Ice Flow Velocity Research Articles

Potential to recover a record of Holocene climate and sea ice from Müller Ice Cap, Canada

Abstract Müller Ice Cap sits on Umingmat Nunaat (Axel Heiberg Island), Nunavut, Canada, ~ 80°N. Its high latitude and elevation suggest it experiences relatively little melt and preserves an undisturbed paleoclimate record. Here, we present a suite of field measurements, complemented by remote sensing, that constrain the ice thickness, accumulation rate, temperature, ice-flow velocity, and surface-elevation change of Müller Ice Cap. These measurements show that some areas near the top of the ice cap are more than 600 m thick, have nearly stable surface elevation, and flow slowly, making them good candidates for an ice core. The current mean annual surface temperature is −19.6 °C, which combined with modeling of the temperature profile indicates that the ice is frozen to the bed. Modeling of the depth-age scale indicates that Pleistocene ice is likely to exist with measurable resolution (300–1000 yr m−1) 20–90 m from the bed, assuming that Müller Ice Cap survived the Holocene Climatic Optimum with substantial ice thickness (~400 m or more). These conditions suggest that an undisturbed Holocene climate record could likely be recovered from Müller Ice Cap. We suggest 91.795°W, 79.874°N as the most promising drill site.

Long-term evolution of the Sulzberger Ice Shelf, West Antarctica: Insights from 74-year observations and 2022 Hunga-Tonga volcanic tsunami-induced calving

On January 15, 2022, the eruption of the Hunga-Tonga volcano unleashed a tsunami that rapidly traversed the Pacific Ocean, soon reaching the Sulzberger Ice Shelf (SIS), West Antarctica. In the aftermath, the West Sulzberger Ice Shelf (WSIS) experienced a significant calving event, shedding 106 km2 of ice and reducing its size to the smallest recorded since 1948. To investigate the potential association between this calving event and the tsunami, and to elucidate the long-term evolution of the WSIS, this study employed tide gage records and remote sensing data for an extensive cross-cycle observation spanning 74 years. The results indicate that post-2014, the WSIS exhibited heightened instability, manifesting as an increased frequency of calving events, a shift from an expanding to a contracting shelf area, and accelerated ice flow velocities (Video S1). The critical rift, instrumental in the 2022 calving, also displayed an accelerated widening rate post-2014, culminating in rapid expansion upon the tsunami's arrival, completing the final 2% of the iceberg's detachment boundary. Modeling results quantify the tsunami induced flexural strains on the ice shelf, with peak values occurring near the region of the subsequent calving event. Notably, multiple calving events during the study period coincided with local minima in landfast sea ice extent, underscoring its protective role for the ice shelf. Furthermore, a significant decline in landfast sea ice near the SIS had been observed over the past two decades, suggesting a weakening of this protective effect. A combination of modeling results and comparative analysis with other similar calving events suggests that tsunamis tend to expedite ice shelf calving predominantly when the shelf is already teetering on instability, which casts a shadow on the SIS's future resilience against natural hazards.

Investigating the dynamics and interactions of surface features on Pine Island Glacier using remote sensing and deep learning

Pine Island Glacier (PIG), the largest glacier in the Amundsen Sea Embayment of West Antarctica, has contributed to over a quarter of the observed sea level rise around Antarctica. In recent years, multiple observations have confirmed its continuous retreat, ice flow acceleration and profound surface melt. Understanding these changes is crucial for accurately monitoring ice mass discharge and future Antarctic contributions to sea level rise. Therefore, it is essential to investigate the complex interactions between these variables to comprehend how they collectively affect the overall stability of the intricate PIG system. In this study, we utilized high-resolution remote sensing data and deep learning method to detect and analyze the spatio-temporal variations of surface melt, ice shelf calving, and ice flow velocity of the PIG from 2015 to 2023. We explored the correlations among these factors to understand their long-term impacts on the glacier's stability. Our findings reveal a retreat of 26.3 km and a mass loss of 1001.6 km2 during 2015–2023. Notably, extensive surface melting was observed, particularly in the 2016/2017 and 2019/2020 melting seasons. Satellite data vividly illustrate prolonged and intense melting periods, correlating with a significant retreat in the glacier's terminus position in 2019/2020. Furthermore, the comprehensive analysis of surface melting and the cumulative retreat of the ice shelf from 2017 to 2020 on the PIG shows a temporal relationship with subsequent significant changes in ice flow velocity, ranging from 10.9 to 12.2 m d−1, with an average acceleration rate of 12%. These empirical findings elucidate the intricate relationship among surface melt, ice flow velocity, and consequential glacier dynamics. A profound understanding of these interrelationships holds paramount importance in glacier dynamic changes and modeling, providing invaluable insights into potential glacier responses to global climate change.

Rapid deceleration in the ice-flow velocity of the Shirase Glacier ice tongue and its influence on the velocity field: Observations from Sentinel-1 C-SAR

Temporal and spatial variations in the ice-flow speed of Shirase Glacier ice tongue in East Antarctica between July 2018 and December 2021 were investigated using Sentinel-1 C-band Synthetic Aperture Radar (C-SAR) imagery. We identified pronounced slowdown events in the eastern part of the outer ice tongue, 30–40 km from the grounding line in 2020 and 55 km in 2021. Comparison of ice thickness and bathymetry in areas where the deceleration events occurred suggests that the events were caused by icebergs grounding or landing on the seafloor. The absence of slowdown propagation towards the grounding line demonstrates the ice tongue offers very limited buttressing. This study contributes to a better understanding of the factors influencing glacier dynamics, particularly in the context of grounding events and their localized impacts.

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.

Dynamic change of a typical surging glacier in the Qinghai tibet plateau based on satellite remote sensing

With global climate change, some mountain glaciers in the Qinghai–Tibet Plateau region are experiencing rapid melting, retreating, and acceleration. Surge-type glaciers are important objects for glacier dynamics research in this region, as sudden surge may threaten human activities and lives. This study focuses on the Shahrek Glacier. Based on multi-source remote sensing images from 2000 to 2023, we generated long-term ice flow velocity maps of the glacier using image template matching technology. Together with its terminus position over this period, the surge dynamics of Shahrek Glacier were analyzed. The glacier surge commenced in September 2016 and terminated in November 2018, reaching a maximum ice velocity of almost 1,200 m/a, which is 9–10 times its ice velocity in the quiescent phase. A substantial change in the magnitude of the ice flow before and after the onset of the Shahrek Glacier surge was observed; the surge comprised five main phases: pre-surge stable, accelerated, surge, decelerated, and stabilized periods. The Shahrek Glacier was retreating from the position of the glacier-terminal ablation zone prior to the onset of leapfrogging. We analyzed the relationship between Shahrek Glacier dynamics and climate and the surge mechanism surge, considering data from meteorological stations in neighboring regions.

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.

Evolution of sub-ice-shelf channels reveals changes in ocean-driven melt in West Antarctica

Abstract Basal channels, which are troughs carved into the undersides of ice shelves by buoyant plumes of water, are modulators of ice-shelf basal melt and structural stability. In this study, we track the evolution of 12 large basal channels beneath ice shelves of the Amundsen and Bellingshausen seas region in West Antarctica using the Landsat record since its start in the 1970s through 2020. We observe examples of channel growth, interactions with ice-shelf features, and systematic changes in sinuosity that give insight into the life cycles of basal channels. We use the last two decades of the record, combined with contemporary ice-flow velocity datasets, to separate channel-path evolution into components related to advection by ice flow and those controlled by other forcings, such as ocean melt or surface accumulation. Our results show that ice-flow-independent lateral channel migration is overwhelmingly to the left when viewed down-flow, suggesting that it is dominated by Coriolis-influenced ocean melt. By applying a model of channel-path evolution dominantly controlled by ice flow and ocean melt, we show that the majority of channels surveyed exhibit non-steady behavior that serves as a novel proxy for increased ocean forcing in West Antarctica starting at least in the early 1970s.

60-YEAR REMOTE SENSING OBSERVATIONS REVEALED CROSS-CYCLE EVOLUTION OF THE BRUNT ICE SHELF IN THE CONTEXT OF GLOBAL WARMING

Abstract. The Antarctic Ice Sheet (AIS) holds the potential to raise global sea levels by a staggering 57 m. Ice shelves, extensions of these ice sheets into the ocean, play a crucial role in stabilizing the upstream ice sheet. The Brunt Ice Shelf (BIS), located in the Southern Weddell Sea region and proximal to the continental shelf break, stands as a vital indicator for the region's response to global climate warming. Hence, this study systematically employs a range of remote sensing and field data, including remote sensing data from 1963 to 2023 (ARGON images, Landsat1-9 images, Sentinel-1 images, ICESat-2 altimetry data, etc.) and in-situ ice flow velocity data since 1956, to conduct a comprehensive analysis of the BIS's calving cycle and evolution over nearly six decades. The results reveal a significant exacerbation of both dynamical and structural instabilities in the BIS compared to the calving cycle in the 1970s. Combining analyses of air temperature from meteorological station, water temperature from ocean models and in-situ measurements such as Conductivity-Temperature-Depth profiles, the study suggests that the increased instability of the BIS is likely linked to the intrusion of warmer currents over the continental shelf. This research provides valuable insights into the evolving behavior of the BIS in response to changing climate conditions, underscoring the critical role of remote sensing data in advancing our understanding of these processes on a global scale.

Response of lacustrine glacier dynamics to atmospheric forcing in the Cordillera Darwin

Abstract Calving glaciers respond quickly to atmospheric variability through ice dynamic adjustment. Particularly, single weather extremes may cause changes in ice-flow velocity and terminus position. Occasionally, this can lead to substantial event-driven mass loss at the ice front. We examine changes in terminus position, ice-flow velocity, and calving flux at the grounded lacustrine Schiaparelli Glacier in the Cordillera Darwin using geo-referenced time-lapse camera images and remote sensing data (Sentinel-1) from 2015 to 2022. Lake-level records, lake discharge measurements, and a coupled energy and mass balance model provide insight into the subglacial water discharge. We use downscaled reanalysis data (ERA5) to identify climate extremes and track land-falling atmospheric rivers to investigate the ice-dynamic response on possible atmospheric drivers. Meltwater controls seasonal variations in ice-flow velocity, with an efficient subglacial drainage system developing during the warm season and propagating up-glacier. Calving accounts for 4.2% of the ice loss. Throughout the year, warm spells, wet spells, and landfalling atmospheric rivers promote calving. The progressive thinning of the ice destabilizes the terminus position, highlighting the positive feedback between glacier thinning, near-terminus ice-flow acceleration, and calving flux.

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.

Flow regimes and basal normal stresses in rock–ice avalanches by experimental rotating drum tests

Rock–ice avalanches have been observed to travel longer distances than rock avalanches, and their flow regime may vary as ice melts. Several reports on the deposition characteristics, mobility, and hazard assessment of rock–ice avalanches have been published. However, thus far, no systematic investigation on the flow regime evolution and basal stress characteristics of rock–ice avalanches have been conducted. In this study, flow regime is characterized by several dimensionless spaces bounded by parameters (Froude number, Savage number, Friction number, Mass number, and Reynolds number). To examine the mechanisms controlling basal stress, a 12.56-cm2 load plate was used to measure the basal normal stress in a 1.5-m-diameter 30-cm-wide vertically rotating drum in a temperature-controlled laboratory. Results demonstrate that the flow regimes of rock–ice avalanche, dominated by short-term collision or long-term friction, considerably vary due to the influence of initial conditions (ice content, grain size, flow velocity, and meltwater). Although rock–ice avalanches under experimental and natural conditions substantially differ, the dominant stress mechanism is the same as that in the movement process. Other findings show that the average normal stress profiles vary significantly with the ice content and meltwater volume. Furthermore, the mean stress (σ¯), maximum stress (σ1%), and standard deviation (σsd) demonstrate the close relationship between fluctuations, static loads of flow, and grain interactions. Grain agitation in the rock–ice avalanche is caused by intense collisions depending on grain size, velocity, and fluid matrix at the grain scale level.

Satellite record reveals 1960s acceleration of Totten Ice Shelf in East Antarctica

Wilkes Land and Totten Glacier (TG) in East Antarctica (EA) have been losing ice mass significantly since 1989. There is a lack of knowledge of long-term mass balance in the region which hinders the estimation of its contribution to global sea level rise. Here we show that this acceleration trend in TG has occurred since the 1960s. We reconstruct ice flow velocity fields of 1963–1989 in TG from the first-generation satellite images of ARGON and Landsat-1&4, and build a five decade-long record of ice dynamics. We find a persistent long-term ice discharge rate of 68 ± 1 Gt/y and an acceleration of 0.17 ± 0.02 Gt/y2 from 1963 to 2018, making TG the greatest contributor to global sea level rise in EA. We attribute the long-term acceleration near grounding line from 1963 to 2018 to basal melting likely induced by warm modified Circumpolar Deep Water. The speed up in shelf front during 1973–1989 was caused by a large calving front retreat. As the current trend continues, intensified monitoring in the TG region is recommended in the next decades.

Monitoring ice flow velocity of Petermann glacier combined with Sentinel-1 and −2 imagery

Synthetic Aperture Radar (SAR) images are commonly used to monitor glacier flow velocity at Greenland Ice Sheet (GrIS). However, offset-tracking with SAR imagery in summer usually show poor quality because the rapid ice surface freezing-melting cycles contaminating the surface backscattering characteristic, while optical images are less sensitive to this phenomenon. In this study, we combine Sentinel-1 and -2 images to create the glacier velocity time series for the Petermann glacier, located in the northern GrIS. Firstly, the offset-tracking technique is employed to acquire the initial deformation fields with SAR and optical sensors separately, each SAR and/or optical acquisition is tracked with its closest next three acquisitions. Next, after removing the bad matchings, the least squares method based on connected components is employed to calculate the time series of glacier velocity for Sentinel-1 and −2, separately. Finally, these two kinds of derived time series are integrated with a weighted least squares method, where weights are evaluated according to the estimated RMSEs in the last step. Error propagation analysis suggests RMSEs of the single pair of Sentinel-1 and −2 images offset-tracking are ∼ 0.22 m and ∼ 2.5 m for Petermann glaciers. Standard deviation of the difference between Sentinel-1 and Sentinel-2 measured velocity are ∼ 0.25 m/day. Compared with 6-day velocity fields product, NSIDC (National Snow and Ice Data Center) −0766, which is only derived with Sentinel-1observations, our results show good agreement and less defects in summer. The differences are ∼ 0.20 m/day in non-melting seasons and ∼ 0.34 m/day in summer. Longitudinal velocity differences growing in 2019 and 2020 at ∼ 20 Km up to the terminus are consistency with the crevasse expansion, indicating another calving event is approaching. This research finds that the fusion of Sentinel-1 and −2 offset-tracking results improves the completeness of the ice movement time series for polar glaciers.

A REPLICABLE OPEN-SOURCE MULTI-CAMERA SYSTEM FOR LOW-COST 4D GLACIER MONITORING

Abstract. Image-based monitoring has emerged as a prevalent technique for sensing mountain environments. Monoscopic time-lapse cameras, which rely on digital image correlation to quantify glacier motion, have limitations due to the need for a Digital Elevation Model for deriving 3D flow velocity fields. Multi-camera systems overcome this limitation, as they allow for a 3D reconstruction of the scene. This paper presents a replicable low-cost stereoscopic system designed for 4D glacier monitoring. The system consists of independent and autonomous units, built from off-the-shelves components, such as a DSLR camera, an Arduino microcontroller, and a Raspberry Pi Zero, reducing costs compared to pre-built time-lapse cameras. The units are energetically self-sufficient and resistant to harsh alpine conditions. The system was successfully tested for more than a year to monitor the northwest terminus of the Belvedere Glacier (Italian Alps). Daily stereo-pairs acquired were processed with Structure-from-Motion to derive 3D point clouds of the glacier terminus and estimate glacier retreat and ice volume loss. By combining the information about ice volume loss with ablation estimates and ice flow velocity information, e.g., derived from monoscopic-camera time series, a multi-camera system enables a comprehensive understanding of sub-seasonal glacier dynamics.

Sea Tide Influence on Ice Flow of David Drygalski’s Ice Tongue Inferred from Geodetic GNSS Observations and SAR Offset Tracking Analysis

David Glacier and Drygalski Ice Tongue are massive glaciers in Victoria Land, Antarctica. The ice from the East Antarctic Ice Sheet is drained through the former, and then discharged into the western Ross Sea through the latter. David Drygalski is the largest outlet glacier in Northern Victoria Land, floating kilometers out to sea. The floating and grounded part of the David Glacier are the main focus of this article. During the XXI Italian Antarctic Expedition (2005–2006), within the framework of the National Antarctic Research Programme (PNRA), two GNSS stations were installed at different points: the first close to the grounding line of David Glacier, and the second approximately 40 km downstream of the first one. Simultaneous data logging was performed by both GNSS stations for 24 days. In the latest data processing, the kinematic PPP technique was adopted to evaluate the dominant diurnal components and the very small semi-diurnal variations in ice motion induced by the ocean tide and the mean ice flow rates of both GNSS stations. Comparison of the GNSS time series with predicted ocean tide calculated from harmonic coefficients of the nearest tide gauge stations, installed at Cape Roberts and Mario Zucchelli Station, highlight different local response of the glacier to ocean tide, with a minor amplitude of vertical motion at a point partially anchored at the bedrock close to the grounding line. During low tide, the velocity of the ice flow reaches its daily maximum, in accordance with the direction of seawater outflow from the fjord into the ocean, while the greatest daily tidal excursion generates an increase in the horizontal ice flow velocity. With the aim to extend the analysis in spatial terms, five COSMO-SkyMED Stripmap scenes were processed. The comparison of the co-registered offset tracking rates, obtained from SAR images, with the GNSS estimation shows good agreement.

Estimating thickness of Zemu glacier, Sikkim (India) using ice-flow velocity approach: a geoinformatics based perspective

Estimating thickness of Zemu glacier, Sikkim (India) using ice-flow velocity approach: a geoinformatics based perspective

New metrics reveal the evolutionary continuum behind the morphological diversity of subglacial bedforms

Understanding the formation of subglacial bedforms is primordial to constrain ice-meltwater-bed interactions and the dynamics of past and present ice sheets. However, the difficulty to observe active subglacial bedforms below present-day ice sheets implies that their formation and evolution are essentially deduced from the inversion of morphological and sedimentological data from palaeo-subglacial bedforms. In this study, the morphological characteristics of subglacial bedforms are explored with a new approach based on the combination of three dimensionless morphometric indices i.e., circularity index, sinuosity index and elongation component ratio. We measure the spatial distribution of these indices on an unpublished database composed of ~13,500 digitized bedforms taken from two selected portions of the Irish Ice Sheet and Laurentide Ice Sheet beds considering that (1) all subglacial bedforms in each region were formed under a single ice flow configuration and (2) the bedforms may have developed either orthogonal, parallel, or oblique to ice displacement directions. Our results reveal a morphometric and spatial continuum along which ribbed bedforms of various lengths and shapes – ranging from circular to elongated flow-transverse forms – are incipient bedforms that can evolve into transitional sinuous ribbed bedforms, then into predominantly flow-parallel sinuous bedforms that progressively realign to form streamlined bedforms. Assuming the glaciological contexts of selected study areas, this continuum may provide a new geomorphic criterion to constrain spatial variations in subglacial conditions (e.g. ice flow velocity, bedrock characteristics, meltwater pressure).

An Improved Intersection Method for Positioning and Its Application to Dalk Glacier, East Antarctica

Stake measurement is a significant ground-observation method used to monitor glacier dynamics in the cryosphere and validate the reliability of remotely sensed investigations. However, some stake observation records obtained by total stations have not been efficiently utilized via the classic forward intersection method. The forward intersection method requires a pair of cognominal observation records and cannot function if stakes are only observed from one control point at a stake measurement, which commonly occurs in measurements. Therefore, we propose an improved intersection method that combines stake trajectories and sightlines, the trajectory-sightline intersection method, which requires only a single observation record. In the processing of stake identification, location and elevation from the trajectory-sightline intersection method are constrained by the velocity and surface altitude of the glacier. Then, the trajectory-sightline intersection method is applied to the stake measurement of Dalk Glacier in East Antarctica. The results show that the trajectory-sightline intersection method extracted an additional 44 intersections, thus increasing the data utilization ratio by 20.35%. Moreover, leave-p-out cross-validation indicated that the trajectory-sightline intersection method, with an average offset of 0.88±0.54 m in the horizontal position and 0.26±0.12 m at the elevation, has similar accuracy to the differential global positioning system (DGPS) applied to Livingston Island. The ice flow velocities of Dalk Glacier calculated from trajectory-sightline intersections agree with those from forward intersections (the mean velocity difference is 0.47 m·year−1). Therefore, the trajectory-sightline intersection method is an effective method for improving data utilization and obtaining stake locations and glacier velocities.

Timescales of outlet-glacier flow with negligible basal friction: theory, observations and modeling

Abstract. The timescales of the flow and retreat of Greenland's and Antarctica's outlet glaciers and their potential instabilities are arguably the largest uncertainty in future sea-level projections. Here we derive a scaling relation that allows the comparison of the timescales of observed complex ice flow fields with geometric similarity. The scaling relation is derived under the assumption of fast, laterally confined, geometrically similar outlet-glacier flow over a slippery bed, i.e., with negligible basal friction. According to the relation, the time scaling of the outlet flow is determined by the product of the inverse of (1) the fourth power of the width-to-length ratio of its confinement, (2) the third power of the confinement depth and (3) the temperature-dependent ice softness. For the outflow at the grounding line of streams with negligible basal friction, this means that the volume flux is proportional to the ice softness and the bed depth, but goes with the fourth power of the gradient of the bed and with the fifth power of the width of the stream. We show that the theoretically derived scaling relation is supported by the observed velocity scaling of outlet glaciers across Greenland as well as by idealized numerical simulations of marine ice-sheet instabilities (MISIs) as found in Antarctica. Assuming that changes in the ice-flow velocity due to ice-dynamic imbalance are proportional to the equilibrium velocity, we combine the scaling relation with a statistical analysis of the topography of 13 MISI-prone Antarctic outlets. Under these assumptions, the timescales in response to a potential destabilization are fastest for Thwaites Glacier in West Antarctica and Mellor, Ninnis and Cook Glaciers in East Antarctica; between 16 and 67 times faster than for Pine Island Glacier. While the applicability of our results is limited by several strong assumptions, the utilization and potential further development of the presented scaling approach may help to constrain timescale estimates of outlet-glacier flow, augmenting the commonly exploited and comparatively computationally expensive approach of numerical modeling.