diurnal seismicity cycle linked to subsurface melting on an ice shelf seismograms acquired on the mcmurdo ice shelf antarctica during an austral summer melt season november 2016 january 2017 reveal a diurnal cycle of seismicity consisting of hundreds of thousands of small ice quakes limited to a 6 12 hour period during the evening in an area where there is substantial subsurface melting this cycle is explained by thermally induced bending and fracture of a frozen surface superimposed on a subsurface slush water layer that is supported by solar radiation penetration and absorption a simple one dimensional model of heat transfer driven by observed surface air temperature and shortwave absorption reproduces the presence and absence as daily weather dictated of the observed diurnal seismicity cycle seismic event statistics comparing event occurrence with amplitude suggest that the events are generated in a fractured medium featuring relatively low stresses as is consistent with a frozen surface superimposed on subsurface slush waveforms of the icequakes are consistent with hydroacoustic phases at frequency bf gt bf 75 bf hz and flexural gravity waves at frequency bf bf lt 25 bf hz our results suggest that seismic observation may prove useful in monitoring subsurface melting in a manner that complements other ground based methods as well as remote sensing

the potential of osl and tl for dating lateglacial and holocene dune sands tested with independent age control of the laacher see tephra 12 880 a at the section mainz gonsenheim abstract optically stimulated luminescence osl and thermoluminescence tl are applied in this study to date a lateglacial and holocene aeolian sediment sequence quartz and potassium rich feldspars extracted from dune sands from western germany were dated using both multiple aliquot ma and single aliquot sa protocols for luminescence dating this particular dune section was chosen for this test study because an independent age control is provided by a horizon of the laacher seetephra 12 880 a in contrast to the results for potassium feldspars which show underestimation of up to 25 the quartz fraction provides promising results with respect to the presumed geological ages

crevasse analysis reveals vulnerability of ice shelves to global warming an ingenious combination of satellite imaging machine learning and stress analysis has revealed the antarctic ice shelves that are most at risk of disintegrating as a result of atmospheric warming ice shelves at greatest risk of future hydrofracturing identified

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

measurement and modeling of ablation of the bottom of supraglacial lakes in western greenland 1 we report measurements of ablation rates of the bottom of two supraglacial lakes and of temperatures at different depths collected during the summers of 2010 and 2011 in west greenland to our knowledge this is the first time that such data sets are reported and discussed in the literature the measured ablation rates at the bottom of the two lakes are of the order of 6 cm day versus a rate of 2 5 3 cm day in the case of bare ice of surrounding areas though our measurements suggest the presence of a vertical temperature gradient it is not possible to draw final conclusions as the measured gradient is smaller than the accuracy of our temperature sensors in situ measurements are compared with the results of a thermodynamic model forced with the outputs of a regional climate model in general the model is able to satisfactorily reproduce the measured quantities with rmse of the order of 3 4 cm for the ablation and 1 5 c in the case of water temperature our results confirm that the ablation at the bottom of supraglacial lakes plays an important role on the overall lake volume with the ablation in the case of ice covered by a lake being 110 135 of that over bare ice at nearby locations beside ice sheet hydrological implications melting at the bottom of a supraglacial lake might affect estimates of lake volume from spaceborne visible and near infrared measurements

supraglacial lakes on the larsen b ice shelf antarctica and at paakitsoq west greenland a comparative study we acknowledge the support of the u s national science foundation under grant ant 0944248

catastrophic ice shelf break up by an ice shelf fragment capsize mechanism two disintegration events leading to the loss of larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively proceeded with extreme rapidity order of several days and reduced an extensive seemingly integrated ice shelf to a jumble of small fragments these events strongly correlate with warming regional climate and accumulation of surface meltwater supporting a hypothesis that meltwater induced propagation of pre existing surface crevasses may have initiated ice shelf fragmentation we address here an additional subsequent mechanism that may sustain and accelerate the ice shelf break up once it begins the proposed mechanism involves the coherent capsize of narrow less than thickness ice shelf fragments by rolling 90 in a direction toward or away from the ice front fragment capsize liberates gravitational potential energy forces open ice shelf rifts and contributes to further fragmentation of the surrounding ice shelf

seasonal evolution of supraglacial lakes on an east antarctic outlet glacier supraglacial lakes are known to influence ice melt and ice flow on the greenland ice sheet and potentially cause ice shelf disintegration on the antarctic peninsula in east antarctica however our understanding of their behavior and impact is more limited using 150 optical satellite images and meteorological records from 2000 to 2013 we provide the first multiyear analysis of lake evolution on langhovde glacier dronning maud land 69 11 s 39 32 e we mapped 7990 lakes and 855 surface channels up to 18 1 km inland 670 m above sea level from the grounding line and document three pathways of lake demise i refreezing ii drainage to the englacial subglacial environment on the floating ice and iii overflow into surface channels on both the floating and grounded ice the parallels between these mechanisms and those observed on greenland and the antarctic peninsula suggest that lakes may similarly affect rates and patterns of ice melt ice flow and ice shelf disintegration in east antarctica

potential antarctic ice sheet retreat driven by hydrofracturing and ice cliff failure abstract geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last 25 million years at times reaching 20 m or more above modern if correct this implies substantial variations in the size of the east antarctic ice sheet eais however most climate and ice sheet models have not been able to simulate significant eais retreat from continental size given that atmospheric co2 levels were relatively low throughout this period here we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model data conflict in response to atmospheric and ocean temperatures typical of past warm periods floating ice shelves may be drastically reduced or removed completely by increased oceanic melting and by hydrofracturing due to surface melt draining into crevasses ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing and may fail structurally if stresses exceed the ice yield strength producing rapid retreat incorporating these mechanisms in our ice sheet model accelerates the expected collapse of the west antarctic ice sheet to decadal time scales and also causes retreat into major east antarctic subglacial basins producing 17 m global sea level rise within a few thousand years the mechanisms are highly parameterized and should be tested by further process studies but if accurate they offer one explanation for past sea level high stands and suggest that antarctica may be more vulnerable to warm climates than in most previous studies

breakup of the larsen b ice shelf triggered by chain reaction drainage of supraglacial lakes this research is supported by the u s national science foundation under grant geop ant 0944248 awarded to d r m and grants ant 0838811 and arc 0934534 awarded to o v s

reconstructing the eruptive history of a monogenetic volcano through a combination of fieldwork and geophysical surveys the example of puig d adri garrotxa volcanic field puig d adri is a complex volcano in the garrotxa volcanic field 0 7 0 01 ma the youngest part of the catalan volcanic zone ne iberian peninsula the construction of this volcano involved the superimposition of three volcanic edifices with five lithostratigraphic units in which several strombolian and phreatomagmatic episodes alternated geological and geophysical surveys performed using electrical resistivity tomography and self potential have contributed to revealing the internal structure of the volcano and the succession of deposits the ring cone morphology of the phreatomagmatic part of the structure shows how a number of variables including the way in which magma and water interacted greatly influenced the eruptive dynamics and the mechanisms of formation a further major issue reflected in the final structure of the edifice is the process of vent migration which was controlled by the characteristics of the substrate and its interaction with the magma as it rose supplementary material granulometric and component histograms of the samples not shown in figure 4 are available at http doi org 10 6084 m9 figshare c 3262498

laboratory investigations of iceberg capsize dynamics energy dissipation and tsunamigenesis 1 we present laboratory experiments designed to quantify the stability and energy budget of buoyancy driven iceberg capsize box shaped icebergs were constructed out of low density plastic hydrostatically placed in an acrylic water tank containing freshwater of uniform density and allowed or forced if necessary to capsize the maximum kinetic energy translational plus rotational of the icebergs was 15 of the total energy released during capsize and radiated surface wave energy was 1 of the total energy released the remaining energy was directly transferred into the water via hydrodynamic coupling viscous drag and turbulence the dependence of iceberg capsize instability on iceberg aspect ratio implied by the tank experiments was found to closely agree with analytical predictions based on a simple hydrostatic treatment of iceberg capsize this analytical treatment along with the high reynolds numbers for the experiments and considerably higher values for capsizing icebergs in nature indicates that turbulence is an important mechanism of energy dissipation during iceberg capsize and can contribute a potentially important source of mixing in the stratified ocean proximal to marine ice margins

a computational investigation of iceberg capsize as a driver of explosive ice shelf disintegration potential energy released from the capsize of ice shelf fragments icebergs is the immediate driver of the brief explosive phase of ice shelf disintegration along the antarctic peninsula e g the larsen a larsen b and wilkins ice shelves the majority of this energy powers the rapidly expanding plume of ice shelf fragments that expands outward into the open ocean a smaller fraction of this energy goes into surface gravity waves and other dynamic interactions between ice and water that can sustain the continued fragmentation and break up of the original ice shelf as an initial approach to the investigation of ice shelf fragment capsize in ice shelf collapse we develop a simple conceptual model involving ideal rectangular icebergs initially in unstable or metastable orientations which are assembled into a tightly packed mass that subsequently disassembles via massed capsize computations based on this conceptual model display phenomenological similarity to aspects of real ice shelf collapse a promising result of the conceptual model presented here is a description of how iceberg aspect ratio and its statistical variance the two parameters related to ice shelf fracture patterns influence the enabling conditions to be satisfied by slow acting processes e g environmentally driven melting that facilitate ice shelf disintegration

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

the flexural dynamics of melting ice shelves a conspicuous precursor of catastrophic ice shelf break up along the antarctic peninsula reported widely in the literature is the gradual increase in surface melting and consequent proliferation of supraglacial lakes and dolines here we present analytical and numerical solutions for the flexure stresses within an ice shelf covered by lakes and dolines both isolated and arrayed we conclude that surface water promotes ice shelf instability in two ways 1 by water assisted crevasse penetration as previously noted and 2 by the inducement of strong tensile flexure stresses exceeding background spreading stress by 10 100 times in response to surface water mass loads and hydrostatic rebound occurring when meltwater lakes drain

calving and rifting on the mcmurdo ice shelf antarctica on 2 march 2016 several small en echelon tabular icebergs calved from the seaward front of the mcmurdo ice shelf and a previously inactive rift widened and propagated by 3 km 25 of its previous length setting the stage for the future calving of a 14 km2 iceberg within 24 h of these events all remaining land fast sea ice that had been stabilizing the ice shelf broke up the events were witnessed by time lapse cameras at nearby scott base and put into context using nearby seismic and automatic weather station data satellite imagery and subsequent ground observation although the exact trigger of calving and rifting cannot be identified definitively seismic records reveal superimposed sets of both long period 10 s sea swell propagating into mcmurdo sound from storm sources beyond antarctica and high energy locally sourced short period 10 s sea swell in the 4 days before the fast ice break up and associated ice shelf calving and rifting this suggests that sea swell should be studied further as a proximal cause of ice shelf calving and rifting if proven it suggests that ice shelf stability is tele connected with far field storm conditions at lower latitudes adding a global dimension to the physics of ice shelf break up

a model of viscoelastic ice shelf flexure we develop a formal thin plate treatment of the viscoelastic flexure of floating ice shelves as an initial step in treating various problems relevant to ice shelf response to sudden changes of surface loads and applied bending moments e g draining supraglacial lakes iceberg calving surface and basal crevassing our analysis is based on the assumption that total deformation is the sum of elastic and viscous or power law creep deformations i e akin to a maxwell model of viscoelasticity having a spring and dashpot in series the treatment follows the assumptions of well known thin plate approximation but is presented in a manner familiar to glaciologists and with glen s flow law we present an analysis of the viscoelastic evolution of an ice shelf subject to a filling and draining supraglacial lake this demonstration is motivated by the proposition that flexure in response to the filling drainage of meltwater features on the larsen b ice shelf antarctica contributed to the fragmentation process that accompanied its collapse in 2002

englacial drainage structures in an east antarctic outlet glacier ground penetrating radar data acquired in the 2016 17 austral summer on sorsdal glacier east antarctica provide evidence for meltwater lenses within porous surface ice that are conceptually similar to firn aquifers observed on the greenland ice sheet and the arctic and alpine glaciers these englacial water bodies are associated with a dry relict surface basin and consistent with perennial drainage into an interconnected englacial drainage system which may explain a large englacial outburst flood observed in satellite imagery in the early 2016 17 melt season our observations indicate the rarely documented presence of an englacial hydrological system in antarctica with implications for the storage and routing of surface meltwater future work should ascertain the spatial prevalence of such systems around the antarctic coastline and identify the degree of surface runoff redistribution and storage in the near surface to quantify their impact on surface mass balance

dynamic perennial firn aquifer on an arctic glacier ice penetrating radar and gps observations reveal a perennial firn aquifer pfa on a svalbard ice field similar to those recently discovered in southeastern greenland a bright widespread radar reflector separates relatively dry and water saturated firn this surface the phreatic firn water table is deeper beneath local surface elevation maxima shallower in surface lows and steeper where the surface is steep the reflector crosscuts snow stratigraphy we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases our observations indicate that pfas respond rapidly subannually to surface forcing and are capable of providing significant input to the englacial hydrology system

a structural glaciological analysis of the 2002 larsen b ice shelf collapse this study provides a detailed structural glaciological analysis of changes in surface structures on the larsen b ice shelf on the antarctic peninsula prior to its collapse in february march 2002 mapped features include the ice shelf front rifts crevasses longitudinal linear surface structures and meltwater features we define domains on the ice shelf related to glacier source areas and demonstrate that prior to collapse the central larsen b ice shelf consisted of four sutured flow units fed by crane jorum punchbowl and hektoria green evans glaciers between these flow units were suture zones of thinner ice where the feeder glaciers merged prior to collapse large open rift systems were present offshore of foyn point and cape disappointment these rifts became more pronounced in the years preceding break up and ice blocks in the rifts rotated because of the strong lateral shear in this zone velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago we suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units this we believe was the result of ice shelf front retreat during 1998 2000 reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units ice shelf thinning and pre shelf break up glacier acceleration

causes of pre collapse changes of the larsen b ice shelf numerical modelling and assimilation of satellite observations satellite observations revealed that beside a rapid thinning the larsen b ice shelf lbis was undergoing a significant acceleration before its collapse in 2002 this paper investigates the ice shelf acceleration between 1995 and 1999 using a combination of data assimilation and numerical modelling based on a flow model adjusted to the 1995 insar velocities perturbation experiments are performed such as ice front retreat thinning increase in tributary flow and rheological weakening furthermore an inversion for ice shelf rheology and tributary flow velocity is performed for both the 1995 and the 1999 insar velocities the perturbation experiments together with the inversion strongly suggest that the acceleration cannot solely be explained by the retreat of the ice shelf front but relies on a further significant rheological weakening of the already weak shear zones within the lbis minor tributary acceleration is found to be an effect rather than a cause of the ice shelf acceleration furthermore the observed acceleration cannot be explained by the observed recent thinning we conclude that for smaller ice shelves such as the lbis such weak shear margins play a crucial role in controlling their dynamics and are the key to understand changes in the future finally we compare the dynamic thinning likely to be associated with the observed acceleration with the observed thinning for the ice shelf as a whole this thinning accounts for 20 of the observed value which implies that factors such as enhanced basal melt were the primary cause of the observed thinning

tsunami and infragravity waves impacting antarctic ice shelves the responses of the ross ice shelf ris to the september 16 2015 8 3 mw chilean earthquake tsunami 75 s period and to oceanic infragravity ig waves 50 300 s period were recorded by a broadband seismic array deployed on the ris from november 2014 to november 2016 here we show that tsunami and ig generated signals within the ris propagate at gravity wave speeds 70 m s as water ice coupled flexural gravity waves ig band signals show measureable attenuation away from the shelf front the response of the ris to chilean tsunami arrivals is compared with modeled tsunami forcing to assess ice shelf flexural gravity wave excitation by very long period vlp 300 s gravity waves displacements across the ris are affected by gravity wave incident direction bathymetry under and north of the shelf and water layer and ice shelf thicknesses horizontal displacements are typically about 10 times larger than vertical displacements producing dynamical extensional motions that may facilitate expansion of existing fractures vlp excitation is continuously observed throughout the year with horizontal displacements highest during the austral winter with amplitudes exceeding 20 cm because vlp flexural gravity waves exhibit no discernable attenuation this energy must propagate to the grounding zone both ig and vlp band flexural gravity waves excite mechanical perturbations of the ris that likely promote tabular iceberg calving consequently affecting ice shelf evolution understanding these ocean excited mechanical interactions is important to determine their effect on ice shelf stability to reduce uncertainty in the magnitude and rate of global sea level rise

ross ice shelf vibrations broadband seismic stations were deployed across the ross ice shelf ris in november 2014 to study ocean gravity wave induced vibrations initial data from three stations 100 km from the ris front and within 10 km of each other show both dispersed infragravity ig wave and ocean swell generated signals resulting from waves that originate in the north pacific spectral levels from 0 001 to 10 hz have the highest accelerations in the ig band 0 0025 0 03 hz polarization analyses indicate complex frequency dependent particle motions with energy in several frequency bands having distinctly different propagation characteristics the dominant ig band signals exhibit predominantly horizontal propagation from the north particle motion analyses indicate retrograde elliptical particle motions in the ig band consistent with these signals propagating as rayleigh lamb flexural waves in the ice shelf water cavity system that are excited by ocean wave interactions nearer the shelf front

iceberg capsize tsunamigenesis calving from the floating termini of outlet glaciers and ice shelves is just the beginning of an interesting chain of events that can subsequently have important impacts on human life and property immediately after calving many icebergs capsize roll over by 90 due to the instability of their initial geometry as icebergs melt and respond to the cumulative effects of ocean swell they can also reorient their mass distribution by further capsize and fragmentation these processes release gravitational potential energy and can produce impulsive large amplitude surface gravity waves known as tsunamis a term derived from the japanese language iceberg capsize tsunamis in greenland fjords can be of sufficient amplitude to threaten human life and cause destruction of property in settlements iceberg capsize tsunamis may also have a role in determining why some ice shelves along the antarctic peninsula disintegrate explosively in response to general environmental warming to quantify iceberg tsunami hazards we investigate iceberg capsize energetics and develop a rule relating tsunami height to iceberg thickness this rule suggests that the open water tsunami height located far from the iceberg and from shorelines where the height can be amplified has an upper limit of 0 01h where h is the initial vertical dimension of the iceberg

late quaternary deglacial history across the larsen b embayment antarctica abstract we measured meteoric 10 be variation throughout a marine sediment core from the larsen b embayment lbe of the antarctic peninsula and collected in situ 10 be and 14 c exposure ages on terrestrial glacial deposits from the northern and southern margins of the lbe we use these data to reconstruct last glacial maximum lgm to present deglaciation and ice shelf change in the lbe core sedimentary facies and meteoric 10 be data show a monotonic progression from subglacial deposits to sub ice shelf deposits to open marine conditions indicating that its collapse in 2002 was unprecedented since the lgm exposure age data from the southern lbe indicate 40 m of ice surface lowering between 14 and 6 ka then little change between 6 ka and the 2002 collapse exposure age data from the northern lbe show a bimodal distribution in which clusters of apparent exposure ages in the ranges 4 9 5 1 ka and 1 0 2 0 ka coexist near 50 m elevation based on these results other published terrestrial and marine deglaciation ages and a compilation of sea bed imagery we suggest a north to south progression of deglaciation in the northeast antarctic peninsula in response to holocene atmospheric and oceanic warming we argue that local topography and ice configuration inherited from the lgm in addition to climate change are important in controlling the deglaciation history in this region

fracture propagation and stability of ice shelves governed by ice shelf heterogeneity tabular iceberg calving and ice shelf retreat occurs after full thickness fractures known as rifts propagate across an ice shelf a quickly evolving rift signals a threat to the stability of larsen c the antarctic peninsula s largest ice shelf here we reveal the influence of ice shelf heterogeneity on the growth of this rift with implications that challenge existing notions of ice shelf stability most of the rift extension has occurred in bursts after overcoming the resistance of suture zones that bind together neighboring glacier inflows we model the stresses in the ice shelf to determine potential rift trajectories calving perturbations to ice flow will likely reach the grounding line the stability of larsen c may hinge on a single suture zone that stabilizes numerous upstream rifts elevated fracture toughness of suture zones may be the most important property that allows ice shelves to modulate antarctica s contribution to sea level rise

damage accelerates ice shelf instability and mass loss in amundsen sea embayment pine island glacier and thwaites glacier in the amundsen sea embayment are among the fastest changing outlet glaciers in west antarctica with large consequences for global sea level yet assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood here we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of pine island and thwaites ice shelves these damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones which results in further speedup shearing and weakening hence promoting additional damage development this damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat the results of this study suggest that damage feedback processes are key to future ice shelf stability grounding line retreat and sea level contributions from antarctica moreover they underline the need for incorporating these feedback processes which are currently not accounted for in most ice sheet models to improve sea level rise projections

modelling channelized surface drainage of supraglacial lakes supraglacial lakes can drain to the bed of ice sheets affecting ice dynamics or over their surface relocating surface water focusing on surface drainage we first discuss observations of lake drainage in particular for the first time lakes are observed to drain 70 km across the nivlisen ice shelf east antarctica inspired by these observations we develop a model of lake drainage through a channel that incises into an ice sheet surface by frictional heat dissipated in the flow modelled lake drainage can be stable or unstable during stable drainage the rate of lake level drawdown exceeds the rate of channel incision so discharge from the lake decreases with time this can prevent the lake from emptying completely during unstable drainage discharge grows unstably with time and always empties the lake model lakes are more prone to drain unstably when the initial lake area the lake input and the channel slope are larger these parameters will vary during atmospheric warming induced ablation area expansion hence the mechanisms revealed by our analysis can influence the dynamic response of ice sheets to warming through their impact on surface water routing and storage

ice dolines on larsen ice shelf antarctica abstract ice dolines on the larsen ice shelf antarctica are observed to beelongated depressions a few hundred meters across and up to 19m deep one meterresolution imagery is used to quantify these dimensions elevation profiles across fivedolines are derivedby photoclinometry landsat and radar imagery is also usedto showthatdolinescanforminasinglemeltseasonandpersistforyears dolinesoccurinclustersandindirectproximitytosurfacemeltwaterlakes fieldobservationssuggestdolinesformby collapse into a subsurface cavity a direct hydraulic connection with the underlyingocean is believed necessary to drain water that would otherwise collect in dolines aformation hypothesis is discussed consistent with these observations and with energy andhydrostatic imbalance considerations introduction doline isageologictermdescribingaroundedhollowthatcanrange in width from 1 to 100m and in depth from ten tohundredsof meters agi 1976 mellor 1960 wasthefirsttosuggest the term icedoline be applied to depression featuresseen on ice their size hundreds of meters across is theprincipal characteristic distinguishing them from

seasonal evolution of supraglacial lakes on a floating ice tongue petermann glacier greenland supraglacial lakes are known to trigger antarctic ice shelf instability and break up however to date no study has focused on lakes on greenland s floating termini here we apply lake boundary area and depth algorithms to landsat 8 imagery to analyse the inter and intraseasonal evolution of supraglacial lakes across petermann glacier s 81 n floating tongue from 2014 to 2016 while also comparing these lakes to those on the grounded ice lakes start to fill in june and quickly peak in total number volume and area in late june early july in response to increases in air temperatures however through july and august total lake number volume and area all decline despite sustained high temperatures these observations may be explained by the transportation of meltwater into the ocean by a river and by lake drainage events on the floating tongue further as mean lake depth remains relatively constant during this time we suggest that a large proportion of the lakes that drain do so completely likely by rapid hydrofracture the mean areas of lakes on the tongue are only 20 of those on the grounded ice and exhibit lower variability in maximum and mean depth differences likely attributable to the contrasting formation processes of lakes in each environment

fracture field for large scale ice dynamics recent observations and modeling studies emphasize the crucial role of fracture mechanics for the stability of ice shelves and thereby the evolution of ice sheets here we introduce a macroscopic fracture density field into a prognostic continuum ice flow model and compute its evolution incorporating the initiation and growth of fractures as well as their advection with two dimensional ice flow to a first approximation fracture growth is assumed to depend on the spreading rate only while fracture initiation is defined in terms of principal stresses the inferred fracture density fields compare well with observed elongate surface structures since crevasses and other deep reaching fracture structures have been shown to influence the overall ice shelf dynamics we propose the fracture density field introduced here be used as a measure for ice softening and decoupling of the ice flow in fracture weakened zones this may yield more accurate and realistic velocity patterns in prognostic simulations additionally the memory of past fracture events links the calving front to the upstream dynamics thus the fracture density field proposed here may be employed in fracture based calving parameterizations the aim of this study is to introduce the field and investigate which of the observed surface structures can be reproduced by the simplest physically motivated fracture source terms

alternative ice shelf equilibria determined by ocean environment 1 dynamic and thermodynamic regimes of ice shelves experiencing weak 1 m year 1 to strong 10 m year 1 basal melting in cold bottom temperature close to the in situ freezing point and warm oceans bottom temperature more than half of a degree warmer than the in situ freezing point are investigated using a 1 d coupled ice ocean model complemented with a newly derived analytic expression for the steady state temperature distribution in ice shelves this expression suggests the existence of a basal thermal boundary layer with thickness inversely proportional to the basal melt rate model simulations show that ice shelves afloat in warm ocean waters have significantly colder internal ice temperatures than those that float in cold waters our results indicate that in steady states the mass balance of ice shelves experiencing strong and weak melting is controlled by different processes in ice shelves with strong melting it is a balance between ice advection and basal melting and in ice shelves with weak melting it is a balance between ice advection and deformation sensitivity simulations show that ice shelves in cold and warm oceans respond differently to increase of the ocean heat content ice shelves in cold waters are more sensitive to warming of the ocean bottom waters while ice shelves in warm waters are more sensitive to shallowing of the depth of the thermocline

observations of buried lake drainage on the antarctic ice sheet between 1992 and 2017 the antarctic ice sheet ais lost ice equivalent to 7 6 3 9 mm of sea level rise ais mass loss is mitigated by ice shelves that provide a buttress by regulating ice flow from tributary glaciers however ice shelf stability is threatened by meltwater ponding which may initiate or reactivate preexisting fractures currently poorly understood processes here through ground penetrating radar gpr analysis over a buried lake in the grounding zone of an east antarctic ice shelf we present the first field observations of a lake drainage event in antarctica via vertical fractures concurrent with the lake drainage event we observe a decrease in surface elevation and an increase in sentinel 1 backscatter finally we suggest that fractures that are initiated or reactivated by lake drainage events in a grounding zone will propagate with ice flow onto the ice shelf itself where they may have implications for its stability

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis