antarctic ice sheet melting in the southeast pacific the first oceanographic measurements across a deep channel beneath the calving front of pine island glacier reveal a sub ice circulation driven by basal melting of 10 12 m yr 1 a salt box model described here gives a melt rate similar to that of ice balance and numerical models 5 50 times higher than averages for the george vi and ross ice shelves melting is fueled by relatively warm circumpolar deep water that floods the deep floor of the amundsen and bellingshausen sea continental shelves reaching the deep draft of this floating glacier a revised melt rate for ice shelves in the southeast pacific sector raises circumpolar ice shelf melting to 756 gt yr 1 given prior estimates of surface accumulation and iceberg calving this suggests that the antarctic ice sheet is currently losing mass to the ocean

volume loss from antarctic ice shelves is accelerating the floating ice shelves surrounding the antarctic ice sheet restrain the grounded ice sheet flow thinning of an ice shelf reduces this effect leading to an increase in ice discharge to the ocean using 18 years of continuous satellite radar altimeter observations we have computed decadal scale changes in ice shelf thickness around the antarctic continent overall average ice shelf volume change accelerated from negligible loss at 25 64 cubic kilometers per year for 1994 2003 to rapid loss of 310 74 cubic kilometers per year for 2003 2012 west antarctic losses increased by 70 in the past decade and earlier volume gain by east antarctic ice shelves ceased in the amundsen and bellingshausen regions some ice shelves have lost up to 18 of their thickness in less than two decades

sustained increase in ice discharge from the amundsen sea embayment west antarctica from 1973 to 2013 we combine measurements of ice velocity from landsat feature tracking and satellite radar interferometry and ice thickness from existing compilations to document 41 years of mass flux from the amundsen sea embayment ase of west antarctica the total ice discharge has increased by 77 since 1973 half of the increase occurred between 2003 and 2009 grounding line ice speeds of pine island glacier stabilized between 2009 and 2013 following a decade of rapid acceleration but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes flow speeds across thwaites glacier increased rapidly after 2006 following a decade of near stability leading to a 33 increase in flux between 2006 and 2013 haynes smith pope and kohler glaciers all accelerated during the entire study period the sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of antarctica key points sustained ase mass flux increase 77 since 1973 thwaites accelerated by 33 during the last 6 years speed changes are pervasive and rapid major implications for ice flow modeling 2014 american geophysical union all rights reserved

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

predicting the morphodynamic response of silt laden rivers to water and sediment release from reservoirs lower yellow river china the high sediment load of the yellow river results in rapid infilling of its reservoirs when sediment is not regularly flushed simultaneously the downstream reaches of the yellow river experience extremely high siltation rates which are reduced when sediment is retained in its reservoirs to minimize siltation in the reservoirs and the downstream river bed water and sediment are released from the reservoir in a controlled way through flushing experiments in this paper we analyze the effect of such a flushing event on the downstream river bed through data analysis and numerical modeling sedimentation may be minimized by relating the amount of sediment released from the reservoir to the sediment available for release through operational monitoring and by releasing relatively clear water after turbid water despite this flushing of sediment the reservoir will eventually fill up and more sediment released again into the lower yellow river the change in discharge magnitude and frequency brought about by the reservoir will then probably result in increased siltation rates in the lower yellow river compared to the predam situation

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

distinct patterns of seasonal greenland glacier velocity predicting greenland ice sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms we present a 5 year record of seasonal velocity measurements for 55 marine terminating glaciers distributed around the ice sheet margin along with ice front position and runoff data sets for each glacier among glaciers with substantial speed variations we find three distinct seasonal velocity patterns one pattern indicates relatively high glacier sensitivity to ice front position the other two patterns are more prevalent and appear to be meltwater controlled these patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient distributed hydrologic networks to efficient channelized drainage while others do not the difference may be determined by meltwater availability which in some regions may be influenced by perennial firn aquifers our results highlight the need to understand subglacial meltwater availability on an ice sheet wide scale to predict future dynamic changes

impact of atmospheric forcing on antarctic continental shelf water masses the antarctic continental shelf seas feature a bimodal distribution of water mass temperature with the amundsen and bellingshausen seas flooded by circumpolar deep water that is several degrees celsius warmer than the cold shelf waters prevalent in the weddell and ross seas this bimodal distribution could be caused by differences in atmospheric forcing ocean dynamics ocean and ice feedbacks or some combination of these factors in this study a highly simplified coupled sea ice mixed layer model is developed to investigate the physical processes controlling this situation under regional atmospheric forcings and parameter choices the 10 yr simulations demonstrate a complete destratification of the weddell sea water column in winter forming cold relatively saline shelf waters while the amundsen sea winter mixed layer remains shallower allowing a layer of deep warm water to persist applying the weddell atmospheric forcing to the amundsen sea model destratifies the water column after two years and applying the amundsen forcing to the weddell sea model results in a shallower steady state winter mixed layer that no longer destratifies the water column this suggests that the regional difference in atmospheric forcings alone is sufficient to account for the bimodal distribution in antarctic shelf sea temperatures the model prediction of mixed layer depth is most sensitive to the air temperature forcing but a switch in all forcings is required to prevent destratification of the weddell sea water column

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

responses of basal melting of antarctic ice shelves to the climatic forcing of the last glacial maximum and co2 doubling abstractbasal melting of the antarctic ice shelves is an important factor in determining the stability of the antarctic ice sheet this study used the climatic outputs of an atmosphere ocean general circulation model to force a circumpolar ocean model that resolves ice shelf cavity circulation to investigate the response of antarctic ice shelf melting to different climatic conditions i e to a doubling of co2 and to the last glacial maximum conditions sensitivity experiments were also conducted to investigate the roles of both surface atmospheric change and changes of oceanic lateral boundary conditions it was found that the rate of change of basal melt due to climate warming is much greater by an order of magnitude than that due to cooling this is mainly because the intrusion of warm water onto the continental shelves linked to sea ice production and climate change is crucial in determining the basal melt rate of many ice shelves sensitivity experiments showed that changes of atmospheric heat

climate and surface mass balance of coastal west antarctica resolved by regional climate modelling west antarctic climate and surface mass balance smb records are sparse to fill this gap regional atmospheric climate modelling is useful providing that such models are employed at sufficiently high horizontal resolution and coupled with a snow model here we present the results of a high resolution 5 5 km regional atmospheric climate model racmo2 simulation of coastal west antarctica for the period 1979 2015 we evaluate the results with available in situ weather observations remote sensing estimates of surface melt and smb estimates derived from radar and firn cores moreover results are compared with those from a lower resolution version to assess the added value of the resolution the high resolution model resolves small scale climate variability invoked by topography such as the relatively warm conditions over ice shelf grounding zones and local wind speed accelerations surface melt and smb are well reproduced by racmo2 this dataset will prove useful for picking ice core locations converting elevation changes to mass changes for driving ocean ice sheet and coupled models and for attributing changes in the west antarctic ice sheet and shelves to changes in atmospheric forcing

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

retreat of northern margins of george vi and wilkins ice shelves antarctic peninsula the george vi and wilkins ice shelves are considered at risk of disinteg ration due to a regional atmospheric warming trend on the antarctic peninsula retreat of the northern margin of the george vi ice shelf has been observed previously but the wilkins ice shelf was thought to be stable we investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 landsat and 1992 and 1995 european remote sensing satellite ers synthetic aperture radar images our investigation shows that the northern george vi ice shelf lost a total of 906 km 2 between 1974 and 1992 and an additional 87 km2 by 1995 the northern margin of the wilkins ice shelf lost 796 km2 between 1990 and 1992 and another 564 km2 between 1992 and 1995 armadas of tabular icebergs were visible in front of this shelf in the ers images these two ice shelves mark the southern most documented conspicuous retreat of ice shelf margins

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

rifting evolution in geological history abstract rift and rift like zones global linear extensional structures of the crust have appeared during most periods of the earth s history rifting as a geological process has undergone a complex evolution with its historical roots in the early precambrian the development of the oldest linear mobile tectonic zones archean greenstone belts and granulite belts combined the features of both rift and geosynclinal processes in the following epochs early proterozoic mobile zones protogeosynclinal regions and protorift zones evolved under similar tectonic regimes of crustal destruction in the early stages and compression in the late stages of their development but different in size scale and intensity of the deformations and thermal processes experienced typical rift structures have existed since the late proterozoic in the late proterozoic and paleozoic continental intracratonic rifting in the form of aulacogen and aulacogeosynclinal zone development was a process related and subordinated to a geosynclinal process in the adjacent mobile belts in the paleozoic the first epiorogenic postorogenic rift zones appeared within the epigeosynclinal folded belts during the meso cenozoic epoch of the earth s history rifting increased considerably and became independent of geosynclinal processes it is believed to be one of the main forms of continental crust destruction and formation of the oceanic basins and probably occurred under conditions of some general expansion of the earth

deep structure and metallogeny of early proterozoic mobile belts in the light of superdeep drilling in russia abstract superdeep drilling in russia and ukraine provides new direct information about the internal structure of the continental crust its evolution and associated ore forming processes deep levels of early proterozoic mobile belts have been investigated with two superdeep boreholes in russia and ukraine 1 in the kola peninsula in the baltic shield and 2 in the krivoy rog basin in the ukrainian shield the investigations of the kola superdeep borehole invalidate previous hypotheses on the conrad discontinuity they prove intensive proterozoic tectonic and metamorphic reworking of archaean rocks and reveal mineralizations of sulphide copper nickel and gold at depth in the light of the new evidence two geotectonic models of the pechenga imandra varzuga belt are reviewed 1 an intracontinental rift subject to the later compression and 2 an ocean opening followed by development of a collisional suture zone the krivoy rog belt has traditionally been described as a deep synclinorium filled with banded iron formations and cut in the west by a steep regional fault the krivoy rog superdeep hole was predicted to intersect all members of the early proterozoic krivoy rog group and to meet tonalites of the archaean basement at 9 10 km depth contrary to expectations however the borehole reached the basement complex at a depth of 2350 m the drilling stimulated geological and geophysical studies of adjacent territories and the results are reviewed in the light of two geotectonic models for the central part of the ukranian shield 1 a plate tectonic model involving westward subduction of oceanic crust and 2 a model implying a rise of asthenolite during early proterozoic times west of the krivoy rog basin the superdeep borehole data lead to better understanding of the structures of the continental crust and its metallogeny but at the same time pose new questions to which answers have yet to be found

trends in antarctic ice sheet elevation and mass fluctuations in antarctic ice sheet elevation and mass occur over a variety of timescales owing to changes in snowfall and ice flow here we disentangle these signals by combining 25 years of satellite radar altimeter observations and a regional climate model from these measurements patterns of change that are strongly associated with glaciological events emerge while the majority of the ice sheet has remained stable 24 of west antarctica is now in a state of dynamical imbalance thinning of the pine island and thwaites glacier basins reaches 122 m in places and their rates of ice loss are now five times greater than at the start of our survey by partitioning elevation changes into areas of snow and ice variability we estimate that east and west antarctica have contributed 1 1 0 4 and 5 7 0 8 mm to global sea level between 1992 and 2017

major stages of rifting evolution in the earth s history abstract linear extensional rift and rift like structures have been generated many times during various periods of the earth s history since early times these structures have varied with time however in scale morphology formations paragenesis of tectonic features regularity of distribution and evolution i distinguish and consider five major stages of rifting they are katarchean archean early proterozoic late proterozoic paleozoic and mesozoic cenozoic linear structures of the oldest stage combine features of development and structure similar to those typical of the rift and geosynclinal zones in the later periods of the earth s history at the second stage proto rift and proto geosynclinal structures can be distinguished for the first time though differences are not distinct paleo rift zones of the third and fourth stages differ from geosynclinal belts and zones their structural and genetic evolution however is related to the development of the latter in contrast the distribution and evolution of the rift zones and belts during the fifth stage are connected mainly with the destruction of the continents and formation of the secondary oceanic basins they are complementary to the mesozoic cenozoic geosynclinal orogenic belts periods of the greatest development of rift and rift like structures in the archean riphean and mesozoic cenozoic probably correspond to the major phases of the earth s expansion which can be distinguished in its general pulsating evolution

sustained retreat of the pine island glacier we use satellite observations to show that between 1992 and 2011 the pine island glacier hinge line retreated at a rate of 0 95 0 09 km yr 1 despite a progressive steepening and shoaling of the glacier surface and bedrock slopes respectively which ought to impede retreat the retreat has remained constant because the glacier terminus has thinned at an accelerating rate of 0 53 0 15 m yr 2 with comparable changes upstream this acceleration is consistent with an intensification of ocean driven melting in the cavity beneath the floating section of the glacier the pattern of hinge line retreat meanders and is concentrated in isolated regions until ice becomes locally buoyant because the glacier ocean system does not appear to have reached a position of relative stability the lower limit of sea level projections may be too conservative

a doubling in snow accumulation in the western antarctic peninsula since 1850 1 we present results from a new medium depth 136 metres ice core drilled in a high accumulation site 73 59 s 70 36 w on the south western antarctic peninsula during 2007 the gomez record reveals a doubling of accumulation since the 1850s from a decadal average of 0 49 mweq y 1 in 1855 1864 to 1 10 mweq y 1 in 1997 2006 with acceleration in recent decades comparison with published accumulation records indicates that this rapid increase is the largest observed across the region evaluation of the relationships between gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong temporally stable and positive relationship with the southern annular mode sam furthermore the sam is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site r 0 66 the association between gomez accumulation and enso is complex while sometimes statistically significant the relationship is not temporally stable thus at decadal scales we can utilise the gomez accumulation as a suitable proxy for sam variability but not for enso

a tutorial on the use of control methods in ice sheet modeling control methods are recommended as an efficient means to estimate undetermined physical parameters and boundary conditions and in so doing to improve the fidelity of a given ice sheet flow model to specific ice sheet velocity observations to accomplish this task the underlying dynamics of the model are inverted this permits model tuning adjustments to be represented explicitly in terms of model observation misfit

oxygen isotope and total beta radioactivity measurements on 10 m ice cores from the antarctic peninsula as part of the glaciology of the antarctic peninsula gap programme the snow cover at 25 stations was sampled to 10 m depth for oxygen isotope and total radioactivity analysis the mean annual oxygen isotope ratio correlates satisfactorily with 10 m temperature despite the complex topography of the area and suggests on average that climatic trends in the region are fairly systematic the relationship with temperature is similar to that derived from a simple model in which an air mass initially of maritime subtropical characteristics is progressively cooled as it moves towards the region the detailed isotope profiles show that for future deep drilling the most easily interpretable climatic information will be found in the more continental areas on the cast coast and on the plateau in the south of the region the degree of continentality of particular sites is reflected in the amplitude of the annual wave in the upper portion of the isotope ratio profile as well as in the accumulation rate

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

flow of glaciar moreno argentina from repeat pass shuttle imaging radar images comparison of the phase correlation method with radar interferometry high resolution radar images of glaciar moreno argentina acquired by the shuttle imaging radar c sir c on 9 and 10 october 1994 at 24 cm wavelength l band are utilized to map the glacier velocity both interferometrically and using the phase correlation method the precision of the interferometric ice velocities is 1 8 cm d 1 6 m a 1 1 the phase correlation method measures ice velocity with a precision of 14 cm d 1 50 m a 1 with image data at a 6 m sample spacing acquired 1 day apart averaged strain rates are measured with a precision of 10 4 d 1 at a 240 m sample spacing with the phase correlation method and 10 5 d 1 with radar interferometry the phase correlation method is less precise than radar interferometry but it performs better in areas of rapid flow is more robust to temporal changes in glacier scattering and measures the glacier velocity in two dimensions with only one image pair using this technique we find that glaciar moreno flows at 400 m a 1 in the terminal valley and 800 m a 1 at the calving front in agreement with velocities recorded a decade ago assuming steady state flow conditions the vertical strain rates measured by sir c are combined with prior data on mass ablation to estimate the glacier thickness and ice discharge the calculated discharge is 0 6 0 2 km3 ice a 1 at 300 m elevation and 1 1 0 2 km3 ice a 1 at the equilibrium line elevation 1150 m which yields a balance accumulation of 6 1m ice a 1

increased ice losses from antarctica detected by cryosat 2 we use 3 years of cryosat 2 radar altimeter data to develop the first comprehensive assessment of antarctic ice sheet elevation change this new data set provides near continuous 96 coverage of the entire continent extending to within 215 km of the south pole and leading to a fivefold increase in the sampling of coastal regions where the vast majority of all ice losses occur between 2010 and 2013 west antarctica east antarctica and the antarctic peninsula changed in mass by 134 27 3 36 and 23 18 gt yr 1 respectively in west antarctica signals of imbalance are present in areas that were poorly surveyed by past missions contributing additional losses that bring altimeter observations closer to estimates based on other geodetic techniques however the average rate of ice thinning in west antarctica has also continued to rise and mass losses from this sector are now 31 greater than over the period 2005 2010

increased ice flow in western palmer land linked to ocean melting a decrease in the mass and volume of western palmer land has raised the prospect that ice speed has increased in this marine based sector of antarctica to assess this possibility we measure ice velocity over 25 years using satellite imagery and an optimised modelling approach more than 30 unnamed outlet glaciers drain the 800 km coastline of western palmer land at speeds ranging from 0 5 to 2 5 m day interspersed with near stagnant ice between 1992 and 2015 most of the outlet glaciers sped up by 0 2 to 0 3 m day leading to a 13 increase in ice flow and a 15 km3 yr increase in ice discharge across the sector as a whole speedup is greatest where glaciers are grounded more than 300 m below sea level consistent with a loss of buttressing caused by ice shelf thinning in a region of shoaling warm circumpolar water

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

ice and ocean processes in the bellingshausen sea antarctica 1 in the vicinity of the antarctic peninsula observations show diminishing sea ice and a rapid warming of atmosphere and ocean these changes have led to the collapse of ice shelves and retreat acceleration and thinning of inland ice however ocean observations in the center of the nearby bellingshausen sea are spatially and temporally coarse in this study ocean and sea ice models forced by atmospheric reanalyses are used to investigate this data gap by simulating processes in the bellingshausen sea for the years 1979 2007 the model suggests flow features in the region and predicts the basal melting of local ice shelves modeled ocean conditions are found to be less variable than in the nearby amundsen sea which is situated closer to foci of annual and interannual atmospheric variability melt rates beneath george vi ice shelf are investigated in detail concluding that the ice shelf may have been melting out of balance and therefore thinning for decades the melt rate contains significant interannual variability that the model links to variation in sea ice conditions offshore of the southern end of the ice shelf this stands in contrast to the amundsen sea where models suggest that ice shelf melting is controlled by variable transport of circumpolar deep water onto the continental shelf

four decades of antarctic ice sheet mass balance from 1979 2017 we use updated drainage inventory ice thickness and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the antarctic ice sheet from 1979 to 2017 we compare the results with a surface mass balance model to deduce the ice sheet mass balance the total mass loss increased from 40 9 gt y in 1979 1990 to 50 14 gt y in 1989 2000 166 18 gt y in 1999 2009 and 252 26 gt y in 2009 2017 in 2009 2017 the mass loss was dominated by the amundsen bellingshausen sea sectors in west antarctica 159 8 gt y wilkes land in east antarctica 51 13 gt y and west and northeast peninsula 42 5 gt y the contribution to sea level rise from antarctica averaged 3 6 0 5 mm per decade with a cumulative 14 0 2 0 mm since 1979 including 6 9 0 6 mm from west antarctica 4 4 0 9 mm from east antarctica and 2 5 0 4 mm from the peninsula i e east antarctica is a major participant in the mass loss during the entire period the mass loss concentrated in areas closest to warm salty subsurface circumpolar deep water cdw that is consistent with enhanced polar westerlies pushing cdw toward antarctica to melt its floating ice shelves destabilize the glaciers and raise sea level

on the characteristics of circumpolar deep water intrusions to the west antarctic peninsula continental shelf 1 hydrographic and current velocity observations collected from march 2001 to february 2003 on the west antarctic peninsula shelf as part of the southern ocean global ecosystems dynamics program are used to characterize intrusions of upper circumpolar deep water ucdw and lower circumpolar deep water lcdw onto the shelf and marguerite bay ucdw is found on the middle and outer shelf along marguerite trough which connects the shelf break to marguerite bay and at another location farther south ucdw intrudes in the form of frequent four per month and small horizontal scales 4 km warm eddy like structures with maximum vertical scales of a few hundred meters however no evidence of ucdw intrusions was found in marguerite bay lcdw was found in several deep depressions connected to the shelf break including marguerite trough forming a tongue of relatively dense water 95 m thick on average that reaches into marguerite bay through marguerite trough a steady advective diffusive balance for the lcdw intrusion is used to make an estimation of the average upwelling rate and diffusivity in the deep layer within marguerite trough which suggest the lcdw layer is renewed approximately every six weeks

circulation and meltwater distribution in the bellingshausen sea from shelf break to coast west antarctic ice shelves have thinned dramatically over recent decades oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry toward ice shelves are needed to constrain future changes in melt rates six years of seal acquired observations provide extensive hydrographic coverage in the bellingshausen sea where ship based measurements are scarce warm but modified circumpolar deep water floods the shelf and establishes a cyclonic circulation within the belgica trough with flow extending toward the coast along the eastern boundaries and returning to the shelf break along western boundaries these boundary currents are the primary water mass pathways that carry heat toward the coast and advect ice shelf meltwater offshore the modified circumpolar deep water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break suggesting the presence of the antarctic slope current constraining meltwater pathways is a key step in monitoring the stability of the west antarctic ice sheet

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

estimation of ice shelf melt rate in the presence of a thermohaline staircase abstractdiffusive convection favorable thermohaline staircases are observed directly beneath george vi ice shelf antarctica a thermohaline staircase is one of the most pronounced manifestations of double diffusive convection cooling and freshening of the ocean by melting ice produces cool freshwater above the warmer saltier water the water mass distribution favorable to a type of double diffusive convection known as diffusive convection while the vertical distribution of water masses can be susceptible to diffusive convection none of the observations beneath ice shelves so far have shown signals of this process and its effect on melting ice shelves is uncertain the melt rate of ice shelves is commonly estimated using a parameterization based on a three equation model which assumes a fully developed unstratified turbulent flow over hydraulically smooth surfaces these prerequisites are clearly not met in the presence of a thermohaline staircase the basal melt rate is estimated by applying an ex

water mass properties and circulation on the west antarctic peninsula continental shelf in austral fall and winter 2001 abstract hydrographic measurements made during the us southern ocean global ocean ecosystem dynamics cruises which took place from april to june and july to september 2001 provide a description of changes in water mass distributions and circulation patterns in the marguerite bay region of the west antarctic peninsula continental shelf that result from seasonal variability and offshore forcing by the southern boundary of the antarctic circumpolar current acc the primary seasonal change in water mass properties is the reduction in antarctic surface water and replacement by a thick winter water layer the primary effect of the acc is to pump warm 1 5 c salty 34 65 34 7 and nutrient rich circumpolar deep water cdw onto the continental shelf below 200 m at specific sites that correspond to bathymetric features such as marguerite trough the cdw intruded onto the continental shelf moved across shelf and entered marguerite bay this flow pattern was observed during both cruises suggesting that onshelf intrusions of cdw are a regular occurrence on this shelf the number of cdw intrusions observed suggests that 4 6 events can occur in a year regions where cdw intrusions occur are characterized by surface waters that are above freezing in winter diffusive heat fluxes based on estimated diffusivities are insufficient for the observed rate of temperature decay of cdw intrusions localized bathymetrically controlled vertical mixing is suggested as the primary heat transfer mechanism the hydrographic and acoustic doppler current profiler measurements show a southwesterly flowing coastal current along adelaide island that enters the north side of marguerite bay and exits around alexander island this current which may result from seasonal coastal buoyancy forcing was present in fall and winter but was better developed in fall this current may be part of a larger cyclonic gyre that overlies the northern part of the area surveyed during the two cruises

case study of variation of sedimentation in the yellow and wei rivers abstractthe sanmenxia dam built in 1960 in the middle reach of the yellow river has experienced severe sedimentation problems not only in the reservoir area itself but also extending hundreds of kilometers in the backwater region morphological responses in the middle yellow river and its tributary the wei river upstream of the dam have generally lagged behind the causal changes in upstream and downstream controls based on the geometrical characteristics of a wedge shaped sedimentation body a method was derived for calculating equilibrium values of the accumulated sedimentation volume ve in the channel reaches combining the method for calculating ve with rate law models for channel morphological adjustment a method for calculating the accumulated deposition volumes was derived the results showed that the proposed method can accurately simulate sedimentation processes in the study reaches during 1960 and 2011 in the response to the integrated impacts of base level fluctuations and changes in incom

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

estimation of soil loss by water erosion in the chinese loess plateau using universal soil loss equation and grace s schnitzer 1 2 f seitz 2 3 a eicker 4 a guntner 5 m wattenbach5 and a menzel1 1technische universitat munchen hans carl von carlowitz platz 2 85354 freising germany e mail schnitzer bv tum de 2technische universitat munchen arcisstrase 21 80333munich germany 3deutsches geodatisches forschungsinstitut dgfi alfons goppel str 11 d 80539munich germany 4bonn university institute of geodesy and geoinformation nusallee 17 53115 bonn germany 5gfz german research centre for geosciences section 5 4 hydrology telegrafenberg 14473 potsdam germany

remote sensing of glacier and ice sheet grounding lines a review abstract the precise positioning and long term monitoring of the grounding line forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers is critical for assessing ice sheet glacier stability ice sheet glacier mass balance calculations and numerical ice modelling however mapping of the grounding line is a challenging task since it is a subglacial and transient feature remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position the large variety of methods products and publications as well as an inconsistent use of terminology additionally complicate the topic we present the first detailed review of existing remote sensing techniques and data for grounding line mapping benefits and limitations of the different techniques and data sources are discussed and illustrated with examples we identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products rather new methods like sentinel 1 sar synthetic aperture radar differential range offset tracking drot and pseudo crossover radar altimetry pcra offer the potential for recent measurements and to fill gaps in some areas nevertheless there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate differential sar interferometry dinsar on a continental scale

on the nature of greenstone belts in the precambrian abstract grachev a f and fedorovsky v s 1981 on the nature of greenstone belts in the precambrian in j h illies editor mechanism of graben formation tectonophysics 73 195 212 at present there is considerable speculation concerning the origin of greenstone belts they are compared with phanerozoic geosynclines fold belts modern island arcs or with the rift structures formed above subduction zones in marginal seas four stages in greenstone belt development can be determined 3 8 3 0 3 0 2 6 2 6 1 9 and 1 9 b y and younger sections of early greenstone belts contain all the essential features of the modern oceanic sequences their peculiarities are great thickness presence of jaspilites and scarce occurrence of very coarse clastics on the contrary the latter type of sediment is widespread in younger greenstone belts and in those of the last stage which are completely formed in continental environment whole rock chemistry of precambrian volcanics more than 1800 analyses all over the world confirms that alkali olivine basalts are absent till 1 9 b y and andesites are generally rare widespread type of early precambrian basalts are ol hy and q normative ones showing close similarity to typical abyssal tholeiites the presence of basaltic komatiites is not a unique petrochemical feature of volcanism in the early precambrian as one thinks now similar rocks have been found in phanerozoic rift zones there is no evidence suggesting significant shortening of initial crustal complexes and greenstone belts these data along with slight metamorphism and above features can only be explained by the formation of greenstone belts in rifting environment during the early stages 3 8 1 9 b y the thickness of the protocrust was not more than 10 20 km it allows us to understand the rare occurrence of intermediate volcanics at early stages of the earth s evolution in summary it is argued that in the early precambrian the spread of primitive oceanic lithosphere was not compensated by the consumption in subduction zones consequently plate tectonics cannot explain the formation of the crust in the early history of the earth

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

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

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

observations of surface mass balance on pine island glacier west antarctica and the effect of strain history in fast flowing sections surface mass balance smb is the net input of mass on a glacier s upper surface composed of snow deposition melt and erosion processes and is a major contributor to the overall mass balance pine island glacier pig in west antarctica has been dynamically imbalanced since the early 1990s indicating that discharge of solid ice into the oceans exceeds snow deposition however observations of the smb pattern on the fast flowing regions are scarce and are potentially affected by the firn s strain history here we present new observations from radar derived stratigraphy and a relatively dense network of firn cores collected along a 900 km traverse of pig between 1986 and 2014 the smb along the traverse was 0 505 m w e a 1 on average with a gradient of higher snow deposition in the south west compared with the north east of the catchment we show that along 80 of the traverse the strain history amounts to a misestimation of smb below the nominal uncertainty but can exceed it by a factor 5 in places making it a significant correction to the smb estimate locally we find that the strain correction changes the basin wide smb by 0 7 gt a 1 and thus forms a negligible 1 correction to the glacier s total smb

shelf ocean exchange and hydrography west of the antarctic peninsula a review the west antarctic peninsula wap is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat reduction of sea ice cover and shifts

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

dynamic thinning of glaciers on the southern antarctic peninsula growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice especially if it is resting on bedrock below sea level much of the southern antarctic peninsula satisfies this condition and also possesses a bed slope that deepens inland such ice sheet geometry is potentially unstable we use satellite altimetry and gravity observations to show that a major portion of the region has since 2009 destabilized ice mass loss of the marine terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of 56 8 gigatons per year constituting a major fraction of antarctica s contribution to rising sea level the widespread simultaneous nature of the acceleration in the absence of a persistent atmospheric forcing points to an oceanic driving mechanism

a one dimensional model of ice shelf ocean interaction large scale oceanic circulation beneath antarctic ice shelves is driven by the thenmohaline differences which result from mass and energy exchange at the ice ocean interface dense saline waters are drawn underneath the ice shelves and emerge cooled and diluted as plumes of ice shelf water a simple one dimensional model of this process has been developed in which the ice shelf water plume is treated as a turbulent gravity current initiated at the inland margin by a flow of fresh meltwater emerging from beneath the grounded ice subsequent evolution of the plume as it ascends along an ice shelf base of specified geometry can be simulated the model has been applied to a flow line on ronne ice shelf antarctica to explain the observed distribution and rate of basal melting and freezing calculations indicate that the present mean melt rate of 0 6 m yr 1 would increase to 2 6 m yr 1 if the underlying water were to warm by 0 6 c this would not only lead to significant thinning of the ice shelf but could also cause a profound change in ocean circulation on the open continental shelf

rapid large area mapping of ice flow using landsat 8 abstract we report on the maturation of optical satellite image based ice velocity mapping over the ice sheets and large glacierized areas enabled by the high radiometric resolution and internal geometric accuracy of landsat 8 s operational land imager oli detailed large area single season mosaics and time series maps of ice flow were created using data spanning june 2013 to june 2015 the 12 bit radiometric quantization and 15 m pixel scale resolution of oli band 8 enable displacement tracking of subtle snow drift patterns on ice sheet surfaces at 1 m precision ice sheet and snowfield snow drift features persist for typically 16 to 64 days and up to 432 days depending primarily on snow accumulation rates this results in spatially continuous mapping of ice flow extending the mapping capability beyond crevassed areas our method uses image chip cross correlation and sub pixel peak fitting in matching landsat path row pairs high pass filtering is applied to the imagery to enhance local surface texture the current high image acquisition rates of landsat 8 725 scenes per day globally reduces the impact of high cloudiness in polar and mountain terrain and allows rapid compilation of large areas or dense temporal coverage of seasonal ice flow variations the results rival the coverage and accuracy of interferometric synthetic aperture radar insar mapping

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 drawdown of antarctica s wordie ice shelf glaciers in response to enso southern annular mode driven warming in the southern ocean abstract here we investigate the largest acceleration in ice flow across all of antarctica between 2008 insar and 2014 landsat velocity mappings this occurred in glaciers that used to feed into the wordie ice shelf on the west antarctic peninsula which rapidly disintegrated in 1989 between 2008 and 2014 these glaciers experienced at least a threefold increase in surface elevation drawdown relative to the 2002 2008 time period after 20 yrs of relative stability it is unlikely that the ice shelf collapse played a role in the large response instead we find that the rapid acceleration and surface drawdown is linked to enhanced melting at the ice ocean boundary attributable to changes in winds driven by global atmospheric circulation patterns namely the el nino southern oscillation enso and southern annular mode sam linking changes in grounded ice to atmospheric driven ocean warming

widespread rapid grounding line retreat of pine island thwaites smith and kohler glaciers west antarctica from 1992 to 2011 we measure the grounding line retreat of glaciers draining the amundsen sea sector of west antarctica using earth remote sensing ers 1 2 satellite radar interferometry from 1992 to 2011 pine island glacier retreated 31 km at its center with most retreat in 2005 2009 when the glacier ungrounded from its ice plain thwaites glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides haynes glacier retreated 10 km along its flanks smith kohler glaciers retreated the most 35 km along its ice plain and its ice shelf pinning points are vanishing these rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings upstream of the 2011 grounding line positions we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin 2014 american geophysical union all rights reserved

antarctic grounding line mapping from differential satellite radar interferometry 1 the delineation of an ice sheet grounding line i e the transition boundary where ice detaches from the bed and becomes afloat in the ocean is critical to ice sheet mass budget calculations numerical modeling of ice sheet dynamics ice ocean interactions oceanic tides and subglacial environments here we present 15 years of comprehensive high resolution mapping of grounding lines in antarctica using differential satellite synthetic aperture radar interferometry dinsar data from the earth remote sensing satellites 1 2 ers 1 2 radarsat 1 and 2 and the advanced land observing system alos palsar for years 1994 to 2009 dinsar directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision at a sample spacing better than 50 m simultaneously over areas several 100 km wide in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data on stagnant and slow moving areas we find that breaks in surface slope are reliable indicators of grounding lines but on most fast moving glaciers and ice streams our dinsar results reveal that prior mappings have positioning errors ranging from a few km to over 100 km a better agreement is found with icesat s data also based on measurements of vertical motion but with a detection noise one order of magnitude larger than with dinsar overall the dinsar mapping of antarctic grounding lines completely redefines the coastline of antarctica

ice ocean interaction on ronne ice shelf antarctica detailed glaciological studies have been completed at 28 sites lying on an approximate flow line extending 760 km across ronne ice shelf parameters measured at each location include ice velocity thickness principal strain rates surface elevation temperature and accumulation rate the data have been used in a steady state model to derive the basal mass flux and the temperature profile with depth at each site from the principles of mass and energy conservation these calculations indicate basal melting in excess of 1 m yr 1 over the first 100 km of the flow line downstream of the grounding line where the ice shelf is between 1200 m and 1600 m thick the maximum melt rates in this region occur near the inland margin and exceed 4 m yr 1 melting continues at a lesser rate over the next 200 km before freezing commences freezing then dominates up to the final 100 km before the ice front resulting in the accumulation of a layer of basal sea ice up to 50 m thick this is rapidly removed as melt rates increase to over 6 m yr 1 at the ice front the cumulative effect of this pattern of basal accumulation and ablation is the wastage by melting of 85 of the mass discharged across the grounding line before it reaches the ice front supporting evidence for a layer of saline ice underlying the ice shelf is provided by the strength of basal radar reflections observed during radio echo sounding of ice thickness in the region where mass balance calculations suggest an accretion of basal sea ice reflection coefficients are consistently low ranging from 6 db to 38 db most of these weak reflections are believed to originate from the true base of the ice shelf the additional energy loss being the result of increased attenuation of the radar signal within the saline layer the derived pattern of basal melting and freezing is consistent with a simple model of sub ice shelf oceanic circulation involving a deep thermohaline convection cell dense saline water which is formed over the continental shelf during winter when the sea surface freezes drains into the deepest parts of the sub ice shelf cavity at the inland margin where this water mass comes into contact with the ice shelf its temperature is 1 c above the local pressure freezing point melting of ice results producing a buoyant outflow of cold relatively fresh water along the ice shelf base basal freezing occurs towards the ice front where the ascending water becomes supercooled this circulation has important implications for the production of antarctic bottom water and for the response of the ice shelf to driving stresses through the temperature dependent viscosity of ice

glacier motion estimation using sar offset tracking procedures two image to image patch offset techniques for estimating feature motion between satellite synthetic aperture radar sar images are discussed intensity tracking based on patch intensity cross correlation optimization and coherence tracking based on patch coherence optimization are used to estimate the movement of glacier surfaces between two sar images in both slant range and azimuth direction the accuracy and application range of the two methods are examined in the case of the surge of monacobreen in northern svalbard between 1992 and 1996 offset tracking procedures of sar images are an alternative to differential sar interferometry for the estimation of glacier motion when differential sar interferometry is limited by loss of coherence i e in the case of rapid and incoherent flow and of large acquisition time intervals between the two sar images in addition an offset tracking procedure in the azimuth direction may be combined with differential sar interferometry in the slant range direction in order to retrieve a two dimensional displacement map when sar data of only one orbit configuration are available

interferometric estimation of three dimensional ice flow using ascending and descending passes satellite radar interferometry sri provides an important new tool for determining ice flow velocity interferometric measurements made from a single track direction are sensitive only to a single component of the three component velocity vector observations from along three different track directions would allow the full velocity vector to be determined a north south looking synthetic aperture radar sar could provide these observations over large portions of the globe but not over large areas of the polar ice sheets the authors develop and demonstrate a technique that allows the three component velocity vector to be estimated from data acquired along two track directions ascending and descending under a surface parallel flow assumption this technique requires that there are accurate estimates of the surface slope which are also determined interferometrically to demonstrate the technique the authors estimate the three component velocity field for the ryder glacier greenland their results are promising although they do not have yet ground truth data with which to determine the accuracy of their estimates

remote sensing of ice motion in antarctica a review abstract the antarctic ice sheet holds 91 of the global ice mass making it the biggest potential contributor to global sea level rise in order to evaluate the ice sheet s present and future response to global climate change detailed information about spatial and temporal ice mass dynamics is required while ice sheet surface mass balance can be estimated from regional climate models ice discharge is often determined from spaceborne measurements of ice thickness and ice motion at selected flux gates the retrieval of ice motion is not only critical for analysing the rate of ice transport into the ocean but also for investigating the spatial and temporal pattern or the driving forcings of antarctic ice flow dynamics this study provides a comprehensive review of state of the art spaceborne ice velocity measurements in antarctica based on 201 scientific papers published over the last three decades our analysis revealed a dominant interest in local and regional scale investigations yet the launch of the ers 1 2 and radarsat 1 sar satellites in the 1990s dramatically increased data coverage over the antarctic continent and enabled the first circum antarctic velocity product to be published in the late 2000s in recent years the improved imaging capabilities of landsat 8 led to a shift towards using mainly optical satellite data and enabled great advances in circum antarctic velocity mapping data from the currently operating sentinel 1 2 missions was applied in fewer studies but will play a crucial role in future ice motion studies e g as part of esa cci projects in addition we found a growing interest in high temporal resolution velocity change analyses based on the reviewed studies we moreover summarized the highly dynamic and locally variable flow pattern over the antarctic continent being in accordance with varying local and regional driving mechanisms despite the great advances in spaceborne ice velocity mapping in antarctica we report some major drawbacks and discuss future challenges and requirements to start with our study uncovered strong variations regarding the spatial availability of investigations while we found an aggregation of studies over selected glaciers we report a major lack of studies in all three antarctic sectors additionally many velocity datasets were created with strongly heterogeneous output parameters and were provided at coarse temporal resolution or at point based measurement locations only future studies should consequently aim at creating more uniform ice motion products at defined spatial and temporal coverage and resolution standards and at analysing particularly the least studied glaciers

glaciological and oceanographic calculations of the mass balance and oxygen isotope ratio of a melting ice shelf on a etudie l alimentation du george vi ice shelf en relation avec l accumulation le velage et la fonte on releve la relation temperature taux d isotope de l oxygene ces donnees sont couplees a des donnees oceanologiques sur les eaux chaudes et son interaction avec le shelf

case study delayed sedimentation response to inflow and operations at sanmenxia dam this paper presents a study on the reservoir sedimentation processes in response to changes in incoming flow at the upstream and changes in the pool level at the downstream for sanmenxia reservoir which is located on the middle reach of the yellow river in china and has experienced serious sedimentation problems even since its impoundment in 1960 the hysteresis effect in reservoir sedimentation was used as the basis for analysis and its behavior was fully investigated throughout this study the research found that the rise in the elevation of tongguan which is located in the backwater region at a distance of 113 5 km upstream of the sanmenxia dam had a time delay of about 2 years compared with the sediment deposition in the reservoir area downstream of tongguan moreover the accumulated sediment deposition in the reservoir area was closely related not only to the current year s flow and dam operational conditions but also to the preceding 3 4 years flow and dam operational conditions likewise the

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

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

modeling the dynamic response of outlet glaciers to observed ice shelf thinning in the bellingshausen sea sector west antarctica satellite observations of gravity anomalies ice surface elevation and glacier velocity show significant increases in net grounded ice mass loss over the past decade along the bellingshausen sea sector bss west antarctica in areas where warm 1 c sea water floods the continental shelf these observations provide compelling but indirect evidence that mass losses are driven primarily by reduced buttressing from the floating ice shelves caused by ocean driven ice shelf thinning here we combine recent observations of ice velocity thickness and thickness changes with an ice flow model to study the instantaneous dynamic response of bss outlet glaciers to observed ice shelf thinning alone our model results show that multiple bss outlet glaciers respond instantaneously to observed ice shelf thinning particularly in areas where ice shelves ground at discrete points increases in modeled and observed dynamic mass losses however account for 5 of the mass loss rates estimated from gravity anomalies and changes in ice surface elevation suggesting that variations in surface mass balance may be key to understanding recent bss mass loss our approach isolates the impact of ice shelf thinning on glacier flow and shows that if ice shelf thinning continues at or above current rates total bss mass loss will increase in the next decade

inland thinning of the amundsen sea sector west antarctica 1 together with the pine island glacier pig the thwaites tg and smith sg glaciers are the principal drainage systems of the amundsen sea as sector of western antarctica here we use satellite radar altimetry and interferometry to show that a rapid thinning of ice has occurred within the fastest flowing sections of all as outlet glaciers the pattern of thinning extends to distances greater than 150 km inland between 1991 and 2001 the tg and sg thinned by more than 25 and 45 m at their grounding lines and a total of 154 16 km 3 of ice or 0 43 mm of eustatic sea level rise was lost from the as sector glaciers to the ocean we show that the thickness changes may have caused the pig tg and sg to retreat inland by over 8 4 and 7 km respectively in line with independent estimates of grounding line migration

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

the effect of atmospheric forcing resolution on delivery of ocean heat to the antarctic floating ice shelves abstractoceanic melting at the base of the floating antarctic ice shelves is now thought to be a more significant cause of mass loss for the antarctic ice sheet than iceberg calving in this study a 10 km horizontal resolution circum antarctic ocean sea ice ice shelf model based on the regional ocean modeling system roms is used to study the delivery of ocean heat to the base of the ice shelves the atmospheric forcing comes from the era interim reanalysis 80 km resolution and from simulations using the polar optimized weather research and forecasting model 30 km resolution where the upper atmosphere was relaxed to the era interim reanalysis the modeled total basal ice shelf melt is low compared to observational estimates but increases by 14 with the higher resolution winds and just 3 with both the higher resolution winds and atmospheric surface temperatures the higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the

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

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

circulation and heat fluxes during the austral fall in george vi sound antarctic peninsula abstract a mesoscale survey was conducted in northern george vi sound as part of the united states southern ocean global ocean ecosystems dynamics program in austral fall 2001 to examine the circulation and heat fluxes the absolute dynamic height field is determined from a combination of measured currents detided using model predicted tidal currents streamfunction fitting and the thermal wind equation based on hydrographic measurements the results have revealed surface coastal currents of 0 2 m s 1 intruding into northern george vi sound from marguerite bay mb and mesoscale eddies formed within the deep trough both antarctic surface waters and modified circumpolar deep water were transported into the sound along the eastern side of the sound while ice shelf influenced waters exited to mb along the western side analysis indicates that predominant southward winds during the season were responsible for driving the basin wide circulation in the sound both convergence of horizontal heat transports and vertical upwelling heat fluxes were significant to the contribution or delay of local ice formation in george vi sound which is critical for the austral winter ecosystem

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

basal conditions for pine island and thwaites glaciers west antarctica determined using satellite and airborne data we use models constrained by remotely sensed data from pine island and thwaites glaciers west antarctica to infer basal properties that are difficult to observe directly the results indicate strong basal melting in areas upstream of the grounding lines of both glaciers where the ice flow is fast and the basal shear stress is large farther inland we find that both glaciers have mixed bed conditions with extensive areas of both bedrock and weak till in particular there are weak areas along much of pine island glacier s main trunk that could prove unstable if it retreats past the band of strong bed just above its current grounding line in agreement with earlier studies our forward ice stream model shows a strong sensitivity to small perturbations in the grounding line position these results also reveal a large sensitivity to the assumed bed sliding or deforming model with non linear sliding laws producing substantially greater dynamic response than earlier simulations that assume a linear viscous till rheology finally comparison indicates that our results using a plastic bed are compatible with the limited observational constraints and theoretical work that suggests an upper bound exists on maximum basal shear stress

response of bankfull discharge to discharge and sediment load in the lower yellow river this paper presents a study on the response of bankfull discharge to incoming discharge and sediment load based on long term hydrological and bankfull discharge data measured on the lower reaches of the yellow river the analysis indicated that the bankfull discharge was a function of the preceding 5 to 6 years flow regimes revealing that bankfull channel dimensions were a result of the accumulative effect of several consecutive years flow discharge and sediment load conditions in other words the mean relaxation time was about 5 to 6 years for channel adjustment theoretical methods for the prediction of bankfull discharge were developed in which the response time or the relaxation time was fully considered testing of the methods using data observed at five hydrologic stations in the lower reaches of the yellow river from 1960 to 2003 showed that the proposed methods can predict the variation of bankfull discharge in response to changes in the incoming discharge and sediment load the proposed methods hold promise for predicting the magnitude and trend of channel response to other rivers undergoing aggradation or degradation from changes in hydrologic or sediment regime

changes in west antarctic ice stream dynamics observed with alos palsar data the advanced land observation system alos phased array synthetic aperture radar palsar is an l band frequency 1 27 ghz radar capable of continental scale interferometric observations of ice sheet motion here we show that palsar data yield excellent measurements of ice motion compared to c band 5 6 ghz radar data because of greater temporal coherence over snow and firn we compare palsar velocities from year 2006 in pine island bay west antarctica with those spanning years 1974 to 2007 between 1996 and 2007 pine island glacier sped up 42 and ungrounded over most of its ice plain smith glacier accelerated 83 and ungrounded as well their largest speed up are recorded in 2007 thwaites glacier is not accelerating but widening with time and its eastern ice shelf doubled its speed total ice discharge from these glaciers increased 30 in 12 yr and the net mass loss increased 170 from 39 15 gt yr to 105 27 gt yr longer term velocity changes suggest only a moderate loss in the 1970s as the glaciers unground into the deeper smoother beds inland the mass loss from this region will grow considerably larger in years to come copyright 2008 by the american geophysical union

calibrated seismic imaging of eddy dominated warm water transport across the bellingshausen sea southern ocean seismic reflection images of thermohaline circulation from the bellingshausen sea adjacent to the west antarctica peninsula were acquired during february 2015 this survey shows that bright reflectivity occurs throughout the upper 300 m by calibrating these seismic images with coeval hydrographic measurements intrusion of warm water features onto the continental shelf at marguerite and belgica troughs is identified and characterized these features have distinctive lens shaped patterns of reflectivity with lengths of 0 75 11 00 km and thicknesses of 100 150 m suggesting that they are small mesoscale to submesoscale eddies abundant eddies are observed along a transect that crosses belgica trough near alexander island drift a large of order urn x wiley 21699275 media jgrc22803 jgrc22803 math 0001 km3 bowl like feature that may represent an anticyclonic taylor column is imaged on a pair of orthogonal images a modified iterative procedure is used to convert seismic imagery into maps of temperature that enable the number and size of eddies being transported onto the shelf to be quantified finally analysis of prestack shot records suggests that these eddies are advecting southward at speeds of urn x wiley 21699275 media jgrc22803 jgrc22803 math 0002 m s 1 consistent with limited legacy hydrographic measurements concentration of observed eddies south of the southern antarctic circumpolar current front implies they represent both a dominant and a long lived mechanism of warm water transport especially across belgica trough our observations suggest that previous estimates of eddy frequency may have been underestimated by up to 1 order of magnitude which has significant implications for calculations of ice mass loss on the shelf of the west antarctic peninsula

mass changes of outlet glaciers along the nordensjkold coast northern antarctic peninsula based on tandem x satellite measurements we analyzed volume change and mass balance of outlet glaciers of the northern antarctic peninsula over the period 2011 to 2013 using topographic data of high vertical accuracy and great spatial detail acquired by bistatic radar interferometry of the tandem x terrasar x satellite formation the study area includes glaciers draining into the larsen a larsen inlet and prince gustav channel embayments after collapse of buttressing ice shelves in 1995 the glaciers became tidewater calving glaciers and accelerated resulting in increased ice export downwasting of most glaciers is going on but at reduced rates compared to previous years in accordance with deceleration of ice flow the rate of mass depletion is 4 2 0 4 gt a 1 with the largest contribution by drygalski glacier amounting to 2 2 0 2 gt a 1 on the technological side the investigations demonstrate the capability of satellite borne single pass radar interferometry as a new tool for accurate and detailed monitoring of glacier volume change

net retreat of antarctic glacier grounding lines grounding lines are a key indicator of ice sheet instability because changes in their position reflect imbalance with the surrounding ocean and affect the flow of inland ice although the grounding lines of several antarctic glaciers have retreated rapidly due to ocean driven melting records are too scarce to assess the scale of the imbalance here we combine satellite altimeter observations of ice elevation change and measurements of ice geometry to track grounding line movement around the entire continent tripling the coverage of previous surveys between 2010 and 2016 22 3 and 10 of surveyed grounding lines in west antarctica east antarctica and at the antarctic peninsula retreated at rates faster than 25 m yr 1 the typical pace since the last glacial maximum and the continent has lost 1 463 km2 791 km2 of grounded ice area although by far the fastest rates of retreat occurred in the amundsen sea sector we show that the pine island glacier grounding line has stabilized probably as a consequence of abated ocean forcing on average antarctica s fast flowing ice streams retreat by 110 metres per metre of ice thinning grounding lines in parts of west antarctica east antarctica and the antarctic peninsula retreated faster than typical post glacial pace according to satellite observations and ice geometry measurements

a model study of circumpolar deep water on the west antarctic peninsula and ross sea continental shelves abstract transport of relatively warm nutrient rich circumpolar deep water cdw onto continental shelves around antarctica has important effects on physical and biological processes however the characteristics of the cdw along the shelf break as well as what happens to it once it has been advected onto the continental shelf differ spatially in the present study high resolution 4 5 km regional models of the ross sea and the west antarctic peninsula coastal ocean are used to compare differences in cdw transport the models compared very well with observations from both regions examining the fluxes not only of heat but also of a simulated dye representing cdw shows that in both cases cdw crosses the shelf break in specific locations primarily determined by the bathymetry but eventually floods much of the shelf the frequency of intrusions in marguerite trough was ca 2 3 per month similar to recent mooring observations a significant correlation between the along shelf break wind stress and the cross shelf break dye flux through marguerite trough was observed suggesting that intrusions are at least partially related to short duration wind events the primary difference between the cdw intrusions on the ross and west antarctic peninsula shelves is that there is more vigorous mixing of the cdw with the surface waters in the ross sea especially in the west where high salinity shelf water is created the models show that the cdw moving across the antarctic peninsula continental shelf towards the base of the ice shelves not only is warmer initially and travels a shorter distance than that advected towards the base of the ross ice shelf but it is also subjected to less vertical mixing with surface waters which conserves the heat available to be advected under the ice shelves this difference in vertical mixing also likely leads to differences in the supply of nutrients from the cdw into the upper water column and thus modulates the impacts on surface biogeochemical processes