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1
Scherrenberg, Meike D. W., Constantijn J. Berends, Lennert B. Stap und Roderik S. W. van de Wal. „Modelling feedbacks between the Northern Hemisphere ice sheets and climate during the last glacial cycle“. Climate of the Past 19, Nr. 2 (08.02.2023): 399–418. http://dx.doi.org/10.5194/cp-19-399-2023.
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Abstract. During the last glacial cycle (LGC), ice sheets covered large parts of Eurasia and North America, which resulted in ∼120 m of sea level change. Ice sheet–climate interactions have considerable influence on temperature and precipitation patterns and therefore need to be included when simulating this time period. Ideally, ice sheet–climate interactions are simulated by a high-resolution Earth system model. While these models are capable of simulating climates at a certain point in time, such as the pre-industrial (PI) or the Last Glacial Maximum (LGM; 21 000 years ago), a full transient glacial cycle is currently computationally unfeasible as it requires a too-large amount of computation time. Nevertheless, ice sheet models require forcing that captures the gradual change in climate over time to calculate the accumulation and melt of ice and its effect on ice sheet extent and volume changes. Here we simulate the LGC using an ice sheet model forced by LGM and PI climates. The gradual change in climate is modelled by transiently interpolating between pre-calculated results from a climate model for the LGM and the PI. To assess the influence of ice sheet–climate interactions, we use two different interpolation methods: the climate matrix method, which includes a temperature–albedo and precipitation–topography feedback, and the glacial index method, which does not. To investigate the sensitivity of the results to the prescribed climate forcing, we use the output of several models that are part of the Paleoclimate Modelling Intercomparison Project Phase III (PMIP3). In these simulations, ice volume is prescribed, and the climate is reconstructed with a general circulation model (GCM). Here we test those models by using their climate to drive an ice sheet model over the LGC. We find that the ice volume differences caused by the climate forcing exceed the differences caused by the interpolation method. Some GCMs produced unrealistic LGM volumes, and only four resulted in reasonable ice sheets, with LGM Northern Hemisphere sea level contribution ranging between 74–113 m with respect to the present day. The glacial index and climate matrix methods result in similar ice volumes at the LGM but yield a different ice evolution with different ice domes during the inception phase of the glacial cycle and different sea level rates during the deglaciation phase. The temperature–albedo feedback is the main cause of differences between the glacial index and climate matrix methods.
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Gregory, J. M., O. J. H. Browne, A. J. Payne, J. K. Ridley und I. C. Rutt. „Modelling large-scale ice-sheet–climate interactions following glacial inception“. Climate of the Past 8, Nr. 5 (11.10.2012): 1565–80. http://dx.doi.org/10.5194/cp-8-1565-2012.
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Abstract. We have coupled the FAMOUS global AOGCM (atmosphere-ocean general circulation model) to the Glimmer thermomechanical ice-sheet model in order to study the development of ice-sheets in north-east America (Laurentia) and north-west Europe (Fennoscandia) following glacial inception. This first use of a coupled AOGCM–ice-sheet model for a study of change on long palæoclimate timescales is made possible by the low computational cost of FAMOUS, despite its inclusion of physical parameterisations similar in complexity to higher-resolution AOGCMs. With the orbital forcing of 115 ka BP, FAMOUS–Glimmer produces ice caps on the Canadian Arctic islands, on the north-west coast of Hudson Bay and in southern Scandinavia, which grow to occupy the Keewatin region of the Canadian mainland and all of Fennoscandia over 50 ka. Their growth is eventually halted by increasing coastal ice discharge. The expansion of the ice-sheets influences the regional climate, which becomes cooler, reducing the ablation, and ice accumulates in places that initially do not have positive surface mass balance. The results suggest the possibility that the glaciation of north-east America could have begun on the Canadian Arctic islands, producing a regional climate change that caused or enhanced the growth of ice on the mainland. The increase in albedo (due to snow and ice cover) is the dominant feedback on the area of the ice-sheets and acts rapidly, whereas the feedback of topography on SMB does not become significant for several centuries, but eventually has a large effect on the thickening of the ice-sheets. These two positive feedbacks are mutually reinforcing. In addition, the change in topography perturbs the tropospheric circulation, producing some reduction of cloud, and mitigating the local cooling along the margin of the Laurentide ice-sheet. Our experiments demonstrate the importance and complexity of the interactions between ice-sheets and local climate.
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Gregory, J. M., O. J. H. Browne, A. J. Payne, J. K. Ridley und I. C. Rutt. „Modelling large-scale ice-sheet–climate interactions following glacial inception“. Climate of the Past Discussions 8, Nr. 1 (09.01.2012): 169–213. http://dx.doi.org/10.5194/cpd-8-169-2012.
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Abstract. We have coupled the FAMOUS global AOGCM (atmosphere–ocean general circulation model) to the Glimmer thermomechanical ice-sheet model in order to study the development of ice-sheets in North-East America (Laurentia) and North-West Europe (Fennoscandia) following glacial inception. This first use of a coupled AOGCM-ice-sheet model for a study of change on long palæoclimate timescales is made possible by the low computational cost of FAMOUS, despite its inclusion of physical parameterisations of a similar complexity to those of higher-resolution AOGCMs. With the orbital forcing of 115 ka BP, FAMOUS-Glimmer produces ice-caps on the Canadian Arctic islands, on the north-west coast of Hudson Bay, and in Southern Scandinavia, which over 50 ka grow to occupy the Keewatin region of the Canadian mainland and all of Fennoscandia. Their growth is eventually halted by increasing coastal ice discharge. The expansion of the ice-sheets influences the regional climate, which becomes cooler, reducing the ablation, while precipitation increases. Ice accumulates in places that initially do not have positive surface mass balance. The results suggest the possibility that the Laurentide glaciation could have begun on the Canadian Arctic islands, producing a regional climate change that caused or enhanced the growth of ice on the mainland. The increase in albedo due to snow and ice cover is the dominant feedback on the area of the ice-sheets, and acts rapidly, whereas the feedback of topography on SMB does not become significant for several centuries, but eventually has a large effect on the thickening of the ice-sheets. These two positive feedbacks are mutually reinforcing. In addition the change in topography perturbs the tropospheric circulation, producing some reduction of cloud and mitigating the local cooling along the margin of the Laurentide ice-sheet. Our experiments demonstrate the importance and complexity of the interactions between ice-sheets and local climate.
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Abe-Ouchi, Ayako, und Bette Otto-Bliesner. „Ice sheet-climate interactions during the ice age cycle“. PAGES news 17, Nr. 2 (Juni 2009): 73–74. http://dx.doi.org/10.22498/pages.17.2.73.
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NIU, LU, GERRIT LOHMANN, SEBASTIAN HINCK, EVAN J. GOWAN und UTA KREBS-KANZOW. „The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models“. Journal of Glaciology 65, Nr. 252 (03.07.2019): 645–61. http://dx.doi.org/10.1017/jog.2019.42.
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ABSTRACTThe evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one General Circulation Model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice-sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice-sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets.
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Xie, Zhiang, Dietmar Dommenget, Felicity S. McCormack und Andrew N. Mackintosh. „GREB-ISM v1.0: A coupled ice sheet model for the Globally Resolved Energy Balance model for global simulations on timescales of 100 kyr“. Geoscientific Model Development 15, Nr. 9 (10.05.2022): 3691–719. http://dx.doi.org/10.5194/gmd-15-3691-2022.
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Abstract. We introduce a newly developed global ice sheet model coupled to the Globally Resolved Energy Balance (GREB) climate model for the simulation of global ice sheet evolution on timescales of 100 kyr or longer (GREB-ISM v1.0). Ice sheets and ice shelves are simulated on a global grid, fully interacting with the climate simulation of surface temperature, precipitation, albedo, land–sea mask, topography and sea level. Thus, it is a fully coupled atmosphere, ocean, land and ice sheet model. We test the model in ice sheet stand-alone and fully coupled simulations. The ice sheet model dynamics behave similarly to other hybrid SIA (shallow ice approximation) and SSA (shallow shelf approximation) models, but the West Antarctic Ice Sheet accumulates too much ice using present-day boundary conditions. The coupled model simulations produce global equilibrium ice sheet volumes and calving rates like those observed for present-day boundary conditions. We designed a series of idealized experiments driven by oscillating solar radiation forcing on periods of 20, 50 and 100 kyr in the Northern Hemisphere. These simulations show clear interactions between the climate system and ice sheets, resulting in slow buildup and fast decay of ice-covered areas and global ice volume. The results also show that Northern Hemisphere ice sheets respond more strongly to timescales longer than 100 kyr. The coupling to the atmosphere and sea level leads to climate interactions between the Northern and Southern Hemispheres. The model can run global simulations of 100 kyr d−1 on a desktop computer, allowing the simulation of the whole Quaternary period (2.6 Myr) within 1 month.
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Dutton, Andrea, EJ Stone und A. Carlson. „Ice sheet climate interactions: Implications for coastal engineering“. PAGES news 21, Nr. 1 (März 2013): 40. http://dx.doi.org/10.22498/pages.21.1.40.
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Stap, L. B., R. S. W. van de Wal, B. de Boer, R. Bintanja und L. J. Lourens. „Interaction of ice sheets and climate during the past 800 000 years“. Climate of the Past Discussions 10, Nr. 3 (23.06.2014): 2547–94. http://dx.doi.org/10.5194/cpd-10-2547-2014.
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Abstract. During the Cenozoic, land ice and climate have interacted on many different time scales. On long time scales, the effect of land ice on global climate and sea level is mainly set by large ice sheets on North America, Eurasia, Greenland and Antarctica. The climatic forcing of these ice sheets is largely determined by the meridional temperature profile resulting from radiation and greenhouse gas (GHG) forcing. As response, the ice sheets cause an increase in albedo and surface elevation, which operates as a feedback in the climate system. To quantify the importance of these climate-land ice processes, a zonally-averaged energy balance climate model is coupled to five one-dimensional ice-sheet models, representing the major ice sheets. In this study, we focus on the transient simulation of the past 800 000 years, where a high-confidence CO2-record from ice cores samples is used as input in combination with Milankovitch radiation changes. We obtain simulations of atmospheric temperature, ice volume and sea level, that are in good agreement with recent proxy-data reconstructions. We examine long-term climate-ice sheet interactions by a comparison of simulations with uncoupled and coupled ice sheets. We show that these interactions amplify global temperature anomalies by up to a factor 2.6, and that they increase polar amplification by 94%. We demonstrate that, on these long time scales, the ice-albedo feedback has a larger and more global influence on the meridional atmospheric temperature profile than the surface-height temperature feedback. Furthermore, we assess the influence of CO2 and insolation, by performing runs with one or both of these variables held constant. We find that atmospheric temperature is controlled by a complex interaction of CO2 and insolation, and both variables serve as thresholds for Northern Hemispheric glaciation.
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Stap, L. B., R. S. W. van de Wal, B. de Boer, R. Bintanja und L. J. Lourens. „Interaction of ice sheets and climate during the past 800 000 years“. Climate of the Past 10, Nr. 6 (04.12.2014): 2135–52. http://dx.doi.org/10.5194/cp-10-2135-2014.
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Abstract. During the Cenozoic, land ice and climate interacted on many different timescales. On long timescales, the effect of land ice on global climate and sea level is mainly set by large ice sheets in North America, Eurasia, Greenland and Antarctica. The climatic forcing of these ice sheets is largely determined by the meridional temperature profile resulting from radiation and greenhouse gas (GHG) forcing. As a response, the ice sheets cause an increase in albedo and surface elevation, which operates as a feedback in the climate system. To quantify the importance of these climate–land ice processes, a zonally averaged energy balance climate model is coupled to five one-dimensional ice sheet models, representing the major ice sheets. In this study, we focus on the transient simulation of the past 800 000 years, where a high-confidence CO2 record from ice core samples is used as input in combination with Milankovitch radiation changes. We obtain simulations of atmospheric temperature, ice volume and sea level that are in good agreement with recent proxy-data reconstructions. We examine long-term climate–ice-sheet interactions by a comparison of simulations with uncoupled and coupled ice sheets. We show that these interactions amplify global temperature anomalies by up to a factor of 2.6, and that they increase polar amplification by 94%. We demonstrate that, on these long timescales, the ice-albedo feedback has a larger and more global influence on the meridional atmospheric temperature profile than the surface-height-temperature feedback. Furthermore, we assess the influence of CO2 and insolation by performing runs with one or both of these variables held constant. We find that atmospheric temperature is controlled by a complex interaction of CO2 and insolation, and both variables serve as thresholds for northern hemispheric glaciation.
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Van Breedam, Jonas, Philippe Huybrechts und Michel Crucifix. „A Gaussian process emulator for simulating ice sheet–climate interactions on a multi-million-year timescale: CLISEMv1.0“. Geoscientific Model Development 14, Nr. 10 (25.10.2021): 6373–401. http://dx.doi.org/10.5194/gmd-14-6373-2021.
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Abstract. On multi-million-year timescales, fully coupled ice sheet–climate simulations are hampered by computational limitations, even at coarser resolutions and when using asynchronous coupling schemes. In this study, a novel coupling method CLISEMv1.0 (CLimate–Ice Sheet EMulator version 1.0) is presented, where a Gaussian process emulator is applied to the climate model HadSM3 and coupled to the ice sheet model AISMPALEO. The temperature and precipitation fields from HadSM3 are emulated to feed the mass balance model in AISMPALEO. The sensitivity of the evolution of the ice sheet over time is tested with respect to the number of predefined ice sheet geometries that the emulator is calibrated on. Additionally, the model performance is evaluated in terms of the formulation of the ice sheet parameter (being ice sheet volume, ice sheet area or both) and the coupling time. Sensitivity experiments are conducted to explore the uncertainty introduced by the emulator. In addition, different lapse rate adjustments are used between the relatively coarse climate model and the much finer ice sheet model topography. It is shown that the ice sheet evolution over a million-year timescale is strongly sensitive to the definition of the ice sheet parameter and to the number of predefined ice sheet geometries. With the new coupling procedure, we provide a computationally efficient framework for simulating ice sheet–climate interactions on a multi-million-year timescale that allows for a large number of sensitivity tests.
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Smith, Robin S., Steve George und Jonathan M. Gregory. „FAMOUS version xotzt (FAMOUS-ice): a general circulation model (GCM) capable of energy- and water-conserving coupling to an ice sheet model“. Geoscientific Model Development 14, Nr. 9 (17.09.2021): 5769–87. http://dx.doi.org/10.5194/gmd-14-5769-2021.
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Abstract. The physical interactions between ice sheets and their surroundings are major factors in determining the state of the climate system, yet many current Earth system models omit them entirely or approximate them in a heavily parameterised manner. In this work we have improved the snow and ice sheet surface physics in the FAMOUS climate model, with the aim of improving the representation of polar climate and implementing a bidirectional coupling to the Glimmer dynamic ice sheet model using the water and energy fluxes calculated by FAMOUS. FAMOUS and Glimmer are both low-resolution, computationally affordable models used for multi-millennial simulations. Glaciated surfaces in the new FAMOUS-ice are modelled using a multi-layer snow scheme capable of simulating compaction of firn and the percolation and refreezing of surface melt. The low horizontal resolution of FAMOUS compared to Glimmer is mitigated by implementing this snow model on sub-grid-scale tiles that represent different elevations on the ice sheet within each FAMOUS grid box. We show that with this approach FAMOUS-ice can simulate relevant physical processes on the surface of the modern Greenland ice sheet well compared to higher-resolution climate models and that the ice sheet state in the coupled FAMOUS-ice–Glimmer system does not drift unacceptably. FAMOUS-ice coupled to Glimmer is thus a useful tool for modelling the physics and co-evolution of climate and grounded ice sheets on centennial and millennial timescales, with applications to scientific questions relevant to both paleoclimate and future sea level rise.
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Goelzer, Heiko, Philippe Huybrechts, Marie-France Loutre und Thierry Fichefet. „Last Interglacial climate and sea-level evolution from a coupled ice sheet–climate model“. Climate of the Past 12, Nr. 12 (15.12.2016): 2195–213. http://dx.doi.org/10.5194/cp-12-2195-2016.
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Abstract. As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ∼ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate–ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet–climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.
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Stap, Lennert B., Constantijn J. Berends, Meike D. W. Scherrenberg, Roderik S. W. van de Wal und Edward G. W. Gasson. „Net effect of ice-sheet–atmosphere interactions reduces simulated transient Miocene Antarctic ice-sheet variability“. Cryosphere 16, Nr. 4 (11.04.2022): 1315–32. http://dx.doi.org/10.5194/tc-16-1315-2022.
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Abstract. Benthic δ18O levels vary strongly during the warmer-than-modern early and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO2 levels and orbital settings. Earlier transient simulations lacked ice-sheet–atmosphere interactions and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet–atmosphere interactions, running the ice-sheet model IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO2 levels (between 280 and 840 ppm), as well as varying ice-sheet configurations (between no ice and a large East Antarctic Ice Sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo–temperature feedback, partly compensated for by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO2 and ice volume. Together, these ice-sheet–atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations. Forced by quasi-orbital 40 kyr forcing CO2 cycles, the ice volume variability reduces by 21 % when ice-sheet–atmosphere interactions are included compared to when forcing variability is only based on CO2 changes. Thereby, these interactions also diminish the contribution of AIS variability to benthic δ18O fluctuations. Evolving bedrock topography during the early and mid-Miocene also reduces ice volume variability by 10 % under equal 40 kyr cycles of atmosphere and ocean forcing.
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Bradley, Sarah L., Raymond Sellevold, Michele Petrini, Miren Vizcaino, Sotiria Georgiou, Jiang Zhu, Bette L. Otto-Bliesner und Marcus Lofverstrom. „Surface mass balance and climate of the Last Glacial Maximum Northern Hemisphere ice sheets: simulations with CESM2.1“. Climate of the Past 20, Nr. 1 (24.01.2024): 211–35. http://dx.doi.org/10.5194/cp-20-211-2024.
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Abstract. The Last Glacial Maximum (LGM, from ∼26 to 20 ka BP) was the most recent period with large ice sheets in Eurasia and North America. At that time, global temperatures were 5–7 ∘C lower than today, and sea level ∼125 m lower. LGM simulations are useful to understand earth system dynamics, including climate–ice sheet interactions, and to evaluate and improve the models representing those dynamics. Here, we present two simulations of the Northern Hemisphere ice sheet climate and surface mass balance (SMB) with the Community Earth System Model v2.1 (CESM2.1) using the Community Atmosphere Model v5 (CAM5) with prescribed ice sheets for two time periods that bracket the LGM period: 26 and 21 ka BP. CESM2.1 includes an explicit simulation of snow/firn compaction, albedo, refreezing, and direct coupling of the ice sheet surface energy fluxes with the atmosphere. The simulated mean snow accumulation is lowest for the Greenland and Barents–Kara Sea ice sheets (GrIS, BKIS) and highest for British and Irish (BIIS) and Icelandic (IcIS) ice sheets. Melt rates are negligible for the dry BKIS and GrIS, and relatively large for the BIIS, North American ice sheet complex (NAISC; i.e. Laurentide, Cordilleran, and Innuitian), Scandinavian ice sheet (SIS), and IcIS, and are reduced by almost a third in the colder (lower temperature) 26 ka BP climate compared with 21 ka BP. The SMB is positive for the GrIS, BKIS, SIS, and IcIS during the LGM (26 and 21 ka BP) and negative for the NAISC and BIIS. Relatively wide ablation areas are simulated along the southern (terrestrial), Pacific and Atlantic margins of the NAISC, across the majority of the BIIS, and along the terrestrial southern margin of the SIS. The integrated SMB substantially increases for the NAISC and BIIS in the 26 ka BP climate, but it does not reverse the negative sign. Summer incoming surface solar radiation is largest over the high interior of the NAISC and GrIS, and minimum over the BIIS and southern margin of NAISC. Summer net radiation is maximum over the ablation areas and minimum where the albedo is highest, namely in the interior of the GrIS, northern NAISC, and all of the BKIS. Summer sensible and latent heat fluxes are highest over the ablation areas, positively contributing to melt energy. Refreezing is largest along the equilibrium line altitude for all ice sheets and prevents 40 %–50 % of meltwater entering the ocean. The large simulated melt for the NAISC suggests potential biases in the climate simulation, ice sheet reconstruction, and/or highly non-equilibrated climate and ice sheet at the LGM time.
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Ely, Jeremy C., Chris D. Clark, David Small und Richard C. A. Hindmarsh. „ATAT 1.1, the Automated Timing Accordance Tool for comparing ice-sheet model output with geochronological data“. Geoscientific Model Development 12, Nr. 3 (12.03.2019): 933–53. http://dx.doi.org/10.5194/gmd-12-933-2019.
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Abstract. Earth's extant ice sheets are of great societal importance given their ongoing and potential future contributions to sea-level rise. Numerical models of ice sheets are designed to simulate ice-sheet behaviour in response to climate changes but to be improved require validation against observations. The direct observational record of extant ice sheets is limited to a few recent decades, but there is a large and growing body of geochronological evidence spanning millennia constraining the behaviour of palaeo-ice sheets. Hindcasts can be used to improve model formulations and study interactions between ice sheets, the climate system and landscape. However, ice-sheet modelling results have inherent quantitative errors stemming from parameter uncertainty and their internal dynamics, leading many modellers to perform ensemble simulations, while uncertainty in geochronological evidence necessitates expert interpretation. Quantitative tools are essential to examine which members of an ice-sheet model ensemble best fit the constraints provided by geochronological data. We present the Automated Timing Accordance Tool (ATAT version 1.1) used to quantify differences between model results and geochronological data on the timing of ice-sheet advance and/or retreat. To demonstrate its utility, we perform three simplified ice-sheet modelling experiments of the former British–Irish ice sheet. These illustrate how ATAT can be used to quantify model performance, either by using the discrete locations where the data originated together with dating constraints or by comparing model outputs with empirically derived reconstructions that have used these data along with wider expert knowledge. The ATAT code is made available and can be used by ice-sheet modellers to quantify the goodness of fit of hindcasts. ATAT may also be useful for highlighting data inconsistent with glaciological principles or reconstructions that cannot be replicated by an ice-sheet model.
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Nowicki, Sophie, Heiko Goelzer, Hélène Seroussi, Anthony J. Payne, William H. Lipscomb, Ayako Abe-Ouchi, Cécile Agosta et al. „Experimental protocol for sea level projections from ISMIP6 stand-alone ice sheet models“. Cryosphere 14, Nr. 7 (23.07.2020): 2331–68. http://dx.doi.org/10.5194/tc-14-2331-2020.
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Abstract. Projection of the contribution of ice sheets to sea level change as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the form of simulations from coupled ice sheet–climate models and stand-alone ice sheet models, overseen by the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). This paper describes the experimental setup for process-based sea level change projections to be performed with stand-alone Greenland and Antarctic ice sheet models in the context of ISMIP6. The ISMIP6 protocol relies on a suite of polar atmospheric and oceanic CMIP-based forcing for ice sheet models, in order to explore the uncertainty in projected sea level change due to future emissions scenarios, CMIP models, ice sheet models, and parameterizations for ice–ocean interactions. We describe here the approach taken for defining the suite of ISMIP6 stand-alone ice sheet simulations, document the experimental framework and implementation, and present an overview of the ISMIP6 forcing to be used by participating ice sheet modeling groups.
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Siahaan, Antony, Robin S. Smith, Paul R. Holland, Adrian Jenkins, Jonathan M. Gregory, Victoria Lee, Pierre Mathiot, Antony J. Payne, Jeff K. Ridley und Colin G. Jones. „The Antarctic contribution to 21st-century sea-level rise predicted by the UK Earth System Model with an interactive ice sheet“. Cryosphere 16, Nr. 10 (07.10.2022): 4053–86. http://dx.doi.org/10.5194/tc-16-4053-2022.
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Abstract. The Antarctic Ice Sheet will play a crucial role in the evolution of global mean sea level as the climate warms. An interactively coupled climate and ice sheet model is needed to understand the impacts of ice–climate feedbacks during this evolution. Here we use a two-way coupling between the UK Earth System Model and the BISICLES (Berkeley Ice Sheet Initiative for Climate at Extreme Scales) dynamic ice sheet model to investigate Antarctic ice–climate interactions under two climate change scenarios. We perform ensembles of SSP1–1.9 and SSP5–8.5 (Shared Socioeconomic Pathway) scenario simulations to 2100, which we believe are the first such simulations with a climate model that include two-way coupling of atmosphere and ocean models to dynamic models of the Greenland and Antarctic ice sheets. We focus our analysis on the latter. In SSP1–1.9 simulations, ice shelf basal melting and grounded ice mass loss from the Antarctic Ice Sheet are generally lower than present rates during the entire simulation period. In contrast, the responses to SSP5–8.5 forcing are strong. By the end of the 21st century, these simulations feature order-of-magnitude increases in basal melting of the Ross and Filchner–Ronne ice shelves, caused by intrusions of masses of warm ocean water. Due to the slow response of ice sheet drawdown, this strong melting does not cause a substantial increase in ice discharge during the simulations. The surface mass balance in SSP5–8.5 simulations shows a pattern of strong decrease on ice shelves, caused by increased melting, and strong increase on grounded ice, caused by increased snowfall. Despite strong surface and basal melting of the ice shelves, increased snowfall dominates the mass budget of the grounded ice, leading to an ensemble mean Antarctic contribution to global mean sea level of a fall of 22 mm by 2100 in the SSP5–8.5 scenario. We hypothesise that this signal would revert to sea-level rise on longer timescales, caused by the ice sheet dynamic response to ice shelf thinning. These results demonstrate the need for fully coupled ice–climate models in reducing the substantial uncertainty in sea-level rise from the Antarctic Ice Sheet.
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Fong, Peter. „Influence Of Ice Sheets On Climate and Ice-Sheet Dynamics“. Annals of Glaciology 14 (1990): 335. http://dx.doi.org/10.3189/s026030550000896x.
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The important role played by ice on climate is recognized in the ice–albedo feedback effect which is incorporated in most climate models. But the ice under consideration is two-dimensional and only its surface area enters into the interaction. Whereas this applies well to the seasonal ice and sea ice, it does not to the permanent ice sheets on earth because they are three-dimensional. A new feature is the ice flow down the ice-sheet slope. This increases the amount of ice on the ice-sheet periphery above that produced by local precipitation that is considered in most climate models. As a result the ice–albedo effect will be greater than that given in most climate models. The latter (a positive feedback) is generally smaller than the major negative feedback due to the infrared effect and therefore stable equilibrium is achieved in most climate models. When the positive feedback is thus increased to an amount equal to the infrared negative feedback, stable equilibrium is destroyed and the system changes to netural equilibrium – a mildly unstable form. This may be just what is necessary to explain the advance and retreat of the ice sheets, which cannot be explained by most climate models because in stable equilibrium an ice sheet cannot advance and retreat.The advance and retreat can be proven to be the manifestation of a neutral equilibrium. At any instant of time in an ice age, including the present time, the climate system is nearly in equilibrium. But as time goes on the equilibrium point shifts continuously, reflecting the advance of the ice sheet and the cooling of the ocean. Thus an ice age is represented by a continuous sequence of equilibrium points, which, by definition, constitutes a netural equilibrium. The argument is reinforced by the observation that the “cause” of ice ages is a very small perturbation – the variation of the eccentricity of the earth orbit. According to most climate models, this effect is one order of magnitude too small to generate the climate changes in an ice age. On the other hand in a neutral equilibrium a very weak perturbation can generate slow progressive changes, like the rolling of a cylinder on a plane. As a matter of fact, the small periodic changes of the eccentricity pace the advance and retreat of the ice sheets almost in phase; this is not possible in stable and unstable equilibrium and can be possible only in neutral equilibrium. The empirical conclusion of neutral equilibrium is solidly established. Any theory and any climate model must accommodate this fact.A deeper understanding requires the pinpointing of the physical origin of the meutral equilibrium. The origin can be shown, though not obviously, to be just the phase equilibrium of water and ice, which is quasi-static and may be considered as neutral equilibrium in a mechanical analogy. The argument is complicated by the fact that the temperature does not remain constant as expected in phase equilibrium but does decrease in an ice age. However, this can be accounted for by the complication of the albedo effect. Hypothetically if ice were brown and without albedo effect, then in an ice age the temperature would not decrease and the situation would be just like ice-water phase equilibrium. The physical origin of neutral equilibrium clarifies the fundamental principle but is not necessary for the mathematical formulation of a dynamic theory of the ice sheets that is given as follows. Instead neutral equilibrium emerges naturally from that theory and the advance and retreat can be explained readily.Most climate models are static models which cannot explain the advance and retreat – a manifestly dynamic process. A simple but adequate dynamic theory can be formulated considering the ice volume V(t) and the ocean surface temperature T(t) as the basic dynamic variables. The equations for their changes can be written down, making use of the latent heat of fusion of ice and the sensible heat capacity of the ocean mixed layer. Albedo positive feedback and infrared negative feedback will be included in the heat balance. The three-dimensional effect of the ice sheet will be introduced in the albedo effect. This involves the geometry of the ice sheet which will be specified in a constraint equation. Then a closed, deterministic set of intergral-differential equations may be formulated to describe the dynamics of the ice sheets. The equations may be solved without adjustable parameters. The solutions agree with the observed advance and retreat of ice sheets and the cooling and warming of the ocean. A close examination of the feedbacks involved reveals that the dynamics is indeed like a mechanical system in neutral equilibrium. However, the detailed mathematical theory shows that the netural equilibrium changes to stable when the ice sheets reach the middle latitudes. They thus stop there in maximum glaciation.There is no limit on the other end. The northern ice sheet did melt completely. So could the Antarctic ice sheet though it has not in the ice ages. But before the Pleistocene in 99% of the geological time the earth was free of ice sheets. Then, why did the “cause” of ice ages, the eccentricity variations, not generate ice ages in 99% of the earth history? Ice and water can co-exist (in equilibrium) only under unusual conditions, which are not fulfilled generally. But in recent geological times Antarctica drifted to the pole position and high mountains arose on the continents so that permanent ice can survive the summer season and accumulate year after year. Most important, the CO2 content in the atmosphere has been decreasing (Budyko, 1974), cooling down the earth. Eventually the earth was cool enough in Pleistocene to satisfy the neutral equilibrium condition. Then the ice ages began.But we are now burning fossil fuels to put CO2 back into the atmosphere, going back to pre-Pleistocene conditions. The Antarctic ice sheet will melt away; this will be the principal result of the greenhouse effect. However, current discussion of the greenhouse effect deals with only the warming of the earth and neglects the more serious effect of the melting of the Antarctic ice sheet because climatologists overlooked the effect of ice sheets on climate. This study will change the outlook.
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Fong, Peter. „Influence Of Ice Sheets On Climate and Ice-Sheet Dynamics“. Annals of Glaciology 14 (1990): 335. http://dx.doi.org/10.1017/s026030550000896x.
Der volle Inhalt der QuelleAnnotation:
The important role played by ice on climate is recognized in the ice–albedo feedback effect which is incorporated in most climate models. But the ice under consideration is two-dimensional and only its surface area enters into the interaction. Whereas this applies well to the seasonal ice and sea ice, it does not to the permanent ice sheets on earth because they are three-dimensional. A new feature is the ice flow down the ice-sheet slope. This increases the amount of ice on the ice-sheet periphery above that produced by local precipitation that is considered in most climate models. As a result the ice–albedo effect will be greater than that given in most climate models. The latter (a positive feedback) is generally smaller than the major negative feedback due to the infrared effect and therefore stable equilibrium is achieved in most climate models. When the positive feedback is thus increased to an amount equal to the infrared negative feedback, stable equilibrium is destroyed and the system changes to netural equilibrium – a mildly unstable form. This may be just what is necessary to explain the advance and retreat of the ice sheets, which cannot be explained by most climate models because in stable equilibrium an ice sheet cannot advance and retreat. The advance and retreat can be proven to be the manifestation of a neutral equilibrium. At any instant of time in an ice age, including the present time, the climate system is nearly in equilibrium. But as time goes on the equilibrium point shifts continuously, reflecting the advance of the ice sheet and the cooling of the ocean. Thus an ice age is represented by a continuous sequence of equilibrium points, which, by definition, constitutes a netural equilibrium. The argument is reinforced by the observation that the “cause” of ice ages is a very small perturbation – the variation of the eccentricity of the earth orbit. According to most climate models, this effect is one order of magnitude too small to generate the climate changes in an ice age. On the other hand in a neutral equilibrium a very weak perturbation can generate slow progressive changes, like the rolling of a cylinder on a plane. As a matter of fact, the small periodic changes of the eccentricity pace the advance and retreat of the ice sheets almost in phase; this is not possible in stable and unstable equilibrium and can be possible only in neutral equilibrium. The empirical conclusion of neutral equilibrium is solidly established. Any theory and any climate model must accommodate this fact. A deeper understanding requires the pinpointing of the physical origin of the meutral equilibrium. The origin can be shown, though not obviously, to be just the phase equilibrium of water and ice, which is quasi-static and may be considered as neutral equilibrium in a mechanical analogy. The argument is complicated by the fact that the temperature does not remain constant as expected in phase equilibrium but does decrease in an ice age. However, this can be accounted for by the complication of the albedo effect. Hypothetically if ice were brown and without albedo effect, then in an ice age the temperature would not decrease and the situation would be just like ice-water phase equilibrium. The physical origin of neutral equilibrium clarifies the fundamental principle but is not necessary for the mathematical formulation of a dynamic theory of the ice sheets that is given as follows. Instead neutral equilibrium emerges naturally from that theory and the advance and retreat can be explained readily. Most climate models are static models which cannot explain the advance and retreat – a manifestly dynamic process. A simple but adequate dynamic theory can be formulated considering the ice volume V(t) and the ocean surface temperature T(t) as the basic dynamic variables. The equations for their changes can be written down, making use of the latent heat of fusion of ice and the sensible heat capacity of the ocean mixed layer. Albedo positive feedback and infrared negative feedback will be included in the heat balance. The three-dimensional effect of the ice sheet will be introduced in the albedo effect. This involves the geometry of the ice sheet which will be specified in a constraint equation. Then a closed, deterministic set of intergral-differential equations may be formulated to describe the dynamics of the ice sheets. The equations may be solved without adjustable parameters. The solutions agree with the observed advance and retreat of ice sheets and the cooling and warming of the ocean. A close examination of the feedbacks involved reveals that the dynamics is indeed like a mechanical system in neutral equilibrium. However, the detailed mathematical theory shows that the netural equilibrium changes to stable when the ice sheets reach the middle latitudes. They thus stop there in maximum glaciation. There is no limit on the other end. The northern ice sheet did melt completely. So could the Antarctic ice sheet though it has not in the ice ages. But before the Pleistocene in 99% of the geological time the earth was free of ice sheets. Then, why did the “cause” of ice ages, the eccentricity variations, not generate ice ages in 99% of the earth history? Ice and water can co-exist (in equilibrium) only under unusual conditions, which are not fulfilled generally. But in recent geological times Antarctica drifted to the pole position and high mountains arose on the continents so that permanent ice can survive the summer season and accumulate year after year. Most important, the CO2 content in the atmosphere has been decreasing (Budyko, 1974), cooling down the earth. Eventually the earth was cool enough in Pleistocene to satisfy the neutral equilibrium condition. Then the ice ages began. But we are now burning fossil fuels to put CO2 back into the atmosphere, going back to pre-Pleistocene conditions. The Antarctic ice sheet will melt away; this will be the principal result of the greenhouse effect. However, current discussion of the greenhouse effect deals with only the warming of the earth and neglects the more serious effect of the melting of the Antarctic ice sheet because climatologists overlooked the effect of ice sheets on climate. This study will change the outlook.
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Quiquet, Aurélien, Didier M. Roche, Christophe Dumas, Nathaëlle Bouttes und Fanny Lhardy. „Climate and ice sheet evolutions from the last glacial maximum to the pre-industrial period with an ice-sheet–climate coupled model“. Climate of the Past 17, Nr. 5 (19.10.2021): 2179–99. http://dx.doi.org/10.5194/cp-17-2179-2021.
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Abstract. The last deglaciation offers an unique opportunity to understand the climate–ice-sheet interactions in a global warming context. In this paper, to tackle this question, we use an Earth system model of intermediate complexity coupled to an ice sheet model covering the Northern Hemisphere to simulate the last deglaciation and the Holocene (26–0 ka). We use a synchronous coupling every year between the ice sheet and the rest of the climate system and we ensure a closed water cycle considering the release of freshwater flux to the ocean due to ice sheet melting. Our reference experiment displays a gradual warming in response to the forcings, with no abrupt changes. In this case, while the amplitude of the freshwater flux to the ocean induced by ice sheet retreat is realistic, it is sufficient to shut down the Atlantic meridional overturning circulation from which the model does not recover within the time period simulated. However, with reduced freshwater flux we are nonetheless able to obtain different oceanic circulation evolutions, including some abrupt transitions between shut-down and active circulation states in the course of the deglaciation. The inclusion of a parameterisation for the sinking of brines around Antarctica also produces an abrupt recovery of the Atlantic meridional overturning circulation, absent in the reference experiment. The fast oceanic circulation recoveries lead to abrupt warming phases in Greenland. Our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions, even though the abrupt sea level rise at 14.6 ka is underestimated, possibly because the climate model underestimates the millennial-scale temperature variability. In the course of the deglaciation, large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets. The first instability occurs in the Barents–Kara seas for the Eurasian ice sheet at 14.5 ka. A second grounding line instability occurs ca. 12 ka in the proglacial lake that formed at the southern margin of the North American ice sheet. With additional asynchronously coupled experiments, we assess the sensitivity of our results to different ice sheet model choices related to surface and sub-shelf mass balance, ice deformation and grounding line representation. While the ice sheet evolutions differ within this ensemble, the global climate trajectory is only weakly affected by these choices. In our experiments, only the abrupt shifts in the oceanic circulation due to freshwater fluxes are able to produce some millennial-scale variability since no self-generating abrupt transitions are simulated without these fluxes.
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Stap, Lennert B., Roderik S. W. van de Wal, Bas de Boer, Richard Bintanja und Lucas J. Lourens. „The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model“. Climate of the Past 13, Nr. 9 (25.09.2017): 1243–57. http://dx.doi.org/10.5194/cp-13-1243-2017.
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Abstract. Since the inception of the Antarctic ice sheet at the Eocene–Oligocene transition (∼ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice–albedo and surface–height–temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO2. Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO2 and temperature is subject to hysteresis. When the climate cools from very high CO2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO2, temperature, ice-volume-equivalent sea level, and benthic δ18O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet–climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice–albedo and surface–height–temperature feedbacks. We find that ice volume variability has a strong enhancing effect on atmospheric temperature changes, particularly in the regions where the ice sheets are located. As a result, polar amplification in the Northern Hemisphere decreases towards warmer climates as there is little land ice left to melt. Conversely, decay of the Antarctic ice sheet increases polar amplification in the Southern Hemisphere in the high-CO2 regime. Our results also show that in cooler climates than the pre-industrial, the ice–albedo feedback predominates the surface–height–temperature feedback, while in warmer climates they are more equal in strength.
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Roe, Gerard H. „Modeling precipitation over ice sheets: an assessment using Greenland“. Journal of Glaciology 48, Nr. 160 (2002): 70–80. http://dx.doi.org/10.3189/172756502781831593.
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AbstractThe interaction between ice sheets and the rest of the climate system at long time-scales is not well understood, and studies of the ice ages typically employ simplified parameterizations of the climate forcing on an ice sheet. It is important therefore to understand how an ice sheet responds to climate forcing, and whether the reduced approaches used in modeling studies are capable of providing robust and realistic answers. This work focuses on the accumulation distribution, and in particular considers what features of the accumulation pattern are necessary to model the steady-state response of an ice sheet. We examine the response of a model of the Greenland ice sheet to a variety of accumulation distributions, both observational datasets and simplified parameterizations. The predicted shape of the ice sheet is found to be quite insensitive to changes in the accumulation. The model only differs significantly from the observed ice sheet for a spatially uniform accumulation rate, and the most important factor for the successful simulation of the ice sheet’s shape is that the accumulation decreases with height according to the ability of the atmosphere to hold moisture. However, the internal ice dynamics strongly reflects the influence of the atmospheric circulation on the accumulation distribution.
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Zwally, H. Jay. „Ice-Sheet Elevation Change“. Annals of Glaciology 14 (1990): 366. http://dx.doi.org/10.3189/s0260305500009460.
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Over century time scales, the primary effect of ice-sheet/climate-change interactions is vertical growth or shrinkage of the ice in response to changes in precipitation and surface heat flux. Because the dynamic response of large ice masses is generally slower than climate variations experienced during the last few centuries, the ice sheets are unlikely to be in equilibrium with today’s climate. Uncertainty in the current mass balance has been large, at least ±30% or ±2 mm yr−1 in sea-level equivalent. Estimates of annual snow accumulation, iceberg discharge, and peripheral melting of the Antarctic ice sheet (personal communication from S. Jacobs) would suggest a negative mass-balance equivalent to +2 mm yr−1 of sea-level rise, in contrast to other estimates of a small positive balance for both Antarctica (−0.6 ±0.6 mm yr−1 sea level) and Greenland (−0.1 ±0.4 mm yr−1 sea level) (Meier and others, 1985). For some years, measurement of changes in ice-sheet surface elevation by satellite altimetry has been noted as a potential means of determining the overall ice-sheet mass balance and investigating regional variations. Difficulties in deriving elevation change from a set of sequential measurements from several satellites have been primarily a result of the limited precision (about 1–2 m) of satellite radar altimetry, residual orbit errors, and relative uncertainties in the gravity fields and geoid reference levels used for different satellites. However, recent radar altimeter measurements by the U.S. Navy Geosat to 72°N and 72°S provide a sufficient density of repeated measurements of ice elevation for analysis of elevation change during the life of the satellite. The average elevation change at 224 267 orbital crossovers over southern Greenland is +28.3 ±0.4 cm yr−1. The largest values are observed near the summit and over the southern dome, with smaller values in the saddle region and toward the margins. Local gridded values of thickening and thinning rates agree with estimates from surface studies in the vicinity of the EGIG traverse (Steckel, 1977), Dye 3 (Reeh, 1985), and the OSU survey (Kostecka and Whillans, 1988) within the error limits of the respective measurements. Comparisons with elevations measured by the Seasat altimeter in 1978 and continuing Geosat measurements provide information on the temporal continuity of the thickening. The spatial distribution of the elevation changes is used to estimate an average thickening rate and the current rate of oceanic depletion.
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Zwally, H. Jay. „Ice-Sheet Elevation Change“. Annals of Glaciology 14 (1990): 366. http://dx.doi.org/10.1017/s0260305500009460.
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Over century time scales, the primary effect of ice-sheet/climate-change interactions is vertical growth or shrinkage of the ice in response to changes in precipitation and surface heat flux. Because the dynamic response of large ice masses is generally slower than climate variations experienced during the last few centuries, the ice sheets are unlikely to be in equilibrium with today’s climate. Uncertainty in the current mass balance has been large, at least ±30% or ±2 mm yr−1 in sea-level equivalent. Estimates of annual snow accumulation, iceberg discharge, and peripheral melting of the Antarctic ice sheet (personal communication from S. Jacobs) would suggest a negative mass-balance equivalent to +2 mm yr−1 of sea-level rise, in contrast to other estimates of a small positive balance for both Antarctica (−0.6 ±0.6 mm yr−1 sea level) and Greenland (−0.1 ±0.4 mm yr−1 sea level) (Meier and others, 1985). For some years, measurement of changes in ice-sheet surface elevation by satellite altimetry has been noted as a potential means of determining the overall ice-sheet mass balance and investigating regional variations. Difficulties in deriving elevation change from a set of sequential measurements from several satellites have been primarily a result of the limited precision (about 1–2 m) of satellite radar altimetry, residual orbit errors, and relative uncertainties in the gravity fields and geoid reference levels used for different satellites. However, recent radar altimeter measurements by the U.S. Navy Geosat to 72°N and 72°S provide a sufficient density of repeated measurements of ice elevation for analysis of elevation change during the life of the satellite. The average elevation change at 224 267 orbital crossovers over southern Greenland is +28.3 ±0.4 cm yr−1. The largest values are observed near the summit and over the southern dome, with smaller values in the saddle region and toward the margins. Local gridded values of thickening and thinning rates agree with estimates from surface studies in the vicinity of the EGIG traverse (Steckel, 1977), Dye 3 (Reeh, 1985), and the OSU survey (Kostecka and Whillans, 1988) within the error limits of the respective measurements. Comparisons with elevations measured by the Seasat altimeter in 1978 and continuing Geosat measurements provide information on the temporal continuity of the thickening. The spatial distribution of the elevation changes is used to estimate an average thickening rate and the current rate of oceanic depletion.
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Hinck, Sebastian, Evan J. Gowan, Xu Zhang und Gerrit Lohmann. „PISM-LakeCC: Implementing an adaptive proglacial lake boundary in an ice sheet model“. Cryosphere 16, Nr. 3 (14.03.2022): 941–65. http://dx.doi.org/10.5194/tc-16-941-2022.
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Abstract. During the Late Pleistocene and Holocene retreat of paleo-ice sheets in North America and Europe, vast proglacial lakes existed along the land terminating margins. These proglacial lakes impacted ice sheet dynamics by imposing boundary conditions analogous to a marine terminating margin. Such lacustrine boundary conditions cause changes in the ice sheet geometry, stress balance and frontal ablation and therefore affect the mass balance of the entire ice sheet. Despite this, dynamically evolving proglacial lakes have rarely been considered in detail in ice sheet modeling endeavors. In this study, we describe the implementation of an adaptive lake boundary in the Parallel Ice Sheet Model (PISM), which we call PISM-LakeCC. We test our model with a simplified glacial retreat setup of the Laurentide Ice Sheet (LIS). By comparing the experiments with lakes to control runs with no lakes, we show that the presence of proglacial lakes locally enhances the ice flow, which leads to a lowering of the ice sheet surface. In some cases, this also results in an advance of the ice margin and the emergence of ice lobes. In the warming climate, increased melting on the lowered ice surface drives the glacial retreat. For the LIS, the presence of lakes triggers a process similar to marine ice sheet instability, which caused the collapse of the ice saddle over Hudson Bay. In the control experiments without lakes, Hudson Bay is still glaciated when the climate reaches present-day (PD) conditions. The results of our study demonstrate that glacio-lacustrine interactions play a significant role in the retreat of land terminating ice sheet margins.
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O'Neill, James F., Tamsin L. Edwards, Daniel F. Martin, Courtney Shafer, Stephen L. Cornford, Hélène L. Seroussi, Sophie Nowicki, Mira Adhikari und Lauren J. Gregoire. „ISMIP6-based Antarctic projections to 2100: simulations with the BISICLES ice sheet model“. Cryosphere 19, Nr. 2 (04.02.2025): 541–63. https://doi.org/10.5194/tc-19-541-2025.
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Abstract. The contribution of the Antarctic Ice Sheet is one of the most uncertain components of sea level rise to 2100. Ice sheet models are the primary tool for projecting future sea level contribution from continental ice sheets. The Ice Sheet Model Intercomparison for the Coupled Model Intercomparison Phase 6 (ISMIP6) provided projections of the ice sheet contribution to sea level over the 21st century, quantifying uncertainty due to ice sheet model, climate model, emission scenario, and uncertain parameters. We present simulations following the ISMIP6 framework with the BISICLES ice sheet model and new experiments extending the ISMIP6 protocol to more comprehensively sample uncertainties in future climate, ice shelf sensitivity to ocean melting, and their interactions. These results contributed to the land ice projections of Edwards et al. (2021), which formed the basis of sea level projections for the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (AR6). Our experiments show the important interplay between surface mass balance processes and ocean-driven melt in determining Antarctic sea level contribution. Under higher-warming scenarios, high accumulation offsets more ocean-driven mass loss when sensitivity to ocean-driven melt is low. Conversely, we show that when sensitivity to ocean warming is high, ocean melting drives increased mass loss despite high accumulation. Overall, we simulate a sea level contribution range across our experiments from 2 to 178 mm. Finally, we show that collapse of ice shelves due to surface warming increases sea level contribution by 25 mm relative to the no-collapse experiments, for both moderate and high sensitivity of ice shelf melting to ocean forcing.
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Hoang, Thi-Khanh-Dieu, Aurélien Quiquet, Christophe Dumas, Andreas Born und Didier M. Roche. „Using a multi-layer snow model for transient paleo-studies: surface mass balance evolution during the Last Interglacial“. Climate of the Past 21, Nr. 1 (07.01.2025): 27–51. https://doi.org/10.5194/cp-21-27-2025.
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Abstract. During the Quaternary, ice sheets experienced several retreat–advance cycles, strongly influencing climate patterns. In order to properly simulate these phenomena, it is preferable to use physics-based models instead of parameterizations to estimate the surface mass balance (SMB), which strongly influences the evolution of the ice sheet. To further investigate the potential of these SMB models, this work evaluates the BErgen Snow SImulator (BESSI), a multi-layer snow model with high computational efficiency, as an alternative to providing the SMB for the Earth system model iLOVECLIM for multi-millennial simulations as in paleo-studies. We compare the behaviors of BESSI and insolation temperature melt (ITM), an existing SMB scheme of iLOVECLIM during the Last Interglacial (LIG). Firstly, we validate the two SMB models using the regional climate model Modèle Atmosphérique Régional (MAR) as forcing and reference for the present-day climate over the Greenland and Antarctic ice sheets. The evolution of the SMB over the LIG (130–116 ka) is computed by forcing BESSI and ITM with transient climate forcing obtained from iLOVECLIM for both ice sheets. For present-day climate conditions, both BESSI and ITM exhibit good performance compared to MAR despite a much simpler model setup. While BESSI performs well for both Antarctica and Greenland for the same set of parameters, the ITM parameters need to be adapted specifically for each ice sheet. This suggests that the physics embedded in BESSI allows better capture of SMB changes across varying climate conditions, while ITM displays a much stronger sensitivity to its tunable parameters. The findings suggest that BESSI can provide more reliable SMB estimations for the iLOVECLIM framework to improve the model simulations of the ice sheet evolution and interactions with climate for multi-millennial simulations.
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Kennedy, Joseph H., und Erin C. Pettit. „The response of fabric variations to simple shear and migration recrystallization“. Journal of Glaciology 61, Nr. 227 (2015): 537–50. http://dx.doi.org/10.3189/2015jog14j156.
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AbstractThe observable microstructures in ice are the result of many dynamic and competing processes. These processes are influenced by climate variables in the firn. Layers deposited in different climate regimes may show variations in fabric which can persist deep into the ice sheet; fabric may ‘remember’ these past climate regimes. We model the evolution of fabric variations below the firn–ice transition and show that the addition of shear to compressive-stress regimes preserves the modeled fabric variations longer than compression-only regimes, because shear drives a positive feedback between crystal rotation and deformation. Even without shear, the modeled ice retains memory of the fabric variation for 200 ka in typical polar ice-sheet conditions. Our model shows that temperature affects how long the fabric variation is preserved, but only affects the strain-integrated fabric evolution profile when comparing results straddling the thermal-activation-energy threshold (∼−10°C). Even at high temperatures, migration recrystallization does not eliminate the modeled fabric’s memory under most conditions. High levels of nearest-neighbor interactions will, however, eliminate the modeled fabric’s memory more quickly than low levels of nearest-neighbor interactions. Ultimately, our model predicts that fabrics will retain memory of past climatic variations when subject to a wide variety of conditions found in polar ice sheets.
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Berger, A., Th Fichefet, H. Gallée, I. Marsiat, C. Tricot und J. P. van Ypersele. „Physical interactions within a coupled climate model over the last glacial–interglacial cycle“. Transactions of the Royal Society of Edinburgh: Earth Sciences 81, Nr. 4 (1990): 357–69. http://dx.doi.org/10.1017/s026359330002085x.
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ABSTRACTA two-dimensional (2-D) seasonal model has been developed for simulating the transient response of the climate system to the astronomical forcing. The atmosphere is represented by a zonally averaged quasi-geostrophic model which includes accurate treatment of radiative transfer. The atmospheric model interacts with the other components of the climate system (ocean, sea-ice and land surface covered or not by snow and ice) through vertical fluxes of momentum, heat and humidity. The model explicitly incorporates surface energy balances and has snow and sea-ice mass budgets. The vertical profile of the upper-ocean temperature is computed by an interactive mixed-layer model which takes into account the meridional turbulent diffusion of heat. This model is asynchronously coupled to a model which simulates the dynamics of the Greenland, the northern American and the Eurasian ice sheets. Over the last glacial–interglacial cycle, the coupled model simulates climatic changes which are in general agreement with the low frequency part of deep-sea, ice and sea-level records. However, after 6000 yBP, the remaining ice volume of the Greenland and northern American ice sheets is overestimated in the simulation. The simulated climate is sensitive to the initial size of the Greenland ice sheet, to the ice-albedo positive feedback, to the precipitation-altitude negative feedback over the ice sheets, to the albedo of the aging snow and to the insolation increase, particularly at the southern edge of the ice sheets, which is important for their collapse or surge.
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Alvarez-Solas, Jorge, Rubén Banderas, Alexander Robinson und Marisa Montoya. „Ocean-driven millennial-scale variability of the Eurasian ice sheet during the last glacial period simulated with a hybrid ice-sheet–shelf model“. Climate of the Past 15, Nr. 3 (04.06.2019): 957–79. http://dx.doi.org/10.5194/cp-15-957-2019.
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Abstract. The last glacial period (LGP; ca. 110–10 kyr BP) was marked by the existence of two types of abrupt climatic changes, Dansgaard–Oeschger (DO) and Heinrich (H) events. Although the mechanisms behind these are not fully understood, it is generally accepted that the presence of ice sheets played an important role in their occurrence. While an important effort has been made to investigate the dynamics and evolution of the Laurentide ice sheet (LIS) during this period, the Eurasian ice sheet (EIS) has not received much attention, in particular from a modeling perspective. However, meltwater discharge from this and other ice sheets surrounding the Nordic seas is often implied as a potential cause of ocean instabilities that lead to glacial abrupt climate changes. Thus, a better comprehension of the evolution of the EIS during the LGP is important to understand its role in glacial abrupt climate changes. Here we investigate the response of the EIS to millennial-scale climate variability during the LGP. We use a hybrid, three-dimensional, thermomechanical ice-sheet model that includes ice shelves and ice streams. The model is forced off-line via a novel perturbative approach that, as opposed to conventional methods, clearly differentiates between the spatial patterns of millennial-scale and orbital-scale climate variability. Thus, it provides a more realistic treatment of the forcing at millennial timescales. The effect of both atmospheric and oceanic variations are included. Our results show that the EIS responds with enhanced ice discharge in phase with interstadial warming in the North Atlantic when forced with surface ocean temperatures. Conversely, when subsurface ocean temperatures are used, enhanced ice discharge occurs both during stadials and at the beginning of the interstadials. Separating the atmospheric and oceanic effects demonstrates the major role of the ocean in controlling the dynamics of the EIS on millennial timescales. While the atmospheric forcing alone is only able to produce modest iceberg discharges, warming of the ocean leads to higher rates of iceberg discharges as a result of relatively strong basal melting at the margins of the ice sheet. Our results clearly show the capability of the EIS to react to glacial abrupt climate changes, and highlight the need for stronger constraints on the ice sheet's glacial dynamics and climate–ocean interactions.
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BORN, ANDREAS. „Tracer transport in an isochronal ice-sheet model“. Journal of Glaciology 63, Nr. 237 (20.10.2016): 22–38. http://dx.doi.org/10.1017/jog.2016.111.
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ABSTRACTThe full history of ice sheet and climate interactions is recorded in the vertical profiles of geochemical tracers in polar ice sheets. Numerical simulations of these archives promise great advances both in the interpretation of these reconstructions and the validation of the models themselves. However, fundamental mathematical shortcomings of existing models subject tracers to spurious diffusion, thwarting straightforward solutions. Here, I propose a new vertical discretization for ice-sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world flow of ice as a thinning of underlying layers. A new layer is added to the surface at equidistant time intervals, isochronally, thus identifying each layer uniquely by its time of deposition and age. This new approach is implemented for a two-dimensional section through the summit of the Greenland ice sheet. The ability to directly compare simulations of vertical ice cores with reconstructed data is used to find optimal model parameters from a large ensemble of simulations. It is shown that because this tuning method uses information from all times included in the ice core, it constrains ice-sheet sensitivity more robustly than a realistic reproduction of the modern ice-sheet surface.
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Goelzer, H., P. Huybrechts, M. F. Loutre, H. Goosse, T. Fichefet und A. Mouchet. „Impact of Greenland and Antarctic ice sheet interactions on climate sensitivity“. Climate Dynamics 37, Nr. 5-6 (03.08.2010): 1005–18. http://dx.doi.org/10.1007/s00382-010-0885-0.
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Punge, H. J., H. Gallée, M. Kageyama und G. Krinner. „Modelling snow accumulation on Greenland in Eemian, glacial inception, and modern climates in a GCM“. Climate of the Past 8, Nr. 6 (05.11.2012): 1801–19. http://dx.doi.org/10.5194/cp-8-1801-2012.
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Abstract. Changing climate conditions on Greenland influence the snow accumulation rate and surface mass balance (SMB) on the ice sheet and, ultimately, its shape. This can in turn affect local climate via orography and albedo variations and, potentially, remote areas via changes in ocean circulation triggered by melt water or calving from the ice sheet. Examining these interactions in the IPSL global model requires improving the representation of snow at the ice sheet surface. In this paper, we present a new snow scheme implemented in LMDZ, the atmospheric component of the IPSL coupled model. We analyse surface climate and SMB on the Greenland ice sheet under insolation and oceanic boundary conditions for modern, but also for two different past climates, the last glacial inception (115 kyr BP) and the Eemian (126 kyr BP). While being limited by the low resolution of the general circulation model (GCM), present-day SMB is on the same order of magnitude as recent regional model findings. It is affected by a moist bias of the GCM in Western Greenland and a dry bias in the north-east. Under Eemian conditions, the SMB decreases largely, and melting affects areas in which the ice sheet surface is today at high altitude, including recent ice core drilling sites as NEEM. In contrast, glacial inception conditions lead to a higher mass balance overall due to the reduced melting in the colder summer climate. Compared to the widely applied positive degree-day (PDD) parameterization of SMB, our direct modelling results suggest a weaker sensitivity of SMB to changing climatic forcing. For the Eemian climate, our model simulations using interannually varying monthly mean forcings for the ocean surface temperature and sea ice cover lead to significantly higher SMB in southern Greenland compared to simulations forced with climatological monthly means.
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Abe-Ouchi, A., T. Segawa und F. Saito. „Climatic Conditions for modelling the Northern Hemisphere ice sheets throughout the ice age cycle“. Climate of the Past 3, Nr. 3 (19.07.2007): 423–38. http://dx.doi.org/10.5194/cp-3-423-2007.
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Abstract. The ice sheet-climate interaction as well as the climatic response to orbital parameters and atmospheric CO2 concentration are examined in order to drive an ice sheet model throughout an ice age cycle. Feedback processes between ice sheet and atmosphere are analyzed by numerical experiments using a high resolution General Circulation Model (GCM) under different conditions at the Last Glacial Maximum. Among the proposed processes, the ice albedo feedback, the elevation-mass balance feedback and the desertification effect over the ice sheet were found to be the dominant processes for the ice-sheet mass balance. For the elevation-mass balance feedback, the temperature lapse rate over the ice sheet is proposed to be weaker than assumed in previous studies. Within the plausible range of parameters related to these processes, the ice sheet response to the orbital parameters and atmospheric CO2 concentration for the last glacial/interglacial cycle was simulated in terms of both ice volume and geographical distribution, using a three-dimensional ice-sheet model. Careful treatment of climate-ice sheet feedback is essential for a reliable simulation of the ice sheet changes during ice age cycles.
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Abe-Ouchi, A., T. Segawa und F. Saito. „Climatic conditions for modelling the Northern Hemisphere ice sheets throughout the ice age cycle“. Climate of the Past Discussions 3, Nr. 1 (06.02.2007): 301–36. http://dx.doi.org/10.5194/cpd-3-301-2007.
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Abstract. The ice sheet-climate interaction as well as the climatic response to orbital parameters and atmospheric CO2 content are examined in order to drive an ice sheet model throughout an ice age cycle. Feedback processes between ice sheet and atmosphere are analyzed by numerical experiments using a high resolution General Circulation Model (GCM) under different conditions at the Last Glacial Maximum. Among the proposed processes, the ice albedo feedback, the elevation-mass balance feedback and the desertification effect over ice sheet were found to be the dominant processes for the ice-sheet mass balance. The temperature lapse rate over the ice sheet is proposed to be about 5 °C km–1, which is weaker than assumed in other studies. Within the plausible range of parameters related to these processes, the ice sheet response to orbital parameters and atmospheric CO2 content for the last glacial/interglacial cycle was simulated in terms of both ice volume and geographical distribution, using a three-dimensional ice-sheet model. Careful treatment related to climate-ice sheet feedback is essential for a reliable simulation of ice sheet changes during ice age cycles.
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Andernach, Malena, Marie-Luise Kapsch und Uwe Mikolajewicz. „Impact of Greenland Ice Sheet disintegration on atmosphere and ocean disentangled“. Earth System Dynamics 16, Nr. 2 (14.03.2025): 451–74. https://doi.org/10.5194/esd-16-451-2025.
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Abstract. We analyze the impact of a disintegrated Greenland Ice Sheet (GrIS) on the climate through steady-state simulations with the global Max Planck Institute for Meteorology Earth System Model (MPI-ESM). This advances our understanding of the intricate feedbacks between the GrIS and the full climate system. Sensitivity experiments enable the quantification of the individual contributions of altered Greenland surface elevation and properties (e.g., land cover) to the atmospheric and oceanic climate response. Removing the GrIS results in reduced mechanical atmospheric blocking, warmer air temperatures over Greenland and thereby changes in the atmospheric circulation. The latter alters the wind stress on the ocean, which controls the ocean-mass transport through the Arctic gateways. Without the GrIS, the upper Nordic Seas are fresher, attenuating deep-water formation. In the Labrador Sea, deep-water formation is weaker despite a higher upper-ocean salinity, as the inflow of dense overflow from the Denmark Strait is reduced. Our sensitivity experiments show that the atmospheric response is primarily driven by the lower surface elevation. The lower Greenland elevation dominates the ocean response through wind-stress changes. Only in the Labrador Sea do altered Greenland surface properties dominate the ocean response, as this region stores excessive heat from the Greenland warming. The main drivers vary vertically: the elevation effect controls upper-ocean densities, while surface properties are important for the intermediate and deep ocean. Despite the confinement of most responses to the Arctic, a disintegrated GrIS also influences remote climates, such as air temperatures in Europe, the Atlantic Meridional Overturning Circulation (AMOC) and the subtropical gyre. These interactions and feedbacks between ice sheets and the other climate components highlight the necessity of including dynamic ice sheets in climate models that are used for future projections.
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Albrecht, Torsten, Meike Bagge und Volker Klemann. „Feedback mechanisms controlling Antarctic glacial-cycle dynamics simulated with a coupled ice sheet–solid Earth model“. Cryosphere 18, Nr. 9 (19.09.2024): 4233–55. http://dx.doi.org/10.5194/tc-18-4233-2024.
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Abstract. The dynamics of the ice sheets on glacial timescales are highly controlled by interactions with the solid Earth, i.e., the glacial isostatic adjustment (GIA). Particularly at marine ice sheets, competing feedback mechanisms govern the migration of the ice sheet's grounding line (GL) and hence the ice sheet stability. For this study, we developed a coupling scheme and performed a suite of coupled ice sheet–solid Earth simulations over the last two glacial cycles. To represent ice sheet dynamics we apply the Parallel Ice Sheet Model (PISM), and to represent the solid Earth response we apply the 3D VIscoelastic Lithosphere and MAntle model (VILMA), which, in addition to load deformation and rotation changes, considers the gravitationally consistent redistribution of water (the sea-level equation). We decided on an offline coupling between the two model components. By convergence of trajectories of the Antarctic Ice Sheet deglaciation we determine optimal coupling time step and spatial resolution of the GIA model and compare patterns of inferred relative sea-level change since the Last Glacial Maximum with the results from previous studies. With our coupling setup we evaluate the relevance of feedback mechanisms for the glaciation and deglaciation phases in Antarctica considering different 3D Earth structures resulting in a range of load-response timescales. For rather long timescales, in a glacial climate associated with the far-field sea-level low stand, we find GL advance up to the edge of the continental shelf mainly in West Antarctica, dominated by a self-amplifying GIA feedback, which we call the “forebulge feedback”. For the much shorter timescale of deglaciation, dominated by the marine ice sheet instability, our simulations suggest that the stabilizing sea-level feedback can significantly slow down GL retreat in the Ross sector, which is dominated by a very weak Earth structure (i.e., low mantle viscosity and thin lithosphere). This delaying effect prevents a Holocene GL retreat beyond its present-day position, which is discussed in the scientific community and supported by observational evidence at the Siple Coast and by previous model simulations. The applied coupled framework, PISM–VILMA, allows for defining restart states to run multiple sensitivity simulations from. It can be easily implemented in Earth system models (ESMs) and provides the tools to gain a better understanding of ice sheet stability on glacial timescales as well as in a warmer future climate.
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Zhan, Jingang, Hongling Shi, Yong Wang und Yixin Yao. „Complex Principal Component Analysis of Antarctic Ice Sheet Mass Balance“. Remote Sensing 13, Nr. 3 (29.01.2021): 480. http://dx.doi.org/10.3390/rs13030480.
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Ice sheet changes of the Antarctic are the result of interactions among the ocean, atmosphere, and ice sheet. Studying the ice sheet mass variations helps us to understand the possible reasons for these changes. We used 164 months of Gravity Recovery and Climate Experiment (GRACE) satellite time-varying solutions to study the principal components (PCs) of the Antarctic ice sheet mass change and their time-frequency variation. This assessment was based on complex principal component analysis (CPCA) and the wavelet amplitude-period spectrum (WAPS) method to study the PCs and their time-frequency information. The CPCA results revealed the PCs that affect the ice sheet balance, and the wavelet analysis exposed the time-frequency variation of the quasi-periodic signal in each component. The results show that the first PC, which has a linear term and low-frequency signals with periods greater than five years, dominates the variation trend of ice sheet in the Antarctic. The ratio of its variance to the total variance shows that the first PC explains 83.73% of the mass change in the ice sheet. Similar low-frequency signals are also found in the meridional wind at 700 hPa in the South Pacific and the sea surface temperature anomaly (SSTA) in the equatorial Pacific, with the correlation between the low-frequency periodic signal of SSTA in the equatorial Pacific and the first PC of the ice sheet mass change in Antarctica found to be 0.73. The phase signals in the mass change of West Antarctica indicate the upstream propagation of mass loss information over time from the ocean–ice interface to the southward upslope, which mainly reflects ocean-driven factors such as enhanced ice–ocean interaction and the intrusion of warm saline water into the cavities under ice shelves associated with ice sheets which sit on retrograde slopes. Meanwhile, the phase signals in the mass change of East Antarctica indicate the downstream propagation of mass increase information from the South Pole toward Dronning Maud Land, which mainly reflects atmospheric factors such as precipitation accumulation.
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Borreguero, Laura Herraiz, Ruth Mottram und Ivana Cvijanovic. „Discussing Progress in Understanding Ice Sheet—Ocean Interactions: Advanced Climate Dynamics Course 2010: Ice Sheet—Ocean Interactions; Lyngen, Norway, 8–19 June 2010“. Eos, Transactions American Geophysical Union 91, Nr. 45 (2010): 419. http://dx.doi.org/10.1029/2010eo450006.
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Braithwaite, Roger J. „Models of ice-atmosphere interactions for the Greenland ice sheet“. Annals of Glaciology 23 (1996): 149–53. http://dx.doi.org/10.3189/s0260305500013379.
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Simple models to calculate melt and refreezing are reviewed. Both degree-day and energy-balance models can give distributed melt inputs to ice-dynamics models but have only been tested extensively in West Greenland, and more data are needed from the remoter parts of Greenland. The energy-balance model is more realistic but needs input data that are not generally available over the whole ice sheet. On the other hand, degree-day factors vary from situation to situation although a value of about 8 kg m−2 d−1 deg−1 for ice ablation is a reasonable first approximation as assumed in recent ice-dynamics models. Meltwater refreezing in the accumulation area can be modelled very simply but more detailed physical models are needed to describe the shifts in accumulation zones under different climates.
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Braithwaite, Roger J. „Models of ice-atmosphere interactions for the Greenland ice sheet“. Annals of Glaciology 23 (1996): 149–53. http://dx.doi.org/10.1017/s0260305500013379.
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Simple models to calculate melt and refreezing are reviewed. Both degree-day and energy-balance models can give distributed melt inputs to ice-dynamics models but have only been tested extensively in West Greenland, and more data are needed from the remoter parts of Greenland. The energy-balance model is more realistic but needs input data that are not generally available over the whole ice sheet. On the other hand, degree-day factors vary from situation to situation although a value of about 8 kg m−2d−1deg−1for ice ablation is a reasonable first approximation as assumed in recent ice-dynamics models. Meltwater refreezing in the accumulation area can be modelled very simply but more detailed physical models are needed to describe the shifts in accumulation zones under different climates.
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Ren, Diandong, und Lance M. Leslie. „Three positive feedback mechanisms for ice-sheet melting in a warming climate“. Journal of Glaciology 57, Nr. 206 (2011): 1057–66. http://dx.doi.org/10.3189/002214311798843250.
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AbstractThree positive feedback mechanisms that accelerate ice-sheet melting are assessed in a warming climate, using a numerical ice model driven by atmospheric climate models. The Greenland ice sheet (GrIS) is the modeling test-bed under accelerated melting conditions. The first feedback is the interaction of sea water with ice. It is positive because fresh water melts ice faster than salty water, owing primarily to the reduction in water heat capacity by solutes. It is shown to be limited for the GrIS, which has only a small ocean interface, and the grounding line of some fast glaciers becomes land-terminating during the 21st century. The second positive feedback, strain heating, is positive because it produces further ice heating inside the ice sheet. The third positive feedback, granular basal sliding, applies to all ice sheets and becomes the dominant feedback during the 21st century. A numerical simulation of Jakobshavn Isbræ over the 21st century reveals that all three feedback processes are active for this glacier. Compared with the year 2000 level, annual ice discharge into the ocean could increase by ∼1.4 km3 a−1 (∼5% of the present annual rate) by 2100. Granular basal sliding contributes ∼40% of this increase.
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Bintanja, R., G. J. van Oldenborgh und C. A. Katsman. „The effect of increased fresh water from Antarctic ice shelves on future trends in Antarctic sea ice“. Annals of Glaciology 56, Nr. 69 (2015): 120–26. http://dx.doi.org/10.3189/2015aog69a001.
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AbstractObservations show that, in contrast to the Arctic, the area of Antarctic sea ice has increased since 1979. A potential driver of this significant increase relates to the mass loss of the Antarctic ice sheet. Subsurface ocean warming causes basal ice-shelf melt, freshening the surface waters around Antarctica, which leads to increases in sea-ice cover. With climate warming ongoing, future mass-loss rates are projected to accelerate, which has the potential to affect future Antarctic sea-ice trends. Here we investigate to what extent future sea-ice trends are influenced by projected increases in Antarctic freshwater flux due to subsurface melt, using a state-of-the-art global climate model (EC-Earth) in standardized Climate Model Intercomparison Project phase 5 (CMIP5) climate-change simulations. Virtually all CMIP5 models disregard ocean–ice-sheet interactions and project strongly retreating Antarctic sea ice. Applying various freshwater flux scenarios, we find that the additional fresh water significantly offsets the decline in sea-ice area and is even able to reverse the trend in the strongest freshwater forcing scenario that can reasonably be expected, especially in austral winter. The model also simulates decreasing sea surface temperatures (SSTs), with the SST trends exhibiting strong regional variations that largely correspond to regional sea-ice trends.
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Pérez, Lara F., Paul C. Knutz, John R. Hopper, Marit-Solveig Seidenkrantz, Matt O'Regan und Stephen Jones. „NorthGreen: unlocking records from sea to land in Northeast Greenland“. Scientific Drilling 33, Nr. 1 (02.04.2024): 33–46. http://dx.doi.org/10.5194/sd-33-33-2024.
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Abstract. The increasing anthropogenic CO2 forcing of the climate system calls for a better understanding of how polar ice sheets may respond to accelerating global warming. The sensitivity of the Greenland ice sheet to polar amplification, changes in ocean heat transport, and deteriorating perennial sea ice conditions makes the Northeast Greenland margin a pertinent location with respect to understanding the impact of climate change on ice sheet instability and associated sea level rise. Throughout the Cenozoic, ocean heat fluxes toward and along Northeast Greenland have been controlled by water mass exchanges between the Arctic and Atlantic oceans. A key element here is the current flow through oceanic gateways, notably the Fram Strait and the Greenland–Scotland Ridge. To gain a long-term (million-year) perspective of ice sheet variability in this region, it is essential to understand the broader context of ice–ocean–tectonic interactions. Coupling between the ice sheet, the subsurface, the ocean, and sea ice are readily observable today in Northeast Greenland, but geological records to illuminate long-term trends and their interplay with other parts of the global climate system are lacking. Consequently, the NorthGreen workshop was organized by the Geological Survey of Denmark and Greenland in collaboration with Aarhus (Denmark) and Stockholm (Sweden) universities in November 2022 to develop mission-specific platform (MSP) proposals for drilling the Northeast Greenland margin under the umbrella of the MagellanPlus Workshop Series Programme of the European Consortium for Ocean Research Drilling (ECORD). Seventy-one participants representing a broad scientific community discussed key scientific questions and primary targets that could be addressed through scientific drilling in Northeast Greenland. Three pre-proposals were initiated during the workshop targeting Morris Jesup Rise, the Northeast Greenland continental shelf, and Denmark Strait.
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Goelzer, Heiko, Sophie Nowicki, Anthony Payne, Eric Larour, Helene Seroussi, William H. Lipscomb, Jonathan Gregory et al. „The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6“. Cryosphere 14, Nr. 9 (17.09.2020): 3071–96. http://dx.doi.org/10.5194/tc-14-3071-2020.
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Abstract. The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean.
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Le clec'h, Sébastien, Sylvie Charbit, Aurélien Quiquet, Xavier Fettweis, Christophe Dumas, Masa Kageyama, Coraline Wyard und Catherine Ritz. „Assessment of the Greenland ice sheet–atmosphere feedbacks for the next century with a regional atmospheric model coupled to an ice sheet model“. Cryosphere 13, Nr. 1 (01.02.2019): 373–95. http://dx.doi.org/10.5194/tc-13-373-2019.
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Abstract. In the context of global warming, growing attention is paid to the evolution of the Greenland ice sheet (GrIS) and its contribution to sea-level rise at the centennial timescale. Atmosphere–GrIS interactions, such as the temperature–elevation and the albedo feedbacks, have the potential to modify the surface energy balance and thus to impact the GrIS surface mass balance (SMB). In turn, changes in the geometrical features of the ice sheet may alter both the climate and the ice dynamics governing the ice sheet evolution. However, changes in ice sheet geometry are generally not explicitly accounted for when simulating atmospheric changes over the Greenland ice sheet in the future. To account for ice sheet–climate interactions, we developed the first two-way synchronously coupled model between a regional atmospheric model (MAR) and a 3-D ice sheet model (GRISLI). Using this novel model, we simulate the ice sheet evolution from 2000 to 2150 under a prolonged representative concentration pathway scenario, RCP8.5. Changes in surface elevation and ice sheet extent simulated by GRISLI have a direct impact on the climate simulated by MAR. They are fed to MAR from 2020 onwards, i.e. when changes in SMB produce significant topography changes in GRISLI. We further assess the importance of the atmosphere–ice sheet feedbacks through the comparison of the two-way coupled experiment with two other simulations based on simpler coupling strategies: (i) a one-way coupling with no consideration of any change in ice sheet geometry; (ii) an alternative one-way coupling in which the elevation change feedbacks are parameterized in the ice sheet model (from 2020 onwards) without taking into account the changes in ice sheet topography in the atmospheric model. The two-way coupled experiment simulates an important increase in surface melt below 2000 m of elevation, resulting in an important SMB reduction in 2150 and a shift of the equilibrium line towards elevations as high as 2500 m, despite a slight increase in SMB over the central plateau due to enhanced snowfall. In relation with these SMB changes, modifications of ice sheet geometry favour ice flux convergence towards the margins, with an increase in ice velocities in the GrIS interior due to increased surface slopes and a decrease in ice velocities at the margins due to decreasing ice thickness. This convergence counteracts the SMB signal in these areas. In the two-way coupling, the SMB is also influenced by changes in fine-scale atmospheric dynamical processes, such as the increase in katabatic winds from central to marginal regions induced by increased surface slopes. Altogether, the GrIS contribution to sea-level rise, inferred from variations in ice volume above floatation, is equal to 20.4 cm in 2150. The comparison between the coupled and the two uncoupled experiments suggests that the effect of the different feedbacks is amplified over time with the most important feedbacks being the SMB–elevation feedbacks. As a result, the experiment with parameterized SMB–elevation feedback provides a sea-level contribution from GrIS in 2150 only 2.5 % lower than the two-way coupled experiment, while the experiment with no feedback is 9.3 % lower. The change in the ablation area in the two-way coupled experiment is much larger than those provided by the two simplest methods, with an underestimation of 11.7 % (14 %) with parameterized feedbacks (no feedback). In addition, we quantify that computing the GrIS contribution to sea-level rise from SMB changes only over a fixed ice sheet mask leads to an overestimation of ice loss of at least 6 % compared to the use of a time variable ice sheet mask. Finally, our results suggest that ice-loss estimations diverge when using the different coupling strategies, with differences from the two-way method becoming significant at the end of the 21st century. In particular, even if averaged over the whole GrIS the climatic and ice sheet fields are relatively similar; at the local and regional scale there are important differences, highlighting the importance of correctly representing the interactions when interested in basin scale changes.
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Zhang, Enze, Ginny Catania und Daniel T. Trugman. „AutoTerm: an automated pipeline for glacier terminus extraction using machine learning and a “big data” repository of Greenland glacier termini“. Cryosphere 17, Nr. 8 (24.08.2023): 3485–503. http://dx.doi.org/10.5194/tc-17-3485-2023.
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Abstract. Ice sheet marine margins via outlet glaciers are susceptible to climate change and are expected to respond through retreat, steepening, and acceleration, although with significant spatial heterogeneity. However, research on ice–ocean interactions has continued to rely on decentralized, manual mapping of features at the ice–ocean interface, impeding progress in understanding the response of glaciers and ice sheets to climate change. The proliferation of remote-sensing images lays the foundation for a better understanding of ice–ocean interactions and also necessitates the automation of terminus delineation. While deep learning (DL) techniques have already been applied to automate the terminus delineation, none involve sufficient quality control and automation to enable DL applications to “big data” problems in glaciology. Here, we build on established methods to create a fully automated pipeline for terminus delineation that makes several advances over prior studies. First, we leverage existing manually picked terminus traces (16 440) as training data to significantly improve the generalization of the DL algorithm. Second, we employ a rigorous automated screening module to enhance the data product quality. Third, we perform a thoroughly automated uncertainty quantification on the resulting data. Finally, we automate several steps in the pipeline allowing data to be regularly delivered to public databases with increased frequency. The automation level of our method ensures the sustainability of terminus data production. Altogether, these improvements produce the most complete and high-quality record of terminus data that exists for the Greenland Ice Sheet (GrIS). Our pipeline has successfully picked 278 239 termini for 295 glaciers in Greenland from Landsat 5, 7, 8 and Sentinel-1 and Sentinel-2 images, spanning the period from 1984 to 2021. The pipeline has been tested on glaciers in Greenland with an error of 79 m. The high sampling frequency and the controlled quality of our terminus data will enable better quantification of ice sheet change and model-based parameterizations of ice–ocean interactions.
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Payne, A. J., P. Huybrechts, A. Abe-Ouchi, R. Calov, J. L. Fastook, R. Greve, S. J. Marshall et al. „Results from the EISMINT model intercomparison: the effects of thermomechanical coupling“. Journal of Glaciology 46, Nr. 153 (2000): 227–38. http://dx.doi.org/10.3189/172756500781832891.
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AbstractThis paper discusses results from the second phase of the European Ice Sheet Modelling Initiative (EISMINT). It reports the intercomparison of ten operational ice-sheet models and uses a series of experiments to examine the implications of thermomechanical coupling for model behaviour. A schematic, circular ice sheet is used in the work which investigates both steady states and the response to stepped changes in climate. The major finding is that the radial symmetry implied in the experimental design can, under certain circumstances, break down with the formation of distinct, regularly spaced spokes of cold ice which extended from the interior of the ice sheet outward to the surrounding zone of basal melt. These features also manifest themselves in the thickness and velocity distributions predicted by the models. They appear to be a common feature to all of the models which took part in the intercomparison, and may stem from interactions between ice temperature, flow and surface form. The exact nature of these features varies between models, and their existence appears to be controlled by the overall thermal regime of the ice sheet. A second result is that there is considerable agreement between the models in their predictions of global-scale response to imposed climate change.
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Kreuzer, Moritz, Ronja Reese, Willem Nicholas Huiskamp, Stefan Petri, Torsten Albrecht, Georg Feulner und Ricarda Winkelmann. „Coupling framework (1.0) for the PISM (1.1.4) ice sheet model and the MOM5 (5.1.0) ocean model via the PICO ice shelf cavity model in an Antarctic domain“. Geoscientific Model Development 14, Nr. 6 (22.06.2021): 3697–714. http://dx.doi.org/10.5194/gmd-14-3697-2021.
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Abstract. The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high-resolution configurations, limiting these studies to individual glaciers or regions over short timescales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM (Parallel Ice Sheet Model) with the global ocean general circulation model MOM5 (Modular Ocean Model) via the ice shelf cavity model PICO (Potsdam Ice-shelf Cavity mOdel). As ice shelf cavities are not resolved by MOM5 but are parameterized with the PICO box model, the framework allows the ice sheet and ocean components to be run at resolutions of 16 km and 3∘ respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the Antarctic Ice Sheet and the global ocean over time spans of the order of centuries to millennia. In this study, we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet component is calculated by PICO from modelled ocean temperatures and salinities at the depth of the continental shelf, and, vice versa, the resulting mass and energy fluxes from melting at the ice–ocean interface are transferred to the ocean component. Mass and energy fluxes are shown to be conserved to machine precision across the considered component domains. The implementation is computationally efficient as it introduces only minimal overhead. Furthermore, the coupled model is evaluated in a 4000 year simulation under constant present-day climate forcing and is found to be stable with respect to the ocean and ice sheet spin-up states. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions, and timescales between the ice and ocean component in a generic way; thus, it can be adopted to a wide range of model set-ups.
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Straneo, Fiammetta, Patrick Heimbach, Olga Sergienko, Gordon Hamilton, Ginny Catania, Stephen Griffies, Robert Hallberg et al. „Challenges to Understanding the Dynamic Response of Greenland's Marine Terminating Glaciers to Oceanic and Atmospheric Forcing“. Bulletin of the American Meteorological Society 94, Nr. 8 (01.08.2013): 1131–44. http://dx.doi.org/10.1175/bams-d-12-00100.1.
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The recent retreat and speedup of outlet glaciers, as well as enhanced surface melting around the ice sheet margin, have increased Greenland's contribution to sea level rise to 0.6 ± 0.1 mm yr−1 and its discharge of freshwater into the North Atlantic. The widespread, near-synchronous glacier retreat, and its coincidence with a period of oceanic and atmospheric warming, suggests a common climate driver. Evidence points to the marine margins of these glaciers as the region from which changes propagated inland. Yet, the forcings and mechanisms behind these dynamic responses are poorly understood and are either missing or crudely parameterized in climate and ice sheet models. Resulting projected sea level rise contributions from Greenland by 2100 remain highly uncertain. This paper summarizes the current state of knowledge and highlights key physical aspects of Greenland's coupled ice sheet–ocean–atmosphere system. Three research thrusts are identified to yield fundamental insights into ice sheet, ocean, sea ice, and atmosphere interactions, their role in Earth's climate system, and probable trajectories of future changes: 1) focused process studies addressing critical glacier, ocean, atmosphere, and coupled dynamics; 2) sustained observations at key sites; and 3) inclusion of relevant dynamics in Earth system models. Understanding the dynamic response of Greenland's glaciers to climate forcing constitutes both a scientific and technological frontier, given the challenges of obtaining the appropriate measurements from the glaciers' marine termini and the complexity of the dynamics involved, including the coupling of the ocean, atmosphere, glacier, and sea ice systems. Interdisciplinary and international cooperation are crucial to making progress on this novel and complex problem.