influence of permafrost distribution on groundwater flow in the context of climate driven permafrost thaw example from yukon flats basin alaska united states 1 understanding the role of permafrost in controlling groundwater flow paths and fluxes is central in studies aimed at assessing potential climate change impacts on vegetation species habitat biogeochemical cycling and biodiversity recent field studies in interior alaska show evidence of hydrologic changes hypothesized to result from permafrost degradation this study assesses the hydrologic control exerted by permafrost elucidates modes of regional groundwater flow for various spatial permafrost patterns and evaluates potential hydrologic consequences of permafrost degradation the yukon flats basin yfb a large 118 340 km2 subbasin within the yukon river basin provides the basis for this investigation model simulations that represent an assumed permafrost thaw sequence reveal the following trends with decreasing permafrost coverage 1 increased groundwater discharge to rivers consistent with historical trends in base flow observations in the yukon river basin 2 potential for increased overall groundwater flux 3 increased spatial extent of groundwater discharge in lowlands and 4 decreased proportion of suprapermafrost shallow groundwater contribution to total base flow these trends directly affect the chemical composition and residence time of riverine exports the state of groundwater influenced lakes and wetlands seasonal river ice thickness and stream temperatures presently the yfb is coarsely mapped as spanning the continuous discontinuous permafrost transition that model analysis shows to be a critical threshold thus the yfb may be on the verge of major hydrologic change should the current permafrost extent decrease this possibility underscores the need for improved characterization of permafrost and other hydrogeologic information in the region via geophysical techniques remote sensing and ground based observations

regional trends in evaporation loss and water yield based on stable isotope mass balance of lakes the ontario precambrian shield surveys abstract stable isotopes of water oxygen 18 and deuterium were measured in water samples collected from a network of 300 lakes sampled in six 100 km 2 blocks centred at 49 72 n 91 46 w 48 49 n 91 58 w 50 25 n 86 62 w 49 78 n 83 98 w 48 24 n 85 49 w 47 73 84 52 w within precambrian shield drainages in the vicinity of lake superior northern ontario canada additional sampling was also conducted within the turkey lakes watershed 47 03 n 84 38 w a research basin situated in the algoma region located 50 km north of sault saint marie ontario the studies were undertaken to gain a better understanding of hydrology and geochemistry of watersheds in the region in order to better predict acid sensitivity of lakes the main objective of this paper is to describe the hydrologic variations observed based on stable isotope results evaporative isotopic enrichment of lake water was found to be systematic across the region and its deviation from the isotopic composition of precipitation was used to estimate the evaporation inflow to the lakes as well as runoff or water yield based on a simple isotope mass balance model the analysis illustrates significant variability in the water yield to lakes and reveals a pattern of positively skewed distributions in all six widely spaced blocks suggesting that a high proportion of lakes have relatively limited runoff whereas relatively few have greater runoff such basic information on the drainage structure of an area can be valuable for site specific hydrologic assessments but also has significant implications for critical loads assessment as low runoff systems tend to be less buffered and therefore are more sensitive to acidification importantly the turkey lakes sampling program also suggests that isotope based water yield is comparable in magnitude to hydrometric gauging estimates and also establishes that uncertainty related to stratification can be as high as 20 or more for individual lakes although it likely has only a minor influence on regional survey results while further analysis in gauged lake watersheds would be beneficial to constraining the accuracy of the method or calibrating it for operational use it is nevertheless a powerful tool in its present form for lake to lake and regional runoff inter comparisons

timing of post glacial reinhabitation and ecological development of two new england usa drainages based on trace fossil evidence abstract trace fossils as paleoecological and paleobiogeographical tools in pleistocene glaciolacustrine sediments have been largely ignored combining high resolution varve stratigraphy with trace fossil data can lead to refined paleoenvironmental interpretations during times of rapid climate change based on trace fossils from glaciolacustrine varves in the connecticut and merrimack river valleys a new timeline for the reinhabitation of new england by fish and associated invertebrates has been constructed in addition it appears that colonization of the recently deglaciated environments occurred in at least four successional stages if these stages can be recognized elsewhere it may be possible to accurately model other postglacial migrations using trace fossils and varve chronostratigraphy

modern thermokarst lake dynamics in the continuous permafrost zone northern seward peninsula alaska 1 quantifying changes in thermokarst lake extent is of importance for understanding the permafrost related carbon budget including the potential release of carbon via lake expansion or sequestration as peat in drained lake basins we used high spatial resolution remotely sensed imagery from 1950 51 1978 and 2006 07 to quantify changes in thermokarst lakes for a 700 km2 area on the northern seward peninsula alaska the number of water bodies larger than 0 1 ha increased over the entire observation period 666 to 737 or 10 7 however total surface area decreased 5 066 ha to 4 312 ha or 14 9 this pattern can largely be explained by the formation of remnant ponds following partial drainage of larger water bodies thus analysis of large lakes 40 ha shows a decrease of 24 and 26 in number and area respectively differing from lake changes reported from other continuous permafrost regions thermokarst lake expansion rates did not change substantially between 1950 51 and 1978 0 35 m yr and 1978 and 2006 07 0 39 m yr however most lakes that drained did expand as a result of surface permafrost degradation before lateral drainage drainage rates over the observation period were stable 2 2 to 2 3 per year thus analysis of decadal scale high spatial resolution imagery has shown that lake drainage in this region is triggered by lateral breaching and not subterranean infiltration future research should be directed toward better understanding thermokarst lake dynamics at high spatial and temporal resolution as these systems have implications for landscape scale hydrology and carbon budgets in thermokarst lake rich regions in the circum arctic

surculichnus bifurcauda n igen n isp a trace fossil from late pleistocene glaciolacustrine varves of the connecticut river valley usa attributed to notostracan crustaceans based on neoichnological experimentation abstract new trace fossils found in the late pleistocene glaciolacustrine varves of the connecticut river valley vermont usa represent the first known notostracan presence in glacial lake hitchcock these unique trace fossils warrant a new ichnogenus and ichnospecies surculichnus bifurcauda the new england varve chronology nevc constrains the initial presence of s bifurcauda at 13 3 13 2 kyr the morphology of s bifurcauda correlates well with notostracan characteristics and behavior sieving of bedding planes that contained s bifurcauda produced one chitinous fossil that is suggestive of a notostracan telson neoichnological experimentation was conducted with the species triops longicaudatus during the subadult stage t longicaudatus produced traces representative of locomotion and feeding behaviors and at the adult stage reproduced s bifurcauda as well as rusophycus possible explanations for the productions of these traces are egg laying or predation behaviors that are both related to maturity further research in the paleo and modern ecology of glacial and nearctic lakes may shed more light on the maker of s bifurcauda

trace fossils from late pleistocene varved lacustrine sediments in eastern lithuania abstract trace fossils cochlichnus anguineus glaciichnium liebegastensis gordia carickensis new combination youngest occurrence gordia isp warvichnium ulbrichi cf warvichnium isp have been found in varved sediments of a small proglacial lake 17 16 kyr bp in east lithuania they occur mostly in summer and transitional laminae along bunches of discrete microlaminae vertical reworking is absent horizontal distribution of trace fossils along microlaminae studied in one varved package points to a patchy distribution of trace fossils resulting from a patchy distribution of food locally c anguineus dominates and commonly this is the only trace fossil its co occurrence with g liebegastensis is distinctly rarer than with other ichnotaxa probably due to a competition between their tracemakers the trace fossil assemblage can be ascribed to the mermia ichnofacies in which the glaciichnium ichnocoenosis arthropod trackways dominate and cochlichnus ichnocoenosis grazing traces dominate can be distinguished as the end members replacement of the glaciichnium ichnocoenosis by the cochlichnus ichnocoenosis can be interpreted as shallowing of hypolimnion and degrading ecological conditions

trace fossils from carboniferous floodplain deposits in western argentina implications for ichnofacies models of continental environments abstract floodplain deposits from the carboniferous tupe formation of western argentina contain a low diversity ichnofauna of invertebrates and plants the assemblage consists of archaeonassa fossulata didymaulichnus lyelli helminthoidichnites tenuis palaeophycus tubularis planolites isp and root traces this ichnofauna is characterized by the dominance of very simple forms superficial or very shallow trace fossils combination of locomotion grazing and dwelling structures and production by arthropods and vermiform organisms primary sedimentary fabrics are disturbed only by plant trace fossils while animal trace fossils are mostly restricted to bedding surfaces resulting in the virtual absence of bioturbation the poorly defined morphology of the ichnofossils and the absence of backfilled striated trace fossils and structures indicative of subaerial exposure suggest subaqueous production the envisaged depositional environment is a freshwater body developed in a floodplain and overfilled by overbank deposits a review of floodplain ichnofaunas documented from the stratigraphic record indicates that two recurrent assemblages may be recognized the first assemblage is characterized by low to rarely moderate diversity of invertebrate trace fossils moderate to high diversity of vertebrate structures and common presence of meniscate backfilled structures bilobate trace fossils with scratch marks arthropod trackways and tetrapod trackways it is regarded as an example of the scoyenia ichnofacies developed in desiccated floodplains the second type of floodplain assemblage illustrated by the example documented in this paper is characterized by grazing trails locomotion trails and dwelling burrows low to rarely moderate ichnodiversity simple trace fossils and superficial to very shallow structures although formed in floodplain environments also this type of assemblage is remarkably different from the scoyenia ichnofacies it is here regarded as an example of the mermia ichnofacies basic features of these ichnofaunas reflect subaqueous production of the assemblage the lower ichnodiversity of these floodplain assemblages in comparison with their equivalents from lacustrine basins is probably an expression of the less stable conditions and temporary nature of floodplain water bodies our study supports the view that ichnofacies are not indicators of sedimentary environments but reflect sets of environmental factors

classification of hydrological regimes of northern floodplain basins peace athabasca delta canada from analysis of stable isotopes δ18o δ2h and water chemistry we used stable isotopes 18o and 2h and water chemistry to characterize the water balance and hydrolimnological relationships of 57 shallow aquatic basins in the peace athabasca delta pad northern alberta canada based on sampling at the end of the 2000 thaw season evaporation to inflow ratios e i were estimated using an isotope mass balance model tailored to accommodate basin specific input water compositions which provided an effective first order quantitative framework for identifying water balances and associated limnological characteristics spanning three main previously identified drainage types open drainage basins e i 0 4 n 5 characterized by low alkalinity low concentrations of nitrogen dissolved organic carbon doc and ions and high minerogenic turbidity include large shallow basins that dominate the interior of the pad and experience frequent or continuous river channel connection closed drainage basins e i 1 0 n 16 in contrast possess high alkalinity and high concentrations of nitrogen doc and ions and low minerogenic turbidity and are located primarily in the relict and infrequently flooded landscape of the northern peace sector of the delta several basins fall into the restricted drainage category 0 4 e i 1 0 n 26 with intermediate water chemistries and are predominant in the southern athabasca sector which is subject to active fluviodeltaic processes including intermittent flooding from riverbank overflow integration of isotopic and limnological data also revealed evidence for a new fourth drainage type mainly located near the large open drainage lakes that occupy the central portion of the delta but within the athabasca sector n 10 these basins were very shallow 50 cm deep at the time of sampling and isotopically depleted corresponding to e i characteristic of restricted and open drainage conditions however they are limnologically similar to closed drainage basins except for higher conductivity and higher concentrations of ca2 and na and lower concentrations of sio2 and chlorophyll c these distinct features are due to the overriding influence of recent summer rainfall on the basin water balance and chemistry the close relationships evident between water balances and limnological conditions suggest that past and future changes in hydrology are likely to be coupled with marked alterations in water chemistry and hence the ecology of aquatic environments in the pad copyright 2006 john wiley sons ltd

on isc pp and pp data and their use in delay time tomography of the caribbean region summary a major problem in p delay time tomography is the inhomogeneous sampling of mantle structure by the p wave ray paths resulting in low resolution in images of large regions of the upper mantle incorporation of pp and pp phases can improve the quality and reliability of tomographic images because they 1 sample earth structure not ordinarily sampled by direct p phases 2 add rays that are oblique to rays of direct phases which is especially important where the latter sample mantle structure in selected directions and 3 pp data better constrain the earthquake focal depths pp traveltimes have often been used in combination with p data in differential traveltime studies we show that the assumptions and approximations necessary for this approach are problematic and that they can be avoided when the p pp and p data are used in tomographic inversion we investigated the applicability of pp and pp delay times to the tomographic study of the aspherical mantle structure below the caribbean region the success of the application of data of the later arriving reflected waves depends critically on the quality of these data we examined possible sources of error in the isc pp and pp data and assessed the contribution to the delay times used in this study for the caribbean region analyses of the isc pp and pp delay times do not reveal biases due to effects of pp waveform distortions the asymmetry of the reflections or due to misidentifications of phases that reflect at a surface other than that assumed the noise level of pp and pp data is high with respect to data of the direct p wave this is accommodated by weighting with the inverse of the variance of the data of each of the three phases the independent information that is revealed from the pp and pp data results in modifications of tomographic images based solely on p data these modifications are important if the tomographic images are being used to understand the geodynamical history of convergent margins in the caribbean region we investigated the effect of adding data of later arriving phases to the isc p data with sensitivity tests we inverted synthetic delay times to which we added gaussian noise with a standard error typical for the data of the three seismic phases these tests demonstrate that the image resolution of shallow mantle structure is enhanced significantly by the incorporation of later arriving phases due to the absence of seismicity below 200 km the resolution improved less at deeper levels below the caribbean region in some poorly constrained parts of the solution the test results even indicate an apparent decrease of resolution this is explained by changes in the rate of convergence of the inversion algorithm in mantle regions where the effective sampling of structure improved by the addition of pp and pp wave ray paths the convergence was speeded up at the expense of the convergence rate in regions where fewer or no pp or pp wave ray paths were added a shortcoming of the resolution tests used in our study is that some specific problems of reported delay times are not reflected in synthetic data we observe that isc delay times of later arriving phases are not necessarily consistent with the reported hypocentral parameters as most isc reported earthquake locations are computed from direct p wave data for the pp data the inconsistency with event location not only results in a decrease of focal depths during relocation but in a bias of the imaged velocity perturbations as well this property of reported data is not modelled in resolution tests

ichnological signatures of shallow freshwater lakes in the glacial itarare group mafra formation upper carboniferous lower permian of parana basin s brazil abstract the upper carboniferous lower permian glacigenic deposits of the itarare group parana basin are widely known and cover an extensive area in the southern brazil these deposits consist of different arrangements of massive shales diamictites rhythmites and fine to medium grained sandstones with trough cross stratification five genetically distinct thickening locally coarsening upward successions of regular rhythmites can be distinguished in the mafra rio negro region santa catarina and parana states southern brazil representing the landward portion of an incised valley filled during deglaciation a low diversity invertebrate ichnofauna composed of a freshwater shallow burrow dominated suite and trackway dominated suite occurs in these rhythmites the freshwater shallow burrow dominated suite is composed of cochlichnus anguineus cruziana cf problematica gordia arcuata gordia marina hormosiroidea meandrica rusophycus cf carbonarius and treptichnus pollardi as well as undichnia consulca and intermittent rusophiciform traces it represents a mermia ichnocoenosis and occurs in the rhythmites of the upper sets commonly overlapped by d gouldi and d biformis in palimpsest preservation d gouldi and d biformis compose the trackway dominated suite which occur in all ichnofossiliferous paired mudstone siltstone of the basal sets of the rhythmite succession and in almost all of the upper sets it represents an atypical scoyenia ichnocoenosis and is generally preserved over microbially induced wrinkle structures the rhythmic deposition suggests distal underwater gravity flow deposits filling shallow lakes or ponds in depressed areas the siltstones deposited by melting currents and the mudstones by sediment fall out after the flux ceased the abundant wrinkle structures suggest quiet waters the overlying deposits bearing a brackish water ichnofauna and marine fossils suggest a coastal setting connected with the sea although atypical the occurrence of a scoyenia ichnocoenosis in almost all ichnofossiliferous rhythmite couplets preserved over wrinkle structures or overlapping mermia ichnocoenosis suggests that these shallow lakes were episodically dried up at least partially the present data allow interpreting the regular ichnofossiliferous rhythmites of the mafra formation as deposited in shallow lakes or ponds developed in outwash plains at the landward side of a fjord embayment during deglaciation

reconstruction of a late cisuralian early permian floodplain lake environment palaeontology and sedimentology of the tregiovo basin trentino alto adige northern italy abstract the late cisuralian is known as a time of increasing aridity compared to the late pennsylvanian early cisuralian although several studies highlighted this trend at low latitudes of western pangaea little is known from central pangaea environments the discovery of new fossiliferous horizons in the late cisuralian tregiovo formation northern italy allowed a new palaeoenvironmental study based on facies analysis ichnology palaeobotany plant insect interaction and palynology three facies associations were identified a c and correspond to floodplain lake ephemeral lacustrine and distal alluvial fan environments respectively the tetrapod ichnoassociation is more diverse than previously known including abundant diapsid and non diapsid reptile tracks and rarer temnospondyl amphibian tracks plant fossils are characterized by a predominance of hinterland taxa conifers hygrophytic plants are present as well the sporomorph association is dominated by miospores of cordaitales voltziales and peltaspermales while trilete lycopsid and fern miospores are rare which corresponds well with the macroflora invertebrate trace fossils and feeding traces on plant fossils are described for the first time from the tregiovo basin suggesting transitional low energy environments and a relatively low level of herbivory respectively this study evidences the development in the tregiovo basin of a wet and dry probably seasonal climate which became drier between facies associations a b this environment constitutes an important reference since few data are known to infer the late cisuralian climatic conditions of central pangaea

applications of ichnology in lacustrine sequence stratigraphy potential and limitations abstract in comparison with their marine counterparts lacustrine ichnofaunas have not been extensively used in sequence stratigraphy application of trace fossils in continental sequence stratigraphy cannot be based simply on the extrapolation of marine sequence stratigraphy marine substrate controlled ichnofacies in particular the firmground glossifungites ichnofacies develop in stable and cohesive substrates reflecting erosive exhumation of the sediment in contrast in lacustrine sequences substrate controlled ichnofossils only rarely indicate erosional exhumation because they are commonly related to desiccation of water bodies the tripartite division of overfilled balanced fill and underfilled lakes provides a comprehensive framework to evaluate the potential and limitations of lacustrine ichnofaunas in sequence stratigraphy based on a number of case studies spanning the three lake basin types a model of trace fossil distribution in overfilled balanced fill and underfilled basins is proposed overfilled lake basins contain well developed softground trace fossils mermia and skolithos ichnofacies and the softground suite of the scoyenia ichnofacies that are useful to delineate parasequences and parasequence sets fluvial discharge into overfilled lakes usually generates density currents that oxygenate lake bottoms allowing the establishment of epifaunal and infaunal communities additionally these are freshwater lakes where no stress due to hypersalinity occurs leading to the development of a relatively diverse benthos land plant derived organic matter is the prime source of nutrients favoring the development of a deposit feeding benthic fauna in permanently subaqueous low energy zones firmground suites are rare because such large lakes usually do not experience desiccation abundant firmground trace fossil suites of the scoyenia ichnofacies occur in balanced fill lakes but softground assemblages are usually depauperate lowstand deposits contain abundant and widespread ichnofaunas commonly meniscate trace fossils and arthropod trackways of the scoyenia ichnofacies lake hydrology is closed during lowstands and salinity usually increases imposing a stress factor on the lake biota and therefore softground ichnofaunas are depauperate ichnofaunas from turbidite systems in balanced fill lakes are less abundant and diverse than those from overfilled lacustrine turbidites freshwater conditions are common during transgression but dysaerobic conditions may prevail imparting a stress factor on the benthic biota in hydrologically closed lakes the scoyenia ichnofacies is widespread but the mermia ichnofacies is commonly absent or impoverished the scoyenia ichnofacies is associated with lowstand desiccated substrates in underfilled lakes the density of arthropod trackways may be high forming tracked omission surfaces some of these omission surfaces may represent sequence boundaries expressed by co planar surfaces of lowstand and subsequent flooding rapid changes in depositional conditions reflecting desiccation during vertical aggradation can lead to the formation of composite ichnofabrics that reflect successive bioturbation events

holocene climatic change in the alaskan arctic as inferred from oxygen isotope and lake sediment analyses at wahoo lake despite recent progress in understanding high latitude climate variability paleoclimate records are scarce from the alaskan arctic we conducted isotopic and sediment analyses at wahoo lake to infer holocene climate variability in northeastern alaska water 18o and d values from the lake and its inlet outlet streams suggest that winter precipitation dominates modern water inputs and that evaporation has limited influence on the lake s hydrological budget the isotopic composition of pisidium exhibits marked variations during the past 11 500 years with 18o ranging between 18 7 and 16 2 and 13c between 7 1 and 2 3 vienna pee dee belemnite vpdb elevated 18o and sediment composition from 11 5 to 8 9 kcal bp suggest evaporative 18o enrichment and arid conditions rising lake levels are evidenced by the disappearance of pisidium and a transition to low carbonate gyttja ca 6 3 kcal bp and by the onset of sediment deposition on an adjacent shelf by 5 3 kcal bp these changes coincided with

new permafrost is forming around shrinking arctic lakes but will it last widespread lake shrinkage in cold regions has been linked to climate warming and permafrost thaw permafrost aggradation however has been observed within the margins of recently receded lakes in seeming contradiction of climate warming here permafrost aggradation dynamics are examined at twelvemile lake a retreating lake in interior alaska observations reveal patches of recently formed permafrost within the dried lake margin colocated with discrete bands of willow shrub we test ecological succession which alters shading infiltration and heat transport as the driver of aggradation using numerical simulation of variably saturated groundwater flow and heat transport with phase change i e freeze thaw simulations support permafrost development under current climatic conditions but only when net effects of vegetation on soil conditions are incorporated thus pointing to the role of ecological succession furthermore model results indicate that permafrost aggradation is transitory with further climate warming as new permafrost thaws within seven decades

travel time residuals of pp waves reflected under the central atlantic ocean abstract travel time residuals of pp for waves generated in south and central america and recorded in africa and europe after reflection under the central atlantic ocean are studied to show possible structural variations in the reflection area the ridge appears as a zone of positive residuals 1 0 s indicative of lower velocities and is clearly differentiated from the surrounding oceanic basins where residuals are negative 3 2 s the ridge influence extends up to about 400 km from the crest

global upper mantle structure from long period differential travel times we have made over ten thousand measurements of pp p and ss s differential travel times from long period global digital seismograph network recordings of all events with mb 5 5 which occurred during the years 1976 to 1986 we have obtained reasonable global coverage with very good sampling of several regions of the world the residuals range from 5 to 5 s for pp p and 12 to 12 s for ss s and reveal a large scale pattern of heterogeneity when plotted at the reflected phase s bounce point our experiments indicate that lower mantle structure and source receiver structure can each contribute approximately 0 5 s to our measured pp p residuals so there is considerable signal to be explained the pattern observed in the pp p measurements is similar to the pattern observed in the ss s measurements with the ss s residuals 2 to 4 times larger in magnitude comparisons of our measured residuals to those predicted by the upper mantle models of woodhouse and dziewonski show that the overall patterns are quite similar but the amplitude of the model residuals is roughly a factor of 2 too small comparisons with the predictions of a whole mantle model of tanimoto again shows that the predicted pattern of residuals is reasonably consistent with the observations but now the predicted residuals are too large by about a factor of 2 this variation in predicted amplitudes is probably mainly due to differences in the near surface structure of the models we have also binned our measurements according to the tectonic regionalization gtr1 of jordan and find a qualitative correlation of average residual with tectonic region in particular precambrian shields show a strong anomaly and there is a correlation of residual size with the age of oceanic crust at the bounce point for all tectonic regions the ratio of ss s to pp p residuals is approximately 2 this ratio is consistent with a thermal origin for the observed signal finally our measurements show no compelling evidence for azimuthal anisotropy which might be related to fossil spreading direction or the direction of absolute plate motion such a signal is probably overwhelmed by the large signal from three dimensional structure

permafrost evidence for severe winter cooling during the younger dryas in northern alaska 1 the younger dryas cold event a rapid reversion to glacial climate conditions at the pleistocene holocene transition has generally been attributed to the release of meltwater from the laurentide ice sheet to the north atlantic or arctic oceans the reaction of the north pacific region to this shutdown of the thermohaline circulation in the north atlantic during younger dryas is little understood in this paper we present the first radiocarbon dated centennial scale stable water isotope record from permafrost in northern alaska this late glacial winter climate reconstruction from barrow ice wedges demonstrates the existence of a younger dryas cold event formerly believed to be reduced or absent in this area our stable isotope data display a gradual change of the atmospheric moisture source conditions during the younger dryas likely associated with the successive opening of the bering strait

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

late holocene moisture balance variability in the southwest yukon territory canada abstract analyses of sediment cores from marcella lake a small hydrologically closed lake in the semi arid southwest yukon provides effective moisture information for the last 4500 years at century scale resolution water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that marcella lake is currently enriched in 18 o by summer evaporation past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal charophyte stem encrustations a record of the 18 o composition of mean annual precipitation at jellybean lake a nearby evaporation insensitive system provides data of simultaneous 18 o variations related to decade to century scale shifts in aleutian low intensity position the difference between the two isotope records represents 18 o enrichment in marcella lake water caused by summer effective moisture conditions results indicate increased effective moisture between 3000 and 1200 cal bp and two marked shifts toward increased aridity at 1200 and between 300 and 200 cal bp these prominent late holocene changes in effective moisture occurred simultaneously with changes in aleutian low circulation patterns over the gulf of alaska indicated by jellybean lake the reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today

airborne electromagnetic imaging of discontinuous permafrost 1 the evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes climate and ecosystems permafrost thawing has been linked to changes in wetland and lake areas alteration of the groundwater contribution to streamflow carbon release and increased fire frequency but detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma here we present the results of a pioneering 1 800 line kilometer airborne electromagnetic survey that shows sediments deposited over the past 4 million years and the configuration of permafrost to depths of 100 meters in the yukon flats area near fort yukon alaska the yukon flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south making it an important location for examining permafrost dynamics our results not only provide a detailed snapshot of the present day configuration of permafrost but they also expose previously unseen details about potential surface groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past 1 000 years this work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic climatic and ecological processes and has significant implications for the stewardship of arctic environments

controls on recent alaskan lake changes identified from water isotopes and remote sensing 1 high latitude lakes are important for terrestrial carbon dynamics and waterfowl habitat driving a need to better understand controls on lake area changes to identify the existence and cause of recent lake area changes in the yukon flats a region of discontinuous permafrost in north central alaska we evaluate remotely sensed imagery with lake water isotope compositions and hydroclimatic parameters isotope compositions indicate that mixtures of precipitation river water and groundwater source 95 of the studied lakes the remaining minority are more dominantly sourced by snowmelt and or permafrost thaw isotope based water balance estimates indicate 58 of lakes lose more than half of inflow by evaporation for 26 of the lakes studied evaporative losses exceeded supply surface area trend analysis indicates that most lakes were near their maximum extent in the early 1980s during a relatively cool and wet period subsequent reductions can be explained by moisture deficits and greater evaporation

lateral variations in mantle velocity structure and discontinuities determined from p pp s ss and ss sds travel time residuals on the basis of p pp s ss arrival times and ss s410s ss s660s differential times we construct models of mantle p and s velocity structure and boundary topography of the 410 km and 660 km discontinuities events from the catalog of the international seismological centre isc are relocated relative to the international association of seismology and physics of the earth s interior 1991 iasp91 velocity model using both p and s arrival times the arrival times are corrected for ellipticity and the pp and ss residuals are corrected for the topography at the bounce point the cap averaged pp p and ss s differential time residuals plotted at the pp and ss surface reflection points form broad coherent patterns the geographic distribution of the cap averaged residuals agrees quite well with pp p and ss s differential time residuals derived from long period global digital seismograph network gdsn data a robust lp inversion scheme is used to infer global mantle structure synthetic tests indicate that for regions well sampled by ss s410s and ss s660s differential times the velocity estimates are not seriously contaminated by the topography of the 410 and 660 km discontinuities however estimates of boundary deflections may be influenced by extensive p and s velocity variations of 3 or greater we find the 410 km discontinuity to be depressed by as much as 24 km beneath north america conversely the discontinuity is deflected upward underneath eurasia in some regions the topography of the 660 km discontinuity is quite distinct from that of the 410 km discontinuity but the two appear to be positively correlated a series of depressions are found at several intersections of the 660 km discontinuity with known subduction zones the elevated topography in the 410 km discontinuity beneath europe is underlain by a trough in the 660 km discontinuity a number of subduction zones are characterized by a thinning of the transition zone negative p and s velocity anomalies underlying back arc basins and tectonically active continental regions encircle the pacific where they are resolved the stable continental cratons are systematically positive velocity features that extend below 200 km with the inclusion of pp and ss travel time residuals we are better able to constrain midmantle structure most notably in the depth range 35 660 km beneath the northwest pacific we observe high p velocity where they are resolved mid ocean ridges are most clearly imaged as low velocity features in the s model the northern portion of the mid atlantic ridge is underlain by negative s velocity anomalies in the pacific the east pacific rise is an extensive low s velocity anomaly

sources of methane to an arctic lake in alaska an isotopic investigation sources of dissolved methane ch4 at toolik lake alaska include both diffusion from lake sediments and groundwater entering the lake from its perimeter here we use hydrogen and oxygen isotopes in water h2o carbon and hydrogen isotopes in ch4 and carbon isotopes in dissolved inorganic carbon dic to calculate the relative importance of lake sediment and groundwater discharge as sources of dissolved ch4 to toolik lake we also resolve the relative importance of the source contribution spatially within the lake and determine the processes controlling ch4 concentrations in groundwater surrounding the lake our findings from a mixing model based on isotopes in ch4 suggest that groundwater is a more important source of ch4 at the perimeter of the lake where the water to air flux is high additionally we find on the local scale that high groundwater methane concentrations may be better linked to areas around the lake where rain is the dominant source of water to the active layer indicating that changes in precipitation and active layer thaw depth will impact methane concentrations in the active layer and ultimately the groundwater associated flux to toolik lake

mapping of upper mantle structure from differential pp p travel time residuals abstract p and pp travel time residuals have been collected from 23 quarters of the regional catalog of earthquakes of the international seismological centre isc the difference in travel time residuals between pp and p are used as an indicator of the p delay time near the pp reflection point global maps of these differential travel time residuals are used to study lateral heterogeneity in the crust and upper mantle two of the regions studied have mean differential travel time residuals significantly different at greater than the 95 confidence level from the global mean of the differential travel time residuals in the central pacific southeast of hawaii differential pp p travel time residuals of 3 8 0 36 s are observed these observations imply an average p delay time of 1 1 0 38 s average p delay times of 0 67 0 20 s are observed beneath the tibetan plateau and the western portion of the people s republic of china these travel time variations basically agree in location and sign with the surface wave results of tanimoto and anderson

paleohydrological significance of trace fossil distribution in oligocene fluvial fan to lacustrine systems of the ebro basin spain the ichnological study of fluvial fan and lacustrine oligocene deposits in the ne ebro basin has allowed the recognition of three ichnoassemblages having a strong correlation with depositional facies associations lacustrine deposits lack bioturbation due to the hydrologically closed character of the lake that caused hypersalinity and made it inhospitable for benthic life terminal lobe deposits of the fluvial fan which were sedimented in low wetland areas around the lake bear a moderately diverse ichnoassemblage dominated by horizontal taenidium barretti cochlichnus anguineus and bird footprints gruipeda isp this assemblage can be assigned to the shorebird ichnofacies a subset of the scoyenia ichnofacies that characterizes the subaerial part of low energy shore areas crevasse splay deposits in medial fluvial fan areas present a different assemblage also belonging to the scoyenia ichnofacies it includes most of the trace fossils found in the terminal lobes except for the bird tracks plus very abundant vertical burrows taenidium barretti and unnamed ornamented burrows the presence of deep tier traces of terrestrial invertebrates is consistent with the more proximal fan setting having greater relief and consequently a lower mean groundwater position than lowland areas fluvial channels only bear irregularly clustered tunnel structures of unknown affinity formed after abandonment of the channel thus trace fossil assemblages are mostly controlled by the position and fluctuations of water tables which are the cause for their composite nature

application of neoichnological studies to behavioural and taphonomic interpretation of fossil bird like tracks from lacustrine settings the late triassic early jurassic santo domingo formation argentina abstract the purpose of this study is to apply neoichnological observations to the behavioural and taphonomic interpretation of a late triassic early jurassic track surface from the santo domingo formation argentina containing hundreds of bird like tracks and trackways in addition the factors affecting the formation and preservation of bird tracks in lacustrine settings are particularly addressed the 5 5 m2 fossil track surface contains different types of trace fossils the avian ichnotaxa gruipeda dominguensis the most abundant bird like tracks with elongated hallux impressions small epichnial rounded pits and invertebrate traces skolithos taenidium the modern environmental analogue chosen for the neoichnological studies was a coastal freshwater pond the bajo de los huesos chubut argentina seasonally occupied by sandpipers calidris bairdii and calidris fuscicollis charadriiformes the comparison between the fossil succession and the modern example suggests that they share lithology and sedimentary structures and that sedimentary processes and local palaeoenvironment were fairly similar and do not bias ichnological comparisons field observations allowed to distinguish twenty one behaviours that produced distinct traces and four modern footprint types 1 to 4 related to specific substrate conditions in particular the preferential formation of bird tracks parallel to the waterline also confirmed by studies on droppings and invertebrate fauna of the pond and other associated sedimentary features ripple marks wrinkle marks mud drape thickness and trace fossils were important for recognition of the shoreline in the fossil example these observations also allowed us to distinguish the adjacent deeper and shallower parts of the fossil pond and can be applicable to other similar case studies contrasting sediment properties and footprint types some relationships and constraints on the formation and preservation of modern footprints are proposed although these are very complex processes that will require further studies five of the behaviours recognised in the modern pond were inferred from the sixteen trackways distinguished on the fossil track surface including walking walking with a zig zag path short runs probing and landing with legs directed forward possible trace of flight the recognition of traces of flight volichnia probing marks and tracks showing morphology similar to modern shorebirds g dominguensis strongly suggest an avian affinity for the producers of the fossil tracks and in consequence the santo domingo track site would be younger than supposed

spatial variability of climate and land use effects on lakes of the northern great plains evaluation of the effects of climate change and human activities on lakes requires improved understanding of how stressors interact and the degree to which individual sentinel lakes represent broad spatial patterns of ecosystem response to disturbance we surveyed modern water chemistry major ions conductivity salinity lake volume and sediments algal pigments stable isotopes in 21 lakes that surround humboldt lake saskatchewan site of a 2 000 yr climate reconstruction to quantify spatial synchrony s the mean among lake correlation coefficient of prairie lake response to climate variability land use and their interactions whole lake mass balances of total dissolved substances constructed at each site revealed that evaporation of water controlled seasonal changes in salt content only in years with dry summers 2003 leading to widespread spatial coherence of ecosystems s 5 0 78 in contrast variations in hydrologic inputs precipitation groundwater and solute fluxes regulated salt balances of lakes during years with wet summers 2004 2005 and substantially reduced lake synchrony s 5 0 13 0 58 furthermore 25 of sites exhibited increased nitrogen influx as d15n and cyanobacterial production as fossil pigments between ca 1920 and 2003 with particularly strong effects of land use recorded for northeastern sites where evaporative forcing was greatest finally principal component and canonical ordinations with redundancy analysis both explained 50 of the variance in lake sensitivity to climate and land use and revealed that the effects of climate and land use interacted strongly but that the unique effects of each factor remained identifiable in modern lake surveys

biogenic structures in exhumed surfaces around saline lakes an example from lake bogoria kenya rift valley abstract five overprinted suites of animal and plant traces around saline alkaline lake bogoria kenya are described from a set of interfingering late pleistocene and holocene exhumed surfaces that reveal a complex story of changes in lake level and environmental controls on trace assemblages through time these stratigraphic surfaces are amalgamated and form a co planar surface the sediments were first deposited during intermediate lake levels then reworked and cemented during low lake levels and were subsequently overlain by transgressive lacustrine sediments during higher lake levels ongoing exhumation of the surface near the present shoreline has reactivated the sediments as a substrate for the activities of epifaunal and infaunal animals as well as plant growth the modern environmental setting at lake bogoria is very similar to that of the preserved exhumed surfaces which allows comparisons between observed sets of environmental factors affecting animal behaviour and their representation in the fossilized examples pronounced lateral environmental heterogeneity around saline and hypersaline lakes may lead to concentrations of life around sites with vital resources such as freshwater at lake bogoria groups of fault controlled hot springs represent these oases and have been a relatively consistent feature in and around the lake during the development of the exhumed surfaces together the diverse assemblage of animal trace suites from lake bogoria represent the mermia and scoyenia ichnofacies but can be divided into five suites that reveal details of laterally heterogeneous sets of environmental factors and are useful indicators of lake level substrate moisture content substrate cohesion etc suite 1 comprises the traces of chironomid larvae diptera chironomidae formed in subaqueous lacustrine settings suite 2 includes the traces of flamingos phoeniconaias minor and phoenicopterus ruber formed at the shoreline suite 3 compares well with the mermia ichnofacies and comprises trails and burrow systems associated with relatively fresh saturated to extremely shallow subaqueous substrates suite 4 is comparable to both the pre and post desiccation suites of the scoyenia ichnofacies is the most diverse suite at lake bogoria and mainly comprises the burrows of beetles earwigs and their larvae as well as a diverse set of rhizoliths and vertebrate tracks suite 5 contains a moderately diverse set of traces attributed to termites and ants

landscape gradient assessment of thermokarst lake hydrology using water isotope tracers thermokarst lakes are widespread in arctic and subarctic regions in subarctic quebec nunavik they have grown in number and size since the mid 20th century recent studies have identified that these lakes are important sources of greenhouse gases this is mainly due to the supply of catchment derived dissolved organic carbon that generates anoxic conditions leading to methane production to assess the potential role of climate driven changes in hydrological processes to influence greenhouse gas emissions we utilized water isotope tracers to characterize the water balance of thermokarst lakes in nunavik during three consecutive mid to late summer seasons 2012 2014 lake distribution stretches from shrub tundra overlying discontinuous permafrost in the north to spruce lichen woodland with sporadic permafrost in the south calculation of lake specific input water isotope compositions i and lake specific evaporation to inflow e i ratios based on an isotope mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics nearly all lakes sampled were predominantly fed by rainfall and or permafrost meltwater which suppressed the effects of evaporative loss only a few lakes in one of the southern sampling locations which overly highly degraded sporadic permafrost terrain appear to be susceptible to evaporative lake level drawdown we attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of nunavik predicted climate driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region if coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff conditions favorable for mineralization and emission of methane these water bodies may become even more important sources of greenhouse gases

revised 14 c dating of ice wedge growth in interior alaska usa to mis 2 reveals cold paleoclimate and carbon recycling in ancient permafrost terrain article i nfo establishing firm radiocarbon chronologies for quaternary permafrost sequences remains a challenge be cause of the persistence of old carbon in younger deposits to investigate carbon dynamics and establish ice wedge formation ages in interior alaska we dated a late pleistocene ice wedge formerly assigned to ma rine isotope stage mis 3 and host sediments near fairbanks alaska with 24 radiocarbon analyses on wood particulate organic carbon poc air bubble co2 and dissolved organic carbon doc our new co2 and doc ages are up to 11 170 yr younger than ice wedge poc ages indicating that poc is detrital in origin we con clude an ice wedge formation age between 28 and 22 cal ka bp during cold stadial conditions of mis 2 and solar insolation minimum possibly associated with heinrich event 2 or the last glacial maximum a doc age for an ice lens in a thaw unconformity above the ice wedge returned a maximum age of 21 470 200 cal yr bp our variable 14 c data indicate recycling of older carbon in ancient permafrost terrain resulting in radiocarbon ages significantly older than the period of ice wedge activity release of ancient carbon with climatic warming will therefore affect the global 14 c budget

the evolution of a thermokarst lake landscape late quaternary permafrost degradation and stabilization in interior alaska thermokarst processes characterize a variety of ice rich permafrost terrains and often lead to lake formation the long term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate vegetation and ground conditions including the volume of excess ground ice and its distribution the current lake status of thermokarst lake landscapes and their future trajectories under climatewarming are better understood in the light of their long term development we studied the lake rich southern marginal upland of the yukon flats northern interior alaska using dated lake sediment cores observations of river cut exposures and remotely sensed data the region features thick up to 40 m quaternary deposits mainly loess that contain massive ground ice two of three studied lakes formed 11 000 12 000 cal yr bp through inferred thermokarst processes and fire may have played a role in initiating thermokarst development from 9000 cal yr bp all lakes exhibited steady sedimentation and pollen stratigraphies are consistentwith regional patterns the current lake expansion rates are low 0 to b7 cmyr 1 shoreline retreat compared with other regions 30 cm yr 1 or more this thermokarst lake rich region does not showevidence of extensive landscape lowering by lake drainage nor of multiple lake generations within a basin however lidar images reveal linear corrugations n5 m amplitude deep thermo erosional gullies and features resembling lake drainage channels suggesting that highly dynamic surface processes have previously shaped the landscape evidently widespread early holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization the latter possibly related to establishment of dense forest cover partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism holocene landscape evolution in the study area differs from that described from other thermokarst affected regions regional responses to future environmental change may be equally individualistic