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

centennial scale variability of the british ice sheet implications for climate forcing and atlantic meridional overturning circulation during the last deglaciation evidence from paleoclimatic archives suggests that earth s climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean s thermohaline circulation but the driving mechanism remains to be identified here we use multidecadal marine records of faunal oxygen isotope and sediment proxies from the northeast atlantic proximal to the western margins of the last glacial british ice sheet bis to document the coupling between ice sheet dynamics ocean circulation and insolation changes the core data reveal successions of short lived 80 100 years high amplitude ice rafted debris ird events that were initiated up to 2000 years before the deposition of detrital carbonate during heinrich events he 1 and 2 progressive disintegration of the bis 19 16 kyr before present b p occurred in response to abrupt ocean climate warmings that impinged on the northeast atlantic during the early deglaciation peak ird deposition recurs at 180 220 year intervals plausibly involving repeated breakup of glacial tidewater margins and fringing marine ice shelves the early deglaciation culminated in a major meltwater pulse at 16 3 kyr b p followed by another discharge associated with he1 some 300 years after we conclude that temperature changes related to external forcing and marine heat transport caused a rapid response of the bis and possibly other margins of the eurasian ice sheet massive but short lived meltwater surges influenced the atlantic meridional overturning circulation thereby contributing to north atlantic climate variability and bipolar climatic asymmetry

acceleration and spatial rheology of larsen c ice shelf antarctic peninsula the disintegration of several antarctic peninsula ice shelves has focused attention on the state of the larsen c ice shelf here we use satellite observations to map ice shelf speed from the years 2000 2006 and 2008 and apply inverse modeling to examine the spatial pattern of ice shelf stiffness results show that the northern half of the ice shelf has been accelerating since 2000 speeding up by 15 between 2000 and 2006 alone the distribution of ice stiffness exhibits large spatial variations that we link to tributary glacier flow and fractures our results reveal that ice down flow from promontories is consistently softer with the exception of churchill peninsula where we infer a stabilizing role for marine ice we conclude that although larsen c is not facing imminent collapse it is undergoing significant change in the form of flow acceleration that is spatially related to thinning and fracture copyright 2011 by the american geophysical union

breakup and conditions for stability of the northern larsen ice shelf antarctica the breakup of ice shelves has been widely regarded as an indicator of climate change1 with observations around the antarctic peninsula having shown a pattern of gradual retreat associated with regional atmospheric warming and increased summer melt and fracturing processes2 3 4 5 6 7 8 9 the rapid collapse of the northernmost section of the larsen ice shelf larsen a over a few days in january 1995 indicated that after retreat beyond a critical limit ice shelves may disintegrate rapidly here we use a finite element numerical model that treats ice as a continuum without fracture10 to examine the breakup history2 between 1986 and 1997 of the two northern sections of larsen ice shelf larsen a and larsen b from which we establish stability criteria for ice shelves analysis of various ice shelf configurations reveals characteristic patterns in the strain rates near the ice front which we use to describe the stability of the ice shelf on larsen a only the initial and final ice front configurations show a stable pattern larsen b at present exhibits a stable pattern but if the ice front were to retreat by a further few kilometres it too is likely to enter an irreversible retreat phase

recent sea level contributions of the antarctic and greenland ice sheets after a century of polar exploration the past decade of satellite measurements has painted an altogether new picture of how earth s ice sheets are changing as global temperatures have risen so have rates of snowfall ice melting and glacier flow although the balance between these opposing processes has varied considerably on a regional scale data show that antarctica and greenland are each losing mass overall our best estimate of their combined imbalance is about 125 gigatons per year of ice enough to raise sea level by 0 35 millimeters per year this is only a modest contribution to the present rate of sea level rise of 3 0 millimeters per year however much of the loss from antarctica and greenland is the result of the flow of ice to the ocean from ice streams and glaciers which has accelerated over the past decade in both continents there are suspected triggers for the accelerated ice discharge surface and ocean warming respectively and over the course of the 21st century these processes could rapidly counteract the snowfall gains predicted by present coupled climate models

long melt seasons on ice shelves of the antarctic peninsula an analysis using satellite based microwave emission measurements we have examined the record of melt season duration on the antarctic peninsula using two techniques for detecting the presence of a melt signal in microwave emission time series covering the period 1978 2000 we have obtained similar estimates of melt season length using the cross polarized gradient ratio xpgr technique and calibrations previously applied in greenland and a technique which detects the jump in emission caused by melt without using a sensor and frequency dependent threshold value the close correspondence between results from the two techniques on peninsula ice shelves suggests that the xpgr analysis can be used over the length of the time series the results show that the long melt seasons of 1992 93 and several later years were exceptional occurrences on the northern parts of the larsen ice shelf these melt seasons were followed by disintegration events supporting a possible cause and effect relationship

properties of a marine ice layer under the amery ice shelf east antarctica the amery ice shelf east antarctica undergoes high basal melt rates near the southern limit of its grounding line where 80 of the ice melts within 240 km of becoming afloat a considerable portion of this later refreezes downstream as marine ice this produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front we drilled through the eastern marine ice band at two locations 70 km apart on the same flowline we determine an average accretion rate of marine ice of 1 1 0 2 m a 1 at a reference density of 920 kg m 3 between borehole sites and infer a similar average rate of 1 3 0 2 m a 1 upstream the deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70 100 m above the ice shelf base below this marine close off depth borehole video imagery showed permeable ice with water filled cavities and individual ice platelets fused together while the upper marine ice was impermeable with small brine cell inclusions we infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf we estimate an average closure rate of 0 3 m a 1 between the borehole sites upstream the average closure rate is faster at 0 9 m a 1 we estimate an average porosity of the total marine ice layer of 14 20 such that the deeper ice must have even higher values high permeability implies that sea water can move relatively freely through the material and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties

ice shelf thickness over larsen c antarctica derived from satellite altimetry 1 satellite radar altimetry can be used to infer the thickness of floating ice shelves around antarctica under the assumption of hydrostatic equilibrium ice shelf thickness is an essential parameter in mass budget calculations and is one of the more poorly characterised using data from the ers 1 radar altimeter recorded in 1994 5 we calculate the thickness of larsen c ice shelf on the antarctic peninsula the surface elevation was determined to an accuracy of 2 3 4 35 m as compared to elevations from the laser altimeter onboard icesat using a model for firn depth and density we created a 1 km grid of ice shelf thickness for larsen c the accuracy of the ice thickness retrieval was determined from independent airborne radio echo sounding data the results indicated a bias of 0 22 m and random error of 36 7 m which is equivalent to 12 7 of the mean thickness for this ice shelf

grounding line migration from 1992 to 2011 on petermann glacier north west greenland we use satellite radar interferometry to investigate changes in the location of the petermann glacier grounding line between 1992 and 2011 the grounding line location was identified in 17 quadruple difference interferograms produced from european remote sensing ers 1 2 data the most extensive time series assembled at any ice stream to date there is close agreement 20 6 cm between vertical displacement of the floating ice shelf and relative tide amplitudes simulated by the arctic ocean dynamics based tide model 5 aodtm 5 arctic tide model over the 19 a period the groundling line position varied by 470 m on average with a maximum range of 7 0 km observed on the north east margin of the ice stream although the mean range 2 8 km and variability 320 m of the grounding line position is considerably lower if the unusually variable north east sector is not considered our observations demonstrate that large isolated movements cannot be precluded thus sparse temporal records should be analysed with care the grounding line migration observed on petermann glacier is not significantly correlated with time r 2 0 22 despite reported ice shelf thinning and episodes of large iceberg calving which suggests that unlike other ice streams on the south west margin of the greenland ice sheet petermann glacier is dynamically stable

the effect of foehn induced surface melt on firn evolution over the northeast antarctic peninsula surface meltwater ponding has been implicated as a major driver for recent ice shelf collapse as well as the speedup of tributary glaciers in the northeast antarctic peninsula surface melt on the nap is impacted by the strength and frequency of westerly winds which result in sporadic foehn flow we estimate changes in the frequency of foehn flow and the associated impact on snow melt density and the percolation depth of meltwater over the period 1982 2017 using a regional climate model and passive microwave data the first of two methods extracts spatial patterns of melt occurrence using empirical orthogonal function analysis the second method applies the foehn index introduced here to capture foehn occurrence over the full study domain both methods show substantial foehn induced melt late in the melt season since 2015 resulting in compounded densification of the near surface snow with potential implications for future ice shelf stability

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

dual frequency altimeter signal from envisat on the amery ice shelf in antarctica radar altimeter measurements are sensitive to dielectric and penetration properties of the sensed medium snow such that the spacecraft s altitude can be biased since 2002 relatively low frequency radar measurements over the amery ice shelf east antarctica have been acquired using the envisat dual frequency altimeter at s 3 2 ghz and ku 13 6 ghz bands which penetrate a few meters into the firn the altimeter signal is however modified in summer by the presence of snowfilled crevasses indeed the specularity of the snow surfaces in summer makes the altimetric signal sensitive mostly to nadir echoes that increases the ratio between the crevasse signal and the surrounding ice shelf signal at nadir crevasses are distinguished by differences in backscattering behavior compared with the surrounding ice shelf signal crevasses are characterized by a strong backscatter coefficient at ku band and anomalies in the s band altitude estimation these two characteristics make snowfilled crevasses detectable by the dual frequency altimeter of envisat we first retrieve the geometric properties of the crevasses using a hyperbolic shape function created by strong crevasse backscatter in the ku waveform measurements from this retrieved crevasse signal and further waveform analysis we assess the properties of the snow surface and its sub surface the crevasse due to its small size compared to the altimeter footprint is found to be an excellent target to study snow properties of the ice shelf the anomalies in the s band altitude measurements over crevasses can then be explained by the presence of a double echo in the s band waveforms this echo is attributed to a reflection at the base of the snowbridge where we see evidence of sub surface echos in the individual altimeter waveforms based on this observation a methodology is developed to estimate the thickness of the snowbridge we calculate the penetration depths in the summer snow surface of the amery at ku band that is found to be around 6 m

a decade of west antarctic subglacial lake interactions from combined icesat and cryosat 2 altimetry we use cryosat 2 interferometric satellite radar altimetry over the mercer and whillans ice streams west antarctica to derive surface elevation changes due to subglacial lake activity at monthly resolution for the period 2010 to 2013 we validate cryosat 2 elevation measurements trends and spatial patterns of change using satellite image differencing and in situ vertical movement from global positioning system gps data two subglacial lake discharge events occur in the same subglacial hydrological catchment within a 9 month period using gps measurements that are spanning the gap between the ice cloud and land elevation satellite and cryosat 2 missions we cross calibrate the two missions to establish the efficacy of cryosat 2 altimetry to measure dynamic changes on the ice sheets

ice shelf history from petrographic and foraminiferal evidence northeast antarctic peninsula a detailed record of late pleistocene deglaciation followed by mid holocene ice shelf breakup and late holocene re growth is contained in continental shelf sediments in the northern larsen area northeast antarctic peninsula the zero age of core tops is confirmed by new and published 210pb profiles and 70 accelerator mass spectrometer ams 14c dates on bulk organic carbon define sedimentation rates of 7 6 92 cm ka the varied geology in the local ice drainage basins facilitates the use of ice rafted debris ird provenance in determining the presence or absence of ice shelves all inshore cores contain an interval of non local ird in the post glacial section demonstrating widespread ice shelf breakup in the mid holocene both breakup and re growth may have taken centuries and there are no widespread debris layers associated with breakup cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied ird provenance throughout the holocene suggesting the maximum ice shelf limit may date only from the little ice age benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes nevertheless we discern a deglaciation signal in prince gustav channel of a calcareous spike in predominantly agglutinated assemblages and this is repeated at the time of mid holocene ice shelf breakup the inferred mid holocene warm period occurred later in the northern larsen area than on the west coast of the antarctic peninsula

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

numerical modelling and data assimilation of the larsen b ice shelf antarctic peninsula in this study the flow and rheology of pre collapse larsen b ice shelf are investigated by using a combination of flow modelling and data assimilation observed shelf velocities from satellite interferometry are used to constrain an ice shelf model by using a data assimilation technique based on the control method in particular the ice rheology field and the velocities at the inland shelf boundary are simultaneously optimized to get a modelled flow and stress field that is consistent with the observed flow the application to the larsen b ice shelf shows that a strong weakening of the ice in the shear zones mostly along the margins is necessary to fit the observed shelf flow this pattern of bands with weak ice is a very robust feature of the inversion whereas the ice rheology within the main shelf body is found to be not well constrained this suggests that these weak zones play a major role in the control of the flow of the larsen b ice shelf and may be the key to understanding the observed pre collapse thinning and acceleration of larsen b regarding the sensitivity of the stress field to rheology the consistency of the model with the observed flow seems crucial for any further analysis such as the application of fracture mechanics or perturbation model experiments

climatically induced retreat and collapse of northern larsen ice shelf antarctic peninsula the areal changes of the northern larsen ite shelf lis antarctic peninsula between march 1986 and march 1997 have been analyzed based on synthetic aperture radar images of the european remote sensing satellites ers 1 and ers 2 and on landsat images this analysis is complemented by data on ice motion and surface mass balance which have been obtained during several field campaigns since the early 1980s after a period of retreat coinciding with atmospheric warming and with decreasing net accumulation at the surface due to melt losses the two northernmost sections of lis disintegrated almost completely within a few days in january 1995 recent observations of the ice shelf section north of jason peninsula which is presently the northernmost section of lis show increased summer melt and intensification of the rifting processes probably causing accelerated retreat of this section in the near future the retreat and the disintegration event of lis indicate high sensitivity of ice shelves to prolonged perturbations of the mass balance

seasonally resolved diatom δ18o records from the west antarctic peninsula over the last deglaciation understanding the response of the antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st century warming a unique diatom 18o record derived from a high resolution deglacial seasonally laminated core section off the west antarctic peninsula wap is presented here by extracting and analysing single species samples from individual laminae season specific isotope records were separately generated to show changes in glacial discharge to the coastal margin during spring and summer months as well as documenting significant intra annual seasonal variability during the deglaciation with increased discharge occurring in summer relative to spring further intra seasonal variations are apparent between individual taxa linked to the environment that individual diatom species live in whilst deglacial 18o are typically lower than those for the holocene indicating glacial discharge to the core site peaked at this time inter annual and inter seasonal alternations in excess of 3 suggest significant variability in the magnitude of these inputs these deglacial variations in glacial discharge are considerably greater than those seen in the modern day water column and would have altered both the supply of oceanic warmth to the wap as well as regional marine atmospheric interactions in constraining changes in glacial discharge over the last deglaciation the records provide a future framework for investigating links between annually resolved records of glacial dynamics and ocean climate variability along the wap

the retreat of jones ice shelf antarctic peninsula in recent decades several ice shelves along the antarctic peninsula have diminished in size as a result of climate warming using aerial photographic satellite and survey data we document a similar retreat of jones ice shelf which was another small ice shelf on the west coast of the antarctic peninsula this ice shelf was roughly stable between 1947 and 1969 but in the early 1970s it began to retreat and had completely disappeared by early 2003 jones ice shelf has two ice fronts only a few kilometres apart and its retreat provides a unique opportunity to examine how different ice fronts retreat when subjected to similar climate forcing we mapped the retreat of both the east and west ice fronts of jones ice shelf and found that although individual episodes of retreat may be related to particularly warm summers the overall progress of retreat of the two ice fronts has been rather different this suggests that in this case the course of retreat is controlled by the geometry of the embayment and location of pinning points as well as climatic events

understanding antarctic peninsula precipitation distribution and variability using a numerical weather prediction model daily precipitation fields and annual means from the european centre for medium range weather forecasts re analysis exercise are used to examine the distribution and variability of precipitation across the antarctic peninsula the annual mean precipitation field from the model agrees well with the available ice core data and suggests that the maximum accumulation for the area is on the western side of the barrier at about the 200 m level where the annual total is close to 1 3 m w e the peninsula is shown to be a very effective barrier to the zonal movement of precipitati ng weather systems which results in quite different atmospheric flow regimes being responsible or significant precipitation events on either side of the divide frontal depressions are the primary source of large daily snowfall totals on both sides of the peninsula on the southern coast of the bellingshausen sea major snowfall events are often linked to strong northerly flow when the atmospheric circulation is blocked predominantly northerly flow is also responsible for significant snowfall on the ronne ice shelf which often occurs in association with lee cyclogenesis events to the east of the peninsula

an observationally validated theory of viscous flow dynamics at the ice shelf calving front an analytical theory is developed for ice flow velocity in a boundary layer couplet at the calving front the theory has simple quantitative characteristics that relate ice front velocity to thickness strain rate and shelf width matching one set of empirically derived relationships alley and others 2008 and implying that these relationships predict ice velocity rather than calving rate the two boundary layers are where longitudinal and transverse flow fields change from the interior flow to patterns consistent with the calving front stress condition numerical simulations confirm the analytical theory the quantitative predictions of the theory have low sensitivity to unmeasured parameters and to shelf plan aspect ratio while its robustness arises from its dependence on the scale invariance of the governing equations the theory provides insights into calving the stability of ice shelf calving fronts the stability of the grounding line of laterally resisted ice streams and also suggests that the calving front is an instructive dynamical analogue to the grounding line

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

marine ice in larsen ice shelf 1 it is argued that larsen ice shelf contains marine ice formed by oceanic freezing and other mechanisms missing basal returns in airborne radar soundings and observations of a smooth and healed surface coincide downstream of regions where an ocean model predicts freezing visible imagery suggests that marine ice currently stabilizes larsen c ice shelf and implicates failure of marine flow bands in the 2002 larsen b ice shelf collapse ocean modeling indicates that any regime change towards the incursion of warmer modified weddell deep water into the larsen c cavity could curtail basal freezing and its stabilizing influence

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

strong surface melting preceded collapse of antarctic peninsula ice shelf 1 during the austral summer of 2001 02 melting at the surface of larsen ice shelf in the antarctic peninsula was three times greater than the average of five previous summers this exceptional melt event lasted for three months and was followed by the collapse of larsen b ice shelf during which 3 200 km2 of ice shelf surface was lost the strong melting was caused by a persistent atmospheric circulation anomaly which depleted sea ice concentrations in front of larsen ice shelf and transported warm air to the ice shelf throughout the 2001 02 summer this supports the theory that large meltwater fluxes accelerate the retreat of antarctic peninsula ice shelves

comment on catastrophic ice shelf breakup as the source of heinrich event icebergs by c l hulbe et al hulbe et al 2004 argue that the original binge purge model of their coauthor macayeal 1993a 1993b is not appropriate for heinrich events but that a new ice shelf collapse mechanism may work we believe that thenew collapse mechanism disagrees with important dataand that macayeal s original model remains viable afterappropriate modifications we have enjoyed a fascinatingdiscussion with hulbe et al on this topic which isstimulating our thinking and research and we presentsome of the arguments here for a wider audience

glacier acceleration and thinning after ice shelf collapse in the larsen b embayment antarctica 1 ice velocities derived from five landsat 7 images acquired between january 2000 and february 2003 show a two to six fold increase in centerline speed of four glaciers flowing into the now collapsed section of the larsen b ice shelf satellite laser altimetry from icesat indicates the surface of hektoria glacier lowered by up to 38 6 m in a six month period beginning one year after the break up in march 2002 smaller elevation losses are observed for crane and jorum glaciers over a later 5 month period two glaciers south of the collapse area flask and leppard show little change in speed or elevation seasonal variations in speed preceding the large post collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics

decadal freshening of the antarctic bottom water exported from the weddell sea recent decadal changes in southern hemisphere climate have driven strong responses from the cryosphere concurrently there has been a marked freshening of the shelf and bottom waters across a wide sector of the southern ocean hypothesised to be caused by accelerated glacial melt in response to a greater flux of warm waters from the antarctic circumpolar current onto the shelves of west antarctica however the circumpolar pattern of changes has been incomplete no decadal freshening in the deep layers of the atlantic sector had been observed in this study we document a significant freshening of the antarctic bottom water exported from the weddell sea which is the source for the abyssal layer of the atlantic overturning circulation and we trace its possible origin to atmospheric forced changes in the ice shelves and sea ice on the eastern flank of the antarctic peninsula that include an anthropogenic component these findings suggest that the expansive and relatively cool weddell gyre does not insulate the bottom water formation regions in the atlantic sector from the ongoing changes in climatic forcing over the antarctic region

observations of change in the southern ocean the southern ocean has been in a state of disequilibrium with its atmosphere and cryosphere during recent decades ocean station and drifting float observations have revealed rising temperatures in

evidence of deep and bottom water formation in the western weddell sea abstract during ice station polarstern ispol r v polarstern cruise ant xxii 2 november 2004 january 2005 hydrographic and tracer observations were obtained in the western weddell sea while drifting closely in front of the larsen ice shelf these observations indicate recently formed weddell sea bottom water which contains significant contributions of glacial melt water in its upper part and high salinity shelf water in its lower layer the formation of this bottom water cannot be related to the known sources in the south the filchner ronne ice shelf we show that this bottom water is formed in the western weddell sea most likely in interaction with the larsen c ice shelf by applying an optimum multiparameter analysis omp using temperature salinity and noble gas observations helium isotopes and neon we obtained mean glacial melt water fractions of about 0 1 in the bottom water on sections across the weddell gyre farther north melt water fractions are still on the order of 0 04 using chlorofluorocarbons cfcs as age tracers we deduced a mean transit time between the western source and the bottom water found on the slope toward the north 9 3 years this transit time is larger and the inferred transport rate is small in comparison to previous findings but accounting for a loss of the initially formed bottom water volume due to mixing and renewal of weddell sea deep water a formation rate of 1 1 0 5 sv in the western weddell sea is plausible this implies a basal melt rate of 35 19 gt year or 0 35 0 19 m year at the larsen ice shelf this bottom water is shallow enough that it could leave the weddell basin through the gaps in the south scotia ridge to supply antarctic bottom water these findings emphasize the role of the western weddell sea in deep and bottom water formation particularly in view of changing environmental conditions due to climate variability which might induce enhanced melting or even decay of ice shelves

trends and connections across the antarctic cryosphere satellite observations have transformed our understanding of the antarctic cryosphere the continent holds the vast majority of earth s fresh water and blankets swathes of the southern hemisphere in ice reductions in the thickness and extent of floating ice shelves have disturbed inland ice triggering retreat acceleration and drawdown of marine terminating glaciers the waxing and waning of antarctic sea ice is one of earth s greatest seasonal habitat changes and although the maximum extent of the sea ice has increased modestly since the 1970s inter annual variability is high and there is evidence of longer term decline in its extent this paper discusses how antarctic ice has changed over recent decades and how these changes have been recorded in satellite observations

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

modeling ice dynamic contributions to sea level rise from the antarctic peninsula the future ice dynamical contribution to sea level rise slr from 199 ice shelf nourishing drainage basins of the antarctic peninsula ice sheet is simulated using the british antarctic survey antarctic peninsula ice sheet model simulations of the grounded ice sheet include response to ice shelf collapse estimated by tracking thermal ice shelf viability limits in 14 intergovernmental panel on climate change global climate models ensemble temperature projections grounding line retreat in response to ice shelf collapse is parameterized with a new multivariate linear regression model utilizing a range of glaciological and geometric predictor variables multimodel means project slr up to 9 4 mm sea level equivalent sle by 2200 and up to 19 mm sle by 2300 rates of slr from individual drainage basins throughout the peninsula are similar to 2100 yet diverge between 2100 and 2300 due to individual basin characteristics major contributors to slr are the outlet glaciers feeding southern george vi ice shelf accounting for 75 of total slr in some model runs ice sheet thinning induced by ice shelf removal is large up to 500 m especially in palmer land in the southern antarctic peninsula and may propagate as far as 135 km inland these results emphasize the importance of the ice dynamical contribution to future sea level of the apis on decadal to centennial timescales

from ice shelf tributary to tidewater glacier continued rapid recession acceleration and thinning of rohss glacier following the 1995 collapse of the prince gustav ice shelf antarctic peninsula glasser n f scambos t a bohlander j truffer m pettit e davies b j 2011 journal of glaciology 57 203 397 406

labile organic carbon dynamics in continental shelf sediments after the recent collapse of the larsen ice shelves off the eastern antarctic peninsula a radiochemical approach abstract labile organic carbon loc dynamics i e of recently produced planktonic material and sediment dynamics were studied in the seabed using naturally occurring 14corg and 210pb measurements in the region where the larsen ice shelves a and b were floating almost two decades ago a non steady state diagenetic model was used to estimate sediment mixing coefficients as well as loc fluxes to the seabed and loc turnover times i e mean residence times in a suite of 14 sediment cores from the continental shelf including a glacial trough at four of the stations cores were collected during 2007 and 2011 cruises enabling a time series approach for understanding the evolution of sedimentary processes and loc dynamics in the deposits below a collapsed ice shelf sediment mixing coefficients based on non steady state 210pb profiles varied between 0 01 cm2 y 1 and 1 6 cm2 y 1 in these post ice shelf sediments these values were similar to those found in polar deep sea environments where sedimentary conditions are less dynamic than in shallower provinces loc whose abundance decreased uniformly with depth was detected to depths ranging from 2 to 16 cm with loc seabed inventories varying from 1 5 to 22 mg loc cm 2 excess 210pb and loc fluxes were relatively uniform across the study area suggesting that similar particle fluxes have taken place within the larsen system since the disintegration of the various ice shelves the loc mean residence time at the different stations varied from 3 y to 60 y the 14corg approach calculating loc content based on a two end member model with planktonic 14corg as the labile carbon end member most closely correlated with the lipid content of the sediment which has been considered one of the best descriptors of reactive organic matter readily available to benthic consumers we suggest that the irregular combination of sea ice coverage organic matter production and supply to the sea floor introduce scatter in the determination of sediment and loc dynamics such that short term temporal

2001 2009 elevation and mass losses in the larsen a and b embayments antarctic peninsula we investigate the elevation and mass balance response of tributary glaciers following the loss of the larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively our study uses modis imagery to track ice extent and aster and spot5 digital elevation models dems plus atm and icesat laser altimetry to track elevation changes spanning the period 2001 09 the measured larsen b tributary glaciers hektoria green evans punchbowl jorum and crane lost up to 160 m in elevation during 2001 06 and thinning continued into 2009 elevation changes were small for the more southerly flask and leppard glaciers which are still constrained by a larsen b ice shelf remnant in the northern embayment continued thinning of 3 m a 1 on drygalski glacier 14 years after the larsen a ice shelf disintegrated suggests that mass losses for the exposed larsen b tributaries will continue for years into the future grounded ice volume losses exceed 13 km 3 for crane glacier and 30 km 3 for the hektoria green evans glaciers the combined mean loss rate for 2001 06 is at least 11 2 gt a 1 our values differ significantly from published mass budget based estimates for these embayments but are a reasonable fraction of grace derived rates for the region 40 gt a 1

antarctic elevation change from 1992 to 1996 satellite radar altimeter measurements show that the average elevation of the antarctic ice sheet interior fell by 0 9 0 5 centimeters per year from 1992 to 1996 if the variability of snowfall observed in antarctic ice cores is allowed for the mass imbalance of the interior this century is only 0 06 0 08 of the mean mass accumulation rate

modeling ice ocean interaction in ice shelf crevasses ocean freezing within ice shelf basal crevasses could potentially act as a stabilizing influence on ice shelves however ice ocean interaction and ocean dynamics within these crevasses are as yet poorly understood to this end an idealized 2 d model of an ice shelf basal crevasse has been developed using fluidity a finite element ocean model using an unstructured mesh a simple model of frazil ice formation and deposition has been incorporated into fluidity to better represent the freezing process model results show two different flow regimes dependent on the amount of freezing in the crevasse one driven by freezing at the top of the crevasse and the other by the ingress of meltwater from outside the crevasse in the first freezing at the top of the crevasse leads to the formation of an unstable overturning circulation due to the rejection of dense salty water in the second a buoyant layer is formed along the sides and roof of the crevasse stratifying the water column frazil ice precipitation is found to be the dominant freezing process at the top of the basal crevasse in the freeze driven case with direct freezing being dominant in the melt driven case in both cases melting occurs lower down on the walls of the crevasse due to the strong overturning circulation the freezing in ice shelf crevasses and rifts is found to be highly dependent upon ocean temperature providing a stabilizing influence on ice shelves underlain by cold waters that is not present elsewhere

ice shelf tidal motion derived from ers altimetry 1 ocean tides beneath floating ice shelves can affect heat and water circulations within the subshelf cavity which may influence patterns of basal melting accurate tidal predictions are essential to eliminate vertical tide motions when mapping the flow speeds and thickness changes of floating ice global ocean tide solutions are typically accurate to 2 3 cm in amplitude however their coarse resolution limits their utility in coastal regions moreover the absence of satellite and extensive gauge station data in the polar regions has resulted in significant differences between recent tide model solutions around the antarctic continent we use 9 years of high resolution european remote sensing ers satellite radar altimeter range measurements and a modified form of the orthotide method to generate tidal solutions for a series of ice shelves around the antarctic peninsula we compare our tidal solution at george vi ice shelf on the western coast of the antarctic peninsula to direct measurements from british antarctic survey tide gauge records and contrast the results with solutions from the fes99 and kantha2 0 global and the cats01 02 antarctic ocean tide models the average root mean square vector difference between the tide gauge and tide model predictions of amplitude and phase was 10 9 17 1 4 2 and 15 4 cm for the ers ice shelf kantha2 0 cats01 02 and fes99 models respectively tidal predictions derived from the ers ice shelf model are closer to the tide gauge recordings than those of the global models and the inclusion of ers altimeter data may lead to improved global model performance

rapid response of modern day ice sheets to external forcing abstract the great ice sheets covering antarctica and greenland were traditionally believed to take thousands of years to respond to external forcing recent observations suggest however that major changes in the dynamics of parts of the ice sheets are taking place over timescales of years these changes were not predicted by numerical models and the underlying cause s remains uncertain it has been suggested that regional oceanic and or atmospheric warming are responsible but separating the influence and importance of these two forcings has not been possible in most cases the role of atmospheric versus oceanic control remains uncertain here we review the observations of rapid change and discuss the possible mechanisms in the light of advances in numerical modelling and our understanding of the processes that may be responsible

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

rapid bottom melting widespread near antarctic ice sheet grounding lines as continental ice from antarctica reaches the grounding line and begins to float its underside melts into the ocean results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed the melting rate is positively correlated with thermal forcing increasing by 1 meter per year for each 0 1 c rise in ocean temperature where deep water has direct access to grounding lines glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature

the effects of rotation and ice shelf topography on frazil laden ice shelf water plumes a model of the dynamics and thermodynamics of a plume of meltwater at the base of an ice shelf is presented such ice shelf water plumes may become supercooled and deposit marine ice if they rise because of the pressure decrease in the in situ freezing temperature so the model incorporates both melting and freezing at the ice shelf base and a multiple size class model of frazil ice dynamics and deposition the plume is considered in two horizontal dimensions so the influence of coriolis forces is incorporated for the first time it is found that rotation is extremely influential with simulated plumes flowing in near geostrophy because of the low friction at a smooth ice shelf base as a result an ice shelf water plume will only rise and become supercooled and thus deposit marine ice if it is constrained to flow upslope by topography this result agrees with the observed distribution of marine ice under filchner ronne ice shelf antarctica in addition it is found that the model only produces reasonable marine ice formation rates when an accurate ice shelf draft is used implying that the characteristics of real ice shelf water plumes can only be captured using models with both rotation and a realistic topography

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

icesat profiles of tabular iceberg margins and iceberg breakup at low latitudes 1 icesat elevation profiles of tabular iceberg margins and the ronne ice shelf edge reveal shapes indicative of two types of bending forces icebergs and shelf fronts in sea ice covered areas have broad 1000 m wide rounded 0 6 m high berms and outer edges that slope down several meters toward the water bergs in warmer water have 2 to 5m ramparts with 1500 m wide edge parallel moats inboard of the edge this latter pattern was first revealed in images from international space station iss showing edge parallel melt ponds on one iceberg just prior to its disintegration model results indicate the patterns are caused by hydrostatic and lithostatic forces acting on the ice face berm profiles arise from differences between ice and water pressure along the face rampart moat profiles result from waterline erosion creating a submerged bench of ice that lifts the ice edge we use the results to discuss iceberg breakup at low latitudes

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

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

inland thinning of pine island glacier west antarctica the pine island glacier pig transports 69 cubic kilometers of ice each year from 10 of the west antarctic ice sheet wais it is possible that a retreat of the pig may accelerate ice discharge from the wais interior satellite altimetry and interferometry show that the grounded pig thinned by up to 1 6 meters per year between 1992 and 1999 affecting 150 kilometers of the inland glacier the thinning cannot be explained by short term variability in accumulation and must result from glacier dynamics

summertime water masses off the northern larsen c ice shelf antarctica 1 we report on oceanographic observations made at the northern end of larsen c ice shelf in the western weddell sea it appears that the larsen c continental shelf is flushed not by high salinity shelf water from the southern continental shelf but by modified weddell deep water mwdw flowing across the shelf break mwdw is observed at the ice front having tracked west along the northward facing slopes of depressions that reach to the shelf break ice shelf water observed near the ice front is not however derived from mwdw directly but from mwdw pre conditioned by winter cooling and by salinification from sea ice production if the ice shelf base generally is being melted only by pre conditioned mwdw then contrary to recent suggestions changes in the temperature of the deep weddell sea are unlikely to have a major impact on melt rates at the base of larsen c ice shelf

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

improving antarctic tide models by assimilation of icesat laser altimetry over ice shelves 1 assimilation of laser altimeter data from the ice cloud and land elevation satellite icesat significantly improves the accuracy of ocean tide models for the ross ice shelf ris for the most energetic tidal harmonic k1 assimilation reduces the root mean square error rmse between the model and a set of 16 independent tide records on and near the ris from 6 0 to 2 8 cm and the combined rmse for the six most energetic tidal harmonics from 7 7 to 5 4 cm when only the six most recent and highest quality tide records are considered the combined rmse is 4 8 cm this value is close to the uncertainty expected from tidal analyses of the short 1 2 month validation records indicating that assessing further improvements in tide model accuracy will require development of a higher quality validation data set

the cavity under the amery ice shelf east antarctica ocean circulation under ice shelves and associated rates of melting and freezing are strongly influenced by the shape of the sub ice shelf cavity we have refined an existing method and used additional in situ measurements to estimate the cavity shape under the amery ice shelf east antarctica a finite element hydrodynamic ocean tide model was used to simulate the major tidal constituents for a range of different sub amery ice shelf cavity water column thicknesses the data are adjusted in the largely unsurveyed southern region of the ice shelf cavity by comparing the complex error between simulated tides and in situ tides derived from gps observations we show a significant improvement in the simulated tides with a combined complex error of 1 8 cm in comparison with past studies which show a complex error of 5 3 cm our bathymetry incorporates ice draft data at the grounding line and seismic surveys which have provided a considerable amount of new data this technique has particular application when the water column beneath ice shelves is inaccessible and in situ gps data are available

the melting of floating ice raises the ocean level summary it is shown that the melting of ice floating on the ocean will introduce a volume of water about 2 6 per cent greater than that of the originally displaced sea water the melting of floating ice in a global warming will cause the ocean to rise if all the extant sea ice and floating shelf ice melted the global sea level would rise about 4 cm the sliding of grounded ice into the sea however produces a mean water level rise in two parts some of the rise is delayed the first part while the ice floats is equal to the volume of displaced sea water the second part equal to 2 6 per cent of the first is contributed as it melts these effects result from the difference in volume of equal weights of fresh and salt water this component of sea rise is apparently unrecognized in the literature to date although it can be interpreted as a form of halosteric sea level change by regarding the displaced salt water and the meltwater even before melting as a unit although salinity changes are known to affect sea level all existing analyses omit our calculated volume change we present a protocol that can be used to calculate global sea level rise on the basis of the addition of meltwater from grounded and floating ice of course thermosteric volume change must be added

ice sheet mass balance assessment attribution and prognosis contrary to prior expectations that warming would cause mass addition averaged over the greenland and antarctic ice sheets and over the next century the ice sheets appear to be losing mass at least partly in response to recent warming with warming projected for the future additional mass loss appears more likely than not

geometry motion and mass balance of dyer plateau antarctica geodetic surveying and ground based radar profiling were used to determine geometry and surface motion of the ice sheet on the dyer plateau antarctica in the vicinity of an ice core site on a local dome vertical strain measurements in the core hole constrain the depth profile of vertical velocity these geophysical measurements are used to analyze the profiles of density and annual layer thickness measured on the ice core to estimate the current mass balance of the ice column and the past history of accumulation rate consideration of horizontal and vertical mass flow divergence shows that the profiles of density and vertical velocity are not fully consistent with steady state mean density of the firn layer appears to be increasing which leads to the deduction of a small rate of mass increase 0 02 m a 1 ice equivalent thickness over the last 200a there has been a gradual increase in accumulation rate from about 0 46 m a 1 to 0 54 m a 1 ice equivalent thickness in recent time

recent loss of floating ice and the consequent sea level contribution we combine new and published satellite observations and the results of a coupled ice ocean model to provide the first estimate of changes in the quantity of ice floating in the global oceans and the consequent sea level contribution rapid losses of arctic sea ice and small antarctic ice shelves are partially offset by thickening of antarctic sea ice and large antarctic ice shelves altogether 746 127 km 3 yr 1 of floating ice was lost between 1994 and 2004 a value that exceeds considerably the reduction in grounded ice over the same period although the losses are equivalent to a small 49 8 m yr 1 rise in mean sea level there may be large regional variations in the degree of ocean freshening and mixing ice shelves at the antarctic peninsula and in the amundsen sea for example have lost 481 38 km 3 yr 1

biological and physical processes structuring deep sea surface sediments in the scotia and weddell seas antarctica abstract five deep sea transects were sampled in the scotia sea and weddell sea from the drake passage to the south sandwich islands antarctica with depths ranging from 767 to 6333 m a combination of sediment surface and sediment profile imaging was used to characterize the physical and biological processes structuring the benthic boundary layer and surface sediments from the sediment water interface swi to as much as 17 cm below the swi the factors structuring surface sediments were related to distance from antarctic landmasses which are the main source of sediment and deposition of water column or sea ice primary productivity stations near the continental shelf and slope tended to have coarse granule to cobble sediments derived from melting sea ice input of fine sediments was estimated to be low at these stations because many of the coarse sediment grains appeared to be manganese coated at the deepest stations in the ona basin south shetland trench and south sandwich trench sediment appeared to be primarily hemipelagite silt clay but were varved with as many as four distinct color laminations these layers varied in thickness fom 0 6 to 10 6 cm and may have been related to turbidite flows while geology and physical processes that deliver sediment to the bottom were the primary factors dictating substratum characteristics biological processes were to varying degrees important in structuring the swi and sediment fabric biological processes primarily in the form of bioturbation were most prominent at fine grained stations but were also obvious even on rock substratum on top of the shackleton fracture zone there were gradients between the degree of bioturbation and type of biogenic structure present with depth at depths 75 of the sediment bioturbated the structure of surficial sediments at 5 of 13 stations at depths 2000 m biological processes were overall less diverse but dominated at 8 of 11 stations

variable basal melt rates of antarctic peninsula ice shelves 1994 2016 we have constructed 23 year 1994 2016 time series of antarctic peninsula ap ice shelf height change using data from four satellite radar altimeters ers 1 ers 2 envisat and cryosat 2 combining these time series with output from atmospheric and firn models we partitioned the total height change signal into contributions from varying surface mass balance firn state ice dynamics and basal mass balance on the bellingshausen coast of the ap ice shelves lost 84 34 gt a 1 to basal melting compared to contributions of 50 7 gt a 1 from surface mass balance and ice dynamics net basal melting on the weddell coast was 51 71 gt a 1 recent changes in ice shelf height include increases over major ap ice shelves driven by changes in firn state basal melt rates near bawden ice rise a major pinning point of larsen c ice shelf showed large increases potentially leading to substantial loss of buttressing if sustained

tidal movement of nioghalvfjerdsfjorden glacier northeast greenland observations and modelling nioghalvfjerdsfjorden glacier is a 60 km long and 20 km wide floating outlet glacier located at 79 30 n 22 w draining a large area of the northeast greenland ice sheet climate mass balance and dynamics studies were carried out on the glacier in three field seasons in 1996 1997 and 1998 as part of this work tidal movement observations were carried out by simultaneous differential global positioning system gps measurements at several locations distributed on the glacier surface the gps observations were performed continously over several tidal cycles at the same time tiltmeter measurements were carried out in the grounding zones along the glaciers margins and upstream where the glacier leaves the main ice sheet a tide gauge installed in the sea immediately in front of the glacier front recorded the tide in the open sea during the field seasons the observations show that the main part of the glacier tongue responds as a freely floating plate to the phase and amplitude of the local tide in the sea however kilometre wide flexure zones exist along the marginal and upstream grounding lines attempts to model the observed tidal defectionand tilt patterns in the flexure zone by elastic beam theory are unsuccessful in contrast to previous findings by other investigators the strongest disagreement between our measurements and results derived from elastic beam theory is a significant variation of the phase of the tidal records with distance from the grounding line most clearly displayed by the tilt records we suggest that the viscous properties of glacier ice must be taken into account and consequently that a viscoelastic beam model must be used to adequately describe tidal bending of floating glaciers

melting and freezing beneath filchner ronne ice shelf antarctica 1 we use remote sensing data sets to evaluate the spatial distribution of melt beneath the filchner ronne ice shelf fris the net melt rate of 83 4 24 8 gtons yr is 2 5 5 times lower than previous glaciological estimates but is similar to existing oceanographic estimates the spatial distribution however differs significantly from standard conceptual and numerical models in which most melt occurs along the grounding lines our results suggest most grounding line melt is refrozen while the dominant ice shelf water isw source is melting near the ice shelf front probably associated with tidal action this suggests that changes in ice shelf extent can impact isw production rates in the weddell sea

future sea level rise from tidewater and ice shelf tributary glaciers of the antarctic peninsula abstract iceberg calving and increased ice discharge from ice shelf tributary glaciers contribute significant amounts to global sea level rise slr from the antarctic peninsula ap owing to ongoing ice dynamical changes collapse of buttressing ice shelves these contributions have accelerated in recent years as the ap is one of the fastest warming regions on earth further ice dynamical adjustment increased ice discharge is expected over the next two centuries in this paper the first regional slr projection of the ap from both iceberg calving and increased ice discharge from ice shelf tributary glaciers in response to ice shelf collapse is presented an ice sheet model forced by temperature output from 13 global climate models gcms in response to the high greenhouse gas emission scenario rcp8 5 projects ap contribution to slr of 28 16 to 32 16 mm by 2300 partitioned approximately equally between contributions from tidewater glaciers and ice shelf tributary glaciers in the rcp4 5 scenario sea level rise projections to 2300 are dominated by tidewater glaciers 8 18 mm in this cooler scenario 2 4 1 mm is added to global sea levels from ice shelf tributary drainage basins as fewer ice shelves are projected to collapse sea level projections from ice shelf tributary glaciers are dominated by drainage basins feeding george vi ice shelf accounting for 70 of simulated slr combined total ice dynamical slr projections to 2300 from the ap vary between 11 2 and 32 16 mm sea level equivalent sle depending on the emission scenario used these simulations suggest that omission of tidewater glaciers could lead to a substantial underestimation of the ice sheet s contribution to regional slr

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

revealing the early ice flow patterns with historical declassified intelligence satellite photographs back to 1960s the reconnaissance argon satellites collected the earliest images of antarctica from space dating back to the 1960s providing valuable historical baseline information for studying polar ice sheets those photographs are underutilized for ice motion mapping due to lack of sufficient ground controls for image orthorectification in this study we orthorectified the argon photographs by fully exploiting the metric qualities of worldview satellite images very high spatial resolution and precise geolocation through a case study over larsen ice shelf we demonstrated that the camera model with bundle block adjustment can achieve geolocation accuracy of better than the nominal resolution 140 m for orthorectifying argon images with worldview imagery as ground control source this allowed us to extend the ice velocity records of larsen ice shelf back into 1960s 1970s for the first time the retrospective analysis revealed that acceleration of the collapsed larsen b occurred much earlier than previously thought

ice loss processes in the seal nunataks ice shelf region from satellite altimetry and imagery the seal nunataks ice shelf snis 743 km 2 in 2013 is an unofficial name for a remnant area between the former larsen a and larsen b ice shelves off the northeastern antarctic peninsula analyses using landsat 7 etm and terra aster images from 2001 to 13 and icesat altimetry from 2003 to 09 show it has retreated and thinned following the larsen a 1995 and larsen b 2002 disintegrations despite some regional cooling and more fast ice since 2008 snis continues to lose ice along its margins and may be losing contact with some nunataks detailed analysis of data from four icesat tracks indicates that ice shelf thinning rates range between 1 9 and 2 7 m a 1 and generally increase from west to east an icesat repeat track crossing the adjacent robertson island shows a mean elevation loss of 1 8 m a 1 two tracks crossing the snis s remaining tributary rogosh glacier show sub meter elevation losses comparing shelf remnant and grounded ice thinning rates implies that basal ocean melting augments snis thinning by 1 m a 1 a rate that is consistent with other estimates of ocean driven shelf thinning in the region

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