Surface Ice Flow Velocity Research Articles

Surface topography modelling and ice flow velocity mapping of Dalk Glacier, East Antarctica: application of UAV remote sensing

Abstract. The Antarctic Ice Sheet is the largest potential contributor to global sea level rise due to global climate warming, making it important to monitor changes in the marginal outlet glacier dynamics and surface topography. The unmanned aerial vehicle (UAV), a new platform, has been proven to be a useful tool in glaciological applications because it can collect data in a variety of ways and has a high spatial and temporal resolution compared to traditional ground-based measurements and remote sensing from space. In this study, we used the combined UAV platform composed of the DJI Mavic 3 Enterprise (M3E) and M300 (L1) versions to perform high-accuracy on-site investigations of Dalk Glacier, a typical outlet glacier near the Zhongshan Station in East Antarctica. During the 39th Chinese Antarctic Expedition (CHINARE) in 2022–2023, UAV surveys with multiple sensors were performed. The M3E optical camera makes it possible to reconstruct high-resolution ortho-mosaic and digital elevation models (DEMs) of Dalk Glacier with high accuracy based on photogrammetric principles, helping us to extract the features of glacier surface topography, while dense point clouds derived from the L1 LiDAR camera are used to validate and improve the three-dimensional accuracy. To further monitor the dynamics and stability of Dalk Glacier, we generate ice flow velocity maps using ortho-mosaics for the years 2019, 2020, and 2023. The spatiotemporal changes in ice flow velocities were further compared with the products derived from satellite remote sensing data.

The Antarctic Subglacial Hydrological Environment and International Drilling Projects: A Review

Subglacial lakes and hydrological systems play crucial roles in Antarctic subglacial hydrology, water balance, subglacial geomorphology, and ice dynamics. Satellite altimetry has revealed that some recurrent water exchange occurs in subglacial lakes. They are referred to as ’active lakes’, which prominently influence a majority of subglacial hydrological processes. Our analysis indicates that active subglacial lakes are more likely to be situated in regions with higher surface ice flow velocities. Nevertheless, the origin of subglacial lakes still remains enigmatic and uncertain. They could have potential associations with geothermal heat, ice sheets melting, and ice flow dynamics. Subglacial lake drilling and water sampling have the potential to provide valuable insights into the origin of subglacial lakes and subglacial hydrological processes. Moreover, they could also offer unique opportunities for the exploration of subglacial microbiology, evolution of the Antarctic ice sheets, and various fundamental scientific inquiries. To date, successful drilling and sampling has been accomplished in Lake Vostok, Lake Mercer, and Lake Whillans. However, the use of drilling fluids caused the water sample contamination in Lake Vostok, and the drilling attempt at Lake Ellsworth failed due to technical issues. To explore more of the conditions of the Antarctic subglacial lakes, the Lake Centro de Estudios Científicos (Lake CECs) and Lake Snow Eagle (LSE) drilling projects are upcoming and in preparation. In this study, we aim to address the following: (1) introduce various aspects of Antarctic subglacial lakes, subglacial hydrological elements, subglacial hydrology, and the interactions between ice sheets and the ocean; and (2) provide an overview and outlook of subglacial lakes drilling projects.

Decoding the Dynamics of Climate Change Impact: Temporal Patterns of Surface Warming and Melting on the Nivlisen Ice Shelf, Dronning Maud Land, East Antarctica

This study analyzes the dynamics of surface melting in Antarctica, which are crucial for understanding glacier and ice sheet behavior and monitoring polar climate change. Specifically, we focus on the Nivlisen ice shelf in East Antarctica, examining melt ponds, supra glacial lakes (SGLs), seasonal surface melt extent, and surface ice flow velocity. Spatial and temporal analysis is based on Landsat and Sentinel-1 data from the austral summers of 2000 to 2023. Between 2000 and 2014, melt ponds and SGLs on the ice shelf covered roughly 1 km2. However, from 2015 to 2023, surface melting increased consistently, leading to more extensive melt ponds and SGLs. Significant SGL depths were observed in 2016, 2017, 2019, and 2020, with 2008, 2016, and 2020 showing the highest volumes and progressive SGL area growth. We also examined the relationship between seasonal surface melt extent and ice flow velocity. Validation efforts involved ground truth data from a melt pond in central Dronning Maud Land (cDML) during the 2022–2023 austral summer, along with model-based results. The observed increase in melt pond depth and volume may significantly impact ice shelf stability, potentially accelerating ice flow and ice shelf destabilization. Continuous monitoring is essential for accurately assessing climate change’s ongoing impact on Antarctic ice shelves.

ICE FLOW VELOCITY MAPPING IN EAST ANTARCTICA USING HISTORICAL IMAGES FROM 1960s TO 1980s: RECENT PROGRESS

Abstract. Recent research indicates that the estimated elevation changes and associated mass balance in East Antarctica are of some degree of uncertainty; a light accumulation has occurred in its vast inland regions, while mass loss in Wilkes Land appears significant. It is necessary to study the mass change trend in the context of a long period of the East Antarctic Ice Sheet (EAIS). The input-output method based on surface ice flow velocity and ice thickness is one of the most important ways to estimate the mass balance, which can provide longer-term knowledge of mass balance because of the availability of the early satellites in 1960s. In this study, we briefly describe the method of extracting ice velocity based on the historical optical images from 1960s to 1980s. Based on the draft ice velocity map of the EAIS using this method, we conduct a series of validation experiments, including comparisons with in-situ measurement, existing historical maps and rock outcrop dataset. Finally, we use the input-output method to estimate mass balance in some regions of EAIS using the generated velocity map.

Not all Icequakes are Created Equal: Basal Icequakes Suggest Diverse Bed Deformation Mechanisms at Rutford Ice Stream, West Antarctica

AbstractMicroseismicity, induced by the sliding of a glacier over its bed, can be used to characterize frictional properties of the ice‐bed interface, which are a key parameter controlling ice stream flow. We use naturally occurring seismicity to monitor spatiotemporally varying bed properties at Rutford Ice Stream, West Antarctica. We locate 230,000 micro‐earthquakes with local magnitudes from −2.0 to −0.3 using 90 days of recordings from a 35‐station seismic network located ∼40 km upstream of the grounding line. Events exclusively occur near the ice‐bed interface and indicate predominantly flow‐parallel stick‐slip. They mostly lie within a region of interpreted stiff till and along the likely stiffer part of mega‐scale glacial lineations. Within these regions, micro‐earthquakes occur in spatially (<100 m radius) and temporally (mostly 1–5 days activity) restricted event‐clusters (up to 4,000 events), which exhibit an increase, followed by a decrease, in event magnitude with time. This may indicate event triggering once activity is initiated. Although ocean tides modulate the surface ice flow velocity, we observe little periodic variation in overall event frequency over time and conclude that water content, bed topography and stiffness are the major factors controlling microseismicity. Based on variable rupture mechanisms and spatiotemporal characteristics, we suggest the event‐clusters relate to three end‐member types of bed deformation: (1) continuous creation and seismogenic destruction of small‐scale bed‐roughness, (2) ploughed clasts, and (3) flow‐oblique deformation during landform formation or along bedrock outcrops. This indicates that multiple processes, simultaneously active during glacial sliding, can accommodate stick‐slip behavior and that the bed continuously reorganizes.

ICE FLOW VELOCITY MAPPING OF EAST ANTARCTICA FROM 1963 TO 1989

Abstract. Long-time serial observation of surface ice flow velocity in Antarctic is a crucial component in estimating the mass balance of Antarctic ice sheet. However, there is a lack of historical continental scale velocity maps of Antarctica before the 1990s. Historical optical images such as ARGON and Landsat images before 1990s are difficult to be used for ice flow velocity mapping, due to the fact that they are mostly not strictly geo-processed (e.g., ortho-rectified) and the image quality is lower than those of recent sensors. This paper presents a systematic framework for developing a surface velocity map of East Antarctica from 1963 to 1989 based on historical ARGON and Landsat images, followed by analysis of spatial-temporal changes of the ice flow velocity in some major glaciers, as well as the dynamic changes. The preliminary comparison with existing products suggests that the glaciers in Wilkes Land experienced an increasing trend with obvious fluctuations during the past ∼50 years, while the glaciers near Transantarctic Mountains tended to be stable or slightly fluctuating to a certain degree.

SEASONAL COMPARISON OF VELOCITY OF THE EASTERN TRIBUTARY GLACIERS, AMERY ICE SHELF, ANTARCTICA, USING SAR OFFSET TRACKING

Abstract. Antarctica and Greenland are two major Earth’s continental ice shelves which play an important role in influencing Earth’s energy balance through their high albedo. The ice sheets comprise of grounded ice or the continental glaciers and their associated ice shelves. Surface velocity is an important parameter that needs to be monitored to understand the glacier dynamics. Marine terminating glaciers have higher velocity than land terminating glaciers. Therefore, ice shelves are generally observed to have higher velocity as compared to continental glaciers. The focus of this study is Amery ice shelf (AIS) which is the third largest ice shelf located in east Antarctica terminating into the Prydz Bay on the eastern Antarctica. The surface ice-flow velocity of AIS is very high compared to its surrounding glaciers which flows at a rate of 1400 m a−1 and drains about 8% of the Antarctic ice sheet. AIS is fed by different glaciers and ice streams at the head, as well as from the western and eastern side of the ice shelf before it terminates into the ocean. The primary objective of this study was to compute velocity of the eastern tributary glaciers of AIS using SAR from Sentinel-1 data. The secondary objective was to compare the winter and summer velocities of the glaciers for 2017–2018. The offset tracking method has been applied to the ground range detected (GRD) product obtained from Sentinel-1 satellite. This method is suitable for regions with higher glacier velocity where interferometry is generally affected by the loss of coherence. The offset tracking method works by tracking the features on the basis of another feature and calculates the offset between the two features in the images. Two tributary glaciers near the Clemence massif and another glacier near the Pickering Nunatak feed into this ice shelf from the eastern glacial basin region that drains ice from the American Highland, east Antarctica. The glaciers near the Clemence massif showed low annual velocity which ranged from 100 m a−1 at the head to ∼300 m a−1 near the end of the glacier, where it merges with AIS. The glaciers flowing near the Pickering Nunatak exhibited moderate velocity ranging from 150 m a−1 at its head and reaching up to 450 m a−1 near the tongue. The summer velocity (March 2018) was observed to be higher than the velocity in winter (July 2017) and the difference between the summer and the winter velocities was found to be between 50 m a−1 and 130 m a−1. The results for the velocity were obtained at 120 m resolution and were compared with the previous MEaSUREs (Making Earth System Data Records for Use in Research Environments) yearly velocity at 450 m and 1 km resolution provided by National Snow and Ice Data Center portal. The results were evaluated using statistical measure- bias and the accuracy was derived using the root mean square error. The bias did not exceed 20 m a−1 for the three glaciers and the accuracy was observed to be more than 85% for most of the regions. The accuracy of the results suggests that the offset tracking technique is useful for future velocity estimation in the regions of high glacier velocity.

Subglacial Topography of an Icefall Inferred From Repeated Terrestrial Laser Scanning

Information about ice thickness and subglacial topography is a key element for ice dynamics modeling and, consequently, for better understanding of current response of glaciers to climatic forcing. While there has been a substantial progress in the measurements of glacial surface, ice thickness measurements still suffer from limited coverage and strong interpolation. Furthermore, there are some glaciated areas where typical remote sensing techniques provide only limited data due to unfavorable climatic conditions and steep topography. A perfect example of such a feature is icefalls dominating landscapes of the maritime Antarctic. In order to close that gap, this letter presents a simple method of inferring the subglacial topography based on repeated terrestrial laser scanning of the ice surface and inverse shallow ice approximation modeling. Emerald Icefalls, King George Island, were surveyed twice within eight-day period, allowing to derive ice surface velocity field by feature tracking analysis and to estimate ice thickness and the subglacial topography. Calculated ice thickness is low, with the mean value of 72±18 m. Therefore, in line with former studies, the overall ice flux of Emerald Icefalls is small despite their relatively high surface ice flow velocities.

Estimation of Glacier Thickness From Surface Mass Balance and Ice Flow Velocities: A Case Study on Argentière Glacier, France

Glacier thickness distribution is a prerequisite to simulate the future of glaciers. Inaccurate thicknesses may lead to significant uncertainties in the timing of future changes to glaciers and their consequences for water resources or sea level rise. Unfortunately, glacier thickness distribution is rarely measured and consequently has to be estimated. In this study, we present an approach developed on the well documented Argentiere Glacier (French Alps) that uses surface mass balance (SMB) together with surface flow velocity data to quantify glacier thickness distribution over the entire surface of the glacier. We compare the results of our approach to those obtained applying Farinotti et al. (2009) approach. Our results show that glacier thickness distribution are significantly biased when the glacier SMB profile used to quantify the ice fluxes is not constrained with in situ measurements. We also show that even with SMB measurements available on the studied glacier, ice flux estimates can be inaccurate. This inability to correctly estimate ice fluxes from the apparent SMB may be due to the steady state assumption that is not respected from the available glacier surface topography data. Therefore, ice thickness measurements on few cross sections (four are used in this study) are required to constrain the ice flux estimates and lead to an overall agreement between the ice thickness estimations and measurements. Using our approach, the ice thicknesses only differ by 10% from observations in average, but can differ by up to 150 m (or 30%) locally. We also show that approaches that use the glacier surface slope can lead to large uncertainties given that the quantification of the slope is highly uncertain. The approach presented here does not pretend to be applied globally but rather as a tool to quantify ice thickness distribution over the entire surface of glaciers for which a few in situ surface mass balance and thickness data are available together with surface flow velocities that can be obtained for example from remote sensing.

Funnel-shaped surface depressions — Indicator or accelerant of rapid glacier disintegration? A case study in the Tyrolean Alps

Alpine glaciers have been retreating at extreme and historically unprecedented rates. While the general course of regional retreat rates reflects long-term climatic change, individual extreme events are closely related to the geomorphological settings and processes of the specific glacier. Nevertheless, these extreme events also influence the regional means and might be an important feedback mechanism accelerating the response of glaciers to climate change. In 2009, during the recent disintegration of the terminus of Gepatschferner (46°52′30″N, 10°45′25″E), a shallow circular depression appeared at the glacier tongue with a decrease of surface ice flow velocity to almost nil. In 2015 the area was ice-free. During a heavy precipitation event in August 2012, a subglacial sediment layer of >10m was flushed out, which accelerated the subsidence of the ice surface.The development of this 15 to 30m deep depression was monitored with a combination of methods in high detail, including direct ablation measurements and a time series of seven high-resolution airborne laser DEMs, plus recordings of ice flow velocity and surface elevation with DGPS. The thickness of ice and sediment layers was measured with vibroseismic soundings in 2012 and 2013. Similar developments were observed at three other glaciers with extreme retreat rates. Our investigation suggests that this mechanism has a major impact on and can be read as an indicator of a nonlinear increased response of glaciers to climate change.

Inversion of geothermal heat flux in a thermomechanically coupled nonlinear Stokes ice sheet model

Abstract. We address the inverse problem of inferring the basal geothermal heat flux from surface velocity observations using a steady-state thermomechanically coupled nonlinear Stokes ice flow model. This is a challenging inverse problem since the map from basal heat flux to surface velocity observables is indirect: the heat flux is a boundary condition for the thermal advection–diffusion equation, which couples to the nonlinear Stokes ice flow equations; together they determine the surface ice flow velocity. This multiphysics inverse problem is formulated as a nonlinear least-squares optimization problem with a cost functional that includes the data misfit between surface velocity observations and model predictions. A Tikhonov regularization term is added to render the problem well posed. We derive adjoint-based gradient and Hessian expressions for the resulting partial differential equation (PDE)-constrained optimization problem and propose an inexact Newton method for its solution. As a consequence of the Petrov–Galerkin discretization of the energy equation, we show that discretization and differentiation do not commute; that is, the order in which we discretize the cost functional and differentiate it affects the correctness of the gradient. Using two- and three-dimensional model problems, we study the prospects for and limitations of the inference of the geothermal heat flux field from surface velocity observations. The results show that the reconstruction improves as the noise level in the observations decreases and that short-wavelength variations in the geothermal heat flux are difficult to recover. We analyze the ill-posedness of the inverse problem as a function of the number of observations by examining the spectrum of the Hessian of the cost functional. Motivated by the popularity of operator-split or staggered solvers for forward multiphysics problems – i.e., those that drop two-way coupling terms to yield a one-way coupled forward Jacobian – we study the effect on the inversion of a one-way coupling of the adjoint energy and Stokes equations. We show that taking such a one-way coupled approach for the adjoint equations can lead to an incorrect gradient and premature termination of optimization iterations. This is due to loss of a descent direction stemming from inconsistency of the gradient with the contours of the cost functional. Nevertheless, one may still obtain a reasonable approximate inverse solution particularly if important features of the reconstructed solution emerge early in optimization iterations, before the premature termination.

Scalable and efficient algorithms for the propagation of uncertainty from data through inference to prediction for large-scale problems, with application to flow of the Antarctic ice sheet

The majority of research on efficient and scalable algorithms in computational science and engineering has focused on the forward problem: given parameter inputs, solve the governing equations to determine output quantities of interest. In contrast, here we consider the broader question: given a (large-scale) model containing uncertain parameters, (possibly) noisy observational data, and a prediction quantity of interest, how do we construct efficient and scalable algorithms to (1) infer the model parameters from the data (the deterministic inverse problem), (2) quantify the uncertainty in the inferred parameters (the Bayesian inference problem), and (3) propagate the resulting uncertain parameters through the model to issue predictions with quantified uncertainties (the forward uncertainty propagation problem)?We present efficient and scalable algorithms for this end-to-end, data-to-prediction process under the Gaussian approximation and in the context of modeling the flow of the Antarctic ice sheet and its effect on loss of grounded ice to the ocean. The ice is modeled as a viscous, incompressible, creeping, shear-thinning fluid. The observational data come from satellite measurements of surface ice flow velocity, and the uncertain parameter field to be inferred is the basal sliding parameter, represented by a heterogeneous coefficient in a Robin boundary condition at the base of the ice sheet. The prediction quantity of interest is the present-day ice mass flux from the Antarctic continent to the ocean.We show that the work required for executing this data-to-prediction process—measured in number of forward (and adjoint) ice sheet model solves—is independent of the state dimension, parameter dimension, data dimension, and the number of processor cores. The key to achieving this dimension independence is to exploit the fact that, despite their large size, the observational data typically provide only sparse information on model parameters. This property can be exploited to construct a low rank approximation of the linearized parameter-to-observable map via randomized SVD methods and adjoint-based actions of Hessians of the data misfit functional.

Recession of glaciers in the Suntar-Khayata Mountains and methodological consideration of its assessment

This study of glacial-cryogenic complexes of Suntar-Khayata Range is a logical continuation of the research started by M.M. Koreysha in 1957–1959. The studied key site is situated in the upstream of the Burgaly River on the northern slope of Mus-Khaya Mountain (2959 m a.s.l.). It includes glaciers № 29–31 and their ice-cored moraines of different ages. Our study is based on field geomorphologic mapping carried out in 2012, as well as on geospatial analysis of multi-temporal high resolution (1–0.6 m) aerial and satellite imagery. The modern terminus elevation of 16 investigated glaciers varies from 2090 to 2350 m a.s.l. It was found that glaciers’ terminal positions have risen on average from 2052±102 to 2226±114 m a.s.l. after 1945 aerial photography. The termini of Glacier № 29 and Glacier № 31 have retreated approximately by 500–650 m, while the ELA has risen by 61±38 m, from 2346±56 to 2407±55 m a.s.l. The total glaciated area has reduced in size by approximately 36%. The surface of Glacier № 31 has lowered by 50–70 m in its terminal part due to ablation. The estimated glacier shrinkage is valid only for the exposed ice area, since the large amount of glacier ice is buried in ablation moraines, glacier-derived rock glaciers and other glacial-cryogenic landforms. Some ice-cored rock glaciers are 30 to 80 m in thickness. A surface ice flow velocity has decreased 5–6 times compared to the 1957–1959 values. A 45-m-deep geothermal borehole drilled in the middle of Glacier № 31 in 1958–1959 has completely melted away and its mouth shifted 150 m down the glacier surface. The drilling equipment of 1958 is now on the top of a steep 70-m-high rock wall which was entirely covered with ice before 1958. This obviously reflects the magnitude of glacier shrinkage.

Radar-detected englacial stratigraphy in the Pensacola Mountains, Antarctica: implications for recent changes in ice flow and accumulation

AbstractWe used measurements of radar-detected stratigraphy, surface ice-flow velocities and accumulation rates to investigate relationships between local valley-glacier and regional ice-sheet dynamics in and around the Schmidt Hills, Pensacola Mountains, Antarctica. Ground-penetrating radar profiles were collected perpendicular to the long axis of the Schmidt Hills and the margin of Foundation Ice Stream (FIS). Within the valley confines, the glacier consists of blue ice, and profiles show internal stratigraphy dipping steeply toward the nunataks and truncated at the present-day ablation surface. Below the valley confines, the blue ice is overlain by firn. Data show that upward-progressing overlap of actively accumulating firn onto valley-glacier ice is slightly less than ice flow out of the valleys over the past ∼1200 years. The apparent slightly negative mass balance (-0.25 cm a-1) suggests that ice-margin elevations in the Schmidt Hills may have lowered over this time period, even without a change in the surface elevation of FIS. Results suggest that (1) mass-balance gradients between local valley glaciers and regional ice sheets should be considered when using local information to estimate regional ice surface elevation changes; and (2) interpretation of shallow ice structures imaged with radar can provide information about local ice elevation changes and stability.

Strain-rate estimates for crevasse formation at an alpine ice divide: Mount Hunter, Alaska

AbstractCrevasse initiation is linked to strain rates that range over three orders of magnitude (0.001 and 0.163 a-1) as a result of the temperature-dependent nonlinear rheological properties of ice and from water and debris inclusions. Here we discuss a small cold glacier that contains buried crevasses at and near an ice divide. Surface-conformable stratigraphy, the glacier’s small size, and cold temperatures argue for limited rheological variability at this site. Surface ice-flow velocities of (1.2-15.5) ± 0.472 m a- 1 imply classic saddle flow surrounding the ice divide. Numerical models that incorporate field-observed boundary conditions suggest extensional strain rates of 0.003-0.015 a- 1 , which fall within the published estimates required for crevasse initiation. The occurrence of one crevasse beginning at 50 m depth that appears to penetrate close to the bed suggests that it formed at depth. Field data and numerical models indicate that a higher interior stress at this crevasse location may be associated with steep convex bed topography; however, the dynamics that caused its formation are not entirely clear.

Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations

The Antarctic ice sheet (AIS) has the greatest potential for global sea level rise. This study simulates AIS ice creeping, sliding, tabular calving, and estimates the total mass balances, using a recently developed, advanced ice dynamics model, known as SEGMENT-Ice. SEGMENT-Ice is written in a spherical Earth coordinate system. Because the AIS contains the South Pole, a projection transfer is performed to displace the pole outside of the simulation domain. The AIS also has complex ice-water-granular material-bedrock configurations, requiring sophisticated lateral and basal boundary conditions. Because of the prevalence of ice shelves, a ‘girder yield’ type calving scheme is activated. The simulations of present surface ice flow velocities compare favorably with InSAR measurements, for various ice-water-bedrock configurations. The estimated ice mass loss rate during 2003–2009 agrees with GRACE measurements and provides more spatial details not represented by the latter. The model estimated calving frequencies of the peripheral ice shelves from 1996 (roughly when the 5-km digital elevation and thickness data for the shelves were collected) to 2009 compare well with archived scatterometer images. SEGMENT-Ice’s unique, non-local systematic calving scheme is found to be relevant for tabular calving. However, the exact timing of calving and of iceberg sizes cannot be simulated accurately at present. A projection of the future mass change of the AIS is made, with SEGMENT-Ice forced by atmospheric conditions from three different coupled general circulation models. The entire AIS is estimated to be losing mass steadily at a rate of ~120 km3/a at present and this rate possibly may double by year 2100.

Surface mass balance and ice flow of the glaciers Austre Lovénbreen and Pedersenbreen, Svalbard, Arctic

The glaciersAustre Lovenbreen and Pedersenbreen are located at Nylesund, Svalbard. The surface mass balance and ice flow velocity of both glaciers have been determined from the first year of observations (2005/2006), while the front edge of Austre Lovenbreen was also surveyed. The results are as follows：(1) The net mass balances of Austre Lovenbreen and Pedersenbreen are -0.44 and -0.20 m w.e., the annual ablation is -0.99 and -0.94 m w.e., and the corresponding equilibrium line altitudes are 478.10 and 494.87 m, respectively. (2) Austre Lovenbreen and Pedersenbreen are characterized as ice flow models of surge type glaciers in Svalbard. The horizontal vectors of the ice flow velocities are parallel or converge to the central lines of both glaciers, with lower velocities in the lower ablation areas and higher velocities in the middle and upper reaches of the glaciers. The vertical vectors of ice flow velocities show that there is a mass loss in the ablation areas, which reduces with increasing altitude, while there is a mass gain near the equilibrium line of Austre Lovenbreen. (3) The front edge of Austre Lovenbreen receded at an average rate of 21.83 m?a -1 , with remarkable variability a maximum rate of 77.30 m?a -1 and a minimum rate of 2.76 m?a -1 .

THE STUDIES OF SURFACE MASS BALANCE AND ICE FLOW ON GLACIERS AUSTRELOVéNBREEN AND PEDERSENBREEN,SVALBARD,ARCTIC

The glaciers Austre Lovenbreen and Pedersenbreen are located at Ny-lesund, Svalbard. Based on the observation of first year (2005/2006), surface mass balance and ice flow velocity of both glaciers have been analysed, while the front edge of Austre Lovenbreen has also been surveyed. The results are as following: (1) The net mass balance of Austre Lovenbreen and Pedersenbreen is -0.44 and -0.20 m w.e., respectively. Their annual ablation is -0.99 and -0.94 m w.e., respectively, and corresponding ELA is 478.10 and 494.87m, respectively. (2) Austre Lovenbreen and Pedersenbreen are characterized as ice flow model of surge-type glaciers in Svalbard. The level vectors of ice flow velocity are parallel or converge to the central lines of both glaciers, with slower velocities at the lower ablation area and relatively faster ones at the middle and upper part of glaciers. The mean, maximum and minimum of ice flow velocities on Austre Lovenbreen are 2.28, 3.91 and 0.81 m·a-1, and Pedersenbreen's are 6.74, 8.13 and 5.49 m·a-1. The vertical vectors of ice flow velocity show that there is a mass loss in the ablation area, which weakness with the increase of altitude, while there exists a mass gain near ELA on Austre Lovenbreen. The actual vertical displacement is in accord with the general pattern that motion is downward in the accumulation area, and is, by contrast, upward in the ablation area. (3) The front edge of Austre Lovenbreen has receded at an average rate of 21.83 m.a-1, with maximum 77.30 m.a-1 and minimum 2.76 m.a-1.

TEMPERATURE VARIATIONS AT THE GREAT WALL STATION (1985—2008) AND ZHONGSHAN STATION (1989—2008),ANTARCTIC

The glaciers Austre Lovenbreen and Pedersenbreen are located at Ny-lesund, Svalbard. Based on the observation of first year (2005/2006), surface mass balance and ice flow velocity of both glaciers have been analysed, while the front edge of Austre Lovenbreen has also been surveyed. The results are as following: (1) The net mass balance of Austre Lovenbreen and Pedersenbreen is -0.44 and -0.20 m w.e., respectively. Their annual ablation is -0.99 and -0.94 m w.e., respectively, and corresponding ELA is 478.10 and 494.87m, respectively. (2) Austre Lovenbreen and Pedersenbreen are characterized as ice flow model of surge-type glaciers in Svalbard. The level vectors of ice flow velocity are parallel or converge to the central lines of both glaciers, with slower velocities at the lower ablation area and relatively faster ones at the middle and upper part of glaciers. The mean, maximum and minimum of ice flow velocities on Austre Lovenbreen are 2.28, 3.91 and 0.81 m·a-1, and Pedersenbreen's are 6.74, 8.13 and 5.49 m·a-1. The vertical vectors of ice flow velocity show that there is a mass loss in the ablation area, which weakness with the increase of altitude, while there exists a mass gain near ELA on Austre Lovenbreen. The actual vertical displacement is in accord with the general pattern that motion is downward in the accumulation area, and is, by contrast, upward in the ablation area. (3) The front edge of Austre Lovenbreen has receded at an average rate of 21.83 m.a-1, with maximum 77.30 m.a-1 and minimum 2.76 m.a-1.

Surface Ice Flow Velocity and Tide Retrieval of the Amery Ice Shelf using Precise Point Positioning

Five days of continuous GPS observation data were collected in the frontal zone of the Amery ice shelf and subsequently post-processed using precise point position (PPP) technology based on precise orbit and clock products from the International GNSS service. The surface ice flow velocity of the observed point was derived from PPP to be 2.25 m/day toward the northeast with an azimuth of 41°. Major semi-diurnal and diurnal oceanic tide constituents could be recovered from the 5 days of PPP-derived height variations and compared well with a hydrodynamic ocean tide model. The PPP technique can replace double-difference GPS positioning in remote or hostile environments, and be used to retrieve the surface ice flow velocity without any reference station. Furthermore, the solution can be derived epoch-by-epoch with accuracy in the centimeters to decimeter range.