scholarly journals Layered seawater intrusion and melt under grounded ice

2021 ◽  
Author(s):  
Alexander A. Robel ◽  
Earle Wilson ◽  
Helene Seroussi
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Seawater Intrusion ◽  
Ice Sheets ◽  
Ice Sheet ◽  
System Model ◽  
Glacier Terminus ◽  
Grounding Line ◽  
Flow Through ◽  
And Sea Level

Abstract. Increasing melt of ice sheets at their floating or vertical interface with the ocean is a major driver of marine ice sheet retreat and sea level rise. However, the extent to which warm, salty seawater may drive melting under the grounded portions of ice sheets is still not well understood. Previous work has explored the possibility that dense seawater intrudes beneath relatively light subglacial freshwater discharge, similar to the salt wedge observed in many estuarine systems. In this study, we develop a generalized theory of layered seawater intrusion under grounded ice, including where subglacial hydrology occurs as a macroporous water sheet over impermeable beds or as microporous Darcy flow through permeable till. Using predictions from this theory, we show that seawater intrusion over hard beds may feasibly occur up to tens of kilometers upstream of a glacier terminus or grounding line. On the other hand, seawater is unlikely to intrude more than tens of meters through subglacial till. High-resolution simulations using the Ice-Sheet and Sea-Level System Model (ISSM) show that even just a few hundred meters of basal melt caused by seawater intrusion upstream of marine ice sheet grounding lines can cause projections of marine ice sheet volume loss to be 10–50 % higher or 100 % higher for kilometers of intrusion-induced basal melt. These results suggest that further observational, experimental and numerical investigations are needed to determine whether the conditions under which extensive seawater intrusion occurs and whether it will indeed drive rapid marine ice sheet retreat and sea level rise in the future.

scholarly journals ISSM-SLPS: geodetically compliant Sea-Level Projection System for the Ice-sheet and Sea-level System Model v4.17

2020 ◽  
Vol 13 (10) ◽  
pp. 4925-4941
Author(s):  
Eric Larour ◽  
Lambert Caron ◽  
Mathieu Morlighem ◽  
Surendra Adhikari ◽  
Thomas Frederikse ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ocean Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
System Model ◽  
Level System ◽  
Projection System ◽  
Forward Models ◽  
And Sea Level

Abstract. Understanding future impacts of sea-level rise at the local level is important for mitigating its effects. In particular, quantifying the range of sea-level rise outcomes in a probabilistic way enables coastal planners to better adapt strategies, depending on cost, timing and risk tolerance. For a time horizon of 100 years, frameworks have been developed that provide such projections by relying on sea-level fingerprints where contributions from different processes are sampled at each individual time step and summed up to create probability distributions of sea-level rise for each desired location. While advantageous, this method does not readily allow for including new physics developed in forward models of each component. For example, couplings and feedbacks between ice sheets, ocean circulation and solid-Earth uplift cannot easily be represented in such frameworks. Indeed, the main impediment to inclusion of more forward model physics in probabilistic sea-level frameworks is the availability of dynamically computed sea-level fingerprints that can be directly linked to local mass changes. Here, we demonstrate such an approach within the Ice-sheet and Sea-level System Model (ISSM), where we develop a probabilistic framework that can readily be coupled to forward process models such as those for ice sheets, glacial isostatic adjustment, hydrology and ocean circulation, among others. Through large-scale uncertainty quantification, we demonstrate how this approach enables inclusion of incremental improvements in all forward models and provides fidelity to time-correlated processes. The projection system may readily process input and output quantities that are geodetically consistent with space and terrestrial measurement systems. The approach can also account for numerous improvements in our understanding of sea-level processes.

scholarly journals ISSM-SLPS: geodetically compliant Sea-Level Projection System for the Ice-sheet and Sea-level System Model v4.17

2020 ◽  
Author(s):  
Eric Larour ◽  
Surendra Adhikari ◽  
Thomas Frederikse ◽  
Lambert Caron ◽  
Benjamin Hamlington ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ocean Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
System Model ◽  
Level System ◽  
Projection System ◽  
Forward Models ◽  
And Sea Level

Abstract. Understanding future impacts of sea-level rise at the local level is paramount to mitigating its effects. In particular, quantifying the range of sea-level rise outcomes in a probabilistic way enables coastal planners to better adapt strategies, depending on cost and timing. For long-term projections, from present-day to the end of the 21st century, frameworks have been developed that provide such probabilistic projections. They rely on sea-level fingerprints where contributions from different processes are sampled at each individual time step and summed up to create probability distributions of sea-level rise for each desired location. While advantageous, this method does not readily allow for including new physics developed in forward models of each component. For example, couplings and feedbacks between ice sheets, ocean circulation, and solid-Earth uplift cannot easily be represented in such frameworks. Indeed, the main impediment to inclusion of more forward model physics in probabilistic sea-level frameworks is the availability of dynamically computed sea-level fingerprints that can be directly linked to local mass changes. Here, we demonstrate such an approach within the Ice-Sheet and Sea-level System Model (ISSM), where we develop a probabilistic framework that can readily be coupled to forward process models such as those for ice sheets, glacial-isostatic adjustment, hydrology and ocean circulation, among others. Through large scale uncertainty quantification, we demonstrate how this approach enables inclusion of incremental improvements in all forward models and provides fidelity to time-correlated processes. The projection system may readily process input and output quantities that are geodetically consistent with space and terrestrial measurement systems. The approach can also account for numerous improvements in our understanding of sea-level processes.

scholarly journals Brief communication: Impact of mesh resolution for MISMIP and MISMIP3d experiments using Elmer/Ice

2016 ◽  
Vol 10 (1) ◽  
pp. 307-312 ◽  
Author(s):  
O. Gagliardini ◽  
J. Brondex ◽  
F. Gillet-Chaulet ◽  
L. Tavard ◽  
V. Peyaud ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Model Intercomparison ◽  
Model Sensitivity ◽  
Close Vicinity ◽  
Grounding Line ◽  
Mesh Resolution ◽  
Intercomparison Exercises

Abstract. The dynamical contribution of marine ice sheets to sea level rise is largely controlled by grounding line (GL) dynamics. Two marine ice sheet model intercomparison exercises, namely MISMIP and MISMIP3d, have been proposed to the community to test and compare the ability of models to capture the GL dynamics. Both exercises are known to present a discontinuity of the friction at the GL, which is believed to increase the model sensitivity to mesh resolution. Here, using Elmer/Ice, the only Stokes model which completed both intercomparisons, the sensitivity to the mesh resolution is studied from an extended MISMIP experiment in which the friction continuously decreases over a transition distance and equals zero at the GL. Using this MISMIP-like setup, it is shown that the sensitivity to the mesh resolution is not improved for a vanishing friction at the GL. For the original MISMIP experiment, i.e. for a discontinuous friction at the GL, we further show that the results are moreover very sensitive to the way the friction is interpolated in the close vicinity of the GL. In the light of these new insights, and thanks to increased computing resources, new results for the MISMIP3d experiments obtained for higher resolutions than previously published are made available for future comparisons as the Supplement.

Relative control of bedrock roughness versus topography on global glacier bed friction

2021 ◽  
Author(s):  
Olivier Gagliardini ◽  
Fabien Gillet-Chaulet ◽  
Florent Gimbert
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Inverse Method ◽  
Ad Hoc ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Grid Resolution ◽  
Classical Approach ◽  
Bed Topography ◽  
Bed Friction

<p>Friction at the base of ice-sheets has been shown to be one of the largest uncertainty of model projections for the contribution of ice-sheet to future sea level rise. On hard beds, most of the apparent friction is the result of ice flowing over the bumps that have a size smaller than described by the grid resolution of ice-sheet models. To account for this friction, the classical approach is to replace this under resolved roughness by an ad-hoc friction law. In an imaginary world of unlimited computing resource and highly resolved bedrock DEM, one should solve for all bed roughnesses assuming pure sliding at the bedrock-ice interface. If such solutions are not affordable at the scale of an ice-sheet or even at the scale of a glacier, the effect of small bumps can be inferred using synthetical periodic geometry. In this presentation,<span>  </span>beds are constructed using the superposition of up to five bed geometries made of sinusoidal bumps of decreasing wavelength and amplitudes. The contribution to the total friction of all five beds is evaluated by inverse methods using the most resolved solution as observation. It is shown that small features of few meters can contribute up to almost half of the total friction, depending on the wavelengths and amplitudes distribution. This work also confirms that the basal friction inferred using inverse method<span>  </span>is very sensitive to how the bed topography is described by the model grid, and therefore depends on the size of the model grid itself.<span> </span></p>

scholarly journals Simulation of the future sea level contribution of Greenland with a new glacial system model

2018 ◽  
Vol 12 (10) ◽  
pp. 3097-3121 ◽  
Author(s):  
Reinhard Calov ◽  
Sebastian Beyer ◽  
Ralf Greve ◽  
Johanna Beckmann ◽  
Matteo Willeit ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Surface Temperature ◽  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
System Model ◽  
Surface Mass Balance ◽  
Surface Mass

Abstract. We introduce the coupled model of the Greenland glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dynamics, the model of basal hydrology HYDRO and a parameterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, imposing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961–1990 standard climatology derived from simulations of the regional atmosphere model MAR with ERA reanalysis boundary conditions. For the palaeo-part of the spin-up, we add the temperature anomaly derived from the GRIP ice core to the years 1961–1990 average surface temperature field. For our projections, we apply surface temperature and surface mass balance anomalies derived from RCP 4.5 and RCP 8.5 scenarios created by MAR with boundary conditions from simulations with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Further on, the impact of elevation–surface mass balance feedback, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation–surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we investigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temperature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.

scholarly journals Last Interglacial climate and sea-level evolution from a coupled ice sheet–climate model

2016 ◽  
Vol 12 (12) ◽  
pp. 2195-2213 ◽  
Author(s):  
Heiko Goelzer ◽  
Philippe Huybrechts ◽  
Marie-France Loutre ◽  
Thierry Fichefet
Keyword(s):  
Surface Temperature ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Last Interglacial ◽  
A Minor ◽  
The Antarctic ◽  
The Impact ◽  
And Sea Level

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.

scholarly journals Brief communication: On calculating the sea-level contribution in marine ice-sheet models

2020 ◽  
Vol 14 (3) ◽  
pp. 833-840 ◽  
Author(s):  
Heiko Goelzer ◽  
Violaine Coulon ◽  
Frank Pattyn ◽  
Bas de Boer ◽  
Roderik van de Wal
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ocean Water ◽  
Ice Volume ◽  
Isostatic Adjustment ◽  
The Common

Abstract. Estimating the contribution of marine ice sheets to sea-level rise is complicated by ice grounded below sea level that is replaced by ocean water when melted. The common approach is to only consider the ice volume above floatation, defined as the volume of ice to be removed from an ice column to become afloat. With isostatic adjustment of the bedrock and external sea-level forcing that is not a result of mass changes of the ice sheet under consideration, this approach breaks down, because ice volume above floatation can be modified without actual changes in the sea-level contribution. We discuss a consistent and generalised approach for estimating the sea-level contribution from marine ice sheets.

ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model

2020 ◽  
Author(s):  
Thomas Kleiner ◽  
Jeremie Schmiedel ◽  
Angelika Humbert
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Climate Models ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Initial State ◽  
Intercomparison Project ◽  
Non Local ◽  
The Impact

<p>Ice sheets constitute the largest and most uncertain potential source of future sea-level rise. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice sheet and climate models to explore the contribution from the Greenland and Antarctic ice sheets to future sea-level rise.</p> <p>We use the Parallel Ice Sheet Model (PISM, pism-docs.org) to carry out spinup and projection simulations for the Antarctic Ice Sheet. Our treatment of the ice-ocean boundary condition previously based on 3D ocean temperatures (initMIP-Antarctica) has been adopted to use the ISMIP6 parameterisation and 3D ocean forcing fields (temperature and salinity) according to the ISMIP6 protocol.</p> <p>In this study, we analyse the impact of the choices made during the model initialisation procedure on the initial state. We present the AWI PISM results of the ISMIP6 projection simulations and investigate the ice sheet response for individual basins. In the analysis, we distinguish between the local and non-local ice shelf basal melt parameterisation.</p>

Trends and projections in ice sheet mass balance

2020 ◽  
Author(s):  
Andrew Shepherd ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Sea Levels ◽  
Global Sea Level

<p>In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. <strong>Since the early 1990’s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance.  </strong>Cumulative ice losses from both ice sheets have been close to the IPCC’s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.</p>

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