ORCID Profile
0000-0001-9201-1644
Current Organisation
Dartmouth College
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Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-11918
Abstract: & & The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort sponsored by the Climate and Cryosphere (CliC) project.& MISOMIP aims to design and coordinate a series of MIPs& #8212 some idealized and realistic& #8212 for model evaluation, verification with observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS).& The first phase of the project, MISOMIP1, was an idealized, coupled set of experiments that combined elements from the MISMIP+ and ISOMIP+ standalone experiments for ice-sheet and ocean models, respectively.& These MIPs had 3 main goals: 1) to provide simplified experiments that allow model developers to compare their results with those from other models 2) to suggest a path for testing components in the process of developing a coupled ice sheet-ocean model and 3) to enable a large variety of parameter and process studies that branch off from these basic experiments.& & & & Here, we describe preliminary analysis of the MISOMIP1 results.& Eight models in 14 configurations participated in the MIP. & In keeping with analysis of the MISMIP+ experiment, we find that the choice of basal friction parameterizations in the ice-sheet component (Weertman vs. Coulomb limited) has a particularly significant impact on the rate of ice-sheet retreat but the choice of stress approximation (SSA, SSA* or L1Lx) seems to have little impact.& Models with Coulomb-limited basal friction also tend to be those with the highest melt rates, confirming a positive feedback between melt and retreat in the MISOMIP1 configuration seen in previous work.& The ocean component& #8217 s treatment of the boundary layer below the ice shelf also has a significant impact on melt rates and resulting retreat, consistent with findings based on ISOMIP+.& Feedbacks between the components lead to localized features in the melt rates and the ice geometry not seen in standalone simulations, though the ~2-km horizontal and ~20-m vertical resolution of these simulations appears to be too coarse to produce long-lived, sub-ice-shelf channels seen at higher resolution.& &
Publisher: American Geophysical Union (AGU)
Date: 11-2022
DOI: 10.1029/2022EF002751
Abstract: Sea level rise (SLR) is a long‐lasting consequence of climate change because global anthropogenic warming takes centuries to millennia to equilibrate for the deep ocean and ice sheets. SLR projections based on climate models support policy analysis, risk assessment and adaptation planning today, despite their large uncertainties. The central range of the SLR distribution is estimated by process‐based models. However, risk‐averse practitioners often require information about plausible future conditions that lie in the tails of the SLR distribution, which are poorly defined by existing models. Here, a community effort combining scientists and practitioners builds on a framework of discussing physical evidence to quantify high‐end global SLR for practitioners. The approach is complementary to the IPCC AR6 report and provides further physically plausible high‐end scenarios. High‐end estimates for the different SLR components are developed for two climate scenarios at two timescales. For global warming of +2°C in 2100 (RCP2.6/SSP1‐2.6) relative to pre‐industrial values our high‐end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in 2300. Similarly, for a (RCP8.5/SSP5‐8.5), we estimate up to 1.6 m in 2100 and up to 10.4 m in 2300. The large and growing differences between the scenarios beyond 2100 emphasize the long‐term benefits of mitigation. However, even a modest 2°C warming may cause multi‐meter SLR on centennial time scales with profound consequences for coastal areas. Earlier high‐end assessments focused on instability mechanisms in Antarctica, while here we emphasize the importance of the timing of ice shelf collapse around Antarctica. This is highly uncertain due to low understanding of the driving processes. Hence both process understanding and emission scenario control high‐end SLR.
Publisher: American Geophysical Union (AGU)
Date: 30-06-2023
DOI: 10.1029/2022GL101595
Abstract: Ice sheet melting into the Southern Ocean can change the formation and properties of the Antarctic Bottom Water (AABW). Ocean models often mimic ice sheet melting by adding freshwater fluxes in the Southern Ocean under erse spatial distributions. We use a global ocean and sea‐ice model to explore whether the spatial distribution and magnitude of meltwater fluxes can alter AABW properties and formation. We find that a realistic spatially varying meltwater flux sustains AABW with higher salinities compared to simulations with uniform meltwater fluxes. Finally, we show that increases in ice sheet melting above 12% since 1958 can trigger AABW freshening rates similar to those observed in the Southern Ocean since 1990, suggesting that the increasing Antarctic meltwater discharge can drive the observed AABW freshening.
Publisher: Copernicus GmbH
Date: 17-09-2020
Abstract: Abstract. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-4188
Abstract: & & Viscous deformation is the main process controlling ice flow in ice shelves and in slow-moving regions of polar ice sheets where ice is frozen to the bed. However, the role of deformation in flow in ice streams and fast-flowing regions is typically poorly represented in ice sheet models due to a major limitation in the current standard flow relation used in most large-scale ice sheet models & #8211 the Glen flow relation & #8211 which does not capture the steady-state flow of anisotropic ice that prevails in polar ice sheets. Here, we highlight recent advances in modeling deformation in the Ice Sheet System Model using the ESTAR (empirical, scalar, tertiary, anisotropic regime) flow relation & #8211 a new description of deformation that takes into account the impact of different types of stresses on the deformation rate. We contrast the influence of the ESTAR and Glen flow relations on the role of deformation in the dynamics of Thwaites Glacier, West Antarctica, using diagnostic simulations. We find key differences in: (1) the slow-flowing interior of the catchment where the unenhanced Glen flow relation simulates unphysical basal sliding (2) over the floating Thwaites Glacier Tongue where the ESTAR flow relation outperforms the Glen flow relation in accounting for tertiary creep and the spatial differences in deformation rates inherent to ice anisotropy and (3) in the grounded region within 80km of the grounding line where the ESTAR flow relation locally predicts up to three times more vertical shear deformation than the unenhanced Glen flow relation, from a combination of enhanced vertical shear flow and differences in the distribution of basal shear stresses. More broadly on grounded ice, the membrane stresses are found to play a key role in the patterns in basal shear stresses and the balance between basal shear stresses and gravitational forces simulated by each of the ESTAR and Glen flow relations. Our results have implications for the suitability of ice flow relations used to constrain uncertainty in reconstructions and projections of global sea levels, warranting further investigation into using the ESTAR flow relation in transient simulations of glacier and ice sheet dynamics. We conclude by discussing how geophysical data might be used to provide insight into the relationship between ice flow processes as captured by the ESTAR flow relation and ice fabric anisotropy.& &
Publisher: Springer Science and Business Media LLC
Date: 12-12-2019
Publisher: Wiley
Date: 02-12-2020
Publisher: American Geophysical Union (AGU)
Date: 03-2022
DOI: 10.1029/2021JF006332
Abstract: Ice deformation dominates the evolution of ice shelf flow and the slow‐moving regions in the interior of ice sheets. However, deformation may be poorly represented in large‐scale ice sheet models that use the Glen flow relation, due to its questionable applicability to the steady‐state flow of anisotropic ice that prevails in ice sheets, having been derived from secondary creep rates of isotropic ice. We assess the deformation regimes of Thwaites Glacier, West Antarctica, using the Glen and “Empirical Scalar Tertiary Anisotropy Regime”, (ESTAR) flow relations, the latter being derived from steady‐state deformation rates of anisotropic ice. For grounded ice, the character of the flow relation determines the contribution of deformation to overall flow, with ESTAR producing greater bed‐parallel shear deformation than the standard Glen flow relation. The ESTAR experiments show larger basal shear stress maxima than the standard Glen experiment because ESTAR treats the responses to simple shear stresses and compression stresses differently, reducing the role of lateral and longitudinal stresses in momentum balance. On the Thwaites Glacier Tongue, ESTAR provides the best match to observed speeds by accounting for the differing effects of stresses on ice flow. Our results highlight the importance of the numerical description of anisotropy, particularly: In regions of transition from deformation‐dominated to sliding‐dominated flow in the approach to the grounding line, and across ice shelves. Given the importance of these locations in determining mass flux into the ocean, our results have implications for projections of sea level change from Antarctic ice loss.
Publisher: Copernicus GmbH
Date: 22-01-2020
DOI: 10.5194/TC-2019-324
Abstract: Abstract. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and inform on the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimated the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes and the forcings employed. This study presents results from 18 simulations from 15 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100, forced with different scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5) representative of the spread in climate model results. The contribution of the Antarctic ice sheet in response to increased warming during this period varies between −7.8 and 30.0 cm of Sea Level Equivalent (SLE). The evolution of the West Antarctic Ice Sheet varies widely among models, with an overall mass loss up to 21.0 cm SLE in response to changes in oceanic conditions. East Antarctica mass change varies between −6.5 and 16.5 cm SLE, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional mass loss of 8 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 AOGCMs show an overall mass loss of 10 mm SLE compared to simulations done under present-day conditions, with limited mass gain in East Antarctica.
Publisher: Copernicus GmbH
Date: 04-08-2023
DOI: 10.5194/TC-2023-109
Abstract: Abstract. The Antarctic Ice Sheet represents the largest source of uncertainty in future sea level rise projections, with a contribution to sea level by 2100 ranging from -5 to 43 cm of sea level equivalent under high carbon emission scenarios estimated by the recent Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). ISMIP6 highlighted the different behaviors of the East and West Antarctic ice sheets, as well as the possible role of increased surface mass balance in offsetting the dynamic ice loss in response to changing oceanic conditions in ice shelf cavities. However, the detailed contribution of in idual glaciers, as well as the partitioning of uncertainty associated with this ensemble, have not yet been investigated. Here, we analyze the ISMIP6 results for high carbon emission scenarios, focusing on key glaciers around the Antarctic Ice Sheet, and we quantify their projected dynamic mass loss, defined here as mass loss through increased ice discharge into the ocean in response to changing oceanic conditions. We highlight glaciers contributing the most to sea level rise as well as their vulnerability to changes in oceanic conditions. We then investigate the different sources of uncertainty and their relative role in projections, for the entire continent and for key in idual glaciers. We show that, in addition to Thwaites and Pine Island glaciers in West Antarctica, Totten and Moscow University glaciers in East Antarctica present comparable future dynamic mass loss and high sensitivity to ice shelf basal melt. The overall uncertainty in additional dynamic mass loss in response to changing oceanic conditions, compared to a scenario with constant oceanic conditions, is dominated by the choice of ice sheet model, accounting for 52 % of the total uncertainty of the Antarctic dynamic mass loss in 2100. Its relative role for the most dynamic glaciers varies between 14 % for MacAyeal and Whillans ice streams and 56 % for Pine Island Glacier at the end of the century. The uncertainty associated with the choice of climate model increases over time and reaches 13 % of the uncertainty by 2100 for the Antarctic Ice Sheet, but varies between 4 % for Thwaites glacier and 53 % for Whillans ice stream. The uncertainty associated with the ice-climate interaction, which captures different treatments of oceanic forcings such as the choice of melt parameterization, its calibration, and simulated ice shelf geometries, accounts for 22 % of the uncertainty at the ice sheet scale, but reaches 36 and 39 % for Institute ice stream and Thwaites Glacier, respectively, by 2100. Overall, this study helps inform future research by highlighting the sectors of the ice sheet most vulnerable to oceanic warming over the 21st century and by quantifying the main sources of uncertainty.
Publisher: Copernicus GmbH
Date: 25-07-2016
Abstract: Abstract. 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 (MISOMIP1) to be compared directly to the in idual 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.
Publisher: Springer Science and Business Media LLC
Date: 05-05-2021
Publisher: American Geophysical Union (AGU)
Date: 19-08-2021
DOI: 10.1029/2020GL091741
Abstract: Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming.
Publisher: Wiley
Date: 07-03-2022
No related grants have been discovered for Helene Seroussi.