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This article uses the resolutional relationship between digital image and planetary surface in satellite remote sensing as a lens through which to view the reliance of visual culture on mineral resources. While most studies of resolution in satellite imaging have focused on visibility and invisibility, the author argues that the equivalence between pictorial and geographic space in its cm/pixel specification offers an opportunity to consider the physical relationship between the two. The proposed inversion enables the satellite and its transmitted images to be understood as contingent upon an unsustainably extractive industrial model. The article then traces the material trajectory in geophysical prospecting applications of remote sensing, identifying a recursive loop in which images are used to produce minerals that are used to produce images. The potential geopolitical impact of this circularity is then assessed with regard to an example of future remote sensing emissions governance. In this, and many other climate-critical applications, remote sensing potentially plays a vital role, yet its instrumental gaze tends to shape the earth as an informational resource whose mineral reserves should be capitalized upon. Ultimately, the author's aim is not to denounce earth observation as ecologically untenable, but to propose that we find a measure with which to assess the planetary impact of the various aspects of industrialized visual culture. Conceiving of resolution not as a measure of pictorial space but of the terrestrial cost of producing, consuming, distributing and permanently storing digital images might enable a more relational understanding of image and ground, pixels and planet. Accounting for the inverse resolution of an image could bring the deep temporal costs of digital visual culture into focus. [ABSTRACT FROM AUTHOR]

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role. [ABSTRACT FROM AUTHOR]

Ice mass loss from the Amundsen Sea Embayment ice streams in West Antarctica is a major source of uncertainty in projections of future sea level rise. Physically based ice flow models rely on a number of parameters that represent unobservable quantities and processes, and accounting for uncertainty in these parameters can lead to a wide range of dynamic responses. Here we perform a Bayesian calibration of a perturbed parameter ensemble, in which we score each ensemble member on its ability to match the magnitude and broad spatial pattern of present‐day observations of ice sheet surface elevation change. We apply an idealized melt rate forcing to extend the most likely simulations forward to 2200. We find that diverging grounding line response between ensemble members drives an exaggeration in the upper tail of the distribution of sea level rise by 2200, demonstrating that extreme future outcomes cannot be excluded. Key Points: We calibrate an ensemble of high‐resolution ice‐flow simulations of the Amundsen Sea Embayment, using surface elevation change observationsThe upper tail of the distribution of sea level contribution produced by the calibrated ensemble becomes more exaggerated over timeProcess‐based modeling is essential for projecting the contribution of ice sheets to sea level [ABSTRACT FROM AUTHOR]

The Antarctic Ice Sheet (AIS) remains the largest uncertainty in projections of future sea level rise. A likely climate‐driven vulnerability of the AIS is thinning of floating ice shelves resulting from surface‐melt‐driven hydrofracture or incursion of relatively warm water into subshelf ocean cavities. The resulting melting, weakening, and potential ice shelf collapse reduces shelf buttressing effects. Upstream ice flow accelerates, causing thinning, grounding‐line retreat, and potential ice sheet collapse. While high‐resolution projections have been performed for localized Antarctic regions, full‐continent simulations have typically been limited to low‐resolution models. Here we quantify the vulnerability of the entire present‐day AIS to regional ice shelf collapse on millennial timescales treating relevant ice flow dynamics at the necessary ∼1‐km resolution. Collapse of any of the ice shelves dynamically connected to the West Antarctic Ice Sheet (WAIS) is sufficient to trigger ice sheet collapse in marine‐grounded portions of the WAIS. Vulnerability elsewhere appears limited to localized responses. Plain Language Summary: The biggest uncertainty in near‐future sea level rise (SLR) comes from the Antarctic Ice Sheet. Antarctic ice flows in relatively fast‐moving ice streams. At the ocean, ice flows into enormous floating ice shelves that push back on their feeder ice streams, buttressing them and slowing their flow. Melting and loss of ice shelves due to climate changes can result in faster‐flowing, thinning, and retreating ice leading to accelerated rates of global SLR. To learn where Antarctica is vulnerable to ice shelf loss, we divided it into 14 sectors, applied extreme melting to each sector's floating ice shelves in turn, then ran our ice flow model 1,000 years into the future for each case. We found three levels of vulnerability. The greatest vulnerability came from attacking any of the three ice shelves connected to West Antarctica, where much of the ice sits on bedrock lying below sea level. Those dramatic responses contributed around 2 m of SLR. The second level came from four other sectors, each with a contribution between 0.5 and 1 m. The remaining sectors produced little to no contribution. We examined combinations of sectors, determining that sectors behave independently of each other for at least a century. Key Points: Sustained ice‐shelf loss in any of the Amundsen Sea, Ronne, or Ross sectors can lead to wholesale West Antarctic ungrounding and collapseEven with extreme forcing, loss is relatively modest for the initial century, increasing markedly after in West Antarctic collapse scenariosModeling suggests Antarctic drainage basins can be assumed to be dynamically independent for one to two centuries before they begin to interact [ABSTRACT FROM AUTHOR]

We observe the evacuation of 11-year-old landfast sea ice in the Larsen B embayment on the East Antarctic Peninsula in January 2022, which was in part triggered by warm atmospheric conditions and strong offshore winds. This evacuation of sea ice was closely followed by major changes in the calving behaviour and dynamics of a subset of the ocean-terminating glaciers in the region. We show using satellite measurements that, following a decade of gradual slow-down, Hektoria, Green, and Crane glaciers sped up by approximately 20 %–50 % between February and the end of 2022, each increasing in speed by more than 100 ma-1. Circumstantially, this is attributable to their transition into tidewater glaciers following the loss of their ice shelves after the landfast sea ice evacuation. However, a question remains as to whether the landfast sea ice could have influenced the dynamics of these glaciers, or the stability of their ice shelves, through a buttressing effect akin to that of confined ice shelves on grounded ice streams. We show, with a series of diagnostic modelling experiments, that direct landfast sea ice buttressing had a negligible impact on the dynamics of the grounded ice streams. Furthermore, we suggest that the loss of landfast sea ice buttressing could have impacted the dynamics of the rheologically weak ice shelves, in turn diminishing their stability over time; however, the accompanying shifts in the distributions of resistive stress within the ice shelves would have been minor. This indicates that this loss of buttressing by landfast sea ice is likely to have been a secondary process in the ice shelf disaggregation compared to, for example, increased ocean swell or the drivers of the initial landfast sea ice disintegration. [ABSTRACT FROM AUTHOR]

Ice shelf break-up and disintegration events over the past 5 decades have led to speed-up, thinning, and retreat of upstream tributary glaciers and increases to rates of global sea-level rise. The southward progression of these episodes indicates a climatic cause and in turn suggests that the larger Larsen C and George VI ice shelves may undergo a similar collapse in the future. However, the extent to which removal of the Larsen C and George VI ice shelves will affect upstream tributary glaciers and add to global sea levels is unknown. Here we apply numerical ice-sheet models of varying complexity to show that the centennial sea-level commitment of Larsen C embayment glaciers following immediate shelf collapse is low ( < 2:5mm to 2100, < 4:2mm to 2300). Despite its large size, Larsen C does not provide strong buttressing forces to upstream basins and its collapse does not result in large additional discharge from its tributary glaciers in any of our model scenarios. In contrast, the response of inland glaciers to a collapse of the George VI Ice Shelf may add up to 8mm to global sea levels by 2100 and 22mm by 2300 due in part to the mechanism of marine ice sheet instability. Our results demonstrate the varying and relative importance to sea level of the large Antarctic Peninsula ice shelves considered to present a risk of collapse. [ABSTRACT FROM AUTHOR]

This is a review of Sonic Time Machine: Explicit Sound, Sirenic Voices, and Implicit Sonicity, Wolfgang Ernst’s first book to be published directly in English. [ABSTRACT FROM AUTHOR]

Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ~ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude. [ABSTRACT FROM AUTHOR]

Coupled ice sheet-ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet-ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP 1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models. [ABSTRACT FROM AUTHOR]

The fracturing of glaciers and ice shelves in Antarctica influences their dynamics and stability. Hence, data on the evolving distribution of crevasses are required to better understand the evolution of the ice sheet, though such data have traditionally been difficult and time-consuming to generate. Here, we present an automated method of mapping crevasses on grounded and floating ice with the application of convolutional neural networks to Sentinel-1 synthetic aperture radar backscatter data. We apply this method across Antarctica to images acquired between 2015 and 2022, producing a 7.5-year record of composite fracture maps at monthly intervals and 50 m spatial resolution and showing the distribution of crevasses around the majority of the ice sheet margin. We develop a method of quantifying changes to the density of ice shelf fractures using a time series of crevasse maps and show increases in crevassing on Thwaites and Pine Island ice shelves over the observational period, with observed changes elsewhere in the Amundsen Sea dominated by the advection of existing crevasses. Using stress fields computed using the BISICLES ice sheet model, we show that much of this structural change has occurred in buttressing regions of these ice shelves, indicating a recent and ongoing link between fracturing and the developing dynamics of the Amundsen Sea sector. [ABSTRACT FROM AUTHOR]

Abstract: Continental scale marine ice sheets such as the present day West Antarctic Ice Sheet are strongly affected by highly localized features, presenting a challenge to numerical models. Perhaps the best known phenomenon of this kind is the migration of the grounding line — the division between ice in contact with bedrock and floating ice shelves — which needs to be treated at sub-kilometer resolution. We implement a block-structured finite volume method with adaptive mesh refinement (AMR) for three dimensional ice sheets, which allows us to discretize a narrow region around the grounding line at high resolution and the remainder of the ice sheet at low resolution. We demonstrate AMR simulations that are in agreement with uniform mesh simulations, but are computationally far cheaper, appropriately and efficiently evolving the mesh as the grounding line moves over significant distances. As an example application, we model rapid deglaciation of Pine Island Glacier in West Antarctica caused by melting beneath its ice shelf. [Copyright &y& Elsevier]

San Quintin glacier is the largest glacier in the North Patagonian Icefield, which nowadays terminates into a proglacial lake. In the last 70 years, San Quintin has experienced a near-complete collapse of its snout as a consequence of prolonged calving and has gone from being piedmont lobe occupying an area larger than the proglacial lake to a short glacier tongue. Its neighbour San Rafael glacier appears to have experienced a similar retreat during the Little Ice Age (LIA). The collapse of these ice tongues has the potential to affect the dynamics of other parts of the icefield, as their icesheds are shared with five other main outlet glaciers. The aim of this study is to use ice sheet modelling to investigate the retreat mechanism of San Quintin glacier and compare its collapse with that of San Rafael glacier, as well as its effect on the remainder of the ice field, and to understand its role in the present-day rates of thinning of the icefield.Using the BISICLES ice sheet model, the piedmont lobes of San Rafael and San Quintin glaciers are allowed to grow to their LIA positions, based on the location of terminal moraines. The collapse of these lobes is then triggered using a combination of climate forcing and crevasse models. Results show that the anomalously high present-day thinning rates are largely attributable to a dynamical response rather than SMB forcing. [ABSTRACT FROM AUTHOR]

Iceberg calving parameterisations currently implemented in ice sheet models do not reproduce the full observed range of calving behaviours. For example, though buoyant forces at the ice front are known to trigger full-depth calving events on major Greenland outlet glaciers, a multi-stage iceberg calving event at Jakobshavn Isbræ is unexplained by existing models. To explain this and similar events, we propose a notch-triggered rotation mechanism, whereby a relatively small subaerial calving event triggers a larger full-depth calving event due to the abrupt increase in buoyant load and the associated stresses generated at the ice–bed interface. We investigate the notch-triggered rotation mechanism by applying a geometric perturbation to the subaerial section of the calving front in a diagnostic flow-line model of an idealised glacier snout, using the full-Stokes, finite element method code Elmer/Ice. Different sliding laws and water pressure boundary conditions are applied at the ice–bed interface. Water pressure has a big influence on the likelihood of calving, and stress concentrations large enough to open crevasses were generated in basal ice. Significantly, the location of stress concentrations produced calving events of approximately the size observed, providing support for future application of the notch-triggered rotation mechanism in ice-sheet models. [ABSTRACT FROM AUTHOR]

The author discusses the inspiration and design of an as-yet-unrealized composition in which participants serve in the roles of composer, performer and consumer all at the same time. Provoked by the passage of a law restricting sharing and distribution of music iles, he explores the potential for ile sharing as a compositional process. [ABSTRACT FROM AUTHOR]

Ice‐marginal lakes can affect glacier dynamics but are ignored in studies of the evolution of the Greenland ice sheet (GrIS) and of peripheral mountain glaciers and ice caps (PGICs). Here we show that lakes occupy 10% of the GrIS ice margin and occur on 5% of PGICs. Ice velocity at the GrIS margin is enhanced by ∼ 25% at lakes versus on land. Mean ice discharge into lakes is ∼4.9 Gt.yr, which is ∼1% of ice discharged through marine termini. We locate thousands of subglacial overdeepenings within which 7,404 km2 of future lakes could form, all of which will be ice‐marginal at some time. Future lakes in the west and east will be restricted to the margin of the GrIS and within alpine valleys, respectively. This status and possible future leads us to contend that lakes should be incorporated into projections of Greenland ice loss. Plain Language Summary: Lakes forming on the edges of glaciers can affect ice dynamics but are not included within numerical models of the Greenland ice sheet (GrIS) or of peripheral mountain glaciers and ice caps (PGICs). We show that lakes presently occupy 10% of the GrIS ice margin and occur on 5% of PGICs. We determine that ice is typically moving 25% faster in the vicinity of lakes than at land margins. We estimate that ice discharge into lakes is ∼4.9 Gt.yr, which is 1% of that through marine glaciers. We identify thousands of depressions in the landscape that could hold future lakes as glaciers retreat from them. Overall, understanding of lake evolution should be incorporated into projections of Greenland ice loss and runoff. Key Points: Lakes occupy 10% of the ice margin and vary between 2% and 26% by regionIce velocity is ∼25% greater into lakes compared to onto land and total ice discharge into lakes is ∼4.9 Gt.yr−1Thousands of overdeepenings have potential to host more and larger lakes in the future but not all will be ice‐marginal simultaneously [ABSTRACT FROM AUTHOR]

Ice shelves play a key role in the dynamics of marine ice sheets by buttressing grounded ice and limiting rates of ice flux to the oceans. In response to recent climatic and oceanic change, ice shelves fringing the West Antarctic Ice Sheet (WAIS) have begun to fragment and retreat, with major implications for ice-sheet stability. Here, we focus on the Thwaites Eastern Ice Shelf (TEIS), the remaining pinned floating extension of Thwaites Glacier. We show that TEIS has undergone a process of fragmentation in the last 5 years, including brittle failure along a major shear zone, formation of tensile cracks on the main body of the shelf, and a release of tabular bergs on both the eastern and western flanks. Simulations with the Helsinki Discrete Element Model (HiDEM) show that this pattern of failure is associated with high backstress from a submarine pinning point at the distal edge of the shelf. We show that a significant zone of shear, upstream of the main pinning point, developed in response to the rapid acceleration of the shelf between 2002 and 2006, seeding damage on the shelf. Subsequently, basal melting and positive feedback between damage and strain rates weakened TEIS, allowing damage to accumulate. Thus, although backstress on TEIS has likely diminished over time as the pinning point shrunk, accumulation of damage has ensured that the ice in the shear zone remained the weakest link in the system. Experiments with the BISICLES ice-sheet model indicate that additional damage to or unpinning of TEIS is unlikely to trigger significantly increased ice loss from WAIS, but the calving response to the loss of TEIS remains highly uncertain. It is widely recognised that ice-shelf fragmentation and collapse can be triggered by hydrofracturing and/or unpinning from ice-shelf margins or grounding points. Our results indicate a third mechanism, backstress triggered failure, that can occur if and when an ice shelf is no longer able to withstand stress imposed by pinning points. In most circumstances, pinning points are essential for ice-shelf stability, but as ice shelves thin and weaken, the concentration of backstress in damaged ice upstream of a pinning point may provide the seeds of their demise. [ABSTRACT FROM AUTHOR]

The predicted Antarctic contribution to global‐mean sea‐level rise is one of the most uncertain among all major sources. Partly this is because of instability mechanisms of the ice flow over deep basins. Errors in bedrock topography can substantially impact the projected resilience of glaciers against such instabilities. Here we analyze the Pine Island Glacier topography to derive a statistical model representation. Our model allows for inhomogeneous and spatially dependent uncertainties and avoids unnecessary smoothing from spatial averaging or interpolation. A set of topography realizations is generated representing our best estimate of the topographic uncertainty in ice sheet model simulations. The bedrock uncertainty alone creates a 5%–25% uncertainty in the predicted sea level rise contribution at year 2100, depending on friction law and climate forcing. Pine Island Glacier simulations on this new set are consistent with simulations on the BedMachine reference topography but diverge from Bedmap2 simulations. Plain Language Summary: We investigate the impact of uncertainties in the elevation of the bedrock underneath the ice of a particularly vulnerable glacier in Antarctica. We propose a new approach to better estimate how much future projections depend on knowledge of bedrock elevation. The main focus of this study is to represent the current understanding of the bedrock elevation as closely as possible so that our simulations accurately reflect the extent of our knowledge of the future glacier behavior. In summary, we find that the mass of ice lost in simulations for year 2100, which contributes to the global mean sea level, can be affected by up to 25%. This highlights the value of closely‐spaced bedrock measurement and of careful consideration of related uncertainties in ice‐sheet simulations. Key Points: Uncertainty in topography estimates has a significant impact on predictions for all tested friction lawsSimulations with BedMachine and statistically generated topographies are more sensitive to upper‐end climate forcing than with Bedmap2Pine Island Glacier is likely to transition into a more unstable state late mid‐century for upper‐end climate forcing [ABSTRACT FROM AUTHOR]

The physical interactions between ice sheets and the atmosphere and ocean around them are major factors in determining the state of the climate system, yet many current Earth System models omit them entirely or treat them very simply. In this work we describe how models of the Greenland and Antarctic ice sheets have been incorporated into the global U.K. Earth System model (UKESM1) via substantial technical developments with a two‐way coupling that passes fluxes of energy and water, and the topography of the ice sheet surface and ice shelf base, between the component models. File‐based coupling outside the running model executables is used throughout to pass information between the components, which we show is both physically appropriate and convenient within the UKESM1 structure. Ice sheet surface mass balance is computed in the land surface model using multi‐layer snowpacks in subgrid‐scale elevation ranges and compares well to the results of regional climate models. Ice shelf front discharge forms icebergs, which drift and melt in the ocean. Ice shelf basal mass balance is simulated using the full three‐dimensional ocean model representation of the circulation in ice‐shelf cavities. We show a range of example results, including from simulations with changes in ice sheet height and thickness of hundreds of meters, and changes in ice sheet grounding line and land‐terminating margin of many tens of kilometres, demonstrating that the coupled model is computationally stable when subject to significant changes in ice sheet geometry. Plain Language Summary: Loss of mass from the ice sheets on Greenland and Antarctica makes an important contribution to global mean sea level (GMSL) rise, and one that will increase significantly in the coming decades and centuries. Our limited ability to predict exactly how the Earth's ice sheets will interact with the changing climate is the main reason we cannot say with confidence whether GMSL will rise by tens of centimeters or a meter or more in this century alone. One way to develop our understanding is to build tools capable of modeling the co‐evolution of ice sheets and climate, a difficult task made yet more challenging by the wide range of spatial‐ and time‐scales that need to be considered to model these systems simultaneously. UKESM1 is a state‐of‐the‐art Earth System model used to predict future climate change. Our work allows UKESM1 to be run with interactive models of the Greenland and Antarctic ice sheets. This is a new and complex model, and there are still problems to solve before such tools can be used to produce complete projections of GMSL rise. Our work nevertheless allows us to investigate new areas of climate physics in ways that have not been possible before. Key Points: A CMIP6 Earth System Model has been coupled to interactive models of both the Greenland and Antarctic ice sheets for the first timeSubstantial technical challenges have been overcome, our solutions and their limitations are describedOur system simulates climate and ice sheet physics reasonably well, and is computationally stable when subject to extreme ice sheet retreat [ABSTRACT FROM AUTHOR]

Since the late 1990s Jakobshavn Isbrae, a major outlet glacier of the Greenland Ice Sheet, has dramatically accelerated, thinned and retreated. The causes of this retreat and acceleration have been the focus of much scientific activity. Previous studies have shown that the loss of buttressing due to retreat of the calving front is the main driver of upstream acceleration and thinning, however the controls on the timing and magnitude of the retreat remain unclear.Ice flow velocities peaked in 2012 and 2013 in excess of 18 km yr-1, and a position of maximal retreat of the calving front was reached between 2013 and 2015. Since then, ice flow has decelerated by ~3 km yr-1, and the calving front has readvanced from its most retreated position by ~2 km. An estimation of the annual calving rate from 2009 to 2017 shows that the strong retreat of 2009 was the result of a very high calving rate. Meanwhile the recent readvance resulted from a ~3 km yr-1 reduction in the calving rate between 2015 and 2016, which was closely followed by a deceleration of ice flow by a similar magnitude.We use the BISICLES ice sheet model to simulate the evolution of Jakobshavn Isbrae over the past decade, from an initial state replicating the geometry and flow structure from early 2009. In our simulations, the glacier evolution is driven by the application of the estimated calving rate. In one branch of experiments, we apply a basal friction parameter and ice stiffening factor calculated for early 2009 while in a parallel series of experiments we apply an evolving set of these parameters calculated quarterly. The results of these experiments, which we will present, will provide insight into the extent to which the dynamical evolution of the glacier is driven by changes to calving occurring at the front, as well as the strength of the influence on the glacier evolution of environmental inputs, parameterised within the basal friction and ice stiffening factors. [ABSTRACT FROM AUTHOR]

Ice sheet numerical modeling is an important tool to estimate the dynamic contribution of the Antarctic ice sheet to sea level rise over the coming centuries. The influence of initial conditions on ice sheet model simulations, however, is still unclear. To better understand this influence, an initial state intercomparison exercise (initMIP) has been developed to compare, evaluate, and improve initialization procedures and estimate their impact on century-scale simulations. initMIP is the first set of experiments of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), which is the primary Coupled Model Intercomparison Project Phase 6 (CMIP6) activity focusing on the Greenland and Antarctic ice sheets. Following initMIP-Greenland, initMIP-Antarctica has been designed to explore uncertainties associated with model initialization and spin-up and to evaluate the impact of changes in external forcings. Starting from the state of the Antarctic ice sheet at the end of the initialization procedure, three forward experiments are each run for 100 years: a control run, a run with a surface mass balance anomaly, and a run with a basal melting anomaly beneath floating ice. This study presents the results of initMIP-Antarctica from 25 simulations performed by 16 international modeling groups. The submitted results use different initial conditions and initialization methods, as well as ice flow model parameters and reference external forcings. We find a good agreement among model responses to the surface mass balance anomaly but large variations in responses to the basal melting anomaly. These variations can be attributed to differences in the extent of ice shelves and their upstream tributaries, the numerical treatment of grounding line, and the initial ocean conditions applied, suggesting that ongoing efforts to better represent ice shelves in continental-scale models should continue. [ABSTRACT FROM AUTHOR]

Abstract: A flowline ice sheet model is coupled to a box model for cavity circulation and configured for the Pine Island Glacier. An ensemble of 5000 simulations are carried out from 1900 to 2200 with varying inputs and parameters, forced by ocean temperatures predicted by a regional ocean model under the A1B ‘business as usual’ emissions scenario. Comparison is made against recent observations to provide a calibrated prediction in the form of a 95% confidence set. Predictions are for monotonic (apart from some small scale fluctuations in a minority of cases) retreat of the grounding line over the next 200yr with huge uncertainty in the rate of retreat. Full collapse of the main trunk of the PIG during the 22nd century remains a possibility. [Copyright &y& Elsevier]

Ice stream evolution is a major uncertainty in projections of the future of the Greenland and Antarctic Ice sheets. Accurate simulation of ice stream evolution requires an understanding of a number of "ingredients" that control the location and behaviour of ice stream flow. Here, we test the influence of geothermal heat flux, grid resolution, and bed hydrology on simulated ice streaming. The palaeo-record provides snapshots of ice stream evolution, with a particularly well constrained ice sheet being the British-Irish Ice Sheet (BIIS). We implement a new basal sliding scheme coupled with thermo-mechanics into the BISICLES ice sheet model, to simulate the evolution of the BIIS ice streams. We find that the simulated location and spacing of ice streams matches well with the empirical reconstructions of ice stream flow in terms of position and direction when simple bed hydrology is included. We show that the new basal sliding scheme allows the accurate simulation for the majority of BIIS ice streams. The extensive empirical record of the BIIS has allowed the testing of model inputs, and has helped demonstrate the skill of the ice sheet model in simulating the evolution of the location, spacing, and migration of ice streams through millennia. Simulated ice streams also prompt new empirical mapping of features indicative of streaming in the North Channel region. Ice sheet model development has allowed accurate simulation of the palaeo record, and allows for improved modelling of future ice stream behaviour. • A new basal sliding scheme is implemented into the BISICLES ice sheet model. • Simulated spacing and location ice streams matches well with empirical palaeo data. • The majority of ice streams of the BIIS are successfully simulated. • Simulated ice streams have prompted new empirical mapping of ice stream evidence. [ABSTRACT FROM AUTHOR]