ice cores record significant 1940s antarctic warmth related to tropical climate variability although the 20th century warming of global climate is well known climate change in the high latitude southern hemisphere sh especially in the first half of the century remains poorly documented we present a composite of water stable isotope data from high resolution ice cores from the west antarctic ice sheet this record representative of west antarctic surface temperature shows extreme positive anomalies in the 1936 45 decade that are significant in the context of the background 20th century warming trend we interpret these anomalies previously undocumented in the high latitude sh as indicative of strong teleconnections in part driven by the major 1939 42 el nino these anomalies are coherent with tropical sea surface temperature mean sh air temperature and north pacific sea level pressure underscoring the sensitivity of west antarctica s climate and potentially its ice sheet to large scale changes in the global climate

active methanogenesis and acetate utilization in powder river basin coals united states coal deposits of the powder river basin prb in wyoming united states contain significant reserves of natural gas proven to be of biogenic origin the timing of gas generation in this basin and many others is either unknown or questionable luca technologies evaluated the prospect that methanogenesis is ongoing in prb coals using a combined laboratory and field approach the anaerobic bioconversion of coal to methane in laboratory experiments was observed in multiple samples indicating that indigenous microorganisms can generate methane from prb coal acetate was found to be a quantitatively important intermediate in methane formation the detection of microbial metabolites including acetate in coalbed methane formation waters and the ability of prb methanogenic consortia to convert the detected metabolites to methane is also consistent with in situ methanogenesis field tests revealed in situ microbial acetate utilization and significant dilution dispersion and migration of injected water and solutes in the coal seam this is believed to be important for contacting significant coal surface area and important for the measurement of in situ microbial activities collectively this information indicates that methanogenesis is active in the coal seams evaluated in the prb and that all of the methane present in the coals need not be a remnant of past methanogenesis

glacial recharge and paleohydrologic flow systems in the illinois basin evidence from chemistry of ordovician carbonate galena formation waters the illinois basin provides an opportune setting for elucidating the roles of remnant evaporite brines and meteoric waters in the evolution of formation waters in an intracratonic sedimentary basin formation waters from carbonate reservoirs in the upper ordovician galena group have been analyzed geochemically to study the origin of their salinity their chemical and isotopic evolution and their relationship to paleohydrologic flow systems chloride bromide ratios and ci br na br relations indicate that initial brine salinity resulted from subaerial evaporation of seawater rather than from halite dissolution subsequent subsurface dilution of the brines by meteoric waters is disclosed by d 18 o covariance however the remnant evaporite brine has not been completely expelled from these ordovician strata galena formation waters have 87 sr 86 sr ratios that range from 0 708 17 a value nearly equal to that of coeval seawater to 0 710 43 this is the greatest range of sr isotopic ratios found in waters from any stratigraphic unit in the basin two fluid mixing events are revealed in plots of 87 sr 86 sr vs 1 sr introduction of 87 sr enriched fluids from a siliciclastic source probably overlying maquoketa shale and a later event that only affected reservoir waters in the western shelf of the basin general covariance between sr and h o isotopes suggests that the later event is related to meteoric water recharge the point of intersection of the d 18 o trend with the meteoric water line implies that this mixing event involved pleistocene glacial meltwater that recharged galena reservoirs near outcrops along the western margin of the basin ordovician galena formation waters are geochemically distinct from those in both silurian devonian and mississippian pennsylvanian strata a distinction that has evidently been maintained by the overlying maquoketa regional aquitard

fluid migration and associated diagenesis in the greater reelfoot rift region midcontinent united states the sources and pathways of basinal fluid flow on the north american craton have been the subjects of intense debate regional dolomitization and the distribution of petroleum and sulfide mineralization on the southern midcontinent are believed to be related to migration of warm basinal fluids from and within the arkoma and illinois basins because of its hydrologic connection with these two basins the reelfoot rift has been postulated as a potential source and or conduit for one or more of these fluids cathodoluminescence petrography has revealed nine distinct carbonate cement microstratigraphies in the reelfoot rift and on its adjacent carbonate platforms in missouri western platform and tennessee eastern platform temporal geochemical trends within each of the three areas are distinct eastern platform carbonate cements and their fluid inclusions exhibit decreasing 13c 18o homogenization temperatures t h and last ice melting t m values with decreasing age reelfoot rift dolomite and calcite cement and their fluid inclusions define a trend of decreasing 13c and 18o values and increasing t h and t m values western platform dolomite cements including those in the nearby southeast missouri mississippi valley type mineral district display a paragenetic trend of increasing 13c and 18o values followed by a return to lower values during the final stage of cement deposition distinct geochemical patterns indicate that stratigraphically controlled fluid flow through carbonate aquifers in the reelfoot rift was restricted within individual fault blocks that had limited communication with the adjacent carbonate platforms lateral fluid migration between fault blocks and vertical migration within fault blocks in the reelfoot rift likely was restricted by faults stratigraphic offset and impermeable units if significant fluid movement occurred from the reelfoot rift onto the adjacent western carbonate platform it likely occurred along northwest striking strike slip faults

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

spatial covariance of water isotope records in a global network of ice cores spanning twentieth century climate change 1 estimating the spatial extent of past climate changes has been an ongoing challenge for paleoclimatology for such estimates to be made with confidence it is important to establish an understanding of the spatial coherence of proxy records during an interval of known climate change we use water stable isotopes from high resolution ice cores and twentieth century observations of sea level pressures and sea surface temperatures to assess the covariance among isotopic records and its link to organized patterns of climate variability covarying signals in the cores are identified using empirical orthogonal function analysis results from regression analysis show that the leading signals are consistent with key climate patterns including the northern atlantic oscillation and southern annular mode and variability in tropical pacific sea surface temperatures associated with the el nino southern oscillation patterns that have recently been identified in instrumental data such as positive tropical pacific sst anomalies associated with the negative phase of the sam are evident in the ice cores these explanations for the variance of stable isotopes are consistent with recent studies using isotope enabled general circulation models and provide a physical basis for interpreting the observed isotopic signals while there is also a global change signal that is evident when analyzing the records collectively there are some limitations in reconstructing global temperatures due to the geographic coverage of the available records and the current lack of modeling studies to explain the observed global scale changes still water stable isotope ratios preserved in ice cores provide a sufficiently rich sampling of large scale climate variability that they can be more widely used in physically based paleoclimate reconstructions covering the last millennium and other periods

origin and chemical evolution of formation waters from silurian devonian strata in the illinois basin usa abstract a suite of formation water samples from silurian devonian reservoirs in the illinois basin has been analyzed for major minor and trace element concentrations and for h o and sr isotopic compositions in order to interpret origin of salinity and geochemical evolution of brine compositions in this evaporite and shale poor cratonic basin although chloride concentrations range from 2000 to 137 000 mg l cl br ratios 291 18 are consistent with those of seawater or seawater evaporated short of halite saturation cl br 292 thus during silurian devonian time subaerially evaporated penesaline brine entered the subsurface where it was chemically modified through brine rock interactions cation br ratios and mineralogy of associated strata indicate that na and k were depleted through interaction with clay minerals ca was enriched and mg depleted by dolomitization and sr was enriched as a result of caco3 recrystallization and dolomitization although significant dilution of the modified brine with meteoric water is supported by d 18o covariance original marine waters have not been completely expelled from silurian devonian strata hydrogen and oxygen isotopes exhibit covariant relations with cation and anion concentrations implying that isotopic exchange between h2o and minerals has not greatly influenced the d 18o trend brine 87 sr 86 sr ratios range from 0 7092 to 0 7108 when these ratios are plotted versus 1 sr a two component mixing trend is suggested although sr concentrations have experienced local diagenetic modification a 87sr enriched fluid may have accompanied petroleum migration from new albany shales into adjacent silurian devonian carbonates where it mixed with remnant evaporated seawater this event probably preceded the influx of meteoric water as gdd and 18o are not correlated with sr isotopic compositions of formation waters

br cl na systematics in illinois basin fluids constraints on fluid origin and evolution the authors present here bromide chloride and sodium data for fluids from reservoirs of ordovician through pennsylvania age in the illinois basic which suggest that remnant marine fluids contribute significantly to fluid cl budgets cl br and nabr ratios for ordovician through devonian formation fluids are relatively uniform and near those for seawater despite greater than a factor of ten range in cl concentration in contrast fluids from mississippian and pennsylvanian reservoirs separated from older reservoirs by the new albany shale group have more variable fluid cl br and na br ratios most of which are significantly greater then those of seawater the 1 1 stoichiometry of cl and na increases for mississippian and pennsylvanian formation fluids is consistent with halite dissolution nevertheless br systematics and mass balance considerations indicate that he overall cl budget of illinois basin formation fluids appears to be more significantly influenced by the contribution from subaerially evaporated seawater than by halite dissolution

groundwater flow beneath ice sheets part ii its impact on glacier tectonic structures and moraine formation abstract meltwater flowing as groundwater from beneath the margin of an ice sheet determines the distribution of sub surface heads and effective pressures a subglacial groundwater flow model is used together with an ice sheet loading model to compute the magnitudes and directions of the principal effective stresses in the subsurface from which the distribution of different types of sub surface failure in the subglacial and proglacial zones are deduced zones of hydrofracturing shear fracture and pervasive shear failure are distinguished beneath the ice sheet divide area intact rocks of high tensile strength may fail hydrofracturing and liquefaction are two coupled processes which lead to the formation of upward filled and downward filled sediment dykes and till wedges quicksand conditions are developed where strong vertical seepage pressures occur producing sediment diapirism it is suggested that subglacial permeability magnitude may be the product of a self organising process certain types of moraine extrusion moraines are suggested to be a consequence of upward movement and surface extrusion of sediment driven by rising groundwater it is suggested that groundwater over pressure associated with narrow proglacial permafrost plates are conductive to the formation of large push moraines and that many large ancient and modern examples are produced in this setting

calibrating the ice core paleothermometer using seasonality high resolution oxygen isotope measurements on the dome summit south dss ice core from law dome antarctica provide a seasonal profile that is sufficiently stable and undistorted by biases in accumulation to permit comparison with measured temperature seasonality this comparison yields an isotope temperature relation with a gradient d dt of 0 44 0 02 c and provides a new method for exploring the isotope temperature relationship at high accumulation sites if applied to the observed isotope record from the dss core which extends through the last glacial and beyond this calibration suggests that at its coldest the last glaciation was 13 c colder than present at this site after correcting for elevation change this finding compares with a temperature difference of 8 c computed by using the local spatially derived calibration

coupled hydrology and biogeochemistry of paleocene eocene coal beds northern gulf of mexico thirty six formation waters gas and microbial samples were collected and analyzed from natural gas and oil wells producing from the paleocene to eocene wilcox group coal beds and adjacent sandstones in north central louisiana usa to investigate the role hydrology plays on the generation and distribution of microbial methane major ion chemistry and cl br relations of wilcox group formation waters suggest mixing of freshwater with halite derived brines high alkalinities up to 47 8 meq l no detectable so4 and elevated 13c values of dissolved inorganic carbon up to 20 5 vienna peedee belemnite vpdb and co2 up to 17 67 vpdb in the wilcox group coals and adjacent sandstones indicate the dominance of microbial methanogenesis the 13c and d values of ch4 and carbon isotope fractionation of co2 and ch4 suggest co2 reduction is the major methanogenic pathway geochemical indicators for methanogenesis drop off significantly at chloride concentrations above 1 7 mol l suggesting that high salinities inhibit microbial activity at depths greater than 1 6 km formation waters in the wilcox group contain up to 1 6 modern carbon a14c to at least 1690 m depth the covariance of d values of co produced h2o and ch4 indicate that the microbial methane was generated in situ with these late pleistocene or younger waters the most enriched carbon isotope values for dissolved inorganic carbon dic and co2 and highest alkalinities were detected in wilcox group sandstone reservoirs that were co2 flooded in the 1980s for enhanced oil recovery leading to the intriguing hypothesis that co2 sequestration may actually enhance methanogenesis in organic rich formations

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

subglacial hydrology in north western germany during the last glaciation groundwater flow tunnel valleys and hydrological cycles abstract numerical modelling of groundwater dynamics in an overpressured system of subglacial aquifers and aquitards under the marginal portion of the scandinavian ice sheet in northwestern germany has been coupled with calculations of basal meltwater production rates and with field evidence of meltwater erosional features largely fine grained subglacial sediments with relatively low hydraulic conductivities had a capacity to drain only about 25 of all basal meltwater produced in the relevant subglacial catchment area the rest of the meltwater was evacuated through tunnel valleys in spontaneous outburst events subglacial drainage cycles are proposed in which each cycle begins with meltwater drainage through the substratum groundwater flow followed by water ponding at the ice bed interface and ends in catastrophic meltwater releases through tunnel valleys

chemical and isotopic tracers of the contribution of microbial gas in devonian organic rich shales and reservoir sandstones northern appalachian basin in this study the geochemistry and origin of natural gas and formation waters in devonian age organic rich shales and reservoir sandstones across the northern appalachian basin margin western new york eastern ohio northwestern pennsylvania and eastern kentucky were investigated additional samples were collected from mississippian berea sandstone silurian medina sandstone and ordovician trenton black river group oil and gas wells for comparison dissolved gases in shallow groundwaters in devonian organic rich shales along lake erie contain detectable ch4 0 01 50 55 mol with low 13c ch4 values 74 68 to 57 86 and no higher chain hydrocarbons characteristics typical of microbial gas nevertheless these groundwaters have only moderate alkalinity 1 14 8 72 meq kg and relatively low 13c values of dissolved inorganic c dic 24 8 to 0 6 suggesting that microbial methanogenesis is limited the majority of natural gases in devonian organic rich shales and sandstones at depth 168 m in the northern appalachian basin have a low ch4 to ethane and propane ratios 3 35 mol c1 c2 c3 and high 13c and d values of ch4 53 35 to 40 24 and 315 0 to 174 6 respectively which increase in depth reservoir age and thermal maturity the molecular and isotopic signature of these gases show that ch4 was generated via thermogenic processes despite this the geochemistry of co produced brines shows evidence for microbial activity high 13c values of dic 10 slightly elevated alkalinity up to 12 01 meq kg and low so4 values 1 mmole l in select devonian organic rich shale and sandstone formation water samples suggest the presence of methanogenesis while low 13c dic values 22 and relatively high so4 concentrations up to 12 31 mmole l in many brine samples point to so4 reduction which likely limits microbial ch4 generation in the appalachian basin together the formation water and gas results suggest that the vast majority of ch4 in the devonian organic rich shales and sandstones across the northern appalachian basin margin is thermogenic in origin small accumulations of microbial ch4 are present at shallow depths along lake erie and in western ny

evidence for dilution of deep confined ground water by vertical recharge of isotopically heavy pleistocene water new analyses of the isotopic composition of water sup 14 c dating of dissolved inorganic carbon and order of magnitude darcy calculations suggest that a dilute body of water trending north south in the cambrian ordovician aquifer of iowa was emplaced as vertical recharge of pleistocene age water from the base of the des moines lobe of late wisconsin time the recharge occurred through more than 300 m of overlaying silurian to mississippian age rocks the delta sup 18 o values range from minus 10 per thousand to minus 9 per thousand for the dilute water body and are consistent with a mixture of des moines lobe meltwater and precipitation found today in the north central us these results suggest that 1 the climate at the end of the last glaciation was mild and 2 a ground water stable isotope signature similar to that of modern precipitation in an aquifers recharge area is not a priori evidence for relatively recent recharge

the international trans antarctic scientific expedition itase an overview from its original formulation in 1990 the international trans antarctic scientific expedition itase has had as its primary aim the collection and interpretation of a continent wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations itase offers the ground based opportunities of traditional style traverse travel coupled with the modern technology of gps crevasse detecting radar satellite communications and multidisciplinary research by operating predominantly in the mode of an oversnow traverse itase offers scientists the opportunity to experience the dynamic range of the antarctic environment itase also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps without the cost of the former or the lack of mobility of the latter more importantly the combination of disciplines represented by itase provides a unique multidimensional space and time view of the ice sheet and its history itase has now collected 20 000 km of snow radar recovered more than 240 firn ice cores total length 7000 m remotely penetrated to 4000 m into the ice sheet and sampled the atmosphere to heights of 20 km

glaciological and climatic significance of hercules dome antarctica an optimal site for deep ice core drilling 1 we present glaciological and climatological characteristics of hercules dome antarctica 86 s 105 w which demonstrate its potential as a deep ice core site annual layering in d ratios from a 72 m ice core collected by the us itase 2002 traverse indicate accumulation rates of 0 16 0 20 m yr ice equivalent over the last 300 years age control from stratigraphy seen in the radio echo sounding data collected during the same traverse suggests a rate of 0 09 0 11 m yr averaged over the past 18 000 years ice stratigraphy also indicates that the ice divide position has been stable through at least this period comparison of satellite derived temperature anomalies with atmospheric reanalysis data show that the site is sensitive to the two dominant patterns of climate variability in the high latitude southern hemisphere climate proxy data from a deep ice core at hercules dome would be indicative of changes in pacific southern hemisphere climate variability and may provide new information on rapid climate change events in antarctica the sensitivity of the site and the combination of relatively high accumulation rates low temperatures mean annual 35 c to 40 c and simple ice flow suggest that hercules dome is an ideal site for a future deep ice core

formation waters from mississippian pennsylvanian reservoirs illinois basin usa chemical and isotopic constraints on evolution and migration we have analyzed a suite of seventy four formation water samples from mississippian and pennsylvanian carbonate and siliciclastic strata in the illinois basin for major minor and trace element concentrations and for strontium isotopic composition a subset of these samples was also analyzed for boron isotopic composition data are used to interpret origin of salinity and chemical and sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from silurian devonian reservoirs systematics of cl br na show that present mississippian pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporation short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle mississippian st louis limestone along with extensive dilution by mixing with meteoric waters additional diagenetic modifications in the subsurface interpreted from cation br ratios include k depletion through interaction with clay minerals ca enrichment and mg depletion by dolomitization and sr enrichment through caco3 recrystallization and dolomitization ste genevieve limestone middle mississippian formation waters show 87sr86sr ratios in the range 0 70782 0 70900 whereas waters from the siliciclastic reservoirs are in the range 0 70900 0 71052 inverse correlations between 87sr86sr and b li and mg concentrations suggest that the brines acquired radiogenic 87sr through interaction with siliciclastic minerals completely unsystematic relations between 87sr86sr and 1 sr are observed sr concentrations in ste genevieve and aux vases middle mississippian waters appear to be buffered by equilibrium with respect to srso4 although there are many similarities in their origin and evolution these formation waters are distinguished from silurian devonian brines in the basin by elevated clbr and nabr ratios and by unsystematic sr isotope relationships thus waters from these two major segments of the illinois basin stratigraphic column form distinct geochemical regimes which are separated by the new albany shale group devonian mississippian regional aquitard geochemical evolution appears to have been influenced significantly by paleozoic and mesozoic hydrologic flow systems in the basin

a 200 year sub annual record of sulfate in west antarctica from 16 ice cores sixteen high resolution ice core records from west antarctica and south pole are used to examine the spatial and temporal distribution of sulfate for the last 200 years the preservation of seasonal layers throughout the length of each record results in a dating accuracy of better than 1 year based on known global scale volcanic events a dual transport source for west antarctic sea salt ss so4 2 and excess xs so4 2 is observed lower tropospheric for areas below 1000 m elevation and mid upper tropospheric stratospheric for areas located above 1000 m our xsso4 2 records with volcanic peaks removed do not display any evidence of an anthropogenic impact on west antarctic so4 2 concentrations but do reveal that a major climate transition takes place over west antarctica at 1940 global scale volcanic eruptions appear as significant peaks in the robust spline residual xsso 4 2 records from sites located above 1000 m elevation but do not appear in the residual records from sites located below 1000 m

recent cross formational fluid flow and mixing in the shallow michigan basin ground water with total dissolved solids tds ranging from 10 to 50 g l exists at depths between 90 and 140 m in devonian oil bearing formations in the shallow michigan basin of southwestern ontario these formations comprise mainly limestone and dolomite and the sources of the saline ground water have not been identified previously isotopic and major ion data from ground water from devonian oil bearing formations in southwestern ontario indicate that the highest salinity fluids were emplaced locally from depths of several hundred meters during the later stages of or following the wisconsinan glaciation saline water and petroleum were also emplaced into overlying pleistocene clay rich glacial deposits isostatic rebound leading to fracturing and enhanced formation permeability due to matrix expansion was probably the primary mechanism that enabled these saline fluids to migrate into discrete areas of the devonian and pleistocene formations the geochemical data presented here support a model involving cross formational fluid flow from depth occurring vertically on the scale of several hundred meters since glaciation the hydrogeologic regime in this shallow basinal system must therefore be viewed as dynamic rather than static to depths of at least 500 m over a time frame of 100 000 yr 54 refs 10more figs 2 tabs less

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

pleistocene recharge to midcontinent basins effects on salinity structure and microbial gas generation the hydrogeochemistry of saline meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history chemical evolution of basinal brines and physical stability of saline formation waters during episodes of freshwater recharge this is especially germane for interior cratonic basins such as the michigan and illinois basins although there are large differences in formation water salinity and hydrostratigraphy in these basins both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the pleistocene exploration for unconventional microbial gas deposits which began in the upper devonian age antrim shale at the northern margin of the michigan basin has recently extended into the age equivalent new albany shale of the neighboring illinois basin providing access to heretofore unavailable fluid samples these reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry new formation water and gas samples were obtained from devonian mississippian strata in the illinois basin these included exploration wells in the new albany shale an organic rich black shale of upper devonian age and formation waters from over and underlying regional aquifer systems siluro devonian and mississippian age the hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the illinois basin critically influenced fluid migration into the new albany shale the new albany shale formation water chemistry indicates significant invasion of meteoric water with d values as low as 46 05 into the shale the carbon stable isotope system 13c values as high as 29 4 coupled with 18o d and alkalinity of formation waters alkalinity 24 08 meq kg identifies the presence of microbial gas associated with meteoric recharge regional geochemical patterns identify the underlying siluro devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured new albany shale reservoirs recharge from overlying mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the new albany shale recharge of dilute waters cl 1000 mm into the siluro devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern illinois basin margin taken together with salinity and stable isotope patterns in age equivalent michigan basin formation waters they suggest a regional impact of recharge of 18o and d depleted fluids related to pleistocene glaciation devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane this recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity given the relatively quiet tectonic history and subdued current topography in the midcontinent region it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale hosted gas deposits

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

isotopic evidence for glacial meltwater recharge to the cambrian ordovician aquifer north central united states the chemistry of water in the cambrian ordovician aquifer in six midwestern states has been studied as part of the northern midwest regional aquifer system analysis of the u s geological survey dissolved solids concentrations generally increase perpendicular to the direction of regional groundwater flow from less than 400 mg liter in southeast minnesota southwest wisconsin and northeast iowa to more than 10 000 mg liter in northwest missouri isotopic ratios of hydrogen and oxygen are significantly depleted from north to south with an areal distribution approximately parallel to the distribution of dissolved solids for example 18o in southern iowa and northern missouri is about 6 parts per thousand lighter than 18o of modern recharge water in minnesota and wisconsin covariance between 18o and d of the groundwater similar to that of modern precipitation suggests that the differences in isotopic ratios between groundwater and modern recharge water reflect meteoric signatures of water during past recharge events rather than geochemical processes such as isotopic exchange with aquifer materials the pronounced parallelism between the distribution of isotopes and dissolved solids over large areas probably reflects largescale recharge of pleistocene glacial meltwater into the aquifer system which probably had a paleoflow system with a gradient from northeast to southwest rather than from northwest to southeast

recent southern indian ocean climate variability inferred from a law dome ice core new insights for the interpretation of coastal antarctic isotopic records stable isotopes in water have been measured along a very high accumulation ice core from law dome on the east antarctic coast these enable a detailed comparison of the isotopic records over sixty years 1934 1992 with local antarctic station data and remote meteorological observations atmospheric reanalyses and sea surface temperature estimates on a seasonal to inter annual time scale using both observations and isotopic atmospheric general circulation model gcm results we quantify the relationships between stable isotopes 18o d and deuterium excess d d 8 18o with site and source temperature at seasonal and decadal time scales showing the large imprint of source conditions on law dome isotopes these calibrations provide new insights for the quantitative interpretation of temporal isotopic fluctuations from coastal antarctic ice cores an abrupt change in the local meridional atmospheric circulation is clearly identified from law dome deuterium excess during the 1970s and analysed using gcm simulations

reversal of the regional scale flow system of the williston basin in response to pleistocene glaciation low 18o values of formation waters collapse structures related to salt dissolution hydrodynamic blowout structures and biodegradation of oils all suggest a significant influx of fresh water into the williston basin along the outcrop belt in southern and central manitoba during pleistocene glaciation the thickness of the continental ice sheet over manitoba would have provided sufficient potentiometric drive to reverse the regional scale flow system of the williston basin the dynamic nature of the flow system suggests that modern day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed

high resolution ice core stable isotopic records from antarctica towards interannual climate reconstruction ice core records are a key resource for reconstructing antarctic climate however a number of physical processes preclude the simple interpretation of ice core properties such as oxygen isotopic ratios in terms of climate variables like temperature or sea level pressure we show that well dated sub annually resolved stable isotopic records from the united states international trans antarctic scientific expedition us itase traverses and other sources have a high correlation with local seasonal temperature variation however this temporal relationship cannot be simply extended to quantitative interannual resolution reconstructions of site temperature we suggest that a consistent and important target for ice core calibrations is a composite of annual mean temperature records from antarctic weather stations which covaries strongly with the dominant mode from principal component analysis of temperature variability in the antarctic significant correlations with this temperature index are found with individual ice core records with a composite of the ice cores and through a multiple linear regression model with the ice cores as predictors these results imply that isotopic signals like the instrumental temperature mode itself have a strong response to large scale atmospheric circulation variability which in the antarctic region is dominated by the southern annular mode

na cl br systematics of mineralizing brines in mississippi valley type deposits new and published analyses of fluid inclusion leachates from mississippi valley type mvt deposits can be divided into two groups on the basis of na br and cl br ratios mvt leachates from the illinois kentucky and cincinnati arch districts and from cubic galena in the viburnum trend have na br and cl br ratios that extend to values significantly above that of seawater which are characteristic of evaporite dissolution brines mvt leachates from polaris and octahedral galena in the viburnum trend have na br and cl br ratios that plot below seawater and along the compositional trend formed by evaporation solubility volume constraints require that brines formed by seawater evaporation had high dissolved metal contents preliminary correlation of leachate compositions allows delineation of two brine provinces in the midcontinent united states 1 an early high br province found only in southeastern missouri and 2 a later low br province of probable permian age that extended from the cincinnati arch to the tri state district these observations along with na cl br data for modern brines from the illinois basin argue against models for single stage midcontinent mvt brine flow based on recharge from late paleozoic arkoma foreland basins to the south

instrument and tree ring based estimates of the antarctic oscillation abstract an estimate of the strength of the austral summer antarctic oscillation using station sea level pressure records for the period 1878 2000 is presented the first to the authors knowledge the reconstruction was obtained by relating the antarctic oscillation aao intensity derived from ncep ncar reanalysis data to the leading principal components of station records using multiple regression analysis particular effort has been made to fit the model in a way that is robust to the questionable trends in the ncep ncar data in the southern hemisphere the trends in the reconstruction are derived from the station data not from the ncep data cross validation with the ncep data and comparison with other analyses of the aao over the late instrumental period give confidence that this station based reconstruction can be regarded as trustworthy with regard to the whole reconstruction period some unquantifiable uncertainty stems from potential instability of the statistical relationships to extend this

seasonal climate information preserved in west antarctic ice core water isotopes relationships to temperature large scale circulation and sea ice as part of the united states contribution to the international trans antarctic scientific expedition itase a network of precisely dated and highly resolved ice cores was retrieved from west antarctica the itase dataset provides a unique record of spatial and temporal variations of stable water isotopes d 18 o and dd across west antarctica we demonstrate that after accounting for water vapor diffusion seasonal information can be suc cessfully extracted from the itase cores we use meteo rological reanalysis weather station and sea ice data to assess the role of temperature sea ice and the state of the large scale atmospheric circulation in controlling seasonal average water isotope variations in west antarctica the strongest relationships for all variables are found in the cores on and west of the west antarctic ice sheet divide and during austral fall during this season positive isotope anomalies in the westernmost itase cores are strongly related to a positive pressure anomaly over west antarctica low sea ice concentrations in the ross and amundsen seas and above normal temperatures analyses suggest that this seasonally distinct climate signal is due to the pronounced meridional oriented circulation and its linkage to enhanced sea ice variations in the adjacent southern ocean during fall both of which also influence local to regional temperatures

the effect of temporal variations in the surface mass balance and temperature inversion strength on the interpretation of ice core signals the proxy for temperature signal in ice cores is stored in the snow ice during precipitation events and hence reflects the temperature at which precipitation is formed here approximated by the inversion temperature t weighted with the accumulation results from a 14 year integration 1980 93 with a regional atmospheric model racmo x 55 km show that the annual mean accumulation weighted inversion temperature t i w and the annual mean t i are not covariant in time at four out of the five deep drilling sites considered mainly due to year to year variations in the seasonality of precipitation as a consequence the surface temperature t s core derived from racmo output using a method analogous to the retrieval of the surface temperature from ice core signals deviates from the directly modelled surface temperature t s on interannual time scales results from a 5 year sensitivity integration forced with a 2 k temperature increase show an 18 overestimation of the increase in t s core relative to the increase in t s due to a change in the relationship between the inversion strength and the surface temperature in a different climate regime similar errors may occur in deriving the temperature difference between last glacial maximum and present day climate from signals in ice cores

variability in the teleconnection between the el nino southern oscillation and west antarctic climate deduced from west antarctic ice core isotope records 1 the u s contribution to the international trans antarctic scientific expedition itase program obtained several ice cores from the west antarctic ice sheet because of proximity to the pacific ocean the west antarctic ice cores are expected to have an el nino southern oscillation enso signature the itase 2001 5 core 18o isotope was selected for detailed analysis here because its location high annual accumulation and record length make it an ideal candidate for capturing the effects of regional circulation anomalies in the isotopic composition the 2001 5 core is compared to two other cores the 2001 2 and 2001 3 cores which are further west and therefore capture some spatial variability of the regional circulation on various time scales analysis shows that several phenomena including enso leave a signature in the ice cores evidence suggests that enso signals in the ice cores are significantly modulated by low frequency variability correlation with the southern annular mode sam global temperature pacific decadal oscillation and enso shows that temperature and enso generally appear to have the strongest influence on the 2001 5 isotope signal while there is no clearly dominant single influence in the other cores results suggest that the teleconnection between enso and the 2001 5 core is quite dependent on the state of the sam specifically when the southern oscillation index soi and sam are in phase there is an enso related pressure anomaly west of the antarctic peninsula in the vicinity of the ice cores studied this extends previous findings to span the entire 20th century

microbial generation of economic accumulations of methane within a shallow organic rich shale although methane of bacterial origin is ubiquitous in marine and freshwater sediments economic accumulations of bacterial gases occur mainly at depths of several kilometres in tertiary basins that had high sedimentation rates1 2 here we present an integration of geochemical and isotopic data from gas and water extracted from the upper devonian antrim shale along the northern margin of the michigan basin which demonstrates that significant volumes of bacterial gas have been generated in organic rich shales at depths of less than 600 metres the antrim shale is mainly a self sourced reservoir in contrast to conventional gas deposits that have migrated from a source to a reservoir and has become one of the most actively exploited gas reservoirs3 in the united states the gas forming processes operating at shallow depths in the antrim shale are not unique4 and an understanding of these processes should lead to the identification and development of other economic non conventional gas deposits around the world

high resolution ice cores from us itase west antarctica development and validation of chronologies and determination of precision and accuracy shallow ice cores were obtained from widely distributed sites across the west antarctic ice sheet as part of the united states portion of the international trans antarctic scientific expedition us itase program the us itase cores have been dated by annual layer counting primarily through the identification of summer peaks in non sea salt sulfate nssso4 2 concentration absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores tambora indonesia 1815 being the most prominent independent validation is provided by the tracing of isochronal layers from site to site using high frequency ice penetrating radar observations and by the timing of mid winter warming events in stable isotope ratios which demonstrate significantly better than 1 year accuracy in the last 20 years dating precision to 1 month is demonstrated by the occurrence of summer nitrate peaks and stable isotope ratios in phase with nssso4 2 and winter time sea salt peaks out of phase with phase variation of 1 month dating precision and accuracy are uniform with depth for at least the last 100 years

a 700 year record of southern hemisphere extratropical climate variability annually dated ice cores from west and east antarctica provide proxies for past changes in atmospheric circulation over antarctica and portions of the southern ocean temperature in coastal west and east antarctica and the frequency of south polar penetration of el nino events during the period ad 1700 1850 atmospheric circulation over the antarctic and at least portions of the southern hemisphere underwent a mode switch departing from the out of phase alternation of multi decadal long phases of eof1 and eof2 modes of the 850 hpa field over the southern hemisphere as defined in the recent record by thompson and wallace 2000 thompson and solomon 2002 that characterizes the remainder of the 700 year long record from ad 1700 to 1850 lower tropospheric circulation was replaced by in phase behavior of the amundsen sea low component of eof2 and the east antarctic high component of eof1 during the first phase of the mode switch both west and east antarctic temperatures declined potentially in response to the increased extent of sea ice surrounding both regions at the end of the mode switch west antarctic coastal temperatures rose and east antarctic coastal temperatures fell respectively to their second highest and lowest of the record polar penetration of el nino events increased during the mode switch the onset of the ad 1700 1850 mode switch coincides with the extreme state of the maunder minimum in solar variability late 20th century west antarctic coastal temperatures are the highest in the record period and east antarctic coastal temperatures close to the lowest since ad 1700 extratropical regions of the southern hemisphere have experienced significant climate variability coincident with changes in both solar variability and greenhouse gases

paleowaters in silurian devonian carbonate aquifers geochemical evolution of groundwater in the great lakes region since the late pleistocene abstract changes in the climatic conditions during the late quaternary and holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the great lakes region increased hydraulic gradients from melting of kilometer thick pleistocene ice sheets reorganized regional scale groundwater flow in paleozoic aquifers in underlying intracratonic basins here we present new elemental and isotopic analyses of 134 groundwaters from silurian devonian carbonate and overlying glacial drift aquifers along the margins of the illinois and michigan basins to evaluate the paleohydrology age distribution and geochemical evolution of confined aquifer systems this study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the midcontinent region and extends into deeper portions of the illinois and michigan basins focused on the freshwater saline water mixing zones in addition the hydrogeochemical data from silurian devonian aquifers were integrated with deeper basinal fluids and brines in upper devonian black shales and underlying cambrian ordovician aquifers to reveal a regionally extensive recharge system of pleistocene age waters in glaciated sedimentary basins elemental and isotope geochemistry of confined groundwaters in silurian devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals dissolution of halite and anhydrite cation exchange microbial processes and mixing with basinal brines carbon isotope values of dissolved inorganic carbon dic range from 10 to 2 87sr 86sr ratios range from 0 7080 to 0 7090 and 34 s so 4 values range from 10 to 30 a few waters have elevated 13cdic values 15 from microbial methanogenesis in adjacent organic rich upper devonian shales radiocarbon ages and 18o and d values of confined groundwaters indicate they originated as subglacial recharge beneath the laurentide ice sheet 14 50 ka bp 15 to 13 18o these paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake bed clays and or shales the presence of isotopically depleted waters in paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional scale groundwater flow modern groundwater flow in the great lakes region is primarily restricted to shallow unconfined glacial drift aquifers recharge waters in silurian devonian and unconfined drift aquifers have 18o values within the range of holocene precipitation 11 to 8 and 7 to 4 5 for northern michigan and northern indiana ohio respectively carbon and sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions 13cdic 14 7 to 11 1 and 87sr 86sr 0 7080 0 7103 the distinct elemental and isotope geochemistry of pleistocene versus holocene age waters further confirms that surficial flow systems are out of contact with the deeper basinal scale flow systems these results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes which are important for determining the sustainability of present day water resources and stability of saline fluids in sedimentary basins

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

little ice age neoglacial paleoenvironmental conditions at siple station antarctica the 550 year records of 18 o and dust concentrations from siple station antarctica suggest warmer and less dusty atmospheric conditions from 1600 to 1830 a d which encompasses much of the northern hemisphere little ice age lia dust and 18 o data from south pole station indicate that the opposite conditions e g cooler and more dusty were prevalent there during the lia meteorological data from 1945 85 show that the lia temperature opposition between amundsen scott and siple inferred from 18 o is consistent with the present spatial distribution of surface temperature there is some observational evidence suggesting that under present conditions stronger zonal westerlies produce a temperature pattern similar to that of the lia these regional differences demonstrate that a suite of spatially distributed high resolution ice core records will be necessary to characterize the lia in antarctica

deglacial temperature history of west antarctica the most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how earth s climate responds to various forcings including a rise in atmospheric co2 this transition has left a direct thermal remnant in the polar ice sheets where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings for antarctica the deglacial warming has previously been constrained only by the water isotopic composition in ice cores without an absolute thermometric assessment of the isotopes sensitivity to temperature to overcome this limitation we measured temperatures in a deep borehole and analyzed them together with ice core data to reconstruct the surface temperature history of west antarctica the deglacial warming was formula see text c approximately two to three times the global average in agreement with theoretical expectations for antarctic amplification of planetary temperature changes consistent with evidence from glacier retreat in southern hemisphere mountain ranges the antarctic warming was mostly completed by 15 kybp several millennia earlier than in the northern hemisphere these results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on antarctic temperature although climate models perform well on average in this context some recent syntheses of deglacial climate history have underestimated antarctic warming and the models with lowest sensitivity can be discounted

meltwater discharge through the subglacial bed and its land forming consequences from numerical experiments in the polish lowland during the last glaciation numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in nw poland primarily its flow pattern velocities and fluxes we have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady state and transient conditions the results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin all model runs show water discharge at the ice forefield driven by ice sheet thickness modulated down ice decreasing hydraulic heads in relation to non glacial times the transient 3d model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca 90 m below the ice bed interface and up to 40 km in front of the glacier comparison with empirical data suggests that depending on the model run only between 5 and 24 of the meltwater formed at the ice sole drained through the bed as groundwater this is consistent with field observations documenting abundant occurrence of tunnel valleys indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely in these areas the relief shows distinct palaeo ice lobes indicating fast ice flow possibly triggered by the undrained water at the ice bed interface owing to the abundance of low permeability strata in the bed the simulated groundwater flow depth is less than ca 200 m copyright 2009 john wiley sons ltd

isotopic diffusion in polar firn implications for interpretation of seasonal climate parameters in ice core records with emphasis on central greenland if it were possible to properly extract seasonal information from ice core isotopic records paleoclimate researchers could retrieve a wealth of new information concerning the nature of climate changes and the meaning of trends observed in ice core proxy records it is widely recognized however that the diffusional smoothing of the seasonal record makes a proper extraction very difficult in this paper we examine the extent to which seasonal information specifically the amplitude and shape of the seasonal cycle is irrecoverably destroyed by diffusion in the firn first we show that isotopic diffusion firn is reasonably well understood we do this by showing that a slightly modified version of the whillans and grootes 1985 theory makes a tenable a priori prediction of the decay of seasonal isotopic amplitudes with depth at the gisp2 site though a small adjustment to one parameter significantly improves the prediction further we calculate the amplitude decay at various other ice core sites and show that these predictions compare favorably with published data from south pole and locations in southern and central greenland and the antarctic peninsula we then present numerical experiments wherein synthetic ice core records are created diffused sampled reconstituted and compared to the original these show that alter diffusive mixing in the entire fini column seasonal amplitudes can be reconstructed to within about 20 error in central greenland but that all information about sub annual signals is permanently lost there furthermore most of the error in the amplitude reconstructions is due to the unknowable variations in the sub annual signal finally we explore how these results can be applied to other locations and suggest that dye 3 has a high potential for meaningful seasonal reconstructions while siple dome has no potential at all an optimal ice core site for seasonal reconstructions has a high accumulation rate and a low temperature

late glacial and holocene sequences in rockshelters and adjacent wetlands of northern bohemia czech republic correlation of environmental and archaeological records this paper combines complex archaeological records from excavations of sandstone rockshelters with paleobotanical investigations in the adjacent wetlands of northern bohemia czech republic several pollen diagramms from nearby peatbogs are used to document the paleoenvironmental development from the late glacial to the middle holocene in addition two recently excavated key archaeological sections were selected to document human behavioral responses to the climatic development kostelni rokle and smoln kamen this region remained mostly unsettled during the upper paleolithic magdalenian or epigravettian so that the late paleolithic colonization after the lgm appears to be a major behavioral adaptation the early and middle mesolithic foragers developed this pattern to be optimally adapted to the versatile landscape of sandstone plateaus and canyons during the holocene the aim was to exploit its changing vegetational aquatic and terrestric faunal resources until the late mesolithic