scholarly journals Response to Filchner-Ronne Ice Shelf cavity warming in a coupled ocean–ice sheet model. Part I: The ocean perspective

2017 ◽  
Author(s):  
Ralph Timmermann ◽  
Sebastian Goeller
Keyword(s):  
World Ocean ◽  
Ice Sheet ◽  
Coupled Model ◽  
Freezing Temperature ◽  
Ocean Model ◽  
Climate Forcing ◽  
Global Ocean ◽  
Ice Shelf ◽  
Marginal Seas ◽  
Grounding Line

Abstract. A Regional Antarctic and Global Ocean (RAnGO) model has been developed to study the interaction between the world ocean and the Antarctic ice sheet. The coupled model is based on a global implementation of the Finite Element Sea-ice Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY comprising the Filchner-Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice-shelf component are supplied. RIMBAY returns ice thickness and the position of the grounding line. The ocean model uses a pre-computed mesh to allow for an easy adjustment of the model domain to a varying cavity geometry. RAnGO simulations with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a local retreat of the grounding line. The potentially negative feedback from ice-shelf thinning through a rising in-situ freezing temperature is more than outweighed by the increasing water column thickness in the deepest parts of the cavity. Compared to a control simulation with fixed ice-shelf geometry, the coupled model thus yields a slightly stronger increase of ice-shelf basal melt rates.

scholarly journals Response to Filchner–Ronne Ice Shelf cavity warming in a coupled ocean–ice sheet model – Part 1: The ocean perspective

Ocean Science ◽  
2017 ◽  
Vol 13 (5) ◽  
pp. 765-776 ◽  
Author(s):  
Ralph Timmermann ◽  
Sebastian Goeller
Keyword(s):  
World Ocean ◽  
Ice Sheet ◽  
Coupled Model ◽  
Freezing Temperature ◽  
Ocean Model ◽  
Climate Forcing ◽  
Global Ocean ◽  
Ice Shelf ◽  
Marginal Seas ◽  
Grounding Line

Abstract. The Regional Antarctic ice and Global Ocean (RAnGO) model has been developed to study the interaction between the world ocean and the Antarctic ice sheet. The coupled model is based on a global implementation of the Finite Element Sea-ice Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice-shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY comprising the Filchner–Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice-shelf component are supplied. RIMBAY returns ice thickness and the position of the grounding line. The ocean model uses a pre-computed mesh to allow for an easy adjustment of the model domain to a varying cavity geometry. RAnGO simulations with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a local retreat of the grounding line. The potentially negative feedback from ice-shelf thinning through a rising in situ freezing temperature is more than outweighed by the increasing water column thickness in the deepest parts of the cavity. Compared to a control simulation with fixed ice-shelf geometry, the coupled model thus yields a slightly stronger increase in ice-shelf basal melt rates.

Coupled ocean—ice shelf—ice sheet projections for the Weddell Sea Basin, Antarctica

2020 ◽  
Author(s):  
Ralph Timmermann ◽  
Torsten Albrecht
Keyword(s):  
Ice Sheet ◽  
Coupled Model ◽  
Ocean Model ◽  
Weddell Sea ◽  
Global Ocean ◽  
Ice Shelf ◽  
Vertical Coordinate ◽  
Stress Criterion ◽  
Marginal Seas ◽  
Grounding Line

<p>To study Antarctica’s contribution to ongoing and future sea level rise, a coupled ice sheet – ice shelf – ocean model with an explicit representation of ice shelf cavities has been developed. The coupled model is based on a global implementation of the Finite Element Sea ice Ocean Model (FESOM) with a mesh that is substantially refined in the marginal seas of the Southern Ocean. The Antarctic Ice Sheet is represented by a regional setup of the Parallel Ice Sheet Model PISM, comprising the Filchner-Ronne Ice Shelf (FRIS) and the grounded ice in its catchment area up to the ice divides.  At the base of the FRIS, melt rates and ocean temperatures from FESOM are applied. PISM returns ice thickness and the position of the grounding line. Buildung on infrastructure developed for the Regional Antarctic and Global Ocean (RAnGO) model, we use a pre-computed FESOM mesh that is adopted to the varying cavity geometry in each coupling step, i.e. currently once per model year. Changes in water column thickness are easily accounted for by the terrain-following vertical coordinate system in the ice shelf cavity. The ice sheet model is run on a horizontal grid with 1 km resolution to ensure an appropriate representation of grounding line processes. Enhancement factors for the approximation of the stress balance, as often used in coarse-resolution ice sheet models, become obsolete at such high resolution. Ice stream flow is well captured by polythermal coupling of the ice flow and a Mohr-Coulomb yield stress criterion that accounts for properties of the till material and the effective pressure on the saturated till. We present results from model runs with a 20<sup>th</sup>-century climate forcing and projections until the end of the 22<sup>nd</sup> century. We will show that cavity hydrography, ice shelf basal melt rates and thickness evolution as well as the feedback on grounded ice  in the coupled model simulations are very sensitive to the atmospheric forcing scenario applied.</p><p> </p><p> </p>

scholarly journals Modelling the response of the Lambert Glacier–Amery Ice Shelf system, East Antarctica, to uncertain climate forcing over the 21st and 22nd centuries

2014 ◽  
Vol 8 (3) ◽  
pp. 1057-1068 ◽  
Author(s):  
Y. Gong ◽  
S. L. Cornford ◽  
A. J. Payne
Keyword(s):  
Climate Model ◽  
Global Environmental Change ◽  
Ice Sheet ◽  
Adaptive Mesh ◽  
Ocean Model ◽  
East Antarctica ◽  
Ice Shelf ◽  
Amery Ice Shelf ◽  
Grounding Line ◽  
Lambert Glacier

Abstract. The interaction between the climate system and the large polar ice sheet regions is a key process in global environmental change. We carried out dynamic ice simulations of one of the largest drainage systems in East Antarctica: the Lambert Glacier–Amery Ice Shelf system, with an adaptive mesh ice sheet model. The ice sheet model is driven by surface accumulation and basal melt rates computed by the FESOM (Finite-Element Sea-Ice Ocean Model) ocean model and the RACMO2 (Regional Atmospheric Climate Model) and LMDZ4 (Laboratoire de Météorologie Dynamique Zoom) atmosphere models. The change of ice thickness and velocity in the ice shelf is mainly influenced by the basal melt distribution, but, although the ice shelf thins in most of the simulations, there is little grounding line retreat. We find that the Lambert Glacier grounding line can retreat as much as 40 km if there is sufficient thinning of the ice shelf south of Clemence Massif, but the ocean model does not provide sufficiently high melt rates in that region. Overall, the increased accumulation computed by the atmosphere models outweighs ice stream acceleration so that the net contribution to sea level rise is negative.

Representation of basal melting in idealised coupled ice sheet ocean models

2021 ◽  
Author(s):  
Chen Zhao ◽  
Rupert Gladstone ◽  
Ben Galton-Fenzi ◽  
David Gwyther
Keyword(s):  
Ocean Circulation ◽  
Critical Role ◽  
Ice Sheet ◽  
Ocean Model ◽  
Periodic Pattern ◽  
Regional Ocean Modeling System ◽  
Ice Shelf ◽  
Grounding Line ◽  
Ocean Models ◽  
Basal Melting

<p>The ocean-driven basal melting has important implications for the stability of ice shelves in Antarctic, which largely affects the ice sheet mass balance, ocean circulation, and subsequently global sea level rise. Due to the limited observations in the ice shelf cavities, the couple ice sheet ocean models have been playing a critical role in examining the processes governing basal melting. In this study we use the Framework for Ice Sheet-Ocean Coupling (FISOC) to couple the Elmer/Ice full-stokes ice sheet model and the Regional Ocean Modeling System (ROMS) ocean model to model ice shelf/ocean interactions for an idealised three-dimensional domain. Experiments followed the coupled ice sheet–ocean experiments under the first phase of the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP1). A periodic pattern in the simulated mean basal melting rates is found to be highly consistent with the maximum barotropic stream function and also the grounding line retreat row by row,  which is likely to be related with the gyre break down near the grounding line caused by some non-physical instability events from the ocean bottom. Sensitivity tests are carried out, showing that this periodic pattern is not sensitive to the choice of couple time intervals and horizontal eddy viscosities but sensitive to vertical resolution in the ocean model, the chosen critical water column thickness in the wet-dry scheme, and the tracer properties for the nudging dry cells at the ice-ocean interface boundary. Further simulations are necessary to better explain the mechanism involved in the couple ice-ocean system, which is very significant for its application on the realistic ice-ocean systems in polar regions.</p>

First results from coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module

2021 ◽  
Author(s):  
Moritz Kreuzer ◽  
Ronja Reese ◽  
Willem Huiskamp ◽  
Stefan Petri ◽  
Torsten Albrecht ◽  
...  
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
First Results ◽  
The Antarctic

<p>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 time scales of decades to a few centuries. To study global and long term interactions, we developed a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16 km and 3 degrees, respectively. We present first results from our coupled setup and discuss stability, feedbacks, and interactions of the Antarctic Ice Sheet and the global ocean system on millennial time scales.</p>

scholarly journals Ocean tides under the Filchner-Ronne Ice Shelf, Antarctica

1996 ◽  
Vol 23 ◽  
pp. 217-225 ◽  
Author(s):  
M. J. Smithson ◽  
A. V. Robinson ◽  
R. A. Flather
Keyword(s):  
Friction Coefficient ◽  
Ocean Model ◽  
Global Ocean ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Ocean Tides ◽  
Ice Shelf ◽  
Grounding Line ◽  
Preliminary Study ◽  
Tidal Constituents

A depth-averaged finite-difference numerical model has been used to make a preliminary study of the tides under the Filchner–Ronne Ice Shelf. Open boundary conditions were specified using the global ocean model of Schwiderski. Tidal constituents for the two principal semi-diurnal constituents M2 and S2, and the two principal diurnal constituents Ο1 and K1 were extracted from computed sea-surface elevations by harmonic analysis. Measured values near to the grounding line could only be reproduced satisfactorily by increasing the bottom friction coefficient under the ice to 50 times the open-ocean value. This destroys any agreement near the ice front or at pelagic sites. It is thought that a friction coefficient which varies with distance under the ice would be able to reproduce better all the available measurements. More tidal measurements are required to validate any model of the region with model experiments being used to help pinpoint possible sites for instrument deployment.

scholarly journals 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

2021 ◽  
Vol 14 (6) ◽  
pp. 3697-3714
Author(s):  
Moritz Kreuzer ◽  
Ronja Reese ◽  
Willem Nicholas Huiskamp ◽  
Stefan Petri ◽  
Torsten Albrecht ◽  
...  
Keyword(s):  
General Circulation ◽  
Ice Sheet ◽  
Ocean Model ◽  
Global Ocean ◽  
Cavity Model ◽  
Energy Fluxes ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Wide Range ◽  
The Antarctic

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.

scholarly journals Ocean tides under the Filchner-Ronne Ice Shelf, Antarctica

1996 ◽  
Vol 23 ◽  
pp. 217-225 ◽  
Author(s):  
M. J. Smithson ◽  
A. V. Robinson ◽  
R. A. Flather
Keyword(s):  
Friction Coefficient ◽  
Ocean Model ◽  
Global Ocean ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Ocean Tides ◽  
Ice Shelf ◽  
Grounding Line ◽  
Preliminary Study ◽  
Tidal Constituents

A depth-averaged finite-difference numerical model has been used to make a preliminary study of the tides under the Filchner–Ronne Ice Shelf. Open boundary conditions were specified using the global ocean model of Schwiderski. Tidal constituents for the two principal semi-diurnal constituents M2 and S2, and the two principal diurnal constituents Ο1 and K1 were extracted from computed sea-surface elevations by harmonic analysis. Measured values near to the grounding line could only be reproduced satisfactorily by increasing the bottom friction coefficient under the ice to 50 times the open-ocean value. This destroys any agreement near the ice front or at pelagic sites. It is thought that a friction coefficient which varies with distance under the ice would be able to reproduce better all the available measurements. More tidal measurements are required to validate any model of the region with model experiments being used to help pinpoint possible sites for instrument deployment.

scholarly journals Coupling framework (1.0) for the ice sheet model PISM (1.1.1) and the ocean model MOM5 (5.1.0) via the ice-shelf cavity module PICO

2020 ◽  
Author(s):  
Moritz Kreuzer ◽  
Ronja Reese ◽  
Willem Nicholas Huiskamp ◽  
Stefan Petri ◽  
Torsten Albrecht ◽  
...  
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Energy Fluxes ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Wide Range

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 time scales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16 km and 3 degree, respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the entire Antarctic Ice Sheet and the Earth system over time spans on 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 model is calculated by PICO from modeled ocean temperatures and salinities at the depth of the continental shelf and, vice versa, the resulting mass and energy fluxes from the melting at the ice-ocean interface are transferred to the ocean model. Mass and energy fluxes are shown to be conserved to machine precision across the considered model domains. The implementation is computationally efficient as it introduces only minimal overhead. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions and time scales between the ice and ocean model in a generic way, and can thus be adopted to a wide range of model setups.

scholarly journals Dynamical processes involved in the retreat of marine ice sheets

2001 ◽  
Vol 47 (157) ◽  
pp. 271-282 ◽  
Author(s):  
Richard C.A. Hindmarsh ◽  
E. Le Meur
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Grounding Line ◽  
Neutral Equilibrium ◽  
Generally True

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.

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