iceberg calving flux and mass balance of the austfonna ice cap on nordaustlandet svalbard 1 satellite radar interferometry 60 mhz airborne ice penetrating radar data and visible band satellite imagery were used to calculate the velocity structure ice thickness and the changing ice marginal extent of austfonna 8000 km2 and 2500 km3 the largest ice cap in the eurasian arctic ice cap motion is generally less than about 10 m a 1 except where faster flowing curvilinear features with velocities of several tens to over 200 m a 1 are present most drainage basins of austfonna have undergone ice marginal retreat over the past few decades at an average of a few tens of meters per year integrating margin change around the whole ice cap gives a total area loss of about 10 km2 a 1 iceberg flux from the marine margins of austfonna is about 2 5 0 5 km3 a 1 water equivalent about 45 of the total calving flux from the whole svalbard archipelago when mass loss by iceberg production is taken into account the total mass balance of austfonna is negative by between about 2 5 and 4 5 km3 a 1 this iceberg flux represents about 33 5 of total annual mass loss from austfonna with the remainder lost through surface ablation iceberg flux should be included in calculations of the total mass balance of the many large arctic ice caps including those located in the russian and canadian arctic that end in tidewater the neglect of this term has led to underestimates of mass loss from these ice caps and thus to underestimates of the contribution of arctic ice caps to global sea level rise

rapid circulation of warm subtropical waters in a major glacial fjord in east greenland the recent rapid increase in mass loss from the greenland ice sheet is primarily attributed to an acceleration of outlet glaciers oceanographic data obtained in summer 2008 show that subtropical waters that reside year round in the shelf ocean off greenland continuously enter a large glacial fjord in east greenland and contribute to melting at the glacier terminus the recent rapid increase in mass loss from the greenland ice sheet1 2 is primarily attributed to an acceleration of outlet glaciers3 4 5 one possible cause of this acceleration is increased melting at the ice ocean interface6 7 driven by the synchronous warming8 9 10 of subtropical waters offshore of greenland however because of the lack of observations from greenland s glacial fjords and our limited understanding of their dynamics this hypothesis is largely untested here we present oceanographic data collected in sermilik fjord east greenland by ship in summer 2008 and from moorings our data reveal the presence of subtropical waters throughout the fjord these waters are continuously replenished through a wind driven exchange with the shelf where they are present all year the temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus key controls on the melting rate are the volume and properties of the subtropical waters on the shelf and the patterns of along shore winds suggesting that the glaciers acceleration has been triggered by a combination of atmospheric and oceanic changes our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice sheet margins

the retreat of a tidewater glacier observations and model calculations on hansbreen spitsbergen based on observations and model calculations the retreat over the last two decades of hansbreen a tidewater glacier in southern spitsbergen svalbard is investigated the observations of the calving front position between 1982 and 1998 show an abrupt retreat in 1990 which is suggested to be related to a depression in the glacier bed the observed seasonal variations of the front position are mainly due to variations of the calving rate the observations of hansbreen further indicate that during periods of slow front position changes melting at the water line may play an important role in triggering the process of calving the evolution of hansbreen between 1982 and 1998 is simulated with a numerical model for the dynamics of tidewater glaciers using a flotation criterion for calving in which for each time step the part of the glacier terminus which is below a critical height above buoyancy is removed we are able to reproduce the observed rapid retreat of hansbreen through the depression in the glacier bed from the observations and model calculations we conclude that the rapid retreat is mainly an effect of basal topography in the terminus region and not a direct response to a change in mass balance

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

recent mass changes of glaciers in the russian high arctic 1 glaciers and ice caps are known to contribute significantly to present day sea level rise but there are still glaciated regions where little is known about modern changes in glacier mass one of these regions is the russian high arctic archipelagos which has a total glaciated area of 51 500 km2 we have assessed the glacier mass budget of this region for a 6 year period between october 2003 and october 2009 using independent icesat laser altimetry and grace gravimetry over this period we found that the archipelagos have lost ice at a rate of 9 1 2 0 gt a 1 which corresponds to a sea level contribution of 0 025 mm a 1 approximately 80 of the ice loss came from novaya zemlya with the remaining 20 coming from franz josef land and severnaya zemlya meteorological records of temperature and precipitation for the period 1980 2009 suggest that the recent climatic mass budget is not substantially different from the longer term trend

shear margins in glaciers and ice sheets analytical and numerical techniques are used to examine the flow response of a sloped slab of power law fluid power n subjected to basal boundary conditions that vary spatially across the flow direction as for example near an ice stream margin with planar basal topography the primary assumption is that basal shear stress is proportional to the basal speed time a spatially variable slip resistance the ratio of mean basal speed to the speed originating from shearing through the thickness denoted as r gives a measure of how slippery the bed is the principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow in units of ice thickness h the spatial scale of spreading is proportional to a single dimensionless number r n r n 1 1 n 1 derived from n and r the consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to r n for an ice stream caused by a band of low slip resistance with a half width of wh the margins influence velocity and stress in the central part of the band depending on r n in comparison to w three regimes can be identified which for n 3 are quantified as follows low r defined as r 3 1w for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag intermediate r for which the driving stress in the center is supported by a combination of basal and side drag shear zones that are narrower than predicted on the basis of this theory r 3 would require localized softening of the ice to explain the concentration of deformation at a shorter scale

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

loss of floating glacier tongues from the yelverton bay region ellesmere island canada a total of eight floating glacier tongues have shrunk in area by 85 from the yelverton bay region of northern ellesmere island since 1959 with unusually large losses since 2005 to better understand the causes of these losses this study undertakes the first examination of ice tongue changes in this region including an assessment of changes in surrounding marine ice i e sea ice sikussak and melange and atmospheric and oceanographic forcings from 1959 to 2017 the total ice tongue area decreased by 49 07 km 2 with the majority of this loss occurring from 2005 to 2009 34 68 km 2 the loss of ice tongues since 2005 occurred when open water replaced multi year landfast sea ice mlsi and first year sea ice in the regions adjacent to the ice tongues these changes were accompanied by an increase in mean annual mid depth i e 100 and 200 m ocean temperatures from 0 29 c from 1999 to 2005 to 0 67 c from 2006 to 2012 despite the recent return of ocean temperatures to below pre 2006 levels atmospheric summer temperatures have continued to rise 0 15 c decade 1 between 1948 and 2016 with open water continuing to occur without the sustained presence of mlsi in this region the ice tongues are unable to stabilize making it unlikely that they will re form in the current climate

the mass balance of circum arctic glaciers and recent climate change the sum of winter accumulation and summer losses of mass from glaciers and ice sheets net surface mass balance varies with changing climate in the arctic glaciers and ice caps excluding the greenland ice sheet cover about 275 000 km2of both the widely glacierized archipelagos of the canadian norwegian and russian high arctic and the area north of about 60 n in alaska iceland and scandinavia since the 1940s surface mass balance time series of varying length have been acquired from more than 40 arctic ice caps and glaciers most arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades there is no uniform recent trend in mass balance for the entire arctic although some regional trends occur examples are the increasingly negative mass balances for northern alaska due to higher summer temperatures and increasingly positive mass balances for maritime scandinavia and iceland due to increased winter precipitation the negative mass balance of most arctic glaciers may be a response to a step like warming in the early twentieth century at the termination of the cold little ice age arctic ice masses outside greenland are at present contributing about 0 13 mm yr 1to global sea level rise

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

irreversible mass loss of canadian arctic archipelago glaciers 1 the canadian arctic archipelago caa contains the largest volume of glacier ice on earth outside of antarctica and greenland in the absence of significant calving caa glacier mass balance is governed by the difference between surface snow accumulation and meltwater runoff surface mass balance here we use a coupled atmosphere snow model to simulate present day and 21st century caa glacier surface mass balance through comparison with gravity recovery and climate experiment mass anomalies and in situ observations we show that the model is capable of representing present day caa glacier mass loss as well as the dynamics of the seasonal snow cover on the caa tundra next we force this model until 2100 with a moderate climate warming scenario ar5 rcp4 5 we show that enhanced meltwater runoff from caa glaciers is not sufficiently compensated by increased snowfall extrapolation of these results toward an ar5 multimodel ensemble results in sustained 21st century caa glacier mass loss in the vast majority 99 of the 7000 temperature realizations

closing the mass budget of a tidewater glacier the example of kronebreen svalbard in this study we combine remote sensing in situ and model derived datasets from 1966 to 2014 to calculate the mass balance components of kronebreen a fast flowing tidewater glacier in svalbard

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 climate driven changes in outlet glaciers on the pacific coast of east antarctica multidecadal trends in the terminus position of outlet glaciers along the margin of the east antarctic ice sheet reveal three epochal patterns of glacier retreat or advance consistent with a rapid and coherent response to air temperature and sea ice trends it is widely known that glaciers in west antarctica and greenland have been discharging ice into the oceans in response to warming in recent years and that sea levels have risen as a result by contrast we hear little about the much larger east antarctic ice sheet which has been viewed as being less vulnerable to climate change owing to its location in an extremely cold climate chris stokes and colleagues have used satellite imagery to map a large sample of glaciers along the pacific coast of east antarctica and show that in fact they are responding to decadal climate variability in concert with climate glaciers retreated in the 1970s and 1980s advanced in the 1990s and approximately split between advance and retreat since the 2000s the authors conclude that parts of the world s largest ice sheet may be more responsive to external forcing than previously recognized observations of ocean terminating outlet glaciers in greenland and west antarctica1 2 3 4 5 6 indicate that their contribution to sea level is accelerating as a result of increased velocity thinning and retreat7 8 9 10 11 thinning has also been reported along the margin of the much larger east antarctic ice sheet1 but whether glaciers are advancing or retreating there is largely unknown and there has been no attempt to place such changes in the context of localized mass loss7 9 or climatic or oceanic forcing here we present multidecadal trends in the terminus position of 175 ocean terminating outlet glaciers along 5 400 kilometres of the margin of the east antarctic ice sheet and reveal widespread and synchronous changes despite large fluctuations between glaciers linked to their size three epochal patterns emerged 63 per cent of glaciers retreated from 1974 to 1990 72 per cent advanced from 1990 to 2000 and 58 per cent advanced from 2000 to 2010 these trends were most pronounced along the warmer western south pacific coast whereas glaciers along the cooler ross sea coast experienced no significant changes we find that glacier change along the pacific coast is consistent with a rapid and coherent response to air temperature and sea ice trends linked through the dominant mode of atmospheric variability the southern annular mode we conclude that parts of the world s largest ice sheet may be more vulnerable to external forcing than recognized previously

characteristics of recessional moraines at a temperate glacier in se iceland insights into patterns rates and drivers of glacier retreat icelandic glaciers are sensitive to climate variability on short term timescales owing to their north atlantic maritime setting and have been undergoing ice marginal retreat since the mid 1990s recent patterns rates and drivers of ice frontal retreat at skalafellsjokull se iceland are examined using small scale recessional moraines as a geomorphological proxy these small scale recessional moraines exhibit distinctive sawtooth planform geometries and are constructed by a range of genetic processes associated with minor ice margin re advance including i combined push squeeze mechanisms ii bulldozing of pre existing proglacial material and iii submarginal freeze on remote sensing investigations and lichenometric dating highlight sequences of annually formed recessional moraines on the northern and central parts of the foreland conversely moraines are forming on a sub annual timescale at the southeastern skalafellsjokull margin using annual moraine spacing as a proxy for annual ice margin retreat rates imrrs we demonstrate that prominent periods of glacier retreat at skalafellsjokull are coincident with those at other icelandic outlet glaciers as well as those identified at greenlandic outlet glaciers analysis of imrrs and climate data suggests summer air temperature sea surface temperature and the north atlantic oscillation have an influence on imrrs at skalafellsjokull with the glacier appearing to be most sensitive to summer air temperature on the basis of further climate data analyses we hypothesise that sea surface temperature may drive air temperature changes in the north atlantic region which in turn forces imrrs the increase in sea surface temperature over recent decades may link to atmospheric driven variations in north atlantic subpolar gyre dynamics

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

changes in glacier extent on north novaya zemlya in the twentieth century glacier retreat on north novaya zemlya for the past century was documented by registering glacier terminus positions from expedition and topographic maps and remotely sensed images recession of tidewater calving glaciers on north novaya zemlya in the first half of the twentieth century was relatively rapid 300 m yr 1 consistent with post little ice age warming documented by a 122 year instrumental record from malye karmakuly the glaciers completed 75 to 100 of the net twentieth century retreat by 1952 between 1964 and 1993 half of the studied glaciers were stable the remainder retreated modest distances of 0 75 elevated sst in the barents sea appear to reflect increased advecti

surge type glaciers in the russian high arctic identified from digital satellite imagery landsat digital imagery was used to search the island archipelagos of franz josef land severnaya zemlya and novaya zemlya russian high arctic for the presence of looped moraines characteristic of past glacier surges the imagery provides almost complete summer time coverage of the 60000 km 2 of ice in these islands very few surge type glaciers are identified none in franz josef land three in novaya zemlya and two on severnaya zemlya this contrasts greatly with svalbard ice covered area 36 600 km 2 to the west where 36 of glaciers and ice cap drainage basins are inferred to surge the strong climatic gradient across the eurasian high arctic with decreasing temperature and moisture eastward may provide a gross control on this pattern through colder glacier thermal structure limiting basal drainage on the thinner ice masses in particular

recent changes on greenland outlet glaciers aircraft laser altimeter surveys during the 1990s showed near coastal parts of the greenland ice sheet to be thinning despite slow thickening at higher elevations the ice sheet lost mass to the ocean many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers indicating dynamic imbalance between glacier velocity and upstream snow accumulation results from more recent surveys presented here show that thinning rates have increased in most coastal regions for almost half of the surveys these increases might have resulted from increases in summer melting but rapid thinning on others is indicative of dynamic changes that increased with time in particular thinning rates on the three fastest glaciers increased to tens of m a 1 after 2000 and other observations show an approximate doubling in their velocities the deep beds of these glaciers appear to have a strong influence on rates of grounding line retreat and thickness change with periods of glacier acceleration and rapid thinning initiated by flotation and break up of lightly grounded glacier snouts or break up of floating ice tongues near simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause nearby glaciers without deep beds are thinning far more slowly suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on greenland outlet glacier acceleration

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

asynchronous response of marine terminating outlet glaciers during deglaciation of the fennoscandian ice sheet this is the accepted manuscript version published version is available at http dx doi org 10 1130 g35299 1

intra and inter annual variability in dynamic discharge from the academy of sciences ice cap severnaya zemlya russian arctic and its role in modulating mass balance

investigation of surface melting and dynamic thinning on jakobshavn isbrae greenland jakobshavn isbrae is the most active glacier in greenland with an annual discharge of about 30 km 3 of ice and it is one of the few recently surveyed glaciers to thicken between 1993 and 1998 despite locally warm summers repeated airborne laser altimeter surveys along a 120 km profile in the glacier basin show slow sporadic thickening between 1991 and 1997 suggesting a small positive mass balance but since 1997 there has been sustained thinning of several m a 1 within 20 km of the ice front with lower rates of thinning further inland here we use weather station data from the coast and the ice sheet to estimate the effects on surface elevation of interannual variability in snowfall and surface melt rates and thus to infer the temporal and spatial patterns of dynamic thinning these show the glacier to have been close to balance before 1997 followed by a sudden transition to rapid thinning initially confined to the lower reaches of the glacier below about 500 m elevation but progressively spreading inland until between 1999 and 2001 thinning predominated over the entire surveyed region up to 2000 m elevation if this continues the glacier calving front and probably its grounding line will retreat substantially in the very near future

committed sea level rise for the next century from greenland ice sheet dynamics during the past decade we use a three dimensional higher order ice flow model and a realistic initial condition to simulate dynamic perturbations to the greenland ice sheet during the last decade and to assess their contribution to sea level by 2100 starting from our initial condition we apply a time series of observationally constrained dynamic perturbations at the marine termini of greenland s three largest outlet glaciers jakobshavn isbrae helheim glacier and kangerdlugssuaq glacier the initial and long term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea level contribution of approximately 1 0 4 mm from these three glaciers by 2100 based on scaling arguments we extend our modeling to all of greenland and estimate a minimum dynamic sea level contribution of approximately 6 2 mm by 2100 this estimate of committed sea level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance importantly 75 of this value is from the long term diffusive response of the ice sheet suggesting that the majority of sea level rise from greenland dynamics during the past decade is yet to come assuming similar and recurring forcing in future decades and a self similar ice dynamical response we estimate an upper bound of 45 mm of sea level rise from greenland dynamics by 2100 these estimates are constrained by recent observations of dynamic mass loss in greenland and by realistic model behavior that accounts for both the long term cumulative mass loss and its decay following episodic boundary forcing

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

impact of fjord dynamics and glacial runoff on the circulation near helheim glacier greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord s externally forced currents and stratification the presence of light arctic and dense atlantic waters in the fjord in particular causes meltwater to be exported at depth and influences the vertical distribution of heat along the ice margin our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters we conclude that the shape and stability of greenland s glaciers may be strongly influenced by the layering of the arctic and atlantic waters in the fjord as well as their variability

large scale changes in greenland outlet glacier dynamics triggered at the terminus the recent dramatic retreat of many outlet glaciers of the greenland ice sheet has raised concerns over greenland s contribution to future sea level rise simulations with a numerical ice flow model indicate that the recent rates of mass loss in greenland s outlet glaciers are transient and should not be extrapolated into the future

ice stream stability on a reverse bed slope marine ice streams whose beds deepen inland are thought to be inherently unstable numerical modelling of the maguerite bay ice stream retreat in west antarctica since the last glacial maximum suggests that an ice stream can stabilize on an inland sloping bed owing to increased lateral drag where the ice stream narrows marine based ice streams whose beds deepen inland are thought to be inherently unstable1 2 3 this instability is of particular concern because significant portions of the marine based west antarctic and greenland ice sheets are losing mass and their retreat could contribute significantly to future sea level rise4 5 6 7 however the present understanding of ice stream stability is limited by observational records that are too short to resolve multi decadal to millennial scale behaviour or to validate numerical models8 here we present a dynamic numerical simulation of antarctic ice stream retreat since the last glacial maximum lgm constrained by geophysical data whose behaviour is consistent with the geomorphological record we find that retreat of marguerite bay ice stream following the lgm was highly nonlinear and was interrupted by stabilizations on a reverse sloping bed where theory predicts rapid unstable retreat we demonstrate that these transient stabilizations were caused by enhanced lateral drag as the ice stream narrowed we conclude that as well as bed topography ice stream width and long term retreat history are crucial for understanding decadal to centennial scale ice stream behaviour and marine ice sheet vulnerability

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

synchronous retreat and acceleration of southeast greenland outlet glaciers 2000 06 ice dynamics and coupling to climate a large portion of the recent increase in the rate of mass loss from the greenland ice sheet is from increased outlet glacier discharge along its southeastern margin while previous investigations of the region s two largest glaciers suggest that acceleration is a dynamic response to thinning and retreat of the calving front it is unknown whether this mechanism can explain regional acceleration and what forcing is responsible for initiating rapid thinning and retreat we examine seasonal and interannual changes in ice front position surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006 while substantial seasonality in front position and speed is apparent nearly all the observed glaciers show net retreat thinning and acceleration with speed up corresponding to retreat the ratio of retreat to the along flow stress coupling length is proportional to the relative increase in speed consistent with typical ice flow and sliding laws this affirms that speed up results from loss of resistive stress at the front during retreat which leads to along flow stress transfer large retreats were often preceded by the formation of a flat or reverse sloped surface near the front indicating that subsequent retreats were influenced by the reversed bed slope many retreats began with an increase in thinning rates near the front in the summer of 2003 a year of record high coastal air and sea surface temperatures this anomaly was driven in part by recent warming suggesting that episodes of speed up and retreat may become more common in a warmer climate

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

svalbard glacier elevation changes and contribution to sea level rise 1 we compare satellite altimetry from the ice cloud and land elevation satellite icesat 2003 2007 to older topographic maps and digital elevation models 1965 1990 to calculate long term elevation changes of glaciers on the svalbard archipelago results indicate significant thinning at most glacier fronts with either slight thinning or thickening in the accumulation areas except for glaciers that surged which show thickening in the ablation area and thinning in the accumulation areas the most negative geodetic balances occur in the south and on glaciers that have surged while the least negative balances occur in the northeast and on glaciers in the quiescent phase of a surge cycle geodetic balances are related to latitude and to the dynamical behavior of the glacier the average volume change rate over the past 40 years for svalbard excluding austfonna and kvitoya is estimated to be 9 71 0 55 km3 yr 1 or 0 36 0 02 m yr 1 w equivalent for an annual contribution to global sea level rise of 0 026 mm yr 1 sea level equivalent

threefold increase in marine terminating outlet glacier retreat rates across the atlantic arctic 1992 2010 accelerated discharge through marine terminating outlet glaciers has been a key component of the rapid mass loss from arctic glaciers since the 1990s however glacier retreat and its climatic controls have not been assessed at the pan arctic scale consequently the spatial and temporal variability in the magnitude of retreat and the possible drivers are uncertain here we use remotely sensed data acquired over 273 outlet glaciers located across the entire atlantic arctic i e areas potentially influenced by north atlantic climate and or ocean conditions specifically greenland novaya zemlya franz josef land and svalbard to demonstrate high magnitude accelerating and near ubiquitous retreat between 1992 and 2010 overall mean retreat rates increased by a factor of 3 5 between 1992 and 2000 30 5 m a 1 and 2000 10 105 8 m a 1 with 97 of the study glaciers retreating during the latter period the retreat was greatest in northern western and south eastern greenland and also increased substantially on the barents sea coast of novaya zemlya glacier retreat showed no significant or consistent relationship with summer air temperatures at decadal timescales the rate of frontal position change showed a significant but weak correlation with changes in sea ice concentrations we highlight large variations in retreat rates within regions and suggest that fjord topography plays an important role we conclude that marine terminating arctic outlet glaciers show a common response of rapid and accelerating retreat at decadal timescales

ice front change of marine terminating outlet glaciers in northwest and southeast greenland during the 21st century the increasingly negative mass balance of the greenland ice sheet gris over the last 25 years has been associated with enhanced surface melt and increased ice loss from marine terminating outlet glaciers accelerated retreat during 2000 2010 was concentrated in the southeast and northwest sectors of the ice sheet however there was considerable spatial and temporal variability in the timing and magnitude of retreat both within and between these regions this behaviour has yet to be quantified and compared for all glaciers in both regions furthermore it is unclear whether retreat has continued after 2010 in the northwest and whether the documented slowdown in the southeast post 2005 has been sustained here we compare spatial and temporal patterns of frontal change in the northwest and southeast gris for the period 2000 2015 our results show near ubiquitous retreat of outlet glaciers across both regions for the study period however the timing and magnitude of inter annual frontal position change is largely asynchronous we also find that since 2010 there is continued terminus retreat in the northwest which contrasts with considerable inter annual variability in the southeast analysis of the role of glacier specific factors demonstrates that fjord and bed geometry are important controls on the timing and magnitude of glacier retreat

sensitivity of greenland ice sheet projections to model formulations physically based projections of the greenland ice sheet contribution to future sea level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself here a higher order three dimensional thermomechanical ice flow model is used initialized to the present day geometry the forcing comes from a high resolution regional climate model and from a flowline model applied to four individual marine terminated glaciers and results are subsequently extended to the entire ice sheet the experiments span the next 200 years and consider climate scenario sres a1b the surface mass balance smb scheme is taken either from a regional climate model or from a positive degree day pdd model using temperature and precipitation anomalies from the underlying climate models our model results show that outlet glacier dynamics only account for 6 18 of the sea level contribution after 200 years confirming earlier findings that stress the dominant effect of smb changes furthermore interaction between smb and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing forcing from the regional climate model produces a 14 31 higher sea level contribution compared to a pdd model run with the same parameters as for ipcc ar4

outlet glacier response to the 2012 collapse of the matusevich ice shelf severnaya zemlya russian arctic the matusevich ice shelf mis located within the severnaya zemlya archipelago in the russian arctic rapidly broke apart between 10 august and 7 september 2012 we examine the response of the outlet glaciers that fed the mis from local ice caps to the removal of the ice shelf we use spaceborne laser altimetry and multiple optically derived digital elevation models to track ice surface elevation change rates dh dt between 1984 and 2014 glacier speeds are measured by pixel tracking from optical and radar imagery between 2010 and 2014 and interferometric synthetic aperture radar in 1995 to compare precollapse and postcollapse velocities we find that the three main outlet glaciers that fed the mis are thinning an order of magnitude more rapidly than most of the rest of severnaya zemyla based upon icesat data from 2003 to 2009 recent 2012 to 2014 thinning rates are three to four times faster than the 30 year average thinning rate calculated between 1984 and 2014 the springtime speeds of the largest outlet glacier issledovateley have increased more than 200 at the terminus between april 2010 and april 2014 to date changes in surface elevation dh dt and velocity at the outlet glaciers near mis are smaller than glacier responses to ice shelf collapse in antarctica it is possible that the mis was already very weak prior to the 2012 collapse and unable to support back stress further observations are required to assess whether the thinning and nonmelt season glacier speeds are continuing to accelerate

recent changes in glacier velocities and thinning at novaya zemlya abstract ice loss from the glaciers of novaya zemlya nvz is the dominant contributor to sea level for the russian arctic here we present maps of glacier elevation change rates dh dt and velocities at novaya zemlya that reveal evidence of the impact of both calving flux and surface melt on ice mass loss dh dt are calculated by applying a weighted linear regression to stacked digital elevation models dems from a 1952 map and dems created from stereo pairs of worldview images acquired between 2012 and 2014 the 60 year average mass change rate is 0 23 0 04 m w e yr 1 the recent short term 2012 2013 2014 average mass change rate is 0 40 0 09 m w e yr 1 we apply the same weighted linear regression to stacked worldview dems and icesat elevations from 2003 to 2009 as well as stacked worldview dems and aster dems from 2000 to 2013 the dh dt from both datasets confirm that thinning has been more rapid than the 60 year average since 2000 average mass loss has accelerated at the lower elevations of land terminating glaciers suggesting that recent near surface warming and increased melt have led to greater thinning marine terminating glaciers along the barents sea coast have substantially higher thinning rates near their termini in recent years than adjacent land terminating glaciers suggesting that calving flux is an important contributor to overall ice mass loss in the region flow velocities are generated by feature tracking on optical and radar image pairs marine terminating glaciers along the barents sea coast have the highest frontal velocities of any glaciers on nvz our surface velocity measurements constrain the calving flux at the two fastest retreating glaciers inostrantseva ino and vil kitskogo vis which are both on the barents sea coast we find that the calving flux is high enough to drive frontal thinning and retreat at those two glaciers summer terminus speeds at inostrantseva glacier have accelerated from a 2006 maximum of 3 m day 1 to a 2012 maximum of 9 to 10 m day 1 and the front has retreated by more than 3 km between 2006 06 27 and 2013 08 17

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

response of glacier flow and structure to proglacial lake development and climate at fjallsjokull south east iceland over recent decades the number of outlet glaciers terminating in lakes in iceland has increased in line with climate warming the mass balance changes of these lake terminating outlet glaciers are sensitive to rising air temperatures due to altered glacier dynamics and increased surface melt this study aims to better understand the relationship between proglacial lake development climate glacier dynamics and glacier structure at fjallsjokull a large lake terminating outlet glacier in south east iceland we used satellite imagery to map glacier terminus position and lake extent between 1973 and 2016 and a combination of aerial and satellite imagery to map the structural architecture of the glacier s terminus in 1982 1994 and 2011 the temporal evolution of ice surface velocities between 1990 and 2018 was calculated using feature tracking statistically significant increases in the rate of terminus retreat and lake expansion were identified in 2001 2009 and 2011 our surface velocity and structural datasets revealed the development of localised flow corridors over time which conveyed relatively faster flow towards the glacier s terminus we attribute the overall changes in dynamics and structural architecture at fjallsjokull to rising air temperatures but argue that the spatial complexities are driven by glacier specific factors such as basal topography

spatial and temporal melt variability at helheim glacier east greenland and its effect on ice dynamics this is the publisher s version also available electronically from http onlinelibrary wiley com

identification and characteristics of surge type glaciers on novaya zemlya russian arctic we present a comprehensive new inventory of surge type glaciers on the novaya zemlya archipelago using high resolution up to 4 m satellite imagery from 1976 77 hexagon 1989 landsat tm 2001 landsat etm and 2006 aster a total of 692 glaciers and their forelands were observed for glaciological and geomorphological criteria indicative of glacier surging e g looped moraines heavy surface crevassing surface potholes thrust block moraines concertina eskers this enabled the identification of 32 potential surge type glaciers compared with four previously identified representing 4 6 of the total but 18 by glacier area we assess the characteristics of surge type glaciers surge type glaciers are statistically different from non surge type glaciers in terms of their area length surface slope minimum elevation mid range elevation and terminus type they are typically long median length 18 5 km large median area 106 8 km 2 outlet glaciers with relatively low overall surface slopes median slope 1 7 and tend to terminate in water marine or lacustrine they are predominantly directed towards and located in the more maritime western region of the russian arctic and we suggest that surge occurrence might be related to large and complex catchment areas that receive increased delivery of precipitation from the barents sea

rapid response of helheim glacier in greenland to climate variability over the past century during the early 2000s the greenland ice sheet experienced the largest ice mass loss of the instrumental record 1 largely as a result of the acceleration thinning and retreat of large outlet glaciers in west and southeast greenland 2 5 the quasi simultaneous change in the glaciers suggests a common climate forcing increasing air 6 and ocean 7 8 temperatures have been indicated as potential triggers here we present a record of calving activity of helheim glacier east greenland that extends back to about ad 1890 based on an analysis of sedimentary deposits from sermilik fjord where helheim glacier terminates specifically we use the annual deposition of sand grains as a proxy for iceberg discharge our record reveals large fluctuations in calving rates but the present high rate was reproduced only in the 1930s a comparison with climate indices indicates that high calving activity coincides with a relatively strong influence of atlantic water and a lower influence of polar water on the shelf off greenland as well as with warm summers and the negative phase of the north atlantic oscillation our analysis provides evidence that helheim glacier responds to short term fluctuations of large scale oceanic and atmospheric conditions on timescales of 3 10 years the forcings behind the rapid increase in mass loss from the greenland ice sheet in the early 2000s ref 1 are still debated it is unclear whether the mass loss will continue in the near future and ifso atwhatrate theseuncertaintiesareaconsequenceofour limited understanding of mechanisms regulating ice sheet variability and the response of fast flowing outlet glaciers to climate variability in southeast greenland helheim glacier one of the regions largestglaciers thinned acceleratedandretreatedduringtheperiod 20032005

sharply increased mass loss from glaciers and ice caps in the canadian arctic archipelago the canadian arctic archipelago contains one third of the global volume of land ice outside the ice sheets but its contribution to sea level change is largely unknown gardner et al use three independent techniques to reveal that mass loss from the archipelago was 92 12 gigatonnes per year in 2007 09 about three times greater than in 2004 06 and coincident with warmer summer temperatures the record is too short to allow a firm conclusion on longer term trends but it is clear that the canadian arctic archipelago is a significant contributor to sea level rise mountain glaciers and ice caps are contributing significantly to present rates of sea level rise and will continue to do so over the next century and beyond1 2 3 4 5 the canadian arctic archipelago located off the northwestern shore of greenland contains one third of the global volume of land ice outside the ice sheets6 but its contribution to sea level change remains largely unknown here we show that the canadian arctic archipelago has recently lost 61 7 gigatonnes per year gt yr 1 of ice contributing 0 17 0 02 mm yr 1 to sea level rise our estimates are of regional mass changes for the ice caps and glaciers of the canadian arctic archipelago referring to the years 2004 to 2009 and are based on three independent approaches surface mass budget modelling plus an estimate of ice discharge smb d repeat satellite laser altimetry icesat and repeat satellite gravimetry grace all three approaches show consistent and large mass loss estimates between the periods 2004 2006 and 2007 2009 the rate of mass loss sharply increased from 31 8 gt yr 1 to 92 12 gt yr 1 in direct response to warmer summer temperatures to which rates of ice loss are highly sensitive 64 14 gt yr 1 per 1 k increase the duration of the study is too short to establish a long term trend but for 2007 2009 the increase in the rate of mass loss makes the canadian arctic archipelago the single largest contributor to eustatic sea level rise outside greenland and antarctica

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

changes in ice front position on greenland s outlet glaciers from 1992 to 2007 1 previous studies in greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss raising greenland s contribution to sea level rise we examined ice front changes of 203 tidewater glaciers land terminating glaciers and glaciers terminating with ice shelves to understand greenland glacier behavior over three periods 1992 2000 2000 2006 and 2006 2007 we observed synchronous ice sheet wide increases in tidewater retreat during 2000 2006 relative to 1992 2000 coinciding with a 1 1 c increase in mean summer temperature at coastal weather stations rates of retreat for the southeast and east slowed during 2006 2007 when temperatures were slightly cooler than the 2000 2006 average our work suggests that regional greenland tidewater retreat responds strongly to climate change with higher temperatures corresponding to increasing retreat and helps confirm a link between ice thickness velocity and ice front position

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

continued evolution of jakobshavn isbrae following its rapid speedup 1 several new data sets reveal that thinning and speedup of jakobshavn isbrae continue following its recent rapid increase in speed as its floating ice tongue disintegrated the present speedup rate of 5 a 1 over much of the fast moving region appears to be a diffusive response to the initial much larger speedup near the front there is strong seasonality in speed over much of the fast flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short typically 6 km floating ice tongue this modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003 analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving major calving only resumes in late winter when much of this ice clears from the fjord the collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea ice concentration in disko bay this decline may have extended the length of the calving season for several consecutive years leading to the ice tongue s collapse

recent changes in thickness of the devon island ice cap canada 1 long term rates of thickness change were derived at several spatial scales using a variety of methods for most of the devon island ice cap nunavut canada basin wide thickness change calculations were derived for the accumulation zones of all major drainage basins as the area averaged volume difference between balance and insar fluxes at the altitude of the long term equilibrium line ela thickness changes for ablation zones were derived as a function of the surface mass balance flux across the el and calving flux averaged across the ablation areas average rates of thickness change are near zero in the accumulation zones of the northern and southwestern basins but reach 0 23 0 11 m a 1 w e in the southeast basin due to dynamic thinning thickness changes were also estimated along five major outlet glaciers as a function of flux divergence and net surface mass balance and along the belcher glacier by comparing elevation values derived from 1960s aerial photography with those derived from 2005 nasa airborne topographic mapper atm surveys ice dynamics have had a significant influence on the pattern of thickness change of all outlet glaciers examined in this study volume changes derived from the basin wide values indicate a net loss of 76 8 7 km3 water equivalent from the main portion of the ice cap from 1960 to 1999 contributing 0 21 0 02 mm to global sea level over this time this value is 44 greater than previous estimates of volume change based on volume area scaling methods and surface mass balance alone

ocean regulation hypothesis for glacier dynamics in southeast greenland and implications for ice sheet mass changes synchronous acceleration and thinning of southeast se greenland glaciers during the early 2000s was the main contributor that resulted in the doubling of annual discharge from the ice sheet we show that this acceleration was followed by a synchronized and widespread slowdown of the same glaciers in many cases associated with a decrease in thinning rates and we propose that ice sheet ocean interactions are the first order regional control on these recent mass changes sea surface temperature and mooring data show that the preceding dynamic thinning coincides with a brief decline in the cold east greenland coastal current egcc and east greenland current we suggest this decline was partly induced by a reduction in ice sheet runoff which allowed warm water from the irminger current to reach the se greenland coast a restrengthening of the cold waters coincides with the glaciers subsequent slowdown we argue that this warming and subsequent cooling of the coastal waters was the cause of the glaciers dynamic changes we further suggest that the restrengthening of the egcc resulted in part from cold water input by increased glacier calving during the speedup and increased ice sheet runoff we hypothesize that the main mechanism for ice sheet mass loss in se greenland is highly sensitive to ocean conditions and is likely subject to negative feedback mechanisms copyright 2010 by the american geophysical union

recent elevation changes of svalbard glaciers derived from icesat laser altimetry abstract we have tested three methods for estimating 2003 2008 elevation changes of svalbard glaciers from multi temporal icesat laser altimetry a linear interpolation of crossover points between ascending and descending tracks b projection of near repeat tracks onto common locations using digital elevation models dems and c least squares fitting of rigid planes to segments of repeat track data assuming a constant elevation change rate the two repeat track methods yield similar results and compare well to the more accurate but sparsely sampled crossover points most glacier regions in svalbard have experienced low elevation thinning combined with high elevation balance or thickening during 2003 2008 the geodetic mass balance excluding calving front retreat or advance of svalbard s 34 600 km2 glaciers is estimated to be 4 3 1 4 gt y 1 corresponding to an area averaged water equivalent w e balance of 0 12 0 04 m w e y 1 the largest ice losses have occurred in the west and south while northeastern spitsbergen and the austfonna ice cap have gained mass winter and summer elevation changes derived from the same methods indicate that the spatial gradient in mass balance is mainly due to a larger summer season thinning in the west and the south than in the northeast our findings are consistent with in situ mass balance measurements from the same period confirming that repeat track satellite altimetry can be a valuable tool for monitoring short term elevation changes of arctic glaciers

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

changes in the dynamics of marine terminating outlet glaciers in west greenland 2000 2009 1 recent changes in the dynamics of greenland s marine terminating outlet glaciers indicate a rapid and complex response to external forcing despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along greenland s northwestern margin it is unclear whether west greenland glaciers have undergone the synchronous speed up and subsequent slow down as observed in southeastern glaciers earlier in the decade to investigate changes in west greenland outlet glacier dynamics and the potential controls behind their behavior we derive time series of front position surface elevation and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west greenland from 2000 to 2009 using these data we look for relationships between retreat thinning acceleration and geometric parameters to determine the first order controls on glacier behavior our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales though nearly all glaciers retreated and thinned over the decade we found no direct relationship between retreat acceleration and external forcing applicable to the entire region in regard to geometry we found that following retreat 1 glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and 2 thinning rates declined more quickly for glaciers with steeper slopes overall glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west greenland

hydrochemical and isotopic patterns in a calc alkaline cu and au rich arid andean basin the elqui river watershed north central chile abstract the geochemistry of surface water and groundwater from the elqui river basin north central chile was studied in spring 2007 and fall 2008 to obtain a general understanding of the factors and mechanisms controlling the water chemistry of steep rivers located in mineral rich arid to semi arid zones besides its uniform intermediate igneous lithology this basin is known for acid drainage and high as contents in the el indio au cu as district in its andean head abundant tailings deposits are present in the middle part of the basin where agricultural activities are important according to the results the chemical and isotopic composition of the elqui basin surface water and groundwater is related to uniform calc alkaline lithology and the major polluting system of the chemically reactive but closed el indio mining district the resulting compositional imprints in surface and ground water are a high so4 levels reaching about 1000 mg l in the toro river water directly draining the mining area b a major depletion of fe and pollutant metals in surface water after the confluence of the toro and la laguna rivers c similar chemical composition of surface and ground waters that differ in h and o isotopic composition reflecting the effect of differential evaporation processes downstream of the puclaro dam and d seasonal variations of fe mn cu and zn in surface water in contrast the groundwater chemistry exhibits moderate seasonal changes mainly in hco 3 content in spite of the acid drainage pollution water quality is adequate for human consumption and irrigation this is a consequence of both the dominant calc alkaline lithology and the existing arid climate resulting in neutral to moderately alkaline ph values that are responsible for the precipitation of metal hydroxides and as sorption by fe oh 3

influence of sea ice decline atmospheric warming and glacier width on marine terminating outlet glacier behavior in northwest greenland at seasonal to interannual timescales 1 discharge from marine terminating outlet glaciers represents a key component of the greenland ice sheet mass budget and observations suggest that mass loss from northwest greenland has recently accelerated despite this the factors controlling outlet glacier dynamics within this region have been comparatively poorly studied here we use remotely sensed data to investigate the influence of atmospheric oceanic and glacier specific controls on the frontal position of alison glacier ag northwest greenland and nine surrounding outlet glaciers ag retreated by 9 7 km between 2001 and 2005 following at least 25 years of minimal change results suggest that sea ice and air temperatures influence glacier frontal position at seasonal and interannual timescales however the response of individual outlet glaciers to forcing was strongly modified by factors specific to each glacier specifically variations in fjord width and terminus type overall our results underscore the need to consider these factors in order to interpret recent rapid changes and predict the dynamic response of marine terminating outlet glaciers to atmospheric and oceanic forcing

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100