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The combination of the Pine Island Ice Shelf (PIIS) draft and a seabed ridge beneath it form a topographic barrier, restricting access of warm Circumpolar Deep Water to a cavity inshore of the ridge, thus exerting an important control on PIIS basal ablation. In addition, PIIS has recently experienced several large calving events and further calving could significantly alter the cavity geometry. Changes in the ice front location, together with changes in ice thickness, might relax the topographic barrier and thus significantly change basal melt rates. Here, we consider the impact of past, and possible future, calving events on PIIS melt rates. We use a high‐resolution ocean model to simulate melt rates in both an idealized domain whose geometry captures the salient features of Pine Island Glacier, and a realistic geometry accurately resembling it, to explore how calving affects melt rates. The idealized simulations reveal that the melt response to calving has a sensitive dependence on the thickness of the gap between PIIS and the seabed ridge and inform our interpretation of the realistic simulations, which suggest that PIIS melt rates did not respond significantly to recent calving. However, the mean melt rate increases approximately linearly with further calving, and is amplified by approximately 10% relative to present day once the ice front reaches the ridge‐crest, taking less than one decade if calving maintains its present rate. This provides strong evidence that calving may represent an important, but as yet unexplored, contribution to the ice‐ocean sensitivity of the West Antarctic Ice Sheet. Plain Language Summary: The seabed beneath Pine Island Ice Shelf (PIIS)—the floating extension of Pine Island Glacier—features a large ridge. The combination of this seabed ridge and ice shelf above it reduce the amount of relatively warm water that is able to reach the ice shelf, therefore restricting the amount of ice shelf melting that can take place. However, the ice shelf has also lost large sections from its front in recent years, in a process referred to as calving. In this paper, we investigate the combined effect of these two processes: how does calving affect the melt rates on PIIS? Using numerical simulations of the ocean flow beneath the ice shelf, we identify a potentially high sensitivity of melt rates to calving, depending on the cavity geometry. This sensitivity is primarily related to changes in the flow strength in the cavity inshore of the ridge. In addition, our simulations suggest that the melt rate will have an approximately linear dependence on the distance that the ice front retreats in further calving events. These results provide strong evidence that changes in the melting of ice shelves in response to calving might represent an important contribution to the response of West Antarctica in a changing climate. Key Points: Melting of Pine Island Ice Shelf is sensitive to calving because of a seabed ridge beneath it which restricts warm water access to the shelfThe melt response to calving has a strong sensitivity to the cavity geometry and results primarily from circulation changesCalving may be an important contribution to the ice‐ocean sensitivity of the Antarctic Ice Sheet [ABSTRACT FROM AUTHOR]

Ice-sheet mass balance and ice behaviour have been effectively monitored remotely by space-borne laser ranging technology, i.e. satellite laser altimetry, and/or satellite gravimetry. ICESat mission launched in 2003 has pioneered laser altimetry providing a large amount of elevation data related to ice sheet change with high spatial and temporal resolution. ICESat-2, the successor to the ICESat mission, was launched in 2018, continuing the legacy of its predecessor. This paper presents an overview of the satellite laser altimetry and a review of Greenland ice sheet change estimated from ICESat data and compared against estimates derived from satellite gravimetry, i.e. changes of the Earth’s gravity field obtained from the GRACE data. In addition to that, it provides an insight into the characteristics and possibilities of ice sheet monitoring with renewed mission ICESat-2, which was compared against ICESat for the examination of ice height changes on the Jakobshavn glacier. ICESat comparison (2004–2008) shows that an average elevation change in different areas on Greenland varies up to ±0.60 m yr−1. Island’s coastal southern regions are most affected by ice loss, while inland areas record near-balance state. In the same period, gravity anomaly measurements showed negative annual mass balance trends in coastal regions ranging from a few cm up to -0.36 m yr-1 w.e. (water equivalent), while inland records show slightly positive trends. According to GRACE observations, in the following years (2009–2017), negative annual mass balance trends on the coast continued.

A hydroelastic model is developed here for studying the interaction of oblique water waves by two fully submerged thin vertical porous barriers placed some distance apart in a homogeneous fluid. The upper surface is a thin ice-sheet covering the standard free surface, and it is treated as a thin elastic plate by following the Euler–Bernoulli beam equation. The roots of the complex dispersion relation are studied with the help of a suitable contour plot. Assuming small-amplitude theory and structural response, the analytical solution is developed. In order to achieve the result, eigenfunction expansion and the least square method are employed to discuss the flexural gravity waves interaction with the submerged porous barriers. One of the current results is validated against two available results, and subsequent to the successful validation, the reflection and transmission coefficients, energy loss, and wave forces are computed and a parametric study is carried out involving different parameter values of the ice-sheet, porous barriers and angle of incidence. It points to an oscillatory behavior of the wave reflection. It further shows that due to an increase in the inertial effect of the porous barrier, the minima for reflection occur. It is observed that the vertical porous barriers succeed in dissipating a substantial amount of the wave energy when the inertial effect of the porous barriers is increased. Similar to the reflection coefficients, the hydrodynamic forces acting on the barriers also exhibit an oscillatory nature, and they can be observed to increase when the height of the barriers is increased. The effects of the floating ice-sheet on flexural waves are examined by obtaining and studying various results on the hydrodynamic forces. An important observation is that variation in the values of the elasticity of the floating ice-sheet has a significant impact on the wave forces acting on the submerged vertical porous barriers. [ABSTRACT FROM AUTHOR]

Reconstructions of postglacial sea-level rise have provided key insight into the rapid disintegration of ice-sheets and the discharge of large meltwater pulses during the last deglaciation. The most complete reconstruction is from Barbados where thick, backstepping sequences of the reef-crest coral 'Acropora palmata' have been recovered in cores from the insular shelf and slope off the Island’s south coast. Differences in the depth, timing, and magnitude of meltwater pulses between the Barbados reconstruction and other reefal records, however, has led to significant uncertainty in their origin, and the consequent timing of ice-sheet collapse. Here we re-analyse the published sedimentary, stratigraphic, and chronological data from Barbados, and find evidence for 'ex-situ' data which indicates that reefal sequences contain coral clasts generated during hurricanes. By adjusting for biases caused by these ex-situ data, we provide a revised sea-level reconstruction which shows that MWP-1b was an 8–11 m rise from –53 m in ~250 years starting at 11.3 ka, which is 5 m smaller, and 150 years younger than previous estimates. It also shows that the onset of MWP-1a cannot be determined at Barbados because the downslope core sequences are not reef-crest deposits due to their association with deeper coral assemblages and lack of depositional relief. The end of this meltwater pulse can however be determined from the upslope reef, and occurred at a similar time and depth to that documented from Tahiti.

The Sea-level Response to Ice Sheet Evolution (SeaRISE) effort explores the sensitivity of the current generation of ice sheet models to external forcing to gain insight into the potential future contribution to sea level from the Greenland and Antarctic ice sheets. All participating models simulated the ice sheet response to three types of external forcings: a change in oceanic condition, a warmer atmospheric environment, and enhanced basal lubrication. Here an analysis of the spatial response of the Greenland ice sheet is presented, and the impact of model physics and spin-up on the projections is explored. Although the modeled responses are not always homogeneous, consistent spatial trends emerge from the ensemble analysis, indicating distinct vulnerabilities of the Greenland ice sheet. There are clear response patterns associated with each forcing, and a similar mass loss at the full ice sheet scale will result in different mass losses at the regional scale, as well as distinct thickness changes over the ice sheet. All forcings lead to an increased mass loss for the coming centuries, with increased basal lubrication and warmer ocean conditions affecting mainly outlet glaciers, while the impacts of atmospheric forcings affect the whole ice sheet. Key Points Sensitivity study of Greenland to atmospheric, oceanic and subglacial forcings Each forcing result in a different regional thickness response All forcings lead to an increased mass loss for the coming centuries ©2013. American Geophysical Union. All Rights Reserved.

Atmospheric, oceanic, and subglacial forcing scenarios from the Sea-level Response to Ice Sheet Evolution (SeaRISE) project are applied to six three-dimensional thermomechanical ice-sheet models to assess Antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies. Results indicate (i) growth with warming, except within low-latitude basins (where inland thickening is outpaced by marginal thinning); (ii) mass loss with enhanced sliding (with basins dominated by high driving stresses affected more than basins with low-surface-slope streaming ice); and (iii) mass loss with enhanced ice shelf melting (with changes in West Antarctica dominating the signal due to its marine setting and extensive ice shelves; cf. minimal impact in the Terre Adelie, George V, Oates, and Victoria Land region of East Antarctica). Ice loss due to dynamic changes associated with enhanced sliding and/or sub-shelf melting exceeds the gain due to increased precipitation. Furthermore, differences in results between and within basins as well as the controlling impact of sub-shelf melting on ice dynamics highlight the need for improved understanding of basal conditions, grounding-zone processes, ocean-ice interactions, and the numerical representation of all three. Key Points Sensitivity study of Antarctica to atmospheric, oceanic and subglacial forcings Different sectors of Antarctica are vulnerable to the forcings Atmospheric forcing lead to a growth, but dynamic forcing lead to a mass loss ©2013. American Geophysical Union. All Rights Reserved.

Sea-level has been rising at an accelerated rate during recent decades and is projected to continue increasing at an accelerated rate over the twenty-first century and beyond, mostly as a result of anthropogenic warming. A substantially raised sea level can have severe impacts on low-lying coastal areas, including coastal erosion and flooding of inhabited areas. Under continued climate warming, these impacts will be exacerbated by extreme meteorological events and extreme wave heights, posing severe risks to the human communities and coastal ecosystems. In this paper we review the recent advances on the contributions of glaciers and sheets to sea-level rise, in the light of the recently released IPCC Special Report on the Ocean and Cryosphere in a Changing Climate.

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Sea-level has been rising at an accelerated rate during recent decades and is projected to continue increasing at an accelerated rate over the twenty-first century and beyond, mostly as a result of anthropogenic warming. A substantially raised sea level can have severe impacts on low-lying coastal areas, including coastal erosion and flooding of inhabited areas. Under continued climate warming, these impacts will be exacerbated by extreme meteorological events and extreme wave heights, posing severe risks to the human communities and coastal ecosystems. In this paper we review the recent advances on the contributions of glaciers and sheets to sea-level rise, in the light of the recently released IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. [ABSTRACT FROM AUTHOR]

Reconstructions of postglacial sea-level rise have provided key insight into the rapid disintegration of ice-sheets and the discharge of large meltwater pulses during the last deglaciation. The most complete reconstruction is from Barbados where thick, backstepping sequences of the reef-crest coral Acropora palmata have been recovered in cores from the insular shelf and slope off the Island's south coast. Differences in the depth, timing, and magnitude of meltwater pulses between the Barbados reconstruction and other reefal records, however, has led to significant uncertainty in their origin, and the consequent timing of ice-sheet collapse. Here we re-analyse the published sedimentary, stratigraphic, and chronological data from Barbados, and find evidence for ex-situ data which indicates that reefal sequences contain coral clasts generated during hurricanes. By adjusting for biases caused by these ex-situ data, we provide a revised sea-level reconstruction which shows that MWP-1b was an 8-11 m rise from -53 m in ~250 years starting at 11.3 ka, which is 5 m smaller, and 150 years younger than previous estimates. It also shows that the onset of MWP-1a cannot be determined at Barbados because the downslope core sequences are not reef-crest deposits due to their association with deeper coral assemblages and lack of depositional relief. The end of this meltwater pulse can however be determined from the upslope reef, and occurred at a similar time and depth to that documented from Tahiti. [ABSTRACT FROM AUTHOR]

We use 22 monthly GRACE (Gravity Recovery and Climate Experiment) gravity fields to estimate the linear trend in Greenland ice mass during 2002–2004. We recover a decrease in total ice mass of 82 ± 28 km3 of ice per year, consistent with estimates from other techniques. Our uncertainty estimate is dominated by the effects of GRACE measurement errors and errors in our post glacial rebound (PG) correction. The main advantages of GRACE are that it is sensitive to the entire ice sheet, and that it provides mass estimates with only minimal use of supporting physical assumptions or ancillary data.

We use twenty-two monthly GRACE (Gravity Recovery and Climate Experiment) gravity fields to recover nonsecular mass change in Greenland. The results show large seasonal variability. We compare with modeled precipitation, evaporation, and runoff derived from ERA40 (the 40-year ECMWF Re-Analysis of the global atmosphere). The model's seasonal amplitude is controlled by runoff and agrees reasonably well with GRACE. Both GRACE and the model show an April/May maximum. But the GRACE results show a delayed minimum relative to the model. This difference is probably associated with omissions in the runoff model, ice discharge, subglacial hydrology, mass loss by blowing-snow, and hydrology in ice-free regions. The discrepancy is smaller, but still significant, for south Greenland alone. When we include a proxy for ice discharge the agreement is improved.

The most significant climate cooling of the Holocene is centred on 8.2 kyr BP (the ‘8.2 event’). Its cause is widely attributed to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) associated with the sudden drainage of Laurentide proglacial Lakes Agassiz and Ojibway, but model simulations have difficulty reproducing the event with a single-pulse scenario of freshwater input. Several lines of evidence point to multiple episodes of freshwater release from the decaying Laurentide Ice Sheet (LIS) between ∼8900 and ∼8200 cal yr BP, yet the precise number, timing and magnitude of these events – critical constraints for AMOC simulations – are far from resolved. Here we present a high-resolution relative sea level (RSL) record for the period 8800 to 7800 cal yr BP developed from estuarine and salt-marsh deposits in SW Scotland. We find that RSL rose abruptly in three steps by 0.35 m, 0.7 m and 0.4 m (mean) at 8760–8640, 8595–8465, 8323–8218 cal yr BP respectively. The timing of these RSL steps correlate closely with short-lived events expressed in North Atlantic proxy climate and oceanographic records, providing evidence of at least three distinct episodes of enhanced meltwater discharge from the decaying LIS prior to the 8.2 event. Our observations can be used to test the fidelity of both climate and ice-sheet models in simulating abrupt change during the early Holocene. [ABSTRACT FROM AUTHOR]

Abstract: Continued atmospheric and ocean warming places parts of the West Antarctic Ice Sheet at risk for collapse through accelerated ice flow and grounding line retreat over reversed bed slopes. However, understanding of the speed and duration of ice sheet instability events remains incomplete, limiting our ability to include these events in sea level rise projections. Here, we use a first-order, empirical approach, exploring past instability events in the Fennoscandian (FIS) and Laurentide (LIS) ice sheets to establish a relationship between catchment size and the duration of instability events. We also examine how instabilities propagate through ice sheet catchments, and how this propagation is controlled by topography and existing flow organisation at the onset of an event. We find that the fastest documented paleo-collapses involved streaming or surging in corridors that are wide compared to their length, and in which fast flow did not resume after the event. Distributed ice stream networks, in which narrow ice streams were intertwined with slow-flow interstream ridges, are not represented among the fastest documented events. For the FIS and LIS, there is geological evidence for instability events covering areas of ∼100,000 km2, with durations between 100 and 300 yr. Comparison of the spatial patterns and topographic contexts of Lateglacial collapse events in former Northern Hemisphere ice sheets and the current WAIS suggest that only a minor part of the WAIS area may be at risk for unimpeded collapse, and that negative feedbacks will likely slow or halt ice drawdown in remaining areas. The Pine Island Glacier (PIG) and Thwaites Glacier (TG) catchments in West Antarctica are likely to respond in very different ways to possible further grounding line retreat. The PIG may experience a minor collapse over its main trunk, but the bed topography favours a less dramatic retreat thereafter. The TG is probably not as close to a threshold as PIG, but once efficient drainage has progressed inwards to reach the Bentley Subglacial Basin (BSB) and Bentley Subglacial Trench (BST), a full collapse of the area may occur. The likely time perspective for a BSB–BST collapse is the time required for 100–200 km of grounding line retreat in the TG system plus 100–300 years for an actual collapse event. [Copyright &y& Elsevier]

About 75 % of the Antarctic surface mass gain occurs over areas below 2,000 m asl, which cover 40 % of the grounded ice-sheet. As the topography is complex in many of these regions, surface mass balance modelling is highly dependent on horizontal resolution, and studying the impact of Antarctica on the future rise in sea level requires physical approaches. We have developed a computationally efficient, physical downscaling model for high-resolution (15 km) long-term surface mass balance (SMB) projections. Here, we present results of this model, called SMHiL (surface mass balance high-resolution downscaling), which was forced with the LMDZ4 atmospheric general circulation model to assess Antarctic SMB variability in the twenty first and the twenty second centuries under two different scenarios. The higher resolution of SMHiL better reproduces the geographical patterns of SMB and increase significantly the averaged SMB over the grounded ice-sheet for the end of the twentieth century. A comparison with more than 3200 quality-controlled field data shows that LMDZ4 and SMHiL reproduce the observed values equally well. Nevertheless, field data below 2,000 m asl are too scarce to efficiently show the added value of SMHiL and measuring the SMB in these undocumented areas should be a future scientific priority. Our results suggest that running LMDZ4 at a finer resolution (15 km) may give a future increase in SMB in Antarctica that is about 30 % higher than by using its standard resolution (60 km) due to the higher increase in precipitation in coastal areas at 15 km. However, a part (∼15 %) of these discrepancies could be an artefact from SMHiL since it neglects the foehn effect and likely overestimates the precipitation increase. Future changes in the Antarctic SMB at low elevations will result from the competition between higher snow accumulation and runoff. For this reason, developing downscaling models is crucial to represent processes in sufficient detail and correctly model the SMB in coastal areas. [ABSTRACT FROM AUTHOR]

Abstract: The Miocene Climatic Optimum (17–15Ma) and the rapid cooling of the Middle Miocene Climate Transition (15–13Ma) together signal a major change in Earth''s climate system. Here we examine the sediment provenance in the AND-2A drill core, located 10km from the East Antarctic coastline, to significantly increase our understanding of Antarctic ice development, glacial erosion, and transport in the Ross embayment during this time. Heavy minerals are very diagnostic of source rock types and assemblages can be used to track changes in the areas of maximum erosion under the margin of an ice sheet. We used a combination of optical mineralogy and SEM-EDS analysis to characterize the heavy mineral fractions of diamictites and sandstones in the upper 650m of AND-2A, which includes an expanded section dated between ~17 and 14Ma. We find four diagnostic heavy mineral assemblages distributed in intervals throughout the core: I. (650–552mbsf) elevated orthopyroxene, titanaugite, and carbonate contents; II. (552–308mbsf) abundant diopside, pigeonite, and orthopyroxene, with sillimanite and kyanite; III. (308–250mbsf) increasing contents of garnet and green hornblende; and IV. (250–20mbsf) abundant green hornblende, titanaugite, green augite, and carbonate. Based on the heavy mineral analysis we demonstrate that (1) the ice sheet was grounded on the shelf at ~17.7–17.1Ma, and it was eroding Cenozoic volcanic rocks to the south of the drillsite; (2) during the early part of the Miocene Climatic Optimum (~17.1–15.5Ma) the East Antarctic Ice Sheet retreated landward into upland regions of the Transantarctic Mountains, where it eroded dolerite sills and high-grade metamorphic rocks; (3) immediately prior to the Middle Miocene Climate Transition (15.5–14.3Ma), the East Antarctic ice advanced and eroded granitic and low-medium grade metamorphic basement rocks in the coastal sections of the Transantarctic Mountains; and (4) following this initial phase of ice growth, the West Antarctic Ice Sheet and the East Antarctic Ice Sheet coalesced into a larger than modern (interglacial) Antarctic Ice Sheet prior to 14.3Ma and eroded Cenozoic volcanic and low- to medium-grade metamorphic basement rocks to the south of the drillsite. Our results suggest that, although East Antarctica may have remained glaciated during the Miocene Climatic Optimum, ice extent was reduced to a configuration within the present interglacial extent, even during orbital-scale glacial maxima. Ice growth during the Middle Miocene Climate Transition commenced at ca. 15.5Ma in the Ross Sea basin, which is slightly earlier than inferred from deep-sea stable isotope records, but in agreement with low-latitude sea-level reconstructions. [Copyright &y& Elsevier]

Abstract: We propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the NorthGRIP ice core. This method shows unexpected correlations between neighbours in the so-called normal grain growth regime, questioning the classical view on the onset of rotation recrystallization in ice-sheets. Moreover, the fractionation rate associated to the rotation recrystallization appears constant through time. Finally, grains with low-angle boundaries do not present a special distribution pattern of their c-axes. This suggests that rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain. [Copyright &y& Elsevier]