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

flux of debris transported by ice at three alaskan tidewater glaciers the stability of tidewater terminus is controlled by glacial dynamics calving processes and sedimentary processes at the grounding line an investigation of grounding line sediment dynamics and morainal bank sediment budgets in glacier bay alaska u s a has yielded data that enable us to determine the debris fluxes of grand pacific margerie and muir glaciers debris flux ranges from 10 5 to 10 6 m 3 a 1 one to two orders of magnitude lower than the glacifluvial sediment fluxes 10 6 10 7 m 3 a 1 combined these fluxes represent the highest yields known for glacierized basins large debris fluxes reflect the combined effecrs of rapid glacier flow driven by the maritime climate of southeast alaska and highly erodible bedrock englacial debris distribution is affected by valley width and relief both of which control the availability of sediment the number of tributaries controls the distribution and volume of debris in englacial and supraglacial moraines at the terminus iceberg rafting removes up to two orders of magnitude more sediment from the ice proximal environment than is deposited by melt out or is dumped during calving events rough estimates of the sediment flux by deforming beds suggests that soft bed deformation may deliver up to an order of magnitude more sediment to the terminus than is released from within the glacier ice

ocean forcing of the greenland ice sheet calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers 1 we have developed an automatic method to identify changes in the position of calving glacier margins using daily modis imagery application of the method to 32 ocean terminating glaciers in east greenland produced 26 802 margin positions for a 10 year long period 2000 2009 we report these high resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69 n all glaciers above this latitude showed very limited or no change when seasonality was excluded while glaciers south of 69 n retreated significantly between 2001 and 2005 2 3 km on average approximately 26 of the retreat of southern glaciers was regained by readvance from 2005 to 2009 to explain the latitudinal boundary of glacier dynamics we review basic climatic factors including summer and winter atmospheric forcing sea ice conditions and ocean temperature we conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the irminger sea and to fjords and coastal regions south of 69 n northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69 n are less exposed to subtropical waters the southern retreats illustrate sensitive behavior of calving glaciers and we hypothesize that the calving fronts retreated because they were exposed to rapid ice front melting

asynchronous behavior of outlet glaciers feeding godthabsfjord nuup kangerlua and the triggering of narsap sermia s retreat in sw greenland we thank w dryer and d podrasky for assistance with fieldwork and l kenefic for assisting with digitizing glacier front positions ch2 m hill polar services and air greenland provided logistics support the spot 5 images used for the 2008 dem were provided by the spirit program centre national d etudes spatiales france the digitalglobe worldview images used for the 2014 dem were obtained from p morin terminus positions were derived from landsat images courtesy of the u s geological survey funding was provided by the us national science foundation nsf office of polar programs opp grants nsf plr 0909552 and nsf plr 0909333 cassotto is supported by nasa under the earth and space science fellowship program grant nnx14al29h k k kjeldsen acknowledges support from the danish council research for independent research grant no dff 409000151 k kjaer is thanked for his support during the earlier phases of this study on ice weather stations are operated by geus denmark within the programme for monitoring of the greenland ice sheet promice j mortensen acknowledges support from iiknn greenland defrost project of the nordic centre of excellence program interaction between climate change and the cryosphere and the greenland ecosystem monitoring programme www g e m dk s rysgaard was funded by the canada excellence research chair programme additional funding was provided by the geophysical institute university of alaska fairbanks and greenland climate research centre scientific editor h fricker and reviewers h jiskoot and g cogley provided very constructive feedback that helped improve the paper

greenland marine terminating glacier area changes 2000 2010 area changes at 39 of the widest greenland marine terminating glacier outlets are measured in consecutive annual end of melt season moderate resolution imaging spectroradiometer modis scenes spanning ten annual intervals 2000 10 the rates of cumulative area change for glaciers and ice shelves are well represented by linear least squares fits r 0 99 and r 0 94 with average rates of 70 and 65 km 2 a 1 respectively collectively during this decade the 39 glaciers lost a cumulative area of 1368 km 2 more than three quarters of the total area change occurred north of 72 n the largest 11 year area change for a single glacier during the survey period is the 311 km 2 loss at humboldt glacier the largest annual change for a single glacier was extreme compared with the others where petermann glacier retreated 17 km between 3 and 5 august 2010 for the 10 year sample on average the count of glaciers retreating is twice that advancing a larger distinction is evident considering area change with the ratio of retreat and advance on average nine times the gain for glaciers with ice shelves we find no year with collective area gain the area change data from this study are posted at http bprc osu edu jbox data gac

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

annual variation of coastal uplift in greenland as an indicator of variable and accelerating ice mass loss 1 seasonal melting of the coastal part of the greenland ice sheet is investigated using gps vertical displacement data from coastal stations combined with data on atmospheric and ocean temperatures using a high pass filter and cubic spline models we estimate five variables describing seasonal uplift a proxy for proximal mass loss including duration of the melt season and the amount of summer uplift our analysis shows both temporal and spatial variations of uplift southern coastal greenland experienced anomalously large uplift in summer 2010 implying significant melting that year however the northwest coast did not experience significant change in uplift at that time our data suggest that a combination of warm summer air temperature and warm sub surface ocean water temperature drove the large mass losses in 2010 using the uplift pattern of 2008 2010 and comparing to atmospheric data and ocean water temperature data we show that warm irminger water iw exerted significant influence on coastal melting in southeastern southern and southwestern greenland reaching about 69 n in 2010 north of this iw did not exert significant influence in effect defining the northward limit of the sub polar gyre for that year thus short term variability in the coastal gps uplift signal can be used to infer an oceanographic parameter that has a critical influence on greenland ice sheet health

the effect of meltwater plumes on the melting of a vertical glacier face abstractfreshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord terminating glaciers the discharge of the freshwater forms upwelling plumes in front of the glacier calving face this study simulates the meltwater plumes emanated into an unstratified environment using a nonhydrostatic ocean model with an unstructured mesh and subgrid scale mixing calibrated by comparison to established plume theory the presence of an ice face reduces the entrainment of seawater into the meltwater plumes so the plumes remain attached to the ice front in contrast to previous simple models ice melting increases with height above the discharge also in contrast to some simple models and the authors speculate that this overcutting may contribute to the tendency of icebergs to topple inwards toward the ice face upon calving the overall melt rate is found to increase with discharge flux only up to a critical value which depends on the channel size

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

seasonal fluctuations in the advance of a tidewater glacier and potential causes hubbard glacier alaska usa satellite imagery has been used to acquire seasonal terminus positions of tidewater hubbard glacier alaska usa from 1992 to 2006 during this 15 year time period the width averaged advance of the entire terminus has been 620 m at a mean rate of 35 m a 1 seasonal fluctuation of the terminus ranges from 150 to 200 m on average and varies spatially a section of the terminus near a narrow gap where the glacier has now twice closed off 40 km long russell fiord exhibited little to no mean advance during this time period but displayed seasonal fluctuations of 300 500 m seasonal variability in surface ice speeds and surface sea water temperatures was also observed both are potential forcing mechanisms for terminus fluctuations seasonal changes in sea water temperature of 10 128c as well as seasonal changes in subglacial freshwater discharge are inferred to influence calving and submarine melting at the terminus driving seasonal variations displacements of the medial moraine separating hubbard and valerie glaciers at the terminus suggest surge like pulses of the latter with a periodicity of several years the timing of these pulses suggests they may influence the hubbard terminus near gilbert point and have implications for future closures of russell fiord

dynamics of glacier calving at the ungrounded margin of helheim glacier southeast greenland during summer 2013 we installed a network of 19 gps nodes at the ungrounded margin of helheim glacier in southeast greenland together with three cameras to study iceberg calving mechanisms the network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier calved data collection covered 55 days and many nodes survived in locations right at the glacier front to the time of iceberg calving the observations included a number of significant calving events and as a consequence the glacier retreated 1 5 km the data provide real time high frequency observations in unprecedented proximity to the calving front the glacier calved by a process of buoyancy force induced crevassing in which the ice downglacier of flexion zones rotates upward because it is out of buoyant equilibrium calving then occurs back to the flexion zone this calving process provides a compelling and complete explanation for the data tracking of oblique camera images allows identification and characterisation of the flexion zones and their propagation downglacier interpretation of the gps data and camera data in combination allows us to place constraints on the height of the basal cavity that forms beneath the rotating ice downglacier of the flexion zone before calving the flexion zones are probably formed by the exploitation of basal crevasses and theoretical considerations suggest that their propagation is strongly enhanced when the glacier base is deeper than buoyant equilibrium thus this calving mechanism is likely to dominate whenever such geometry occurs and is of increasing importance in greenland

rapid ice discharge from southeast greenland glaciers interferometric synthetic aperture radar insar observations of southeast greenland glaciers acquired by the earth remote sensing satellites ers 1 2 in 1996 were combined with ice sounding radar data collected in the late 1990s to estimate a total discharge of 46 3 km 3 ice per year between 62 n and 66 n which is significantly lower than a mass input of 29 3 km 3 ice per year calculated from a recent compilation of snow accumulation data further north helheim glacier discharges 23 1 km 3 yr vs 30 3 km 3 yr accumulation kangerdlugssuaq glacier discharges 29 2 km 3 yr vs 23 km 3 yr and daugaard jensen glacier discharges 10 5 0 6 km 3 yr vs 10 5 1 km 3 yr the mass balance of east greenland glaciers is therefore dominated by the negative mass balance of southeast greenland glaciers 17 4 km 3 yr equivalent to a sea level rise of 0 04 0 01 mm yr warmer and drier conditions cannot explain the imbalance which we attribute to longterm changes in ice dynamics copyright 2004 by the american geophysical union

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

short term flow dynamics of a retreating tidewater glacier leconte glacier alaska u s a an analysis of motion in the terminus region of leconte glacier alaska u s a delineates mechanisms that are important to tidewater glacier stability this glacier is undergoing rapid retreat since 1995 it has retreated 2 km and thinned 125 m at the present location of the terminus ice velocities in this region are quite high at the terminus they exceed 27 m d 1 our analysis reveals that fluctuations in speed and surface elevation are forced by ocean tides surface melt and precipitation the near terminus ice speed is 180 out of phase with the tide such that high tide corresponds to low speed smaller melt forced diurnal variations in speed are present throughout the lowermost 7 km speed ups in excess of 10 of the mean often occur after rainstorms as a result of increased basal water pressure and storage but the relation is not simple the velocity does not vary over the spring and summer seasons

quantifying energy and mass fluxes controlling godthabsfjord freshwater input in a 5 km simulation 1991 2012 abstractfreshwater runoff to fjords with marine terminating glaciers along the greenland ice sheet margin has an impact on fjord circulation and potentially ice sheet mass balance through increasing heat transport to the glacier front here the authors use the high resolution 5 5 km hirham5 regional climate model allowing high detail in topography and surface types to estimate freshwater input to godthabsfjord in southwest greenland model output is compared to hydrometeorological observations and while simulated daily variability in temperature and downwelling radiation shows high correlation with observations typically 0 9 there are biases that impact the results in particular overestimated albedo leads to underestimation of melt and runoff at low elevations in the model simulation 1991 2012 the ice sheet experiences increasing energy input from the surface turbulent heat flux up to elevations of 2000 m and shortwave radiation at all elevations southerly wind anomalies and declining

ocean forcing of glacier retreat in the western antarctic peninsula in recent decades hundreds of glaciers draining the antarctic peninsula 63 to 70 s have undergone systematic and progressive change these changes are widely attributed to rapid increases in regional surface air temperature but it is now clear that this cannot be the sole driver here we identify a strong correspondence between mid depth ocean temperatures and glacier front changes along the 1000 kilometer western coastline in the south glaciers that terminate in warm circumpolar deep water have undergone considerable retreat whereas those in the far northwest which terminate in cooler waters have not furthermore a mid ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat we conclude that changes in ocean induced melting are the primary cause of retreat for glaciers in this region

relationship between tidewater glacier calving velocity and water depth at the calving front an analysis of the relationship between iceberg calving rates and water depth has been completed for 22 tidewater glaciers a linear relationship provides reasonable accuracy with a correlation coefficient of 0 85 for all tidewater glaciers examined whether they be polar or temperate the polar glaciers have a slightly lower calving rate for a given water depth this relationship indicates a lower calving rate for water depths over 50 m than determined by brown and others 1982 it is based only on glaciers or ice streams and cannot be applied to ice shelves

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 unifying framework for iceberg calving models we propose a general framework for iceberg calving models that can be applied to any calving margin the framework is based on mass continuity the assumption that calving rate and terminus velocity are not independent and the simple idea that terminus thickness following a calving event is larger than terminus thickness at the event onset the theoretical near steady state analysis used to support and analyze the framework indicates that calving rate is governed to first order by ice thickness thickness gradient strain rate mass balance rate and backwards melting of the terminus the analysis furthermore provides a physical explanation for a previously derived empirical relationship for ice shelf calving alley and others 2008 in the calving framework the pre and post calving terminus thicknesses are given by two unknown but related functions the functions can vary independently of changes in glacier flow and geometry and can therefore account for variations in calving behavior due to external forcings and or self sustaining calving processes positive feedbacks although the calving framework does not constitute a complete calving model any thickness based calving criterion can easily be incorporated into the framework the framework should be viewed as a guide for future attempts to parameterize calving

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

localized plumes drive front wide ocean melting of a greenlandic tidewater glacier support was provided by the national science foundation nsf through plr 1418256 and plr 1744835 and through woods hole oceanographic institution whoi ocean and climate change institute occi and the clark foundation this work was also supported by a uk natural environmental research council nerc phd studentship ne l501566 1 and scottish alliance for geoscience environment society sages early career research exchange funding to d a s

the genesis mineralization and stratigraphic significance of phosphatic glauconitic condensed limestone unit in the manavgat basin sw turkey abstract a condensed hemipelagic limestone unit with glauconite and phosphate separates a drowned late burdigalian carbonate platform from overlying langhian pelagic mudstones marls and calcarenitic tempestites within the neogene manavgat basin of southwestern anatolia turkey the unit consists of coeval lenticular limestone bodies between 1 cm and 15 m in thickness ranging from 10 m to 3 km in lateral extent the p2o5 content of this limestone ranges from 0 2 to 10 by weight and the iron oxide clay and other metal oxide contents of this unit substantially exceed those of the underlying and overlying rocks this condensed stratigraphic unit was deposited on the southwesterly outer shelf portions of drowned horsts that directly faced upwelling currents the unit displays three main facies 1 glauconitic phosphate crusts associated with hardgrounds 2 bedded glauconitic phosphatic limestones and 3 glauconitic phosphatic limestones interbedded with resedimented limestones facies 1 forms the thinnest units whereas facies 3 is the thickest since the thickness and spatial distribution of this facies are related to environmental contrasts caused by block faulting of the underlying carbonate platform this lithostratigraphic unit of hemipelagic glauconite phosphate deposition represents an interval of maximum flooding in tectonically active situations and depositional hiatus on submarine highs that separate the carbonate transgressive systems tract from the overlying terigenic tempestite highstand systems tract this appears to be the sole condensed unit within the miocene manavgat basin and is here ascribed to a third order 2 3 eustatic rise in sea level comprising the maximum flooding of the first order cycle this is also the time for early mid miocene major changes in mediterranean climate from tropical to temperate

characteristics and dynamics of two major greenland glacial fjords the circulation regimes of two major outlet glacial fjords in southeastern greenland sermilik fjord sf and kangerdlugssuaq fjord kf are investigated using data collected in summer 2009 the two fjords show similar flow patterns with a time dependent vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input we show that this time dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth often referred to as intermediary circulation one difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three layer in kf in summer compared to two layer in sf outside each fjord large scale geostrophic currents dictate the stratification at the mouth although the way in which these large scale flows impinge on each fjord is distinct combining the observations with estimates from existing theories we find the magnitudes of the estuarine qe and intermediary qi circulation and show that qi qe although along fjord winds can also be significant we expect that the critical parameter determining qi qe is the sill depth compared to the fjord depth with shallower sills corresponding to weaker intermediary circulation finally we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries

does calving matter evidence for significant submarine melt abstract during the summer in the northeast pacific ocean the alaska coastal current sweeps water with temperatures in excess of 12 c past the mouths of glacierized fjords and bays the extent to which these warm waters affect the mass balance of alaskan tidewater glaciers is uncertain here we report hydrographic measurements made within icy bay alaska and calculate rates of submarine melt at yahtse glacier a tidewater glacier terminating in icy bay we find strongly stratified water properties consistent with estuarine circulation and evidence that warm gulf of alaska water reaches the head of 40 km long icy bay largely unaltered a 10 20 m layer of cold fresh glacially modified water overlies warm saline water the saline water is observed to reach up to 10 4 c within 1 5 km of the terminus of yahtse glacier by quantifying the heat and salt deficit within the glacially modified water we place bounds on the rate of submarine melt the submarine melt rate is estimated at 9 m d 1 at least half the rate at which ice flows into the terminus region and can plausibly account for all of the submarine terminus mass loss our measurements suggest that summer and fall subaerial calving is a direct response to thermal undercutting of the terminus further demonstrating the critical role of the ocean in modulating tidewater glacier dynamics

thermo erosional notch development at fresh water calving tasman glacier new zealand controls on glacier calving rates are receiving increased scientific interest at fresh water calving glaciers limnological factors might be more important than glaciological ones measurements of thermo erosional notch development at the calving ice cliff of tasman glacier new zealand suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting notch formation rates typically vary between 10 and 30 cm d 1 maximum rate 65 cm d 1 in summer corresponding to an average calving rate of 34 m a 1 notch formation is slower than waterline melt and is controlled by water temperatures and circulation cliff geometry debris supply and water level fluctuations the latter shift the position of undercutting resetting the level of the notch formation process and thereby slowing it the geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation hence water temperatures in the lake are not necessarily indicative of the rate of notch formation the prediction of rate of notch formation from far field variables is hampered by the complex interaction of the influencing factors the significance of thermal undercutting as a calving rate controlling process decreases with increasing ice velocities calving rates and surface gradients

spatio temporal variations in seasonal ice tongue submarine melt rate at a tidewater glacier in southwest greenland submarine melting of tidewater glaciers is proposed as a trigger for their recent thinning acceleration and retreat we estimate spring submarine melt rates smrs of kangiata nunaata sermia in southwest greenland from 2012 to 2014 by examining changes in along fjord freeboard and velocity of the seasonal floating ice tongue estimated smrs vary spatially and temporally near the grounding line with mean rates of 1 3 0 6 0 8 0 3 and 1 0 0 4 m d 1 across the tongue in 2012 2013 and 2014 respectively higher melt rates correspond with locations of emerging subglacial plumes and terminus calving activity observed during the melt season using time lapse camera imagery modelling of subglacial flow paths suggests a dynamic system capable of rapid re routing of subglacial discharge both within and between melt seasons our results provide an empirically derived link between the presence of subglacial discharge plumes and areas of high spring submarine melting and calving along glacier termini

impact of tide topography interactions on basal melting of larsen c ice shelf antarctica 1 basal melting of ice shelves around antarctica contributes to formation of antarctic bottom water and can affect global sea level by altering the offshore flow of grounded ice streams and glaciers tides influence ice shelf basal melt rate wb by contributing to ocean mixing and mean circulation as well as thermohaline exchanges with the ice shelf we use a three dimensional ocean model thermodynamically coupled to a nonevolving ice shelf to investigate the relationship between topography tides andwb for larsen c ice shelf lcis in the northwestern weddell sea antarctica using our best estimates of ice shelf thickness and seabed topography we find that the largest modeled lcis melt rates occur in the northeast where our model predicts strong diurnal tidal currents 0 4 m s 1 this distribution is significantly different from models with no tidal forcing which predict largest melt rates along the deep grounding lines we compare several model runs to explore melt rate sensitivity to geometry initial ocean potential temperature 0 thermodynamic parameterizations of heat and freshwater ice ocean exchange and tidal forcing the resulting range of lcis averagedwb is 0 11 0 44 m a 1 the spatial distribution of wb is very sensitive to model geometry and thermodynamic parameterization while the overall magnitude of wb is influenced by 0 these sensitivities in wbpredictions reinforce a need for high resolution maps of ice draft and sub ice shelf seabed topography together with ocean temperature measurements at the ice shelf front to improve representation of ice shelves in coupled climate system models

source mechanics for monochromatic icequakes produced during iceberg calving at columbia glacier ak 1 seismograms recorded during iceberg calving contain information pertaining to source processes during calving events however locally variable material properties may cause signal distortions known as site and path effects which must be eliminated prior to commenting on source mechanics we applied the technique of horizontal vertical spectral ratios to passive seismic data collected at columbia glacier ak and found no dominant site or path effects rather monochromatic waveforms generated by calving appear to result from source processes we hypothesize that a fluid filled crack source model offers a potential mechanism for observed seismograms produced by calving and fracture processes preceding calving

rapid submarine melting driven by subglacial discharge leconte glacier alaska 1 we show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers this buoyant discharge draws in warm seawater entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice to capture the effects of subglacial discharge on submarine melting we conducted 4 days of hydrographic transects during late summer 2012 at leconte glacier alaska a major rainstorm allowed us to document the influence of large changes in subglacial discharge we found strong submarine melt fluxes that increased from 9 1 1 0 to 16 8 1 3 m d 1 ice face equivalent frontal ablation as a result of the rainstorm with projected continued global warming and increased glacial runoff our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems these effects must be considered when modeling glacier response to future warming and increased runoff

spatially distributed runoff at the grounding line of a large greenlandic tidewater glacier inferred from plume modelling understanding the drivers of recent change at greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming a poorly constrained component of tidewater glacier processes is the near terminus subglacial hydrology here we present a novel method for constraining near terminus subglacial hydrology with application to marine terminating kangiata nunata sermia in south west greenland by simulating proglacial plume dynamics using buoyant plume theory and a general circulation model we assess the critical subglacial discharge if delivered through a single compact channel required to generate a plume that reaches the fjord surface we then compare catchment runoff to a time series of plume visibility acquired from a time lapse camera we identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface yet we observe no plume we attribute these observations to spatial spreading of runoff across the grounding line persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration

submarine melting of the 1985 jakobshavn isbrae floating tongue and the triggering of the current retreat 1 photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of jakobshavn isbrae west greenland the thickness of the floating tongue determined from hydrostatic equilibrium tapers from 940 m near the grounding zone to 600 m near the terminus feature tracking on orthophotos shows speeds on the july 1985 ice tongue to be nearly constant 18 5 m d 1 indicating negligible dynamic thinning the thinning of the ice tongue is mostly due to submarine melting with average rates of 228 49 m yr 1 0 62 0 13 m d 1 between the summers of 1984 and 1985 the cause of the high melt rate is the circulation of warm seawater thermal forcing of up to 4 2 c beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone we believe that this buoyancy driven convection is responsible for a deep channel incised into the sole of the floating tongue a dramatic thinning retreat and speedup began in 1998 and continues today the timing of the change is coincident with a 1 1 c warming of deep ocean waters entering the fjord after 1997 assuming a linear relationship between thermal forcing and submarine melt rate average melt rates should have increased by 25 57 m yr 1 sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed

subglacial hydrology at rink isbrae west greenland inferred from sediment plume appearance marine terminating outlet glaciers discharge most of the greenland ice sheet s mass through frontal ablation and meltwater runoff while calving can be estimated by in situ and remote sensing observations submarine melting and subglacial meltwater transport are more challenging to quantify here we investigate the subglacial hydrology of rink isbrae a fast flowing west greenland tidewater glacier using time lapse photography modeled runoff estimates and daily satellite imagery from 2007 to 2011 we find that sediment plumes appear episodically at four distinct locations across the terminus and last between 2 h and 17 d this suggests short term variability in discharge and the existence of persistent pathways the seasonal onset of sediment plumes occurs before supraglacial lake drainages shortly after the onset of runoff and only after the wintertime ice melange has begun disintegrating plumes were also visible after the cessation of runoff 23 5 d which is indicative of subglacial storage the lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front

katabatic wind driven exchange in fjords the general issue of katabatic wind driven exchange in fjords is considered using an idealized numerical model theory and observations two regimes are identified for fjords narrower than a viscous boundary layer width the exchange is limited by a balance between wind and friction in lateral boundary layers for the nonlinear viscous parameterization used here this boundary layer thickness depends on the properties of the fjord such as stratification and length as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant for wider fjords typical of east greenland the balance is primarily between wind the along fjord pressure gradient and acceleration in general agreement with previous two layer nonrotating theories it is expected that o 10 of the surface layer will be flushed out of the fjord by a single wind event application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in sermilik fjord the presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness in which cases the exchange is reduced it is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east greenland represent an important mechanism of exchange between the fjord and shelf with implications for the renewal of warm salty waters at depth and for the export of glacial freshwater in the upper layer

tidal and seasonal variations in calving flux observed with passive seismology the seismic signatures of calving events i e calving icequakes offer an opportunity to examine calving variability with greater precision than is available with other methods here using observations from yahtse glacier alaska we describe methods to detect locate and characterize calving icequakes we combine these icequake records with a coincident manually generated record of observed calving events to develop and validate a statistical model through which we can infer iceberg sizes from the properties of calving icequakes we find that the icequake duration is the single most significant predictor of an iceberg s size we then apply this model to 18 months of seismic recordings and find elevated iceberg calving flux during the summer and fall and a pronounced lull in calving during midwinter calving flux is sensitive to semidiurnal tidal stage large calving events are tens of percent more likely during falling and low tides than during rising and high tides consistent with a view that deeper water has a stabilizing influence on glacier termini multiple factors affect the occurrence of mechanical fractures that ultimately lead to iceberg calving at yahtse glacier seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on iceberg calving rates at seasonal timescales on hourly to daily timescales tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near terminus stress field

oceanic boundary conditions for jakobshavn glacier part i variability and renewal of ilulissat icefjord waters 2001 14 jakobshavnglacier west greenland has respondedtotemperaturechangesinilulissaticefjord intowhich it terminates thisstudycollectedhydrographicobservationsinsideilulissaticefjordandfromadjacentdiskobay between2001and2014 thewarmestdeepdiskobaywaterswereblockedbytheentrancesillanddidnotreach jakobshavn glacier in the fjord basin the summer mean temperature was 2 88c from 2009 to 2013 excluding 2010 whenitwas 18c cooler despitethisvariability summerpotential densities in the basinwereinthe narrow range of 27 20 su 27 31kgm 23 and basin water properties matched those of disko bay in this layer each summer this relation has likely held since at least 1980 basin waters from 2009 and 2011 13 were therefore similar tothosein1998 99 whenjakobshavn glacier began toretreat whilebasin watersin2010wereascoolas in the 1980s the 2010 basin temperature anomaly was advected into disko bay not produced by local atmospheric variability this anomaly also shows that ilulissat icefjord basin waters were renewed annually or faster time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually outside of summer fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month in model simulations of the fjord circulation subglacial discharge from jakobshavn glacier could drive renewal of the fjord basin over a single summer while baroclinic forcing from outside the fjord could not because of the sill at the mouth

interpretation of amplitude data from a ground based radar in combination with terrestrial photogrammetry and visual observations for calving monitoring of kronebreen svalbard a ground based radar has been used successfully for monitoring calving events and velocities at kronebreen svalbard for two test seasons in 2007 and 2008 we use daily terrestrial optical photogrammetry and continuous visual observation to validate the interpretation of a 116 hour ground based radar amplitude of return signal data recorded from 26 to 30 august 2008 the radar was placed 4 km from the glacier it measured at high temporal rate 2 hz and the antenna lobe covered a width of 700 m of the front the calving front geometry was extracted from the optical images and its effect on radar backscatter together with the movement of the glacier was identified in the plot of the amplitude of the radar return signal calving events were detected applying an automated change detection technique to the radar dataset this technique allowed us to detect 92 of the events that were observed during the same time in this paper we focus on the method rather than on data interpretation however future use of this method combined with meteorological data tides and ocean temperature will be valuable for calving process studies

ice dammed lake drainage cools and raises surface salinities in a tidewater outlet glacier fjord west greenland the drainage of ice dammed lakes in the form of outburst floods in greenland is detected regularly by remote sensing and these events are expected to occur more frequently in a warmer climate however their impact on ice sheet stability and neighboring water bodies is still unknown in this interdisciplinary study we investigate lake drainages from the greenland ice sheet into a west greenland fjord by analyzing simultaneous time series of satellite observations and direct hydrographic measurements of temperature and salinity in the fjord satellite images show that in general lake drainages have occurred quasiperiodically during the last decade a particular sequence of drainage events was observed by satellite in 2009 and was analyzed together with the first direct hydrographic observations signs of ice dammed lake drainages were observed by a downstream mooring located just below the intertidal zone the release of freshwater occurred at the fjord subsurface at a tidewater outlet glacier the downstream in water sequence of property changes in relation to these drainage events was observed as an almost immediate decrease in surface layer temperature 2 c followed within a week by the arrival of a high saline pulse 5 units with elevated salinity lasting for several days during the passage during lake drainages large amounts of relatively warm and saline intermediate water are brought to the near surface layers by entrainment processes near the glacier front and this influences the hydrography of the fjord but also impacts the ecosystem through upwelling of nutrient rich intermediate water

alaska tidewater glacier terminus positions 1948 2012 a significant portion of the world s glacier ice drains through tidewater outlets though much remains unknown about the response to recent climate change of tidewater glaciers we present a 64 year record of length change for 50 alaska tidewater glaciers we use u s geological survey topographic maps to provide a base length for glaciers before 1970 using all available cloud free landsat images we manually digitize calving front outlines for each glacier between 1972 and 2012 resulting in a total of more than 10 000 outlines tidewater glacier lengths vary seasonally focusing on the 36 glaciers terminating in tidewater throughout the study period we find a mean standard deviation seasonal variation of 60 85 m a 1 we use these oscillations to determine the significance of interannual changes in glacier length all 36 glaciers underwent at least one period 1 year of significant advance or retreat 28 glaciers underwent at least one period of both significant advance and retreat over the entire period 1948 2012 24 of these glaciers retreated a total uncertainty of 107 95 0 29 km 11 advanced a total of 7 71 0 20 and one chenega glacier did not change significantly retreats and advances are highly variable in time several glaciers underwent rapid short term retreats of a few years duration these retreats occurred after large changes in summer sea surface temperature anomalies further study is needed to determine what triggered these retreats no coherent regional behavior signal is apparent in the length record although two subregions show a coherence similar to recent observations in greenland

columbia bay alaska an upside down estuary abstract circulation and water properties within columbia bay alaska are dominated by the effects of columbia glacier at the head of the bay the basin between the glacier terminus and the terminal moraine sill depth of about 22 m responds as an upside down estuary with the subglacial discharge of freshwater entering at the bottom of the basin the intense vertical mixing caused by the bouyant plume of freshwater creates a homogeneous water mass that exchanges with the far field water through either a two or a three layer flow in general the glacier acts as a large heat sink and creates a water mass which is cooler than that in fjords without tidewater glaciers the predicted retreat of columbia glacier would create a 40 km long fjord that has characteristics in common with other fjords in prince william sound

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

mechanical and hydrologic basis for the rapid motion of a large tidewater glacier 1 observations the data presented in part 1 of this paper meier et al this issue are here used to assess the role of water input output water storage and basal water pressure in the rapid movement of columbia glacier alaska consistently high basal water pressures mostly in the range from 300 kpa below to 100 kpa above the ice overburden pressure are responsible in an overall way for the high glacier flow velocities 3 5 9 m d 1 which are due mainly to rapid basal sliding caused by the high water pressure diurnal fluctuation in basal water pressure is accompanied by fluctuation in sliding velocity in what appears to be a direct causal relation at the upglacier observation site the water pressure fluctuation tracks the time integrated water input less a steady withdrawal as expected for the diurnally fluctuating storage of water in the glacier far from the terminus at the downglacier site the situation is more complex diurnal peaks in water level which are directly related to intraglacial water storage as well as to basal water pressure are shifted forward in time by 4 hours probably as a result of the effect of diurnal fluctuation in water output from the glacier which affects the local water storage fluctuations near the terminus because of the forward shift in the basal water pressure peaks which at the downglacier site lead the velocity peaks by 6 hours a mechanical connection between water pressure and sliding there would have to involve a 6 hour quarter period delay however the nearly identical nature of the diurnal fluctuations in velocity at the two sites argues for a single consistent control mechanism at both sites the velocity variations in nondiurnal speed up events caused by extra input of water on the longer timescale of several days are only obscurely if at all correlated with variations in basal water pressure but correlate well with water storage in the glacier it appears that small variations in water pressure 100 kpa sufficient to produce the observed velocity variations 15 30 are mostly masked by pressure fluctuations caused by spontaneous local reorganizations of the basal water conduit system on a spatial scale much smaller than the longitudinal coupling length over which basal water pressure is effectively averaged in determining the sliding velocity at the achieved level of observation the clearest though not complication free control variable for the sliding velocity variations is basal water storage by cavitation at the glacier bed

glacier calving observed with time lapse imagery and tsunami waves at glaciar perito moreno patagonia calving plays a key role in the recent rapid retreat of glaciers around the world however many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain when calving occurs at a glacier front surface water waves arise over the ocean or a lake in front of glaciers to study calving processes from these surface waves we performed field observations at glaciar perito moreno patagonia we synchronized time lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise a total of 1074 calving events were observed over the course of 39 d during austral summer calving occurred twice more frequently than in spring the cumulative distribution of calving interevent time interval followed exponential model implying random occurrence of events in time we further investigated wave properties and found that source to sensor distance can be estimated from wave dispersion within 20 error we also found that waves produced by different calving types showed similar spectra in the same frequency range between 0 05 0 2 hz and that the amplitude of surface waves increased with the size of calving this study demonstrates the potential of surface wave monitoring for understanding calving processes

heat sources for glacial melt in a sub arctic fjord godthabsfjord in contact with the greenland ice sheet 1 recent warming of subpolar mode water off greenland has been suggested to accelerate the mass loss from tidal outlet glaciers of the greenland ice sheet we present a comprehensive analysis of water masses dynamics and interannual hydrographic variability in godthabsfjord a sill fjord in contact with tidal outlet glaciers on the west coast of greenland through seasonal observations we recognize an intermediate baroclinic circulation mode driven by tidal currents and an associated important local heat source for the fjord during summer this results in significant warming and freshening of the intermediate layer of the main fjord and the increase in heat content is equivalent to melting of 2 1 km3 of glacial ice this is comparable to 8 km3 glacial ice discharge estimated from the kangiata nun ta sermia calving front per year during winter the external heat source in the west greenland current enters the fjord as intermittent inflows of either cold 2 c dense water in pulses of 1 to 3 months duration four distinct circulation modes are observed in the fjord of which all can contribute to glacial ice melt an important aspect of the ice distribution in the fjord is that only a minor fraction is exported out of the fjord

impact of periodic intermediary flows on submarine melting of a greenland glacier the submarine melting of a vertical glacier front induced by an intermediary circulation forced by periodic density variations at the mouth of a fjord is investigated using a nonhydrostatic ocean general circulation model and idealized laboratory experiments the idealized configurations broadly match that of sermilik fjord southeast greenland a largely two layers system characterized by strong seasonal variability of subglacial discharge consistent with observations the numerical results suggest that the intermediary circulation is an effective mechanism for the advection of shelf anomalies inside the fjord in the numerical simulations the advection mechanism is a density intrusion with a velocity which is an order of magnitude larger than the velocities associated with a glacier driven circulation in summer submarine melting is mostly influenced by the discharge of surface runoff at the base of the glacier and the intermediary circulation induces small changes in submarine melting in winter on the other hand submarine melting depends only on the water properties and velocity distribution at the glacier front hence the properties of the waters advected by the intermediary circulation to the glacier front are found to be the primary control of the submarine melting when the density of the intrusion is intermediate between those found in the fjord s two layers there is a significant reduction in submarine melting on the other hand when the density is close to that of the bottom layer only a slight reduction in submarine melting is observed the numerical results compare favorably to idealized laboratory experiments with a similar setup

dynamics of tidewater surge type glaciers in northwest svalbard the evolution of ice dynamics through surges of four tidewater terminating glaciers in northwest svalbard is investigated by remote sensing a 20 year time series of glacier surface flow speeds and frontal positions is presented covering the recent surges of monacobreen comfortlessbreen blomstrandbreen and fjortende julibreen surface flow speeds were derived using feature tracking between pairs of ers sar and alos palsar images while frontal positions were taken from the same imagery as well as more frequent but lower spatial resolution envisat wide swath mode images during all four surges increased ice flow caused the tidewater margin to advance while the calving flux was initially reduced to near zero due to compressive stresses limiting crevasse propagation as ice speed decreased the terminus continued to advance until the glacier s speed had returned to its pre surge flow rate only at this time did the terminus start to retreat and peak iceberg calving flux was established we conclude that terminus advance closely tracks glacier speed up that there is little mass loss through calving during the most active phase of the surge and that seasonal cycles of terminus positions diminish during the active surge phase

climate change warm bath for an ice sheet greenland is losing ice through glaciers that flow into deep fjords new observations highlight the important fjord processes that supply warm ocean waters to the melting glaciers and thereby affect greenland s contribution to sea level rise

seasonal variability of the circulation system in a west greenland tidewater outlet glacier fjord godthabsfjord 64 n many tidewater outlet glacier fjords surround the coast of greenland and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet thus fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet however very few observational studies describe the seasonal dynamics of fjord circulation here we present the first continuous current measurements april november from a deep mooring deployed in a west greenland tidewater outlet glacier fjord four distinct circulation phases are identified during the period and they are related to exchange processes with coastal waters tidal mixing and melt processes on the greenland ice sheet during early summer warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s 1 in late summer the average velocity decreases to 3 cm s 1 during a period with significant subglacial freshwater discharges during this period a large variability in current velocities is also observed the associated average heat transport in an intermediate depth range corresponds to 568 gw in early summer and is reduced to 287 gw in late summer these heat fluxes are at the higher end of previously reported fluxes our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and thereby potentially to glacial melt we suggest that intermediate heat transport may play a similar important role in other fjords around greenland

multiple melt plumes observed at the breiðamerkurjokull ice face in the upper waters of jokulsarlon lagoon iceland brei amerkurjokull flows from the vatnajokull ice cap and calves into the jokulsarlon proglacial lagoon the lagoon is connected to the north atlantic ocean through a 6 m deep narrow channel four hydrographic surveys in spring 2012 and a 2011 four month long temperature and salinity time series of lagoon inflow show that the lake has significantly changed since 1976 warm saline ocean water enters each tidal cycle and descends below the maximum sampled depths the lagoon has a surface layer of ice melt freshwater and atlantic derived water beneath 10 m depth an advective diffusive balance is responsible for determining the temperature and salinity of the lagoon waters down to 90 m to maintain the observed hydrographic structure we calculate an upwelling of deep water of 0 2 m per day a survey within 30 m of brei amerkurjokull showed that the warmest and most saline waters sampled within the lagoon below 10 m depth were adjacent to the glacier face along with multiple interleaved warm and cold layers a heat and salt balance model shows that submarine melting along the ice face generates multiple meltwater plumes that are mixed and diluted within 200 m of the ice face

recent retreat of major outlet glaciers on novaya zemlya russian arctic influenced by fjord geometry and sea ice conditions substantial ice loss has occurred in the russian high arctic during the past decade predominantly on novaya zemlya yet the region has been studied relatively little consequently the factors forcing mass loss and the relative contribution of ice dynamics versus surface melt are poorly understood here we evaluate the influence of atmospheric oceanic forcing and variations in fjord width on the behaviour of 38 glaciers on the northern ice cap novaya zemlya we compare retreat rates on land versus marine terminating outlets and on the kara versus barents sea coasts between 1992 and 2010 90 of the study glaciers retreated and retreat rates were an order of magnitude higher for marine terminating outlets 52 1 m a 1 than for land terminating glaciers 4 8 m a 1 we identify a post 2000 acceleration in marine terminating glacier retreat which corresponded closely to changes in sea ice concentrations retreat rates were higher on the barents sea coast which we partly attribute to lower sea ice concentrations but varied dramatically between individual glaciers we use empirical data to categorize changes in along flow fjord width and demonstrate a significant relationship between fjord width variability and retreat rate results suggest that variations in fjord width exert a major influence on glacier retreat

calving event detection by observation of seiche effects on the greenland fjords with mass loss from the greenland ice sheet accelerating and spreading to higher latitudes the quantification of mass discharge in the form of icebergs has recently received much scientific attention here we make use of very low frequency 0 001 0 01 hz seismic data from three permanent broadband stations installed in the summers of 2009 10 in northwest greenland in order to monitor local calving activity at these frequencies calving seismograms are dominated by a tilt signal produced by local ground flexure in response to fjord seiching generated by major iceberg calving events a simple triggering algorithm is proposed to detect calving events from large calving fronts with potentially no user interaction our calving catalogue identifies spatial and temporal differences in calving activity between jakobshavn isbrae and glaciers in the uummannaq district similar to 200 km to the north the uummannaq glaciers show clear seasonal fluctuations in seiche based calving detections as well as seiche amplitudes in contrast the detections at jakobshavn isbrae show little seasonal variation which may be evidence for an ongoing transition to winter calving activity the results offer further evidence that seismometers can provide efficient and inexpensive monitoring of calving fronts

characteristics of tide water calving at glaciar san rafael chile glacial calving is a poorly understood process this study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at glaciar san rafael chile near the terminus of the glacier surface speeds average 17 m d 1 in summer and calving is profuse and continual the size location and characteristics of over 7000 calving events were recorded during 32 d in 1991 and 1992 together with meteorological bathymetric and oceanographic data mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 mm 3 d 1 mean annual calving speed and calving flux are about 4500 m a 1 and 2 0 km 3 a 1 respectively this calving speed is higher than that predicted by the established empirical relationship between tide water calving speed and water depth this is surprising given the low salinity of laguna san rafael and that fresh water calving speeds are commonly much lower than those in tide water daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables but tidal stage may have some control over the timing of large submarine calving events submarine calving produced the largest bergs however the relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates

columbia glacier alaska changes in velocity 1977 1986 the columbia glacier a grounded iceberg calving tidewater glacier near valdez alaska began to retreat about 1977 drastic retreat occurred in 1984 and by early 1986 retreat amounted to 2 km the glacier has thinned more than 100 m since 1974 at a point 4 km behind the 1974 terminus position between 1977 and 1985 the lower glacier ice velocity increased from 3 8 m d to 10 15 m d ice velocity in the region 0 5 km above the terminus was highest near the time the glacier was most receded late fall and lowest near the time of maximum length early summer for years 1977 1982 velocity in the region 52 57 from the head of the glacier was highest in mid spring and lowest in early fall from 1977 to 1985 through the years 1983 1985 the dates of maximum and minimum velocities within 0 5 km of the receding terminus tended toward the dates of the 52 57 km maximum and minimums this occurred because as the terminus receded it was no longer strongly influenced by the reverse slope of the terminal moraine shoal velocities near the terminus fluctuated by 2 3 m d during summer and fall when liquid water input was variable and were relatively constant during winter hourly variations in ice velocities are controlled by liquid water input to the glacier hydraulic system and tide stage velocity increases near periods of high surface water input and decreases during periods of high tide as a result of hydrostatic back pressure

channelization of plumes beneath ice shelves we study a simplified model of ice ocean interaction beneath a floating ice shelf and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line the model combines an extensional thin film description of viscous ice flow in the shelf with melting at its base driven by a turbulent ocean plume small transverse perturbations to the one dimensional steady state are considered driven either by ice thickness or subglacial discharge variations across the grounding line either forcing leads to the growth of channels downstream with melting driven by locally enhanced ocean velocities and thus heat transfer narrow channels are smoothed out due to turbulent mixing in the ocean plume leading to a preferred wavelength for channel growth in the absence of perturbations at the grounding line linear stability analysis suggests that the one dimensional state is stable to initial perturbations chiefly due to the background ice advection

quantifying flow regimes in a greenland glacial fjord using iceberg drifters funded by the national science foundation grant numbers oce 1130008 arc 0909274 and the university of oregon

the supply of subglacial meltwater to the grounding line of the siple coast west antarctica recent satellite studies have shown that active subglacial lakes exist under the antarctic ice streams and persist almost to their grounding lines when the lowest lying lakes flood the water crosses the grounding line and enters the sub ice shelf cavity modeling results suggest that this additional freshwater influx may significantly enhance melting at the ice shelf base we examine the spatial and temporal variability in subglacial water supply to the grounding lines of the siple coast ice streams by combining estimates for lake volume change derived from ice cloud and land elevation satellite icesat data with a model for subglacial water transport our results suggest that subglacial outflow tends to concentrate towards six embayments in the siple coast grounding line although mean grounding line outflow is 60m3 s 1 for the entire siple coast maximum local grounding line outflow may temporarily exceed 300 m3 s 1 during the synchronized flooding of multiple lakes in a hydrologic basin variability in subglacial outflow due to subglacial lake drainage may account for a substantial portion of the observed variability in freshwater flux out of the ross ice shelf cavity the temporal variability in grounding line outflow results in a net reduction in long term average melt rate but temporary peak melting rates may exceed the long term average by a factor of three

glacier velocities from time lapse photos technique development and first results from the extreme ice survey eis in greenland automated digital cameras were installed in may june 2007 beside major west greenland marine terminating glaciers as part of the extreme ice survey eis eis cameras began imaging the lowest 4 km 2 of the glacier at hourly intervals throughout sunlit periods of the year this study presents the development of techniques for quantifying glacier velocity from a single camera perspective a multi image multi chip matching procedure yields higher matching skill than conventional matching and facilitates false match rejection via a clustering scheme the matching of motionless on land features facilitates compensating camera motion ray projection to a known terrain elevation allows the assigning of scale to convert pixel displacements to velocity units with the 10 2 megapixel camera system velocities on relatively fast glaciers can be resolved at distances up to 4 km at a distance of 2 km a demonstrated precision of 0 5 pixels yields a 0 5 m footprint size daily velocities indicate progressive multi day velocity accelerations associated with calving deceleration trends are associated with the regrowth of resistive stress after major calving the higher observation frequency available to terrestrial photogrammetry indicates higher observed intra seasonal velocity range than observable by the at best weekly satellite snapshots

deglacial ocean warming and marine margin retreat of the cordilleran ice sheet in the north pacific ocean abstract a new high resolution planktonic foraminiferal mg ca based ocean temperature record has been generated for deep sea core md02 2496 sited offshore of vancouver island western canada during the last deglaciation 21 12 ka the relationship between cordilleran ice sheet cis retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in md02 2496 that capture tidewater glacier response to surface ocean thermal forcing at cis maximum extent the marine margin of the ice sheet advanced onto the continental shelf during this interval ocean temperatures recorded by surface dwelling globigerina bulloides remained a relatively constant 7 5 c while subsurface dwelling neogloboquadrina pachyderma s recorded temperatures of 5 c these ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern alaskan tidewater glacial systems during the deglacial retreat of the cis the n pachyderma temperature record shows two distinct warming steps of 2 and 2 5 c between 17 2 16 and 15 5 14 ka respectively coincident with ice rafting events from the cis while g bulloides records an 3 c warming from 15 to 14 ka we hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from cis tidewater glaciers during the initial stages of deglaciation

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

calving speed and climatic sensitivity of new zealand lake calving glaciers calving speeds and calving mechanisms in fresh water contrast with those in tidewater we obtained calving speeds for six lake calving glaciers in new zealand s southern alps and surveyed the depths and temperatures of their ice contact lakes the glaciers are temperate grounded in shallow 20 m water and exhibit compressive flow at their termini these data increase the global dataset of fresh water calving statistics by 40 bringing the total to 21 glaciers for this dataset calving rates uc correlate positively with water depths hw r2 0 83 the relationship being expressed by uc 17 4 2 3 hw this is an order of magnitude lower than values of uc at temperate tidewater glaciers for a subset of 10 glaciers for which ice proximal water temperature tw data are available uc also correlates positively with tw supporting a physical relation between calving and melting at and below the water line fluctuations of new zealand lake calving glaciers in the period 1958 97 show that although the transition from non calving to calving dramatically increases frontal retreat rates the onset of calving does not isolate terminus change from climatic forcing in terms of climatic sensitivity lake calving glaciers occupy an intermediate position between tidewater glaciers least sensitive and non calving glaciers most sensitive

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

impact of a localized source of subglacial discharge on the heat flux and submarine melting of a tidewater glacier a laboratory study abstractidealized laboratory experiments have been conducted in a two layer stratified fluid to investigate the leading order dynamics that control submarine melting and meltwater export near a vertical ice ocean interface as a function of subglacial discharge in summer the discharge of surface runoff at the base of a glacier subglacial discharge generates strong buoyant plumes that rise along the glacier front entraining ambient water along the way the entrainment enhances the heat transport toward the glacier front and hence the submarine melt rate increases with the subglacial discharge rate in the laboratory the effect of subglacial discharge is simulated by introducing freshwater at freezing temperature from a point source at the base of an ice block representing the glacier the circulation pattern observed both with and without subglacial discharge resembles those observed in previous observational and numerical studies buoyant plumes rise vertically until they find either their neutrally b

greenland ice sheet mass balance reconstruction part iii marine ice loss and total mass balance 1840 2010 abstractgreenland ice sheet mass loss to the marine environment occurs by some combination of iceberg calving and underwater melting referred to here as marine ice loss lm this study quantifies the relation between lm and meltwater runoff r at the ice sheet scale a theoretical basis is presented explaining how variability in r can be expected to govern much of the lm variability over annual to decadal time scales it is found that r enhances lm through three processes 1 increased glacier discharge by ice warming softening and basal lubrication sliding 2 increased calving susceptibility through undercutting glacier front geometry and reducing ice integrity and 3 increased underwater melting from forcing marine convection applying a semiempirical lm f r parameterization to a surface mass balance reconstruction enables total ice sheet mass budget closure over the 1840 2010 period the estimated cumulative 171 yr net ice sheet sea level contribution is 25 10 mm the rise punctuated by periods