Thwaites Glacier Research Articles

Geological sketch map and implications for ice flow of Thwaites Glacier, West Antarctica, from integrated aerogeophysical observations.

The geology beneath Thwaites Glacier, the Antarctic glacial catchment most vulnerable to climate change, is unknown. Thwaites Glacier lies within the West Antarctic Rift System, but details of the subglacial geology relevant to glacial flow, including sediment availability, underlying lithology, and heat flux, are lacking. We present the first sketch map of the subglacial geology of Thwaites Glacier, interpreted from maps of airborne gravity, magnetic and radar data, supported by 2D models and 3D inversion of subsurface properties, and the regional geological context. A zone of Cretaceous mafic magmatism extending ~200 km inland from the coast is interpreted, while sedimentary basins are restricted to a region 150 to 200 km inboard of the coast, underlying just 20% of the catchment. Several granitic subglacial highlands are identified, forming long-lived topographic highs. Our geological interpretation places constraints on the basal properties of Thwaites Glacier, laying the foundation for both improved predictions of ice sheet change and studies of West Antarctic tectonics.

Volcanogenic fluxes of iron from the seafloor in the Amundsen Sea, West Antarctica

The Amundsen Sea in the Pacific sector of West Antarctica receives meltwater from the fastest retreating Antarctic glaciers, and its coastal polynyas host the highest primary productivity per unit area observed on the Antarctic continental shelf. Polynya productivity provides the base for a robust, diverse ecosystem and is controlled primarily by light and the availability of the micronutrient iron (Fe). While the sources of Fe in the region are not yet certain, Fe could be transported within modified Circumpolar Deep Water (mCDW) that intrudes onto the retrograde shelf and into ice shelf cavities, where it gains buoyancy through the addition of glacial meltwater and is injected into the upper water column when it exits the cavity. Thus, fluxes of dissolved Fe from the seafloor into in-flowing mCDW may ultimately be a source of Fe to the euphotic zone in the Amundsen Sea. To investigate the surface sediment biogeochemistry and the potential for a significant benthic flux of Fe to the waters on the Amundsen Sea shelf, sediment cores were collected at two sites close to the calving fronts of the Pine Island and Thwaites Glacier ice shelves. Pore water was analyzed for trace element content, and sediment was analyzed for physical and chemical properties including organic carbon and trace elements. Using a novel approach based on hypothesized Fe speciation and colloidal particle radius, theoretical Fe fluxes were calculated from pore water gradients and porosity. The fluxes reveal a spatially variable Fe input to the lower water column that could ultimately fertilize primary productivity. Supported by geochemical and physical evidence, we conclude that submarine weathering of volcanic glass grains observed and quantified in seabed sediments at the Pine Island site drives nonreductive Fe fluxes that are 100-fold higher than at the Thwaites site. This study highlights the need for further investigations of benthic-pelagic coupling in the Amundsen Sea region, which will likely be impacted in coming decades by accelerating glacial melting.

Limited Impact of Thwaites Ice Shelf on Future Ice Loss From Antarctica

AbstractThwaites Ice Shelf (TWIS), the floating extension of Thwaites Glacier, West Antarctica, is changing rapidly and may completely disintegrate in the near future. Any buttressing that the ice shelf provides to the upstream grounded Thwaites glacier will then be lost. Previously, it has been argued that this could lead to onset of dynamical instability and the rapid demise of the entire glacier. Here we provide the first systematic quantitative assessment of how strongly the upstream ice is buttressed by TWIS and how its collapse affects future projections. By modeling the stresses acting along the current grounding line, we show that they deviate insignificantly from the stresses after ice shelf collapse. Using three ice‐flow models, we furthermore model the transient evolution of Thwaites Glacier and find that a complete disintegration of the ice shelf will not substantially impact future mass loss over the next 50 years.

In the Quest of a Parametric Relation Between Ice Sheet Model Inferred Weertman's Sliding‐Law Parameter and Airborne Radar‐Derived Basal Reflectivity Underneath Thwaites Glacier, Antarctica

AbstractNumerical ice sheet models use sliding laws to connect basal shear stress and ice velocity to simulate ice sliding. A sliding‐law parameter β2 is used to control Weertman's sliding law in numerical ice sheet models. Basal reflectivity derived from ice‐penetrating radar also provides information about frozen or thawed conditions underneath glaciers. To assess whether basal reflectivity can be used to constrain β2, we carry out statistical experiments between two recently published datasets: β2 inferred from three numerical ice sheet models (ISSM, Úa and STREAMICE) and airborne radar‐derived relative basal reflectivity from the AGASEA‐BBAS mission over Thwaites Glacier (TG). Our results show no robust correlation between the β2–relative reflectivity pair. Pearson's correlation coefficient, a test of linearity, ranges from −0.26 to −0.38. Spearman's correlation coefficient, which does not require a linear assumption, is also modest (∼−0.35). We conclude that β2 and relative basal reflectivity underneath TG do not infer similar basal conditions.

Reconstructing Continuous Ice Sheet Elevation Changes in the Amundsen Sea Sector During 2003–2021 by Merging Envisat, ICESat, CryoSat‐2, and ICESat‐2 Multi‐Altimeter Observations

AbstractThe Amundsen Sea (AS) sector in West Antarctica accounts for a significant proportion of Earth's ice losses and is the largest contributor of Antarctica's mass loss. To evaluate its contribution to global sea‐level rise, we reconstruct the long‐term continuous surface elevation changes (CSEC) record of the AS sector by an improved least‐squares plane fitting method (ILSPFM), which merged the relative surface elevation change (SEC) series instead of height from Envisat, ICESat, CryoSat‐2, and ICESat‐2 missions during 2003–2021. The accuracy of CSEC is improved by 25.9% using ILSPFM. The average rate of CSEC in the AS sector was −24.25 ± 0.48 cm yr−1 during 2003–2021. The largest signals of SEC are found over Pine Island, Thwaites, and Pope Glaciers, with the largest decline of SEC over Pope Glacier with a total SEC of −82.44 ± 7.21 m and an annual change rate of −4.34 ± 0.38 m yr−1. The ridge between Pine Island and Thwaites Glaciers is found in the AS sector, indicating that the change of ice sheet is dynamic thinning and closely related to the topography and the distance from the grounding line. Compared with meteorological data sets, we find that the codirectional fluctuation in CSEC is delayed by 3 months with surface temperature, and the precipitation leading SEC series as the phase arrow points straight down from the cross wavelet transform. Our new record shows that the AS sector thinned rapidly from 2003 to 2021 but decelerated from 2019 to 2021, and it was clearly correlated to the surface temperature, precipitation, and local terrain.

The Influence of Bathymetry Over Heat Transport Onto the Amundsen Sea Continental Shelf

AbstractIce streams such as Pine Island and Thwaites Glaciers which terminate at their ice shelves in the eastern Amundsen Sea, West Antarctica, are losing mass faster than most others about the continent. The mass loss is due to basal melting, which is influenced by a deep current that transports warm Circumpolar Deep Water (CDW) from the continental shelf break toward the ice shelves. This current and associated heat transport are controlled by factors such as bottom bathymetry, near‐surface winds and meltwater. Using a realistic regional model as a reference, in this study we use idealized models to examine the role of bathymetric features in determining the shelf‐wide circulation and in enabling heat transport from the deep ocean onto the continental shelf. We find that a ridge that blocks deep westward inflow from the Bellingshausen Sea enables a deep cyclonic circulation on the shelf with an eastward undercurrent immediately south of the shelf break. Inclusion of the ridge enhances heat transport onto the continental shelf; without the ridge the flow features an along‐shelf break westward current that suppresses cross‐shelf break fluxes. We also consider the effects of shifting the prescribed wind forcing profile to the south—a simplified representation of future potential changes to the winds—and we find that the continental shelf is warmer in this scenario. These fundamental investigations will help refine the aims of future fieldwork and modeling.

Strong Ocean Melting Feedback During the Recent Retreat of Thwaites Glacier

AbstractAccelerating ice loss from Thwaites Glacier is contributing approximately 5% of global sea‐level rise, and could add tens of centimeters to sea level over the coming centuries. We use an ocean model to calculate sub‐ice melting for a succession of Digital Elevation Models of the main trunk of Thwaites Glacier from 2011 to 2022. The ice evolution during this period induces a strong geometrical feedback onto melting. Ice thinning and retreat provides a larger melting area, thicker and better‐connected sub‐ice water column, and steeper ice base. This leads to stronger sub‐ice ocean currents, increasing melting by over 30% without any change in forcing from wider ocean conditions. This geometrical feedback over just 12 years is comparable to melting changes arising from plausible century‐scale changes in ocean conditions and subglacial meltwater inflow. These findings imply that ocean‐driven ice loss from Thwaites Glacier may only be weakly influenced by anthropogenic emissions mitigation.

High mid-Holocene accumulation rates over West Antarctica inferred from a pervasive ice-penetrating radar reflector

Abstract. Understanding the past and future evolution of the Antarctic Ice Sheet is challenged by the availability and quality of observed paleo-boundary conditions. Numerical ice-sheet models often rely on these paleo-boundary conditions to guide and evaluate their models' predictions of sea-level rise, with varying levels of confidence due to the sparsity of existing data across the ice sheet. A key data source for large-scale reconstruction of past ice-sheet processes are internal reflecting horizons (IRHs) detected by radio-echo sounding (RES). When IRHs are isochronal and dated at ice cores, they can be used to determine paleo-accumulation rates and patterns on large spatial scales. Using a spatially extensive IRH over the Pine Island Glacier (PIG), Thwaites Glacier (THW), and the Institute and Möller ice streams (IMIS, covering a total of 610 000 km2 or 30 % of the West Antarctic Ice Sheet (WAIS)), and a local layer approximation model, we infer mid-Holocene accumulation rates over the slow-flowing parts of these catchments for the past ∼4700 years. By comparing our results with modern climate reanalysis models (1979–2019) and observational syntheses (1651–2010), we estimate that accumulation rates over the Amundsen–Weddell–Ross Divide were on average 18 % higher during the mid-Holocene than modern rates. However, no significant spatial changes in the accumulation pattern were observed. The higher mid-Holocene accumulation-rate estimates match previous paleo-accumulation estimates from ice-core records and targeted RES surveys over the ice divide, and they also coincide with periods of grounding-line readvance during the Holocene over the Weddell and Ross sea sectors. We find that our spatially extensive, mid-Holocene-to-present accumulation estimates are consistent with a sustained late-Holocene period of higher accumulation rates occurring over millennia reconstructed from the WAIS Divide ice core (WD14), thus indicating that this ice core is spatially representative of the wider West Antarctic region. We conclude that future regional and continental ice-sheet modelling studies should base their climatic forcings on time-varying accumulation rates from the WAIS Divide ice core through the Holocene to generate more realistic predictions of the West Antarctic Ice Sheet's past contribution to sea-level rise.

Melting underneath Thwaites Glacier is more complicated than expected

A robot exploring beneath the vulnerable Antarctic glacier has found new features that affect its melt rate.

The potential for stabilizing Amundsen Sea glaciers via underwater curtains.

Rapid sea level rise due to an ice sheet collapse has the potential to be extremely damaging the coastal communities and infrastructure. Blocking deep warm water with thin flexible buoyant underwater curtains may reduce melting of buttressing ice shelves and thereby slow the rate of sea level rise. Here, we use new multibeam bathymetric datasets, combined with a cost-benefit model, to evaluate potential curtain routes in the Amundsen Sea. We organize potential curtain routes along a "difficulty ladder" representing an implementation pathway that might be followed as technological capabilities improve. The first curtain blocks a single narrow (5 km) submarine choke point that represents the primary warm water inflow route towards western Thwaites Glacier, the most vulnerable part of the most vulnerable glacier in Antarctica. Later curtains cross larger and deeper swaths of seabed, thus increasing their cost, while also protecting more of the ice sheet, increasing their benefit. In our simple cost-benefit analysis, all of the curtain routes achieve their peak value at target blocking depths between 500 and 550 m. The favorable cost-benefit ratios of these curtain routes, along with the trans-generational and societal equity of preserving the ice sheets near their present state, argue for increased research into buoyant curtains as a means of ice sheet preservation, including high-resolution fluid-structural and oceanographic modeling of deep water flow over and through the curtains, and coupled ice-ocean modeling of the dynamic response of the ice sheet.

Feasibility of ice sheet conservation using seabed anchored curtains.

Sea level rise is expected to be rapid and extremely damaging to coastal communities and infrastructure, with unavoidable losses and coastal protection costs in the tens of billions per year. Retreat of the Thwaites and Pine Island Glaciers is likely already in an unstable regime as their oceanic fronts are ablated by deep intruding layers of relatively warm seawater. Warm water can be blocked from reaching the grounding line by thin flexible buoyant curtains anchored to the seabed. The consequent reduction in ice shelf melting could result in increased ice sheet buttressing as the shelf makes contact with seabed highs. Flexible curtains are less costly than solid artificial barriers, more robust against iceberg collisions, and easier to repair or remove in the event of unforeseen side effects. We illustrate the technical viability of this approach by considering curtain design concepts that should withstand oceanographic forces, and feasible methods of installation. Suitable materials are commonly available. Installation of a seabed curtain in temperate ocean waters would be entirely within the capabilities of existing offshore and deep ocean construction techniques. Installing in polar waters presents severe challenges from icebergs, harsh weather, and brief working seasons, which can however, be overcome with present-day technology. An 80 km long curtain installed in 600 m deep waters on alluvial sediments could help stabilize Pine Island and Thwaites glaciers over the next few centuries at much lower cost ($40-80 billion + $1-2 billion/yr maintenance) than the global coastline protection (∼$40 billion/yr) needed due to their collapse.

The melting underneath the Thwaites Glacier is complicated

The melting underneath the Thwaites Glacier is complicated

Migration of the Shear Margins at Thwaites Glacier: Dependence on Basal Conditions and Testability Against Field Data

AbstractProjections of global sea level depend sensitively on whether Thwaites Glacier, Antarctica, will continue to lose ice rapidly. Prior studies have focused primarily on understanding the evolution of ice velocity and whether the reverse‐sloping bed at Thwaites Glacier could drive irreversible retreat. However, the overall ice flux to the ocean and the possibility of irreversible retreat depend not only on the ice speed but also on the width of the main ice trunk. Here, we complement prior work by focusing specifically on understanding whether the lateral boundaries of the main ice trunk, termed shear margins, might migrate over time. We hypothesize that the shear margins at Thwaites Glacier will migrate on a decadal timescale in response to continued ice thinning and surface steepening. We test this hypothesis by developing a depth‐averaged, thermomechanical free‐boundary model that captures the complex topography underneath the glacier and solves for both the ice velocity and for the position of the shear margins. We find that both shear margins are prone to migration in response to ice thinning with basal strength and surface slope steepening determining their relative motion. We construct four end‐member cases of basal strength that represent different physical properties governing friction at the glacier bed and present two cases of ice thinning to contrast the effects of surface steepening and ice thinning. We test our model by hindcasting historic data and discuss how data from ongoing field campaigns could further be used to test our model.

Multi-Branch Deep Neural Network for Bed Topography of Antarctica Super-Resolution: Reasonable Integration of Multiple Remote Sensing Data

Bed topography and roughness play important roles in numerous ice-sheet analyses. Although the coverage of ice-penetrating radar measurements has vastly increased over recent decades, significant data gaps remain in certain areas of subglacial topography and need interpolation. However, the bed topography generated by interpolation such as kriging and mass conservation is generally smooth at small scales, lacking topographic features important for sub-kilometer roughness. DeepBedMap, a deep learning method combined with multiple surface observation inputs, can generate high-resolution (250 m) bed topography with realistic bed roughness but produces some unrealistic artifacts and higher bed elevation values in certain regions, which could bias ice-sheet models. To address these issues, we present MB_DeepBedMap, a multi-branch deep learning method to generate more realistic bed topography. The model improves upon DeepBedMap by separating inputs into two groups using a multi-branch network structure according to their characteristics, rather than fusing all inputs at an early stage, to reduce artifacts in the generated topography caused by earlier fusion of inputs. A direct upsampling branch preserves large-scale subglacial landforms while generating high-resolution bed topography. We use MB_DeepBedMap to generate a high-resolution (250 m) bed elevation grid product of Antarctica, MB_DeepBedMap_DEM, which can be used in high-resolution ice-sheet modeling studies. Moreover, we test the performance of MB_DeepBedMap model in Thwaites Glacier, Gamburtsev Subglacial Mountains, and several other regions, by comparing the qualitative topographic features and quantitative errors of MB_DeepBedMap, BEDMAP2, BedMachine Antarctica, and DeepBedMap. The results show that MB_DeepBedMap can provide more realistic small-scale topographic features and roughness compared to BEDMAP2, BedMachine Antarctica, and DeepBedMap.

Suppressed basal melting in the eastern Thwaites Glacier grounding zone

Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica1–3. Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland4, making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre2,3,5. The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat3,6, both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base7,8, resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates.

Heterogeneous melting near the Thwaites Glacier grounding line

Thwaites Glacier represents 15% of the ice discharge from the West Antarctic Ice Sheet and influences a wider catchment1–3. Because it is grounded below sea level4,5, Thwaites Glacier is thought to be susceptible to runaway retreat triggered at the grounding line (GL) at which the glacier reaches the ocean6,7. Recent ice-flow acceleration2,8 and retreat of the ice front8–10 and GL11,12 indicate that ice loss will continue. The relative impacts of mechanisms underlying recent retreat are however uncertain. Here we show sustained GL retreat from at least 2011 to 2020 and resolve mechanisms of ice-shelf melt at the submetre scale. Our conclusions are based on observations of the Thwaites Eastern Ice Shelf (TEIS) from an underwater vehicle, extending from the GL to 3 km oceanward and from the ice–ocean interface to the sea floor. These observations show a rough ice base above a sea floor sloping upward towards the GL and an ocean cavity in which the warmest water exceeds 2 °C above freezing. Data closest to the ice base show that enhanced melting occurs along sloped surfaces that initiate near the GL and evolve into steep-sided terraces. This pronounced melting along steep ice faces, including in crevasses, produces stratification that suppresses melt along flat interfaces. These data imply that slope-dependent melting sculpts the ice base and acts as an important response to ocean warming.

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.

Inter-decadal climate variability induces differential ice response along Pacific-facing West Antarctica

West Antarctica has experienced dramatic ice losses contributing to global sea-level rise in recent decades, particularly from Pine Island and Thwaites glaciers. Although these ice losses manifest an ongoing Marine Ice Sheet Instability, projections of their future rate are confounded by limited observations along West Antarctica’s coastal perimeter with respect to how the pace of retreat can be modulated by variations in climate forcing. Here, we derive a comprehensive, 12-year record of glacier retreat around West Antarctica’s Pacific-facing margin and compare this dataset to contemporaneous estimates of ice flow, mass loss, the state of the Southern Ocean and the atmosphere. Between 2003 and 2015, rates of glacier retreat and acceleration were extensive along the Bellingshausen Sea coastline, but slowed along the Amundsen Sea. We attribute this to an interdecadal suppression of westerly winds in the Amundsen Sea, which reduced warm water inflow to the Amundsen Sea Embayment. Our results provide direct observations that the pace, magnitude and extent of ice destabilization around West Antarctica vary by location, with the Amundsen Sea response most sensitive to interdecadal atmosphere-ocean variability. Thus, model projections accounting for regionally resolved ice-ocean-atmosphere interactions will be important for predicting accurately the short-term evolution of the Antarctic Ice Sheet.

An Antenna Solution for Glacial Environmental Sensor Networks

Antennas used in glacial environmental sensor networks and reported in the last two decades have been reviewed. A link budget framework for designing such antenna systems is presented and used to design an antenna system for deployment at the Thwaites glacier, Antarctica. Design details of two left hand circularly polarized cross dipole antennas, one for englacial sensor probes and the other for supraglacial surface receivers are presented. The probe antenna is a 3D bent cross dipole that fits within a borehole of 8 cm diameter while providing a 1 dBic gain at 433 MHz in ice. The surface receiver antenna is a planar printed antenna providing a gain of 6.1 dBic with a quarter wave reflector. Both antennas provide 3 dB beamwidths of at least 50° in the xz and yz vertical planes catering for transmitter-receiver antenna misalignments caused by extended deployments. The antennas displayed good circular polarization and polarization purity traits. The 3 dB axial ratio bandwidths of both the antennas remained 54.9 %. The total efficiencies of the bent cross dipole and the surface receiver antennas were noted as 69.7 % and 86.9 % respectively. Lastly, the 433 MHz band has been validated for achieving englacial communication ranges of up to 2300 metres.

Episodic dynamic change linked to damage on the Thwaites Glacier Ice Tongue

Episodic dynamic change linked to damage on the Thwaites Glacier Ice Tongue