the preferred permeability structure induced by active regional east west extension solute balances support this conclusion however this runs counter to the prevailing model that waters at ash meadows are derived from easterly and northeasterly flows from the spring mountains and pahranagat valley areas by interbasin flow through a continuous fractured carbonate aquifer this work suggests that carbonate aquifer systems in extended terranes are more compartmentalized than previously appreciated and that anisotropy in fracture permeability is key to compartmentalization and the control of flow directions

hydrochemistry and isotope composition of springs in the tecopa basin southeastern california usa abstract springs and seeps in the tecopa basin were sampled and analyzed for their major ion chemistry and oxygen hydrogen and boron isotope compositions in order to assess the possible origins of the waters the tecopa basin is a groundwater discharge area along the amargosa river drainage basin south of the nevada test site and proposed high level nuclear waste repository at yucca mountain nv the spring waters are categorized into three end member hydrochemical facies 1 ph neutral na ca mg so4 hco3 water with moderate to high total dissolved solids 2 mildly alkaline na cl so4 hco3 water with high total dissolved solids and 3 alkaline na hco3 co3 water with high total dissolved solids the temperatures of most of the springs range from 17 c to 32 c however waters in the tecopa hot spring area range from 9 c to 47 c the oxygen and hydrogen isotope compositions normalized to smow of the waters are as follows the facies 1 springs have a mean 18o of 12 77 0 14 1 and d of 94 9 0 5 1 the facies 2 springs have a mean 18o of 12 73 0 19 1 and d of 97 7 0 9 1 the facies 3 spring has a mean 18o of 13 09 0 17 1 and d of 103 5 0 7 1 the mean boron concentrations and isotope compositions range from 2 4 mg l and 11b of 2 5 for facies 1 springs to 72 8 mg l and 11b of 3 8 for the facies 3 spring the facies 1 waters have chemical and isotope compositions consistent with meteoric recharge in the spring mountains nv groundwater flow through the regional carbonate aquifer and minor mixing with more concentrated water the thermal facies 2 waters are isotopically and chemically distinct from waters in the regional basin fill and carbonate aquifer systems these waters are interpreted to originate from fractured water bearing strata beneath the regional carbonate aquifer that discharge only in the southernmost part of the great basin the facies 3 spring is isotopically and chemically similar to basin fill aquifer waters in the amargosa desert but has higher sodium alkalinity and boron contents due to interaction with saline alkaline lake deposits of the plio pleistocene lake tecopa beds geologic geochemical and isotope data suggest that these three distinct water types flow through hydrogeologic compartments in the tecopa basin the compartments are interpreted to have been created by the impermeable lake tecopa beds and geologic structures within the basin

transpolar observations of the morphological properties of arctic sea ice save for an area between 8830 0 n and 8930 0 n where polynyas and thin ice were observed surveys of snow depth ice thickness and ice properties were conducted at ice stations thickness observations suggest a general latitudinal trend of increasing ice thickness moving northward with considerable variability from floe to floe and within a single floe average floe thicknesses varied from 1 0 to 2 8 m and the standard deviation of thickness on an individual floe was as large as 1 m ice crystallography showed a large amount of granular ice the average optical equivalent soot content was 4n g cg 1 for new snow 8 ng c g 1 for the surface granular layer of multiyear ice and 18 ng c g 1 for the interior of multiyear ice indicating a tendency of the particulates to concentrate at the surface with melting

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer