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

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

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

21st century evolution of greenland outlet glacier velocities earlier observations on several of greenland s outlet glaciers starting near the turn of the 21st century indicated rapid annual scale and large 100 increases in glacier velocity combining data from several satellites we produce a decade long 2000 to 2010 record documenting the ongoing velocity evolution of nearly all 200 of greenland s major outlet glaciers revealing complex spatial and temporal patterns changes on fast flow marine terminating glaciers contrast with steady velocities on ice shelf terminating glaciers and slow speeds on land terminating glaciers regionally glaciers in the northwest accelerated steadily with more variability in the southeast and relatively steady flow elsewhere intraregional variability shows a complex response to regional and local forcing observed acceleration indicates that sea level rise from greenland may fall well below proposed upper bounds

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

force perturbation analysis of recent thinning and acceleration of jakobshavn isbrae greenland observations between 1997 and 2001 of a 30 velocity increase and up to 60 m thinning of downstream parts of jakobshavn isbrae greenland immediately following calving of about 4 km of its 15 km floating ice tongue suggest that acceleration may have been initiated by the calving assuming that the force perturbation associated with such weakening is swiftly transmitted far up glacier i develop equations to estimate the perturbation initially the observed changes are consistent with the comparatively small perturbation associated with the calving thereafter it was probably sustained by thinning of the remaining ice tongue at rates of about 80 m a 1 otherwise the force perturbation would soon have been balanced by reduction in the hydrostatic driving force for longitudinal creep as the glacier thinned with velocities dropping to their former values the calculated force perturbation increases to a maximum about 10 km inland of the grounding line consistent with decreasing weight forces as the glacier thins over bedrock that slopes uphill seawards further inland it progressively decreases probably because marginal drag increased as the glacier accelerated both here and on the floating tongue marginal ice appears to have been softened by the influence of locally intense shear on ice temperature and or fabric more recent observations show continued acceleration and thinning and most of the remaining ice tongue calved away in april 2003 so thinning is likely to continue

coherent radar ice thickness measurements over the greenland ice sheet we developed two 150 mhz coherent radar depth sounders for ice thickness measurements over the greenland ice sheet we developed one of these using connectorized components and the other using radio frequency integrated circuits rfics both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice we used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers we operated both radar systems on the nasa p 3b aircraft equipped with gps receivers radar data are tagged with gps derived location information and are collected in conjunction with laser altimeter measurements we have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of program for regional climate assessment parca investigations and the north greenland ice core project radar echograms and derived ice thickness data are placed on a server at the university of kansas http tornado rsl ukans edu greenlanddata htm for easy access by the scientific community we obtained good ice thickness information with an accuracy of 10 m over 90 of the flight lines flown as a part of the parca initiative in this paper we provide a brief description of the system along with samples of data over the interior along the 2000 m contour line in the south and from a few selected outlet glaciers

present and past climate control on fjord glaciations in greenland implications for ird deposition in the sea calving of icebergs is the dominant ablation mechanism for large outlet glaciers from the greenland ice sheet except in northernmost greenland where bottom melting from floating glaciers dominates this difference is controlled by present climate conditions glacial geological evidence indicates that the transition between the associated types of fjord glaciations moved north south in response to past climate change in cold periods local melt out of debris from the bottom of an increasing number of floating glaciers reduces the potential for iceberg transport of ird thus the marine ird signal of greenland origin is not a simple cold climate signal our findings are discussed in the context of the ongoing debate about the kind of ice transporting ird icebergs or sea ice

cover stratigraphy and structure of the southernmost external basement massifs in the appalachian blue ridge evidence for two stage late proterozoic rifting

implications of increased greenland surface melt under global warming scenarios ice sheet simulations abstract the greenland ice sheet is likely to make a faster contribution to sea level rise in a warming world than previously believed based on numerical modelling using a parameterization of recent results showing surface meltwater lubrication of ice flow zwally et al science 297 557 2002 218 documented correlation between increased ice velocity and increased surface melt as parameterized by positive degree days they argued that surface water is piped directly to the bed with little delay causing increased basal water pressures and basal sliding velocities an effect not included in recent greenland ice sheet models known to the authors using the pennsylvania state university university of chicago thermomechanical flowline model numerous simulations were conducted to test a wide range of parameter space linking surface melt with a new sliding law based on the zwally et al data under three different global warming scenarios 2 co2 4 co2 and 8 co2 comparisons to reconstructions generated with a traditional sliding parameterization illustrate an enhanced sensitivity of the ice sheet to surface warming resulting in higher ablation rates additional thinning and retreat of the margin and a reduction in ice volume leading to an increased contribution to global sea level rise

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

jakobshavn glacier west greenland 30 years of spaceborne observations early 1960 s reconnaissance satellite images are compared to more recent image and map data in an inter annual and seasonal study of west central greenland margin fluctuations from 1962 to 1992 ice sheet margins to the north and south of jakobshavn glacier retreated despite a decline in average summer temperatures the retreat may be reversing along the southern flank of the ice stream where regional mass balance estimates are positive from 1950 to fluctuated 2 5 km around its annual mean position the total calving flux during the summer is more than six times that during winter we identified that summer melting and the break up of sea ice and icebergs in the fjord are important in controlling the rate of iceberg production if correct calving rates may be expected to increase should climate become warmer in the near future

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

thermal structure of svalbard glaciers and implications for thermal switch models of glacier surging switches between cold and warm based conditions have long been invoked to explain surges of high arctic glaciers here we compile existing and new data on the thermal regime of six glaciers in svalbard to test the applicability of thermal switch models two of the large glaciers of our sample are water terminating while one is land terminating all three have a well known surge history they have a thick basal layer of temperate ice superimposed by cold ice a cold terminus forms during quiescence but is mechanically removed by calving on tidewater glaciers the other three glaciers are relatively small and are either entirely cold or have a diminishing warm core all three bear evidence of former warm based thermal regimes and in two cases surge like behavior during the little ice age in svalbard therefore three types of glaciers have switched from slow to fast flow 1 small glaciers that underwent thermal cycles during and following the lia switches between cold and warm based conditions 2 large terrestrial glaciers which remain warm based throughout the entire surge cycle but develop cold termini during quiescence and 3 large tidewater glaciers that remain warm based throughout the surge cycle our results demonstrate that thermal switching cannot explain the surges of large glaciers in svalbard we apply the concept of enthalpy cycling to the spectrum of surge and surge like behavior displayed by these glaciers and demonstrate that all svalbard surge type glaciers can be understood within a single conceptual framework

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

recent dramatic thinning of largest west antarctic ice stream triggered by oceans a growing body of observational data suggests that pine island glacier pig is changing on decadal or shorter timescales these changes may have far reaching consequences for the future of the west antarctic ice sheet wais and global sea levels because of pig s role as the ice sheet s primary drainage portal we test the hypothesis that these changes are triggered by the adjoining ocean specifically we employ an advanced numerical ice flow model to simulate the effects of perturbations at the grounding line on pig s dynamics the speed at which these changes are propagated upstream implies a tight coupling between ice sheet interior and surrounding ocean

greenland ice sheet increased coastal thinning repeated laser altimeter surveys and modelled snowfall summer melt show average ice loss from greenland between 1997 and 2003 was 80 12 km3 yr 1 compared to about 60 km3 yr 1 for 1993 4 1998 9 half of the increase was from higher summer melting with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation velocities of one large glacier almost doubled between 1997 and 2003 resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003 copyright 2004 by the american geophysical union

surface mass balance changes of the greenland ice sheet since 1866 mass loss from the greenland ice sheet over the past decade has caused the impression that the ice sheet has been behaving anomalously to the warming of the 1990s we have reconstructed the recent 1866 2005 surface mass balance smb history of the greenland ice sheet on a 5 5 km grid using a runoff retention model based on the positive degree day method the model is forced with new datasets of temperature and precipitation patterns dating back to 1866 we use an innovative method to account for the influence of year on year surface elevation changes on smb estimates and have found this effect to be minor all smb estimates are made relative to the 1961 90 average smb and we compare annual smb estimates from the period 1995 2005 to a similar period in the past 1923 33 where smb was comparable and conclude that the present day changes are not exceptional within the last 140 years peripheral thinning has dominated the smb response during the past decade as in 1923 33 but we also show that thinning was not restricted to the margins during this earlier period

a sar record of early 21st century change in greenland glaciers in greenland are changing rapidly to better understand these changes we have produced a series of seven synthetic aperture radar sar backscatter mosaics for seven winters during the period from 2000 to 2013 six of the mosaics were created using radarsat fine beam data and the seventh used alos palsar fine beam single polarization data the radarsat mosaics are radiometrically calibrated and capture changes in the backscatter coefficient related to melt and other events particularly the strong melting in the summer of 2012 comparison of features in the ascending orbit alos mosaic and the descending orbit radarsat mosaics indicate that in areas of smooth to moderate topography their locations are consistent to within a few 10s of meters the locations of features identifiable in the radarat mosaics which were collected with the same imaging parameters generally agree to within better than the 20 m posting of the data with such geometric accuracy these data establish a record of change in greenland for the early part of the 21st century thus providing a baseline that can be compared with new radar and optical data sets

ice sheet extent and early deglacial history of the southwestern sector of the greenland ice sheet the offshore and coastal geomorphology of southwest greenland records evidence for the advance and decay of the greenland ice sheet during the last glacial maximum regional ice flow patterns in the vicinity of sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf with an ice stream centred over holsteinsborg dyb high level periglacial terrain composed of blockfield and tors is dated to between 101 and 142 ka using 26al and 10be cosmogenic exposure ages these limit the maximum surface elevation of the last glacial maximum ice sheet in this part of southwest greenland to ca 750 810 m asl and demonstrate that terrain above this level has been ice free since mis 6 last glacial maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the outer hellefisk moraines exposure dates record ice surface thinning from 21 0 to 9 8 ka with downwasting rates varying from 0 06 to 0 12 m yr 1 this reflects strong surface ablation associated with increased air temperatures running up to the bolling interstadial gis1e at ca 14 ka and later marine calving under high sea levels the relatively late retreat of the itilleq ice stream inland of the present coastline is similar to the pattern observed at jakobshavn isbrae located 250 km north in disko bugt which also retreated from the continental shelf after ca 10 ka we hypothesise that the ice streams of west greenland persisted on the inner shelf until the early holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet

ice front and flow speed variations of marine terminating outlet glaciers along the coast of prudhoe land northwestern greenland satellite images were analyzed to measure the frontal positions and ice speeds of 19 marine terminating outlet glaciers along the coast of prudhoe land northwestern greenland from 1987 to 2014 all the studied glaciers retreated over the study period at a rate of between 12 and 200 m a 1 with a median mean retreat rate of 30 40 m a 1 the glacier retreat began in the year 2000 which coincided with an increase in summer mean air temperature from 1 4 to 5 5 c between 1996 and 2000 in this region ice speed near the front of the studied glaciers ranged between 20 and 1740 m a 1 in 2014 and many of them accelerated in the early 2000s in general the faster retreat was observed at the glaciers that experienced greater acceleration as represented by tracy glacier which experienced a retreat of 200 m a 1 and a velocity increase of 930 m a 1 during the study period a possible interpretation of this observation is that flow acceleration induced dynamic thinning near the termini resulting in enhanced calving and rapid retreat of the studied glaciers we hypothesize that atmospheric warming conditions in the late 1990s triggered glacier retreat in northwestern greenland since 2000

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

ice sheet velocity mapping a combined interferometric and speckle tracking approach the first and second radarsat antarctic mapping missions amm 1 and 2 have now acquired interferometric synthetic aperture radar sar overmuch of the ice sheet the radarsat 24 day repeat cycle is nearly ideal for measuring slow ice motion e g 1 but application of sar interferometry is limited in faster moving areas with a 1day repeat period ers 1 2 tandem sar data are much better matched to fast motion but are not always available fortunately several authors have demonstrated the ability to measure velocity in fast moving areas by tracking sar speckle from image to image which works well even in the absence of visible features while these estimates have intrinsically lower resolution and poorer accuracy than direct phase measurements they serve well in areas where there are no data suitable for conventional interferometry this paper describes algorithms i have developed for merging interferometric and speckle tracking data from multiple swaths to form a single seamless mosaic of velocity at each point in the mosaic all the available data are combined to produce estimates of the velocity and the associated error this technique is demonstrated using radarsat data collected over lambert glacier antarctica during amm 1 and 2

variations in sediment yield over the advance and retreat of a calving glacier laguna san rafael north patagonian icefield abstract bathymetric and sub bottom acoustic data were collected in laguna san rafael chile to determine sediment yields during the little ice age advance and subsequent retreat of san rafael glacier the sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance retreat cycle sediment yields from san rafael glacier averaged 2 7 107 m3 a since the end of the little ice age circa ad 1898 corresponding to average basin wide erosion rates of 23 9 mm a the highest erosion rates 68 23 mm a occurred at the start of the retreat phase and have since been steadily decreasing erosion rates were much lower during glacial advance averaging at most 7 mm a than during retreat such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today the detailed sub bottom information of a proglacial lagoon yields important clues as to the timing of erosion deposition and transfer of glacigenic sediments from orogens to the continental shelves and the influence of glacier dynamics on this process

rapid retreat and acceleration of helheim glacier east greenland 1 a significant amount of the measured coastal thinning of the greenland ice sheet may be due to recent acceleration of outlet glaciers using remote sensing we measured two major periods of speedup on helheim glacier between 2000 and 2005 that increased peak speeds from approximately 8 to 11 km yr these speedups coincided with rapid retreats of the calving front totaling over 7 5 km the glacier also thinned by over 40 m from 2001 to 2003 retreat of the ice front appears to decrease resistance to flow and concentrates the gravitational driving force over a smaller area farther up glacier acceleration may be a delayed response to surface draw down and steepening of the glacier s main trunk if the 2005 speedup also produces strong thinning then much of the glacier s main trunk may un ground leading to further retreat citation howat i m i joughin s tulaczyk and s gogineni 2005 rapid retreat and acceleration of helheim glacier east greenland geophys res lett 32 l22502 doi 10 1029 2005gl024737

seasonal variation in velocity before retreat of jakobshavn isbrae greenland 1 using repeat pass satellite feature tracking the dynamic behaviour of jakobshavn isbrae which drains around 7 of the greenland ice sheet is investigated in improved detail through its recent period of thinning acceleration and retreat the departure in 1995 from the normal seasonal invariance in velocity near the grounding line suggests a possible change in dynamics well before the subsequent thinning phase the initiation of the acceleration and retreat is pinpointed to spring 1998 and may have been prompted by the same mechanism that gave rise to the spring 1995 flow increase

bathymetry of southeast greenland from oceans melting greenland omg data southeast greenland has been a major participant in the ice sheet mass loss over the last several decades interpreting the evolution of glacier fronts requires information about their depth below