ORCID Profile
0000-0003-0368-1334
Current Organisations
Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies
,
University of Tasmania
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Physical oceanography | Physical geography and environmental geoscience | Glaciology | Groundwater hydrology |
Publisher: Copernicus GmbH
Date: 11-04-2022
Abstract: Abstract. Antarctic sea ice kinematics plays a crucial role in shaping the Southern Ocean climate and ecosystems. Satellite passive-microwave-derived sea ice motion data have been used widely for studying sea ice motion and deformation, and they provide daily global coverage at a relatively low spatial resolution (in the order of 60 km × 60 km). In the Arctic, several validated datasets of satellite observations are available and used to study sea ice kinematics, but far fewer validation studies exist for the Antarctic. Here, we compare the widely used passive-microwave-derived Antarctic sea ice motion product by Kimura et al. (2013) with buoy-derived velocities and interpret the effects of satellite observational configuration on the representation of Antarctic sea ice kinematics. We identify two issues in the Kimura et al. (2013) product: (i) errors in two large triangular areas within the eastern Weddell Sea and western Amundsen Sea relating to an error in the input satellite data composite and (ii) a more subtle error relating to invalid assumptions for the average sensing time of each pixel. Upon rectification of these, performance of the daily composite sea ice motion product is found to be a function of latitude, relating to the number of satellite swaths incorporated (more swaths further south as tracks converge) and the heterogeneity of the underlying satellite signal (brightness temperature here). Daily sea ice motion vectors calculated using ascending- and descending-only satellite tracks (with a true ∼ 24 h timescale) are compared with the widely used combined product (ascending and descending tracks combined together, with an inherent ∼ 39 h timescale). This comparison reveals that kinematic parameters derived from the shorter-timescale velocity datasets are higher in magnitude than the combined dataset, indicating a high degree of sensitivity to observation timescale. We conclude that the new generation of “swath-to-swath” (S2S) sea ice velocity datasets, encompassing a range of observational timescales, is necessary to advance future research into sea ice kinematics.
Publisher: Copernicus GmbH
Date: 15-07-2022
Abstract: Abstract. Changes in ocean-driven basal melting have a key influence on the stability of ice shelves, the mass loss from the ice sheet, ocean circulation, and global sea level rise. Coupled ice sheet–ocean models play a critical role in understanding future ice sheet evolution and examining the processes governing ice sheet responses to basal melting. However, as a new approach, coupled ice sheet–ocean systems come with new challenges, and the impacts of solutions implemented to date have not been investigated. An emergent feature in several contributing coupled models to the 1st Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP1) was a time-varying oscillation in basal melt rates. Here, we use a recently developed coupling framework, FISOC (v1.1), to connect the modified ocean model ROMSIceShelf (v1.0) and ice sheet model Elmer/Ice (v9.0), to investigate the origin and implications of the feature and, more generally, the impact of coupled modeling strategies on the simulated basal melt in an idealized ice shelf cavity based on the MISOMIP setup. We found the spatial-averaged basal melt rates (3.56 m yr−1) oscillated with an litude ∼0.7 m yr−1 and approximate period of ∼6 years between year 30 and 100 depending on the experimental design. The melt oscillations emerged in the coupled system and the standalone ocean model using a prescribed change of cavity geometry. We found that the oscillation feature is closely related to the discretized ungrounding of the ice sheet, exposing new ocean, and is likely strengthened by a combination of positive buoyancy–melt feedback and/or melt–geometry feedback near the grounding line, and the frequent coupling of ice geometry and ocean evolution. Sensitivity tests demonstrate that the oscillation feature is always present, regardless of the choice of coupling interval, vertical resolution in the ocean model, tracer properties of cells ungrounded by the retreating ice sheet, or the dependency of friction velocities to the vertical resolution. However, the litude, phase, and sub-cycle variability of the oscillation varied significantly across the different configurations. We were unable to ultimately determine whether the feature arises purely due to numerical issues (related to discretization) or a compounding of multiple physical processes lifying a numerical artifact. We suggest a pathway and choices of physical parameters to help other efforts understand the coupled ice sheet–ocean system using numerical models.
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: IEEE
Date: 06-2011
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-10448
Abstract: & & The ocean-driven basal melting has important implications for the stability of ice shelves in Antarctic, which largely affects the ice sheet mass balance, ocean circulation, and subsequently global sea level rise. Due to the limited observations in the ice shelf cavities, the couple ice sheet ocean models have been playing a critical role in examining the processes governing basal melting. In this study we use the Framework for Ice Sheet-Ocean Coupling (FISOC) to couple the Elmer/Ice full-stokes ice sheet model and the Regional Ocean Modeling System (ROMS) ocean model to model ice shelf/ocean interactions for an idealised three-dimensional domain. Experiments followed the coupled ice sheet& #8211 ocean experiments under the first phase of the Marine Ice Sheet& #8211 Ocean Model Intercomparison Project (MISOMIP1). A periodic pattern in the simulated mean basal melting rates is found to be highly consistent with the maximum barotropic stream function and also the grounding line retreat row by row, & which is likely to be related with the gyre break down near the grounding line caused by some non-physical instability events from the ocean bottom. Sensitivity tests are carried out, showing that this periodic pattern is not sensitive to the choice of couple time intervals and horizontal eddy viscosities but sensitive to vertical resolution in the ocean model, the chosen critical water column thickness in the wet-dry scheme, and the tracer properties for the nudging dry cells at the ice-ocean interface boundary. Further simulations are necessary to better explain the mechanism involved in the couple ice-ocean system, which is very significant for its application on the realistic ice-ocean systems in polar regions.& &
Publisher: Copernicus GmbH
Date: 04-08-2020
DOI: 10.5194/GMD-2020-206
Abstract: Abstract. A number of important questions concern processes at the margins of ice sheets where multiple components of the Earth System, most crucially ice sheets and oceans, interact. Such processes include thermodynamic interaction at the ice-ocean interface, the impact of melt water on ice shelf cavity circulation, the impact of basal melting of ice shelves on grounded ice dynamics, and ocean controls on iceberg calving. These include fundamentally coupled processes in which feedback mechanisms between ice and ocean play an important role. Some of these mechanisms have major implications for humanity, most notably the impact of retreating marine ice sheets on global sea level. In order to better quantify these mechanisms using computer models, feedbacks need to be incorporated into the modelling system. To achieve this ocean and ice dynamic models must be coupled, allowing run time information sharing between components. We have developed a flexible coupling framework based on existing Earth System coupling technologies. The open-source Framework for Ice Sheet – Ocean Coupling (FISOC) provides a modular approach to online coupling, facilitating switching between different ice dynamic and ocean components. FISOC allows fully synchronous coupling, in which both ice and ocean run on the same time-step, or semi-synchronous coupling in which the ice dynamic model uses a longer time step. Multiple regridding options are available, and multiple methods for coupling the sub ice shelf cavity geometry. Thermodynamic coupling may also be activated. We present idealised simulations using FISOC with a Stokes flow ice dynamic model coupled to a regional ocean model. We demonstrate the modularity of FISOC by switching between two different regional ocean models and presenting outputs for both. We demonstrate conservation of mass and other verification steps during evolution of an idealised coupled ice – ocean system, both with and without grounding line movement.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-7285
Abstract: & & The Amery Ice Shelf (AIS), East Antarctica, has a layered structure, due to the presence of both meteoric and marine ice. In this study, the thermal structures of the AIS are evaluated from vertical temperature profiles, and its formation mechanism are demonstrated by numerical simulations. The temperature profiles, derived from borehole thermistor data at four different locations, indicate distinct temperature regimes in the areas with and without basal marine ice. The former shows a near-isothermal layer over 100 m at the bottom and stable internal temperature gradients, while the latter reveals a cold core ice resulting from upstream cold ice advection and large temperature gradients within 90 m at the bottom. The three-dimensional steady-state temperature fields are simulated by Elmer/Ice, a full-stokes ice sheet model, using three different basal mass balance datasets. We found the simulated temperature fields are highly sensitive to the choice of dynamic boundary conditions on both upper and lower surfaces. To better illustrate the formation of the vertical thermal regimes, we construct a one-dimensional temperature column model to simulate the process of ice columns moving on the flowlines with varying boundary conditions. The comparison of simulated and observed temperature profiles suggests that the basal mass balance and meteoric ice advection are both crucial factors determining the thermal structure of the ice shelf. The different basal mass balance datasets are indirectly evaluated as well. The improved understanding of the thermal structure of the AIS will assist with further studies on its thermodynamics and rheology.& &
Publisher: Copernicus GmbH
Date: 02-01-2018
DOI: 10.5194/TC-2017-242
Abstract: Abstract. The Wordie Ice Shelf-Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. Upstream glacier acceleration and dynamic thinning have been observed over the past two decades, especially after 2008 when only a little constraining ice shelf remained at the Fleming Glacier front. It is important to know whether the substantial speed up and surface draw-down of the glacier since 2008 is a direct response to increasing ocean forcing or driven by the feedback within an unstable marine-based glacier system or both. To explore the mechanism underlying the changes, we use a Stokes (full stress) model to simulate the basal shear stress of the Fleming system in 2008 and 2015. Recent observational studies have suggested the 2008–2015 velocity change was due to the ungrounding of the Fleming Glacier front. Our modelling shows that the fast flowing region of the Fleming Glacier shows a very low basal shear stress in 2008 but with a band of higher basal shear stress along the ice front. It indicates that the ungrounding process might have not started in 2008, which is consistent with the height above buoyancy calculation in 2008. Comparison of our inversions for basal shear stresses for 2008 and 2015 suggests the migration of the grounding line by ~ 9 km upstream from the grounding line position in 1996, a shift which is consistent with the change in floating area deduced from the height above buoyancy in 2015. The southern branch of the Fleming Glacier and the Prospect Glacier apparently have retreated by ~ 1–3 km from 2008 to 2015. The retrograde bed underneath the Fleming Glacier has promoted migration of the grounding line, which we suggest may be triggered by subglacial drainage as a response to the increased basal water supply through greater frictional heating at the ice-bedrock interface further upstream in the fast-flowing region. Improved knowledge of bed topography near the grounding line and further transient simulation is required to predict the future grounding line movement of the Fleming Glacier system precisely and subsequently understand better the ice dynamics and the its future contribution to sea level.
Publisher: Copernicus GmbH
Date: 15-08-2018
Abstract: Abstract. Many glaciers in the Antarctic Peninsula are now rapidly losing mass. Understanding of the dynamics of these fast-flowing glaciers, and their potential future behaviour, can be improved through ice sheet modelling studies. Inverse methods are commonly used in ice sheet models to infer the spatial distribution of a basal friction coefficient, which has a large effect on the basal velocity and ice deformation. Here we use the full-Stokes Elmer/Ice model to simulate the Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula. With an inverse method, we infer the pattern of the basal friction coefficient from surface velocities observed in 2008. We propose a multi-cycle spin-up scheme to reduce the influence of the assumed initial englacial temperature field on the final inversion. This is particularly important for glaciers like the Fleming Glacier, which have areas of strongly temperature-dependent deformational flow in the fast-flowing regions. Sensitivity tests using various bed elevation datasets, ice front positions and boundary conditions demonstrate the importance of high-accuracy ice thickness/bed geometry data and precise location of the ice front boundary.
Publisher: Copernicus GmbH
Date: 02-01-2018
DOI: 10.5194/TC-2017-241
Abstract: Abstract. Many glaciers in West Antarctica and the Antarctic Peninsula are now rapidly losing ice mass. Understanding of the dynamics of these fast-flowing glaciers, and their potential future behavior, can be improved through ice sheet modeling studies. Inverse methods are commonly used in ice sheet models to infer the basal shear stress, which has a large effect on the basal velocity and internal ice deformation. Here we use the full-Stokes Elmer/Ice model to simulate the Wordie Ice Shelf-Fleming Glacier system in the southern Antarctic Peninsula. With a control inverse method, we model the basal drag from the surface velocities observed in 2008. We propose a three-cycle spin-up scheme to remove the influence of initial temperature field on the final inversion. This is particularly important for glaciers with significant temperature-dependent internal deformation. We find that the Fleming Glacier has strong, temperature-dependent, deformational flow in the fast-flowing regions. Sensitivity tests using various bed elevation datasets and ice front boundary conditions demonstrate the importance of high-accuracy ice thickness/bed geometry data and precise location of the ice front boundary.
Publisher: Copernicus GmbH
Date: 18-08-2021
DOI: 10.5194/TC-2021-248
Abstract: Abstract. The Amery Ice Shelf (AIS), East Antarctica, has a layered structure, due to the presence of both meteoric and marine ice. In this study, the thermal structure of the AIS and its spatial pattern are evaluated and analysed through borehole observations and numerical simulations. In the area with marine ice, a near-isothermal basal layer up to 120 m thick is observed, which closely conforms to the pressure-dependent freezing temperature of seawater. In the area experiencing basal melting, large temperature gradients, up to −0.36 °C m−1, are observed at the base. Three-dimensional (3-D) steady-state temperature simulations with four different basal mass balance datasets reveal a high sensitivity of ice-shelf thermal structure to the distribution of basal mass balance. We also construct a one-dimensional (1-D) temperature column model to simulate the process of ice columns moving along flowlines with time-evolving boundary conditions, which achieves slightly better agreement with borehole observations than the 3-D simulations. Our simulations reveal internal cold ice advected from higher elevations by the AIS’s tributary glaciers, warming downstream along the ice flow, and we suggest the thermal structures dominated by the cold core ice may commonly exist among Antarctic ice shelves. For the marine ice, the porous structure of its lower layer and interactions with ocean below determine the local thermal regime and give rise to the near-isothermal phenomenon. The limitations in our simulations identify the need for ice shelf/ocean coupled models with improved thermodynamics and more comprehensive evaluation of boundary conditions. Given the temperature dependence of ice rheology, the depth-averaged ice stiffness factor B(Th) derived from the simulated temperature field is presented to quantify the influence of the temperature distribution on ice shelf dynamics. The full 3-D field of this factor will assist as an input to future modelling studies.
Publisher: Copernicus GmbH
Date: 15-08-2018
Abstract: Abstract. The Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. Increases in the glacier velocity and dynamic thinning have been observed over the past two decades, especially after 2008 when only a small ice shelf remained at the Fleming Glacier front. It is important to know whether the substantial further speed-up and greater surface draw-down of the glacier since 2008 is a direct response to ocean forcing, or driven by feedbacks within the grounded marine-based glacier system, or both. Recent observational studies have suggested the 2008–2015 velocity change was due to the ungrounding of the Fleming Glacier front. To explore the mechanisms underlying the recent changes, we use a full-Stokes ice sheet model to simulate the basal shear stress distribution of the Fleming system in 2008 and 2015. This study is part of the first high resolution modelling c aign of this system. Comparison of inversions for basal shear stresses for 2008 and 2015 suggests the migration of the grounding line ∼9 km upstream by 2015 from the 2008 ice front/grounding line positions, which virtually coincided with the 1996 grounding line position. This migration is consistent with the change in floating area deduced from the calculated height above buoyancy in 2015. The retrograde submarine bed underneath the lowest part of the Fleming Glacier may have promoted retreat of the grounding line. Grounding line retreat may also be enhanced by a feedback mechanism upstream of the grounding line by which increased basal lubrication due to increasing frictional heating enhances sliding and thinning. Improved knowledge of bed topography near the grounding line and further transient simulations with oceanic forcing are required to accurately predict the future movement of the Fleming Glacier system grounding line and better understand its ice dynamics and future contribution to sea level.
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: Elsevier BV
Date: 09-2017
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-10275
Abstract: & & & strong& Coupled ice sheet - ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, and the wider implications of such processes. In particular, ice sheet - ocean interactions have a strong control on ice sheet stability and sea level contribution. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics, which, combined with the high cost of ocean models, can limit the timeframe that can be modelled. Here we present an & quot accelerated oceanic forcing'' approach to the ocean side of the coupling, in which the rates of change passed from ice model to ocean model components are increased by a constant factor and the period for which the & ocean model is run is correspondingly decreased. The ice sheet change over a coupling interval is thus compressed into & a shorter period over which the ocean model is run, based on the assumption that the ocean response time frame is shorter than & /strong& & strong& & the compressed run period. We demonstrate the viability of this approach in an idealised setup based on the Marine Ice Sheet-Ocean Model Intercomparison Project, using the open-source Framework for Ice Sheet-Ocean Coupling (FISOC) combining two different ocean models (FVCOM and ROMS) and the ice-sheet model Elmer/Ice. We also demonstrate that the mean cavity residence time computed from the stand-alone ocean simulations can guide the selection of a suitable enhanced forcing factor for the coupled simulations.& & /strong& & &
Publisher: Copernicus GmbH
Date: 11-02-2021
Abstract: Abstract. A number of important questions concern processes at the margins of ice sheets where multiple components of the Earth system, most crucially ice sheets and oceans, interact. Such processes include thermodynamic interaction at the ice–ocean interface, the impact of meltwater on ice shelf cavity circulation, the impact of basal melting of ice shelves on grounded ice dynamics and ocean controls on iceberg calving. These include fundamentally coupled processes in which feedback mechanisms between ice and ocean play an important role. Some of these mechanisms have major implications for humanity, most notably the impact of retreating marine ice sheets on the global sea level. In order to better quantify these mechanisms using computer models, feedbacks need to be incorporated into the modelling system. To achieve this, ocean and ice dynamic models must be coupled, allowing runtime information sharing between components. We have developed a flexible coupling framework based on existing Earth system coupling technologies. The open-source Framework for Ice Sheet–Ocean Coupling (FISOC) provides a modular approach to coupling, facilitating switching between different ice dynamic and ocean components. FISOC allows fully synchronous coupling, in which both ice and ocean run on the same time step, or semi-synchronous coupling in which the ice dynamic model uses a longer time step. Multiple regridding options are available, and there are multiple methods for coupling the sub-ice-shelf cavity geometry. Thermodynamic coupling may also be activated. We present idealized simulations using FISOC with a Stokes flow ice dynamic model coupled to a regional ocean model. We demonstrate the modularity of FISOC by switching between two different regional ocean models and presenting outputs for both. We demonstrate conservation of mass and other verification steps during evolution of an idealized coupled ice–ocean system, both with and without grounding line movement.
Publisher: Springer Science and Business Media LLC
Date: 05-05-2021
Publisher: Copernicus GmbH
Date: 03-2022
DOI: 10.5194/GMD-2022-21
Abstract: Abstract. Changes in ocean-driven basal melting have a key influence on the stability of ice shelves, the mass loss from the ice sheet, ocean circulation and global sea level rise. Coupled ice sheet – ocean models have a critical role in understanding future ice sheet evolution and examining the processes governing ice sheet response to basal melting. However, as a new approach, coupled ice-sheet/ocean systems come with new challenges, and the impacts of solutions implemented to date have not been investigated. An emergent feature in several contributing coupled models to the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) was a time-varying oscillation in basal melt rates. Here we use a recently developed coupling framework, FISOC (v1.1), to connect the modified ocean model ROMSIceShelf (v1.0) and ice-sheet model Elmer/Ice (v9.0), to investigate the origin and implications of the feature and more generally the impact of coupled modelling strategies on the simulated basal melt in an idealised ice shelf cavity, based on the MISOMIP setup. We found the spatial-averaged basal melt rates (3.56 m yr-1) oscillated with an litude ~ 0.7 m yr-1 and approximate period of ~ 6 years between year 30 and 100, depending on the experimental design. The melt oscillations emerged in the coupled system and the stand-alone ocean model using a prescribed change of cavity geometry. We found that the oscillation feature is closely related to the discretised ungrounding of the ice sheet, exposing new ocean, and is likely strengthened by a combination of positive buoyancy-melt feedback and/or melt-geometry feedback near the grounding line, and the frequent coupling of ice geometry and ocean evolution. Sensitivity tests demonstrate that the response is insensitive to the choice of coupling interval, vertical resolution in the ocean model, tracer properties of immediately ungrounded cells by the retreating ice sheet, or the dependency of friction velocities to the vertical resolution. However, we were unable to ultimately determine if the feature is as a result of either numerical issues due to discritisation, or a compounding of multiple physical processes. We suggest a pathway and choices of physical parameters to help other efforts understand the coupled ice-sheet/ocean system using numerical models.
Publisher: Copernicus GmbH
Date: 26-02-2023
DOI: 10.5194/EGUSPHERE-EGU23-15572
Abstract: & & Small-scale basal features, such as channels and crevasses, are abundant on many ice shelves and play a role in determining spatial basal melt patterns, impacting on freshwater released to the Southern Ocean. & These features may also, either directly or via basal melt patterns, impact on ice shelf stability and therefore also global sea level. However, simulating the effect of these features on basal melting at a hundred-meter scale or smaller is still challenging even for dedicated regional simulations, which typically ignore the small-scale features and instead smooth the ice draft. & In this study, we simulate the effect of small-scale basal features on the Fimbulisen Ice Shelf (FIS) with the unstructured grid Finite-Volume Community Ocean Model (FVCOM), which allows refinement of model resolution in selected regions to resolve the small-scale features. Fine-resolution (8 m) basal topography of the FIS, retrieved from the Reference Elevation Model of Antarctica (REMA) data, reveals that the ice thickness of the Jutulstraum ice stream changes rapidly northwards from ~1500 m to ~ 600 m within 60 km of the grounding line. It also reveals that channelized basal features of several tens of kilometers traverse the ice base both along and across the ice stream, providing an intricate ice base topography. We set up a fine-scale FVCOM model of the FIS ice cavity to resolve the complicated basal topography, with grid resolution varying from 50 m in the focused region along the Jutulstraum ice stream to 1500 m in the open ocean. Sensitivity studies are performed, using the high-resolution ice draft from REMA as well as smoothed versions of it, to assess the effect of small-scale basal features on the cavity circulation and melt rates of the FIS. Ice shelf simulations, using Elmer/Ice, are carried out on the same refined mesh, to investigate the ice dynamic response to finely resolved ocean-induced melting. & Finally, coupled Elmer/Ice - FVCOM simulations are carried out to investigate the coupled evolution of the channelised system. & We aim to quantify the net basal mass balance contributions from small-scale basal features and finally to parameterize their effects in coarser ocean models.& &
Publisher: SAGE Publications
Date: 2021
DOI: 10.1177/11786329211029354
Abstract: Surgical antibiotic prophylaxis (SAP) is considered an important interventional tool for antimicrobial resistance. Guideline compliance was poor across different countries and this results in an inappropriate and overuse of antibiotics. The study was cross-sectional, combining qualitative and quantitative. The Research used the MOH’s Antibiotic Preventive Medicine Guidelines as the standard to verify surgical preventive treatment compliance from patient medical records. Research performed on 373 medical records with surgical indications. The study was conducted from January to June 2019. Data were entered using Epidata software and processed by SPSS software version 19.0. Analysis: calculating OR for related factors. The compliance rate of using prophylactic antibiotics was 83.1%. There is a relationship between the type of incision, the length of time surgery, and compliance with surgical prophylactic use of antibiotics ( P .05). Barriers to adherence to prophylactic antimicrobial therapy include: overcrowding patients, health-care workers “broad-spectrum antibiotic use habits, and health-care workers” views on surgical and muscle environment, the material was not completely sterilized.
Publisher: Copernicus GmbH
Date: 04-08-2020
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: 28-10-2021
DOI: 10.5194/TC-2021-316
Abstract: Abstract. Antarctic sea ice kinematic plays a crucial role in shaping the polar climate and ecosystems. Satellite passive microwave-derived sea ice motion data have been used widely for studying sea ice motion and deformation processes, and provide daily, global coverage at a relatively low spatial-resolution (in the order of 60 × 60 km). In the Arctic, several validated data sets of satellite observations are available and used to study sea ice kinematics, but far fewer validation studies exist for the Antarctic. Here, we compare the widely-used passive microwave-derived Antarctic sea ice motion product by Kimura et al. (2013) with buoy-derived velocities, and interpret the effects of satellite observational configuration on the representation of Antarctic sea ice kinematics. We identify two issues in the Kimura et al. (2013) product: (i) errors in two large triangular areas within the eastern Weddell Sea and western Amundsen Sea relating to an error in the input satellite data composite, and (ii) a more subtle error relating to invalid assumptions for the average sensing time of each pixel. Upon rectification of these, performance of the daily composite sea ice motion product is found to be a function of latitude, relating to the number of satellite swaths incorporated (more swaths further south as tracks converge), and the heterogeneity of the underlying satellite signal (brightness temperature here). Daily sea ice motion vectors calculated using ascending- and descending-only satellite tracks (with a true ~24 h time-scale) are compared with the widely-used combined product (ascending and descending tracks combined together, with an inherent ~39 h time-scale). This comparison reveals that kinematic parameters derived from the shorter time-scale velocity datasets are higher in magnitude than the combined dataset, indicating a high degree of sensitivity to observation time-scale. We conclude that the new generation of “swath-to-swath” (S2S) sea ice velocity datasets, encompassing a range of observational time scales, is necessary to advance future research into sea ice kinematics.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-13125
Abstract: & & Computer models for ice sheet dynamics are the primary tools for making future predictions of ice sheet behaviour, marine ice sheet instability, and ice sheet contributions to sea level change. & Such modelling studies face a number of challenges, and we consider here two ex les. & The dominant mode of flow for ice streams is sliding at the bed, and the physical processes that control sliding are hard to observe. Ice sheet models often prescribe basal resistance as a function of sliding velocity. & But laboratory experiments and real-world observations indicate that basal resistance is also dependent on the water pressure in the sub-glacial hydrologic system, a property that is hard to constrain. & Initialising an ice sheet model for future projections is usually implemented either by a multi-millennial spin up or else by optimisation simulations, both of which have significant drawbacks. & In particular, long spin-up simulations cannot easily ensure a close match to present-day ice geometry, and optimisations cannot easily ensure an overall ice sheet mass balance that matches the present-day mass balance.& & & & Using a 3D Stokes-flow ice dynamic model, we carry out optimisations for two Antarctic catchments: The Pine Island Glacier (PIG) in West Antarctica and the Lambert-Amery Glacier System (LAGS) in East Antarctica. & We optimise both the basal resistance and flow enhancement in order to minimise discrepancy between modelled and observed (from satellite) horizontal velocities at the ice upper surface. & We use these optimised model configurations to estimate the transient mass trend and also look at the 3D velocity field, its sensitivity to choice of boundary conditions in the normal direction at upper and lower surfaces, and its implications for the 3D temperature structure. & These simulations provide an estimate of the present-day thermo-mechanical state of the PIG and LAGS.& & & & We demonstrate that constraining only horizontal velocity in the optimisations can lead to unrealistic normal velocities at the upper surface. & We show that this can, in turn, strongly impact on the catchment& #8217 s total mass budget (through locally unconstrained thinning/thickening rates) and lead to a large-scale bias in temperatures simulated using the optimised model with the steady state assumption, due to unphysical advection of heat through the ice upper surface.& & & & We employ the optimised model to estimate basal melt, due mainly to friction heat, and drive a subglacial hydrology model beneath the PIG, providing a model-based estimate of the distribution of basal water pressure. & We use this, along with simulated sliding velocity and basal resistance, to evaluate some commonly used sliding relations.& &
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-11738
Abstract: & & With recent developments in the modelling of Antarctica and its interactions with the ocean several coupled model frameworks now exist. & This talk will focus on presenting the Framework for Ice Sheet - Ocean Coupling (FISOC), developed to provide a flexible platform for performing coupled ice sheet - ocean modelling experiments. We present progress and preliminary results using FISOC to couple the Regional Ocean Modelling System (ROMS) with Elmer/Ice, a full-Stokes ice sheet model. Idealised experiments have been used that also contribute to the WCRP Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP). & A recent focus is on testing emergent behaviour of the coupled system and the model numerics. The talk will outline future technological applications and developments conducted as part of a broader international consortium effort. These efforts include coupling to sub-glacial hydrology, sea ice and atmospheres to form a complete system-downscaling technology from which to examine the influence of future climate on ice sheet evolution and hence sea level and global climate impacts. Developments to apply the technology to the Greenland Ice Sheet are presently underway.& &
Publisher: International Glaciological Society
Date: 2013
Publisher: Elsevier BV
Date: 12-2023
Publisher: China Science Publishing & Media Ltd.
Date: 08-01-2014
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: Copernicus GmbH
Date: 08-04-2022
Abstract: Abstract. The Amery Ice Shelf (AIS), East Antarctica, has a layered structure, due to the presence of both meteoric and marine ice. In this study, the thermal structure of the AIS and its spatial pattern are evaluated and analysed through borehole observations and numerical simulations with Elmer/Ice, a full-Stokes ice sheet/shelf model. In the area with marine ice, a near-isothermal basal layer up to 120 m thick is observed, which closely conforms to the pressure-dependent freezing temperature of seawater. In the area experiencing basal melting, large temperature gradients, up to −0.36 ∘C m−1, are observed at the base. Three-dimensional (3-D) steady-state temperature simulations with four different basal mass balance (BMB) datasets for the AIS reveal a high sensitivity of ice shelf thermal structure to the distribution of BMB. We also construct a one-dimensional (1-D) transient temperature column model to simulate the process of an ice column moving along a flowline with corresponding boundary conditions, which achieves slightly better agreement with borehole observations than the 3-D simulations. Our simulations reveal internal cold ice advected from higher elevations by the AIS's main inlet glaciers, warming downstream along the ice flow, and we suggest the thermal structures dominated by these cold cores may commonly exist among Antarctic ice shelves. For the marine ice, the porous structure of its lower layer and interactions with ocean below determine the local thermal regime and give rise to the near-isothermal phenomenon. The limitations in our simulations identify the need for ice shelf–ocean coupled models with improved thermodynamics and more comprehensive boundary conditions. Given the temperature dependence of ice rheology, the depth-averaged ice stiffness factor B(T′)‾ derived from the most realistic simulated temperature field is presented to quantify the influence of the temperature distribution on ice shelf dynamics. The full 3-D temperature field provides a useful input to future modelling studies.
Publisher: International Glaciological Society
Date: 2014
Abstract: Blue-ice areas (BIAs) and their geographical distribution in Antarctica were mapped using Landsat-7 ETM+ images with 15 m spatial resolution obtained during the 1999–2003 austral summers and covering the area north of 82.5° S, and a snow grain-size image of the MODIS-based Mosaic of Antarctica (MOA) dataset with 125 m grid spacing acquired during the 2003/04 austral summer from 82.5°S to the South Pole. A map of BIAs was created with algorithms of thresholds based on band ratio and reflectance for ETM+ data and thresholds based on snow grain size for the MOA dataset. The underlying principle is that blue ice can be separated from snow or rock by their spectral discrepancies and by different grain sizes of snow and ice. We estimate the total area of BIAs in Antarctica during the data acquisition period is 234 549 km 2 , or 1.67% of the area of the continent. Blue ice is scattered widely over the continent but is generally located in coastal or mountainous regions. The BIA dataset presented in this study is the first map covering the entire Antarctic continent sourced solely from ETM+ and MODIS data. This dataset can potentially benefit other studies in glaciology, meteorology, climatology and paleoclimate, meteorite collection and airstrip site selection.
Location: Australia
Location: Australia
Location: Australia
Start Date: 2024
End Date: 12-2026
Amount: $444,000.00
Funder: Australian Research Council
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