Ice Shelf Thickness Research Articles

The effect of ice shelf rheology on shelf edge bending

Abstract. The distribution of pressure on the vertical seaward front of an ice shelf has been shown to cause downward bending of the shelf if the ice is assumed to have vertically uniform viscosity. Satellite lidar observations show that many shelf edges bend upward and that the amplitude of upward deflections depends systematically on ice shelf thickness. A simple analysis is presented showing that upward bending of shelf edges can result from vertical variations in ice viscosity that are consistent with field observations and laboratory measurements. Resultant vertical variations in horizontal stress produce an internal bending moment that can counter the bending moment due to the shelf-front water pressure. Assuming a linear profile of ice temperature with depth and an Arrhenius relation between temperature and strain rate allows derivation of an analytic expression for internal bending moments as a function of shelf surface temperatures, shelf thickness and ice rheologic parameters. The effect of a power-law relation between stress difference and strain rate can also be included analytically. The key ice rheologic parameter affecting shelf edge bending is the ratio of the activation energy, Q, and the power-law exponent, n. For cold ice surface temperatures and large values of Q/n, upward bending is expected, while for warm surface temperatures and small values of Q/n downward bending is expected. The amplitude of bending should scale with the ice shelf thickness to the power 3/2, and this is approximately consistent with a recent analysis of shelf edge deflections for the Ross Ice Shelf. These scaling relations should help guide fully two-dimensional numerical simulations of shelf bending.

Pan‐Antarctic Assessment of Ice Shelf Flexural Responses to Ocean Waves

AbstractUnderstanding the drivers of iceberg calving from Antarctic ice shelves is important for future sea level rise projections. Ocean waves promote calving by imposing stresses and strains on the shelves. Previous modeling studies of ice shelf responses to ocean waves have focused on highly idealized geometries with uniform ice thickness and a flat seabed. This study leverages on a recently developed mathematical model that incorporates spatially varying geometries, combined with measured ice shelf thickness and seabed profiles, to conduct a statistical assessment of how 15 Antarctic ice shelves respond to ocean waves over a broad range of relevant wave periods, from swell to infragravity waves to very long period waves. The results show the most extreme responses at a given wave period are generated by features in the ice shelves and/or seabed geometries, depending on the wave regime. Relationships are determined between the median ice shelf response and the median shelf front thickness or the median water cavity depth. The findings provide further evidence of the role of ocean waves in large‐scale calving events for certain ice shelves (particularly the Wilkins) and indicate a possible role of ocean waves in calving events for other shelves (Larsen C and Conger). Further, the relationships determined provide a method to assess the potential for increased calving as ice shelves evolve with climate change, and, hence, contribute to assessments of future sea level rise.

Progressive unanchoring of Antarctic ice shelves since 1973

Mass loss of the Antarctic Ice Sheet has been driven primarily by the thinning of the floating ice shelves that fringe the ice sheet1, reducing their buttressing potential and causing land ice to accelerate into the ocean2. Observations of ice-shelf thickness change by satellite altimetry stretch back only to 1992 (refs. 1,3–5) and previous information about thinning remains unquantified. However, extending the record of ice-shelf thickness change is possible by proxy, by measuring the change in area of the surface expression of pinning points—local bathymetric highs on which ice shelves are anchored6. Here we measure pinning-point change over three epochs spanning the periods 1973–1989, 1989–2000 and 2000−2022, and thus by proxy infer changes to ice-shelf thickness back to 1973–1989. We show that only small localized pockets of ice shelves were thinning between 1973 and 1989, located primarily in the Amundsen Sea Embayment and the Wilkes Land coastline. Ice-shelf thinning spreads rapidly into the 1990s and 2000s and is best characterized by the proportion of pinning points reducing in extent. Only 15% of pinning points reduced from 1973 to 1989, before increasing to 25% from 1989 to 2000 and 37% from 2000 to 2022. A continuation of this trend would further reduce the buttressing potential of ice shelves, enhancing ice discharge and accelerating the contribution of Antarctica to sea-level rise.

Widespread slowdown in thinning rates of West Antarctic ice shelves

Abstract. Antarctica's floating ice shelves modulate discharge of grounded ice into the ocean by providing a backstress. Ice shelf thinning and grounding line retreat have reduced this backstress, driving rapid drawdown of key unstable areas of the Antarctic Ice Sheet, leading to sea-level rise. If ice shelf loss continues, it may initiate irreversible glacier retreat through the marine ice sheet instability. Identification of areas undergoing significant change requires knowledge of spatial and temporal patterns in recent ice shelf loss. We used 26 years (1992–2017) of satellite-derived Antarctic ice shelf thickness, flow, and basal melt rates to construct a time-dependent dataset of ice shelf thickness and basal melt on a 3 km grid every 3 months. We used a novel data fusion approach, state-of-the-art satellite-derived velocities, and a new surface mass balance model. Our data revealed an overall pattern of thinning all around Antarctica, with a thinning slowdown starting around 2008 widespread across the Amundsen, Bellingshausen, and Wilkes sectors. We attribute this slowdown partly to modulation in external ocean forcing, altered in West Antarctica by negative feedbacks between ice shelf thinning rates and grounded ice flow, and sub-ice-shelf cavity geometry and basal melting. In agreement with earlier studies, the highest rates of ice shelf thinning are found for those ice shelves located in the Amundsen and Bellingshausen sectors. Our study reveals that over the 1992–2017 observational period the Amundsen and Bellingshausen ice shelves experienced a slight reduction in rates of basal melting, suggesting that high rates of thinning are largely a response to changes in ocean conditions that predate our satellite altimetry record, with shorter-term variability only resulting in small deviations from the long-term trend. Our work demonstrates that causal inference drawn from ice shelf thinning and basal melt rates must take into account complex feedbacks between thinning and ice advection and between ice shelf draft and basal melt rates.

Ocean wave blocking by periodic surface rolls fortifies Arctic ice shelves

Abstract The Ward Hunt and Milne ice shelves are the present-day remnants of a much larger ice shelf that once fringed the coast of Ellesmere Island, Canada. These ice shelves possess a unique surface morphology consisting of wave-like rolls that run parallel to the shoreline. Setting aside the question of how these rolls originally developed, we consider the impact of this roll morphology on the stability of the ice shelf. In particular, we examine whether periodic variations in ice-shelf thickness and water depth implied by the rolls prevent the excitation of Lamb waves in the ice shelf. Using a hierarchy of numerical models, we find that there are band gaps in the flexural and extensional modes of the ice shelf, implying the existence of frequency ranges that lack wave motion. We show that an ice shelf with rolls is able to reflect waves in these frequency ranges that are incident upon its ice front, thereby mitigating undue stress and calving. We speculate that the roll morphology provides a “fitness” for survival that explains why rolls are observed in the oldest and thickest multiyear sea ice of the Arctic.

A comparison of contemporaneous airborne altimetry and ice-thickness measurements of Antarctic ice shelves

AbstractEstimates of ice shelf mass loss are typically based on surface height measurements, assuming hydrostatic equilibrium and estimated firn thickness. Recent investigations, however, challenge the assumption that ice shelves are freely floating, particularly in proximity to narrow structures such as basal channels and shear margins. We compare contemporaneous measurements of Antarctic ice shelf thickness, from ice-penetrating radar, to freeboard height, from laser altimetry, acquired during multiple airborne surveys. On average, the hydrostatic thickness differs from observed thickness by at least ~17 ± 98 m, but this difference varies well beyond the propagated error within and among ice shelves, and depends on the corrections applied. We find that uncertainty in firn thickness can account for most, but not all, of the imbalance. Overall, errors in hydrostatic thickness do not significantly impact estimated basal melt rates. Our results indicate that localized approaches to estimating ice shelf thickness and rates of change are not applicable at large scales, and vice versa, and point to the need for more abundant and accurate firn and ice thickness measurements to improve estimates and predictions of ice shelf mass loss.

Ocean–Ice Sheet Coupling in the Totten Glacier Area, East Antarctica: Analysis of the Feedbacks and Their Response to a Sudden Ocean Warming

We coupled together high-resolution versions of the ocean–sea ice model NEMO and the ice sheet model BISICLES configured to the Totten Glacier area and ran a series of simulations over the recent past (1995–2014) and under warming conditions (2081–2100; SSP4-4.5) with NEMO in stand-alone mode and with the coupled model to assess the effects of the coupling. During the recent past, the ocean–ice sheet coupling has increased the time-averaged value of the basal melt rate in both the Totten and Moscow University ice shelf cavities by 6.7% and 14.2%, respectively. The relationship between the changes in ice shelf thickness and ice shelf basal melt rate suggests that the effect of the coupling is not a linear response to the melt rate but rather a more complex response, driven partly by the dynamical component of the ice sheet model. The response of the ice sheet–ocean coupling due to the ocean warming is a 10% and 3% basal melt rate decrease in the Totten and Moscow University ice shelf cavities, respectively. This indicates that the ocean–ice sheet coupling under climate warming conditions dampens the basal melt rates. Our study highlights the importance of incorporating ocean–ice sheet coupling in climate simulations, even over short time periods.

The Dynamics of a Barotropic Current Impinging on an Ice Front

Abstract The vertical front of ice shelves represents a topographic barrier for barotropic currents that transport a considerable amount of heat toward the ice shelves. The blocking effect of the ice front on barotropic currents has recently been observed to substantially reduce the heat transport into the cavity beneath the Getz Ice Shelf in West Antarctica. We use an idealized numerical model to study the vorticity dynamics of an externally forced barotropic current at an ice front and the impact of ice shelf thickness, ice front steepness, and ocean stratification on the volume flux entering the cavity. Our simulations show that thicker ice shelves block a larger volume of the barotropic flow, in agreement with geostrophic theory. However, geostrophy breaks locally at the ice front, where relative vorticity and friction become essential for the flow to cross the discontinuity in water column thickness. The flow entering the cavity accelerates and induces high basal melt rates in the frontal region. Tilting the ice front, as undertaken in sigma-coordinate models, reduces this acceleration because the flow is more geostrophic. Viscous processes—typically exaggerated in low-resolution models—break the potential vorticity constraint and bring the flow deeper into the ice shelf cavity. The externally forced barotropic current can only enter the cavity if the stratification is weak, as strong vertical velocities are needed at the ice front to squeeze the water column beneath the ice shelf. If the stratification is strong, vertical velocities are suppressed and the barotropic flow is almost entirely blocked by the ice front. Significance Statement Ice shelves in West Antarctica are thinning, mostly from basal melting through oceanic heat entering the underlying ice shelf cavities. Thinning of ice shelves reduces their ability to buttress the grounded ice resting upstream, leading to sea level rise. To model the ice sheet’s contribution to sea level rise more accurately, the processes governing the oceanic heat flux into the ice shelf cavity must be articulated. This modeling study investigates the dynamics of a depth-independent current approaching the ice shelf; it corroborates previous findings on the blocking of such a current at the ice front. The amount of water that enters the cavity strongly depends on ice shelf thickness and ocean stratification. For a well-mixed ocean, the upper part of the flow can dive underneath the ice shelf and increase basal melting near the ice front. In a stratified ocean, the approaching depth-independent current is almost entirely blocked by the ice front.

Modeling Ocean Wave Transfer to Ross Ice Shelf Flexure

AbstractAn efficient mathematical model is presented for predicting the transfer of ocean waves to ice shelf flexure along two‐dimensional transects. The model incorporates varying ice shelf thickness and seabed bathymetry profiles, and is able to predict responses of large ice shelves over a broad frequency spectrum. The model is used to generate displacement and strain transfer functions for the Ross Ice Shelf (RIS) using geometries from the Bedmap2 data set. The transfer functions are validated against recent observations and used to study the influence of geometrical variations on strain transfer close to the shelf front. Predictions of RIS strain in response to example irregular incident swell and infragravity waves are generated over a wide region, and show similar maximum strains but contrasting spatial strain patterns. The model and results provide a basis for studying destabilizing impacts of ocean waves on the RIS.

Melting and Refreezing in an Ice Shelf Basal Channel at the Grounding Line of the Kamb Ice Stream, West Antarctica

AbstractIce shelves buttress ice streams and glaciers, slowing the rate at which they flow into the ocean. When this buttressing is reduced, either through increased melt or calving, the increased discharge of grounded ice upstream contributes to sea level rise. The thickness, strength, and stability of ice shelves can be influenced by channels in the ice base. Here, we focus on a subglacially sourced basal channel which is observed to have melted up to 50% of the ice shelf thickness. The channel extends 6 km upstream of the previously estimated grounding line of the stagnant Kamb Ice Stream. Using a combination of ground–based observations and remote sensing, we find that the channel is growing upstream over time. Over–snow radar surveying images the shape of the channel, constrains a steep inception, and shows that not all of the basal shape is manifest at the surface. Modern surface lowering at the upstream head of the channel is interpreted as a region of focused melt where a subglacial outlet meets the ocean cavity. We estimate this basal melt to be at least 35 m/a in a narrow (200 m × 1.5 km) zone. Downstream from the melt region, repeat phase sensitive radar observations reveal accretion contributing to the growth of a ledge on the true–right side of the channel. We conclude that the channel is likely formed by a retreating subglacial outlet which enhances basal melt episodically.

The instantaneous impact of calving and thinning on the Larsen C Ice Shelf

Abstract. The Antarctic Peninsula has seen rapid and widespread changes in the extent of its ice shelves in recent decades, including the collapse of the Larsen A and B ice shelves in 1995 and 2002, respectively. In 2017 the Larsen C Ice Shelf (LCIS) lost around 10 % of its area by calving one of the largest icebergs ever recorded (A68). This has raised questions about the structural integrity of the shelf and the impact of any changes in its extent on the flow of its tributary glaciers. In this work, we used an ice flow model to study the instantaneous impact of changes in the thickness and extent of the LCIS on ice dynamics and in particular on changes in the grounding line flux (GLF). We initialised the model to a pre-A68 calving state and first replicated the calving of the A68 iceberg. We found that there was a limited instantaneous impact on upstream flow – with speeds increasing by less than 10 % across almost all of the shelf – and a 0.28 % increase in GLF. This result is supported by observations of ice velocity made before and after the calving event. We then perturbed the ice-shelf geometry through a series of instantaneous, idealised calving and thinning experiments of increasing magnitude. We found that significant changes to the geometry of the ice shelf, through both calving and thinning, resulted in limited instantaneous changes in GLF. For example, to produce a doubling of GLF from calving, the new calving front needed to be moved to 5 km from the grounding line, removing almost the entire ice shelf. For thinning, over 200 m of the ice-shelf thickness had to be removed across the whole shelf to produce a doubling of GLF. Calculating the instantaneous increase in GLF (607 %) after removing the entire ice shelf allowed us to quantify the total amount of buttressing provided by the LCIS. From this, we identified that the region of the ice shelf in the first 5 km downstream of the grounding line provided over 80 % of the buttressing capacity of the shelf. This is due to the large resistive stresses generated in the narrow, local embayments downstream of the largest tributary glaciers.

The effect of compressed ice-shelf on acoustic-gravity wave propagation in a compressible ocean having elastic bottom

Acoustic-gravity wave propagation under a compressed ice-shelf is mathematically modelled under the assumption of small ice-shelf deflection, linearised compressible water wave theory, and ocean floor elasticity. The dispersion relation associated with the acoustic-gravity modes is derived. Special cases of the free surface gravity wave motion with a rigid and elastic bottom, and flexural-gravity wave motion with rigid ocean bottom are approximated by utilising the dispersion relation. The effect of ice-shelf thickness and compressive stress on the propagation speed is investigated for different acoustic-gravity modes. The pressure distribution along the water column and the ice-shelf due to different acoustic-gravity modes are illustrated. While ice thickness significantly alters the phase speed and pressure distribution, the compressive force generally has a negligible effect on the phase speed of acoustic-gravity modes. However, the compression has significant effect on the pressure distribution. A separate treatment for relatively low frequencies shows a significant impact of the compressive force on the spatial pressure distribution. The dominance of the leading acoustic-gravity modes on different physical characteristics is evident from their graphical representations. An orthogonality property for the depth-dependent functions of the velocity potential in the water region is established along with a few approximate forms. This mathematical model can be treated as a more general one that can unify several well-established models of acoustic-gravity wave propagation.

Swell-induced flexural vibrations of a thickening ice shelf over a shoaling seabed

A solution method is developed for a linear model of ice shelf flexural vibrations in response to ocean waves, in which the ice shelf thickness and seabed beneath the ice shelf vary over distance, and the ice shelf/sub–ice-shelf cavity are connected to the open ocean. The method combines a decomposition of the ice shelf displacement profile at a prescribed frequency of motion into mode shapes of free vibrations, a finite-element method for the cavity water motion and a non-local operator to connect to the open ocean. An investigation is conducted into the effects of ice shelf thickening, seabed shoaling and the grounding-line conditions on time-harmonic ice shelf vibrations, induced by regular incident waves in the swell regime. Furthermore, results are given for ice shelf vibrations in response to irregular incident waves by superposing time-harmonic responses, and ocean-to-ice-shelf transfer functions are derived. The findings add to evidence that ice shelves experience appreciable flexural vibrations in response to swell, and that ice shelf thickening and seabed shoaling can have a considerable influence on predictions of how ice shelves respond to ocean waves.

Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics

Abstract. Curvilinear channels on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the grounding line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel, ∼950 m wide and ∼200 m high, and its upstream continuation beneath Support Force Glacier, which feeds into the Filchner Ice Shelf, West Antarctica. Immediately seaward from the grounding line, below the basal channel, the seismic profiles show an ∼6.75 km long, 3.2 km wide and 200 m thick sedimentary sequence with chaotic to weakly stratified reflections we interpret as a grounding line fan deposited by a subglacial drainage channel directly upstream of the basal channel. Further downstream the seabed has a different character; it consists of harder, stratified consolidated sediments, deposited under different glaciological circumstances, or possibly bedrock. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a flat topography of the ice shelf base with an almost constant ice thickness gradient along-flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction between the ocean and subglacial hydrology to form basal channels in ice shelves.

Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves.

Ocean-driven basal melting of Antarctica’s floating ice shelves accounts for about half of their mass loss in steady-state, where gains in ice shelf mass are balanced by losses. Ice shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level, and the changing meltwater fluxes influence climate processes in the Southern Ocean. Existing continent-wide melt rate datasets have no temporal variability, introducing uncertainties in sea level and climate projections. Here, we combine surface height data from satellite radar altimeters with satellite-derived ice velocities and a new model of firn-layer evolution to generate a high-resolution map of time-averaged (2010–2018) basal melt rates, and time series (1994–2018) of meltwater fluxes for most ice shelves. Total basal meltwater flux in 1994 (1090±150 Gt/yr) was not significantly different from the steady-state value (1100±60 Gt/yr), but increased to 1570±140 Gt/yr in 2009, followed by a decline to 1160±150 Gt/yr in 2018. For the four largest “cold-water” ice shelves we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.

Extending the record of Antarctic ice shelf thickness change, from 1992 to 2017

Over the past two decades, Antarctic ice shelves have retreated, thinned and suffered catastrophic collapse. In this study we extended the 25-year long record of ice shelf thickness change in Antarctica, from 2010 to 2017. In the Amundsen Sea Sector where widespread ice shelf thinning dominates the signal, a 51% slowdown in the rate of ice loss over the last 7-years can be attributed to a coincident decrease in ocean temperatures in the region since 2010. Overall, ice shelves in Antarctica have thickened by an average of 1.3 m between 2010 and 2017 as ice losses from West Antarctica are compensated by ice gains in East Antarctica and the Antarctic Peninsula, reversing the negative trend of the previous two decades. The detailed spatial pattern of ice shelf thickness change across Antarctica, demonstrates the need for future investment in high spatial resolution observations and techniques.

Antarctic ice-shelf thickness changes from CryoSat-2 SARIn mode measurements: Assessment and comparison with IceBridge and ICESat

Ice-shelf thickness changes are of critical importance for understanding the stability of the Antarctic ice-sheet because they restrain the seaward flow of grounded glaciers. In this study, we find that neither backscatter nor leading-edge width contained in the least-squares fitting model can improve the accuracy of ice-shelf thickness change estimations from CryoSat-2, which is validated by comparing the CryoSat-2-derived elevation changes from least-squares fitting models with different combinations of waveform parameters against the Operation IceBridge ATM L4 data. Using the model without backscatter and leading-edge width to infer the thickness changes in Antarctic ice shelves from CryoSat-2, we find that the most significant thinning signals are mainly concentrated on the ice shelves along the Amundsen Sea coast, such as Getz, whose thickness variations are dominated by ocean-driven basal melting. This phenomenon has also been confirmed by the ICESat results. Overall, the Antarctic ice shelves volume changed on average by –0.34 ± 66.36 km3 yr−1 during the period from July 2010 to December 2016.

Instantaneous Antarctic ice sheet mass loss driven by thinning ice shelves

AbstractRecent observations show that the rate at which the Antarctic ice sheet (AIS) is contributing to sea level rise is increasing. Increases in ice‐ocean heat exchange have the potential to induce substantial mass loss through the melting of its ice shelves. Lack of data and limitations in modeling, however, has made it challenging to quantify the importance of ocean‐induced changes in ice shelf thickness as a driver for ongoing mass loss. Here, we use a numerical ice sheet model in combination with satellite observations of ice shelf thinning from 1994 to 2017 to quantify instantaneous changes in ice flow across all AIS grounding lines, resulting from changes in ice shelf buttressing alone. Our process‐based predictions are in good agreement with observed spatial patterns of ice loss, providing support for the notion that a significant portion of the current ice loss of the AIS is ocean driven and caused by a reduction in ice shelf buttressing.

A nonconforming hydroelastic triangle for ice shelf modal analysis

Hydroelastic oscillations of ice shelves, induced by the action of ocean waves, produce deflection and stresses that could potentially lead to calving events. Due to the large horizontal span of several Antarctic ice shelves, like the Ross, Ronne or Larsen C, hydroelastic models for the ice shelf/ice shelf cavity configuration based on long wave approximations can be very effective. Such a model, based on the linearised Shallow Water Equations and the Kirchhoff–Love bending theory for slender plates is considered. For ice shelf modal analysis, in the framework of the specific model, a nonconforming hydroelastic finite element is developed. The new hydroelastic triangle is based on coupling Specht’s plate element with a linear triangle for the velocity potential approximation. It enables explicit computation of the hydroelastic coupling matrix and optimal convergence rates for the eigenpairs. The element efficiency is verified against a semi-analytical solution and the theoretically predicted convergence rates are validated for solutions with sufficient regularity. The SHEEL element (Specht HydroElastic ELement) can be used for cases of variable bathymetry and mild variations of the ice shelf thickness. The same element can be employed for time domain hydroelastic analysis with very slight modifications. A model of the Larsen C ice shelf is considered as a case study.

Antarctic ice shelf thickness change from multimission lidar mapping

Abstract. We calculate rates of ice thickness change and bottom melt for ice shelves in West Antarctica and the Antarctic Peninsula from a combination of elevation measurements from NASA–CECS Antarctic ice mapping campaigns and NASA Operation IceBridge corrected for oceanic processes from measurements and models, surface velocity measurements from synthetic aperture radar, and high-resolution outputs from regional climate models. The ice thickness change rates are calculated in a Lagrangian reference frame to reduce the effects from advection of sharp vertical features, such as cracks and crevasses, that can saturate Eulerian-derived estimates. We use our method over different ice shelves in Antarctica, which vary in terms of size, repeat coverage from airborne altimetry, and dominant processes governing their recent changes. We find that the Larsen-C Ice Shelf is close to steady state over our observation period with spatial variations in ice thickness largely due to the flux divergence of the shelf. Firn and surface processes are responsible for some short-term variability in ice thickness of the Larsen-C Ice Shelf over the time period. The Wilkins Ice Shelf is sensitive to short-timescale coastal and upper-ocean processes, and basal melt is the dominant contributor to the ice thickness change over the period. At the Pine Island Ice Shelf in the critical region near the grounding zone, we find that ice shelf thickness change rates exceed 40 m yr−1, with the change dominated by strong submarine melting. Regions near the grounding zones of the Dotson and Crosson ice shelves are decreasing in thickness at rates greater than 40 m yr−1, also due to intense basal melt. NASA–CECS Antarctic ice mapping and NASA Operation IceBridge campaigns provide validation datasets for floating ice shelves at moderately high resolution when coregistered using Lagrangian methods.