impact of iceberg calving on the retreat of thwaites glacier west antarctica over the next century with different calving laws and ocean thermal forcing

timing and structure of mega sacz events during heinrich stadial 1 a substantial strengthening of the south american monsoon system sams during heinrich stadials hs points toward decreased cross equatorial heat transport as the main driver of monsoonal hydroclimate variability at millennial time scales in order to better constrain the exact timing and internal structure of hs1 over tropical south america we assessed two precisely dated speleothem records from central eastern and northeastern brazil in combination with two marine records of terrestrial organic and inorganic matter input into the western equatorial atlantic during hs1 we recognize at least two events of widespread intensification of the sams across the entire region influenced by the south atlantic convergence zone sacz at 16 11 14 69 kyr b p and 18 1 16 66 kyr b p labeled as hs1a and hs1c respectively separated by a dry excursion from 16 66 to 16 11 kyr b p hs1b in view of the spatial structure of precipitation anomalies the widespread increase of monsoon precipitation over the sacz domain was termed mega sacz

a physically based calving model applied to marine outlet glaciers and implications for the glacier dynamics we present results from numerical ice flow models that include calving criteria based on penetration of surface and basal crevasses which in turn is a function of longitudinal strain rates near the glacier front the position of the calving front is defined as the point where either 1 surface crevasses reach the waterline model cdw or 2 surface and basal crevasses penetrate the full thickness of the glacier model cd for comparison with previous studies results are also presented for a height above buoyancy calving model qualitatively both models cdw and cd produce similar behaviour unlike previous models for calving the new calving criteria are applicable to both grounded termini and floating ice shelves and tongues the numerical ice flow model is applied to an idealized geometry characteristic of marine outlet glaciers results indicate that grounding line dynamics are less sensitive to basal topography than previously suggested stable grounding line positions can be obtained even on a reverse bed slope with or without floating termini the proposed calving criteria also allow calving losses to be linked to surface melt and therefore climate in contrast to previous studies in which calving rate or position of the terminus is linked to local water depth the new calving criterion is able to produce seasonal cycles of retreat and advance as observed for greenland marine outlet glaciers the contrasting dynamical behaviour and stability found for different calving models suggests that a realistic parameterization for the process of calving is crucial for any predictions of marine outlet glacier change

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

a numerical investigation of surface crevasse propagation in glaciers using nonlocal continuum damage mechanics 1 we use a nonlocal viscoelastic damage model to investigate the conditions that enable water free surface crevasse propagation in grounded marine terminating glaciers our simulations on idealized rectangular ice slabs in contact with the ocean show that crevasses propagate faster in thicker ice slabs we find that 1 the fraction of ice slab thickness penetrated by surface crevasses decreases with increasing seawater depth near the terminus 2 a no slip fixed basal boundary condition retards crevasse growth and 3 crevasses form closer to the terminus when the seawater depth is larger or when the glacier base is fixed to the bedrock which could lead to calving of smaller icebergs however water free surface crevasses can penetrate nearly the entire ice thickness only in thicker ice slabs terminating in shallow seawater depths this leads us to the conclusion that surface crevasses alone are not responsible for calving events in marine terminating and thin glaciers

the morphology structural evolution and significance of push moraines abstract push moraines glaciotectonic ice marginal moraines have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing pleistocene ice sheets providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland to the wider earth science community push moraines are of interest as analogues for thin skin tectonics within orogenic belts this paper reviews the morphology structural geology formation and significance of push moraines the morphological and structural characteristics of small seasonal push moraines through to large multi crested examples produced by sustained glacier advances are reported before the primary controls on push moraine formation are examined these controls include the nature of the applied glacial stress field the presence and properties of decollement horizons and the shear strength and rheology of the glacial foreland a conceptual model of push moraine formation is introduced in which the range of observed morphological and structural forms are viewed within a matrix defined by the main variables which control their formation the absence of consensus over which of these variables is of greatest importance currently limits the significance of push moraines in palaeoglaciological research as a consequence this review emphasises the need for future research in order to realise the true potential of push moraine in the reconstruction of pleistocene environments

episodic propagation of a rift on the amery ice shelf east antarctica 1 we investigate ice shelf rift propagation using a combination of gps and seismic measurements near the tip of an active rift in the amery ice shelf these measurements reveal that propagation occurs in episodic bursts which were identified based on swarms of seismicity accompanied by rapid rift widening the bursts last approximately 4 hours and are separated by 10 24 days in between bursts the rift widens at a rate comparable to that of ice shelf spreading comparison of automatic weather station data and tidal amplitudes show that the propagation bursts are not directly triggered by winds or tides suggesting that rift propagation is driven by the background glaciological stress in the ice shelf we show that the ice debris that partly fills the rift may play a role in controlling the rate of propagation

a one dimensional model for the interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented a significant topographic obstacle to the westerly winds in northern midlatitudes this work explores how consequent changes in the atmospheric stationary wave pattern might have affected the shape and growth of the ice sheets themselves a one dimensional 1 d model is developed which permits an examination of the types and magnitudes of the feedbacks that might be expected when plausible temperature perturbations are introduced at the ice sheet margin which are proportional to the stationary wave amplitude the equilibrium shape of the ice sheet is significantly altered and depends on the sign of the perturbation the proposed feedback also affects the response of the ice sheet to time varying climate forcing the results suggest that the evolution of a continental scale ice sheet with a land based margin may be significantly determined by the changes it induces in the atmospheric circulation

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

glacier crevasses observations models and mass balance implications we review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses as well as the three broad classes of numerical models now employed to simulate crevasse fracture the relatively new insight that mixed mode fracture in local stress equilibrium rather than downstream advection alone can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies in the past three decades there have been tremendous advances in the spatial resolution of satellite imagery as well as fully automated algorithms capable of tracking crevasse displacements between repeat images despite considerable advances in developing fully transient three dimensional ice flow models over the past two decades both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time in the past decade however multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged the combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large scale ice sheet models finally given the broad interest in the sea level rise implications of recent and future cryospheric change we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

millennial scale precipitation changes in southern brazil over the past 90 000 years 1 a u th dated 90 000 year long speleothem oxygen isotope record from southern brazil anti correlates remarkably with the cave calcite records from eastern china but positively correlates with the speleothem record from northeastern brazil suggesting an interhemispheric anti phasing of rainfall on both millennial and orbital timescales likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in hadley circulation the phase relationships among these records are consistent with the hypothesis that abrupt climate events during the last glacial period are triggered by oceanic circulation changes in the high latitudes and enhanced by tropical feedbacks

impact of bolivian paleolake evaporation on the δ18o of the andean glaciers during the last deglaciation 18 5 11 7 ka diatom inferred δ18o values and hydro isotopic modeling abstract during the last deglaciation the bolivian altiplano 15 23 s 66 70 w was occupied by paleolake tauca covering at least 51 000 km 2 at its maximum highstand between 16 5 and 15 ka twenty five hundred years later after a massive regression a new transgressive phase produced paleolake coipasa smaller than tauca and restricted to the southern part of the basin these paleolakes were overlooked at the west by the sajama ice cap the latter provides a continuous record of the oxygen isotopic composition of paleo precipitation for the last 25 ka contemporaneously to the end of paleolake tauca around 14 3 ka the sajama ice cap recorded a significant increase in ice oxygen isotopic composition 18 o ice this paper examines to what extent the disappearance of lake tauca contributed to precipitation on the sajama summit and this specific isotopic variation the water 18 o values of paleolakes tauca and coipasa 18 o lake were quantitatively reconstructed from 18 5 to 11 7 ka based on diatom isotopic composition 18 o diatoms and ostracod isotopic composition 18 o carbonates retrieved in lacustrine sediments at a centennial time scale a strong trend appears abrupt decreases of 18 o lake during lake fillings are immediately followed by abrupt increases of 18 o lake during lake level stable phases the highest variation occurred at 15 8 ka with a 18 o lake decrease of about 10 concomitant with the lake tauca highstand followed 400 years later by a 7 increase in 18 o lake a simple hydro isotopic modeling approach reproduces consistently this rapid decrease increase feature moreover it suggests that this unexpected re increase in 18 o lake after filling phases can be partly explained by an equilibration of isotopic fluxes during the lake steady state based on isotopic calculations during lake evaporation and a simple water stable isotopes balance between potential moisture sources at sajama advection versus lake evaporation we show that total or partial evaporation from 5 to 60 of paleolake tauca during its major regression phase at 14 3 ka could explain the pronounced isotopic excursion at sajama ice cap these results suggest that perturbations of the local hydrological cycle in lacustrine areas may substantially affect the paleoclimatic interpretation of the near by isotopic signals e g ice core or speleothems

a modified theory of bottom crevasses used as a means for measuring the buttressing effect of ice shelves on inland ice sheets bottom crevasses are fractures that extend upward into floating ice shelves they form when seawater penetrates the base of the ice shelf and ruptures the ice up to the level at which englacial stresses equal the stress of the seawater for a freely floating ice shelf the penetrating level of closely spaced crevasses is estimated at about half the ice thickness h for an isolated crevasse the level is about h 4 however an analysis of the heights and locations of bottom crevasses in the ross ice shelf shows that none of the crevasses approach the predicted limits perhaps because the existing theory does not include the back stress b which is present in bounded ice shelves by reformulating the theory to include a back stress term b can be evaluated experimentally from radar measurements of crevasse height and ice thickness the magnitude of b 2 bars in the grid northwest corner of the ice shelf suggests the ice shelf is playing an important role in buttressing the inland ice sheet

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

a non local continuum poro damage mechanics model for hydrofracturing of surface crevasses in grounded glaciers hydrofracturing can enhance the depth to which crevasses propagate and in some cases allow full depth crevasse penetration and iceberg detachment however many existing crevasse models either do not fully account for the stress field driving the hydrofracture process and or treat glacier ice as elastic neglecting the non linear viscous rheology here we present a non local continuum poro damage mechanics cpdm model for hydrofracturing and implement it within a full stokes finite element formulation we use the cpdm model to simulate the propagation of water filled crevasses in idealized grounded glaciers and compare crevasse depths predicted by this model with those from linear elastic fracture mechanics lefm and zero stress models we find that the cpdm model is in good agreement with the lefm model for isolated crevasses and with the zero stress model for closely spaced crevasses until the glacier approaches buoyancy when the glacier approaches buoyancy we find that the cpdm model does not allow the propagation of water filled crevasses due to the much smaller size of the tensile stress region concentrated near the crevasse tip our study suggests that the combination of non linear viscous and damage processes in ice near the tip of a water filled crevasse can alter calving outcomes

antarctic like temperature variations in the tropical andes recorded by glaciers and lakes during the last deglaciation abstract the respective impacts of northern and southern hemispheric climatic changes on the tropics during the last deglaciation remain poorly understood in the high tropical andes the antarctic cold reversal acr 14 3 12 9 ka bp is better represented among morainic records than the younger dryas 12 9 11 7 ka bp however in the altiplano basin bolivia two cold periods of the northern hemisphere heinrich stadial 1a 16 5 14 5 ka bp and the younger dryas are synchronous with i major advances or standstills of paleoglaciers and ii the highstands of giant paleolakes tauca and coipasa here we present new cosmic ray exposure cre ages from glacial landforms of the bolivian andes that formed during the last deglaciation termination 1 we reconstruct the equilibrium line altitudes ela associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation our temperature reconstruction t relative to present day yields a consistent regional trend of progressive warming from t 5 to 2 5 c during 17 14 5 ka bp followed by a return to colder conditions around 4 c during the acr 14 5 12 9 ka bp the coipasa highstand 12 9 11 8 ka bp is coeval with another warming trend followed by t stabilization at the onset of the holocene ca 10 ka bp around 3 c our results suggest that during the last deglaciation 20 10 ka bp atmospheric temperatures in the tropical andes mimicked antarctic variability whereas precipitation over the altiplano was driven by changes in the northern hemisphere

charging history of paleogene deep gas in the qibei sag bohai bay basin china abstract the qibei sag qs at the western region of the bohai bay basin bbb eastern china has made significant progress in the deep gas exploration recently indicating that the deep gas reservoirs have good exploration prospects the deep gas reservoirs within the second member of the shahejie formation of the paleogene e2s2 are buried at approximately 5000 m the sources and hydrocarbon accumulation mechanisms were investigated by analyzing the regional structure integrating geologic and geochemical parameters of source rocks and natural gas analyzing results show that in the qs and adjacent areas qsaa three sets of source rocks e2s1 e2s2 e2s3 were developed which differ in organic chemical characters but have abundant organic matters in fair good standard affected by burial history e2s3 source rocks have entered into the high mature over mature stage and e2s1 source rocks are mainly in mature stage the methane content of natural gas 78 91 the methane carbon isotope value 41 3 34 6 and the positive carbon isotope sequence 13c1

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

late pleistocene glaciations of the arid subtropical andes and new results from the chajnantor plateau northern chile abstract the spatiotemporal pattern of glaciation along the andes mountains is an important proxy record reflecting the varying influence of global and regional circulation features on south american climate however the timing and extent of glaciation in key parts of the orogen particularly the deglaciated arid andes are poorly constrained we present new cosmogenic 10 be and 36 cl exposure ages for glacial features on and near the chajnantor plateau 23 s the new dates although scattered due to cosmogenic inheritance imply that the most recent extensive glacial occupation ended before or during the global last glacial maximum lgm we discuss this new record in the context of published glacial chronologies from glacial features in peru bolivia and northern chile rescaled using the latest cosmogenic 10 be production rate calibration for the tropical andes the results imply regionally synchronous moraine stabilization ca 25 40 ka 15 17 ka and 12 14 ka with the youngest of these moraines absent in records south of 20 s including in our new chajnantor area chronology this spatial pattern implicates easterly moisture in generating sufficient snowfall to glaciate the driest parts of the andes while allowing a role for westerly moisture possibly modulated by the migration of the southern westerly wind belt in the regions near and south of the atacama desert

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

evolution of basal crevasses links ice shelf stability to ocean forcing abstract iceberg calving is one of the primary mechanisms responsible for transferring ice from the antarctic ice shelves to the ocean but remains poorly understood previous theories of calving have sought to explain the calving process as a brittle phenomenon that occurs rapidly when surface or basal crevasses penetrate the entire ice thickness here we show that the strain rate weakening nature of ice permits initially narrow basal crevasses to seed an instability that gives rise to locally enhanced ductile deformation and thinning over length scales that are large compared to the ice thickness this ductile failure process called necking amplifies long wavelength features of bottom topography and allows basal crevasses to penetrate an increasing fraction of the ice thickness as they advect downstream application of the model to the four largest antarctic ice shelves shows that necking occurs downstream of pinning points and sharp protrusions in the ice shelf embayment where stress is highly concentrated however model predictions are sensitive to assumptions about basal melting and refreezing within crevasses suggesting that the combination of mechanical instability and ice ocean interaction on the scale of an individual crevasse may play a leading role in controlling ice shelf stability

dynamic damage model of crevasse opening and application to glacier calving 1 theory and applications of continuum damage mechanics for ice are discussed and on this basis an ice damage model valid at low stresses is proposed the model describes the damage itself the rheology of the damaged ice and the damage evolution a local damaging and healing law is considered and its parameterization is motivated the model parameters are inferred from published data of laboratory experiments the model is subsequently implemented in a finite element code and applied to the prediction of a calving process and to the destabilization of an ice chunk from a hanging glacier numerical results show good agreement with field measurements

bounds on the calving cliff height of marine terminating glaciers increased calving and rapid retreat of glaciers can contribute significantly to sea level rise but the processes controlling glacier retreat remain poorly understood we seek to improve our understanding of calving by investigating the stress field controlling tensile and shear failure using a 2d full stokes finite element model using idealized rectangular geometries we find that when rapidly sliding glaciers thin to near buoyancy full thickness tensile failure occurs similar to observations motivating height above buoyancy calving laws in contrast when glaciers are frozen to their beds basal crevasse penetration is suppressed and calving is minimal we also find shear stresses are largest when glaciers are thickest together the tensile and shear failure criteria map out a stable envelope in an ice thickness water depth diagram the upper and lower bounds on cliff height can be incorporated into numerical ice sheet models as boundary conditions thus bracketing the magnitude of calving rates in marine terminating glaciers

glacier and climate reconstruction at tres lagunas nw argentina based on 10be surface exposure dating and lake sediment analyses abstract we present 35 10 be surface exposure ages from quartzite moraine boulders at tres lagunas in the sierra de santa victoria nw argentina additionally an 8 m sediment core from a glacial lake was investigated to provide independent radiocarbon age control the oldest and most extensive glaciation occurred 116 3 ka and likely coincides with the lake transgression phase ouki on the altiplano maximum glaciation in phase with the global last glacial maximum lgm is dated to 22 25 ka and documents a glacial mass balance response to substantially lower temperatures and minor precipitation increase in phase with the sajsi lake transgression phase after initial deglaciation and formation of a small paleolake at tres lagunas a glacial readvance is documented by an outwash diamict in the sediment core and radiocarbon dated to 19 17 ka as well as by a moraine surface exposure dated to 17 ka the most prominent moraine was deposited at 14 5 ka coinciding with the lake transgression phase tauca on the altiplano this late glacial advance reflects the massive intensification of the south american summer monsoon sasm in response to northern hemispheric cooling during heinrich i and the resultant southward shift of the intertropical convergence zone itcz and la nina like conditions in the eastern equatorial pacific rapid deglaciation started after 14 5 ka interrupted only by minor glacial still stands at 13 8 1 5 ka and 12 0 1 5 ka the latter one correlating with the coipasa transgression phase on the altiplano and the younger dryas

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

late local glacial maximum in the central altiplano triggered by cold and locally wet conditions during the paleolake tauca episode 17 15 ka heinrich 1 the timing and causes of the last deglaciation in the southern tropical andes is poorly known in the central altiplano recent studies have focused on whether this tropical highland was deglaciated before synchronously or after the global last glacial maximum 21 ka bp in this study we present a new chronology based on cosmogenic 3he 3he c dating of moraines on cerro tunupa a volcano that is located in the centre of the now vanished lake tauca 19 9 s 67 6 w these new 3he c ages suggest that the tunupa glaciers remained close to their maximum extent until 15 ka bp synchronous with the lake tauca highstand 17 15 ka bp glacial retreat and the demise of lake tauca seem to have occurred rapidly and synchronously within dating uncertainties at 15 ka bp we took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the lake tauca highstand this new approach indicates that during the tauca highstand 17 15 ka bp the centre of the altiplano was characterized by temperature 6 5 c cooler and average precipitation higher by a factor ranging between 1 6 and 3 compared to the present cold and wet conditions thus persisted in a significant part of the southern tropical andes during the heinrich 1 event 17 15 ka bp this study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions

modeling hydraulic fracture of glaciers using continuum damage mechanics the presence of water filled crevasses is known to increase the penetration depth of crevasses and this has been hypothesized to play an important role controlling iceberg calving rate here we develop a continuum damage based poro mechanics formulation that enables the simulation of water filled basal and surface crevasse propagation the formulation incorporates a scalar isotropic damage variable into a maxwell type viscoelastic constitutive model for glacial ice and the effect of the water pressure on fracture propagation using the concept of effective solid stress we illustrate the model by simulating quasi static hydrofracture in idealized rectangular slabs of ice in contact with the ocean our results indicate that water filled basal crevasses only propagate when the water pressure is sufficiently large and that the interaction between simultaneously propagating water filled surface and basal crevasses can have a mutually positive influence leading to deeper crevasse propagation which can critically affect glacial stability therefore this study supports the hypothesis that hydraulic fracture is a plausible mechanism for the accelerated breakdown of glaciers

a review of statistical chronology models for high resolution proxy based holocene palaeoenvironmental reconstruction abstract in this paper we explain the background workings and results obtained from three recently developed statistical age depth models implemented in freely available general purpose software packages bpeat oxcal and bchron these models aim to reconstruct the sedimentation rate in a single core typically lake peat or ocean given a limited number of scientific date estimates usually radiocarbon and fixed depths most importantly they provide a suitably qualified estimate of the uncertainty in the age depth chronology and thus can be used in a variety of applications we perform a large data driven study of the three models and discuss their general utility in chronology construction for palaeoenvironmental research

the statistical physics of iceberg calving and the emergence of universal calving laws determining a calving law valid for all glaciological and environmental regimes has proven to be a difficult problem in glaciology for this reason most models of the calving process are semi empirical with little connection to the underlying fracture processes in this study i introduce methods rooted in statistical physics to show how calving laws valid for any glaciological domain can emerge naturally as a large spatial scale long temporal scale limit of an underlying continuous or discrete fracture process an important element of the method developed here is that iceberg calving is treated as a stochastic process and that the probability an iceberg will detach in a given interval of time can be described by a probability distribution function using limiting assumptions about the underlying probability distribution the theory is shown to be able to simulate a range of calving styles including the sporadic detachment of large tabular icebergs from ice tongues and ice shelves and the more steady detachment of smaller sized bergs from tidewater outlet glaciers the method developed has the potential to provide a physical basis to include iceberg calving into numerical ice sheet models that can be used to produce more realistic estimates of the glaciological contribution to sea level rise

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

sermeq model produces a realistic upper bound on calving retreat for 155 greenland outlet glaciers the rate of land ice loss due to iceberg calving is a key source of variability among model projections of 21st century sea level rise it is especially challenging to account for mass loss due to

progressive glacial retreat in the southern altiplano uturuncu volcano 22 s between 65 and 14 ka constrained by cosmogenic 3he dating this work presents the first reconstruction of late pleistocene glacier fluctuations on uturuncu volcano in the southern tropical andes cosmogenic 3he dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka despite important scatter in the exposure ages on the oldest moraines probably resulting from pre exposure these 3he data constrain the timing of the moraine deposits and subsequent glacier recessions the uturuncu glacier may have reached its maximum extent much before the global lgm maybe as early as 65 ka with an equilibrium line altitude ela at 5280 m then the glacier remained close to its maximum position with a main stillstand identified around 40 ka and another one between 35 and 17 ka followed by a limited recession at 17 ka then another glacial stillstand is identified upstream during the late glacial period probably between 16 and 14 ka with an ela standing at 5350 m this stillstand is synchronous with the paleolake tauca highstand this result indicates that this regionally wet and cold episode during the heinrich 1 event also impacted the southern altiplano the ela rose above 5450 m after 14 ka synchronously with the bolling allerod