scholarly journals Individual and combined effects of ice sheets and precession on MIS-13 climate

2009 ◽  
Vol 5 (2) ◽  
pp. 229-243 ◽  
Author(s):  
Q. Z. Yin ◽  
A. Berger ◽  
M. Crucifix
Keyword(s):  
Global Climate ◽  
Wave Train ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Summer Precipitation ◽  
East China ◽  
Thermal Contrast ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. An Earth System Model of Intermediate Complexity is used to investigate the role of insolation and of the size of ice sheets on the regional and global climate of marine isotope stage (MIS) 13. The astronomical forcing is selected at two dates with opposite precession, one when northern hemisphere (NH) summer occurs at perihelion (at 506 ka (1 ka=1000 years) BP), and the other when it occurs at aphelion (at 495 ka BP). Five different volumes of the Eurasian ice sheet (EA) and North American ice sheet (NA), ranging from 0 to the Last Glacial Maximum (LGM) one, are used. The global cooling due to the ice sheets is mainly related to their area, little to their height. The regional cooling and warming anomalies caused by the ice sheets intensify with increasing size. Precipitation over different monsoon regions responds differently to the size of the ice sheets. Over North Africa and India, precipitation decreases with increasing ice sheet size due to the southward shift of the Intertropical Convergence Zone (ITCZ), whatever the astronomical configuration is. However, the situation is more complicated over East Asia. The ice sheets play a role through both reducing the land/ocean thermal contrast and generating a wave train which is topographically induced by the EA ice sheet. This wave train contributes to amplify the Asian land/ocean pressure gradient in summer and finally reinforces the precipitation. The presence of this wave train depends on the combined effect of the ice sheet size and insolation. When NH summer occurs at perihelion, the EA is able to induce this wave train whatever its size is, and this wave train plays a more important role than the reduction of the land/ocean thermal contrast. Therefore, the ice sheets reinforce the summer precipitation over East China whatever their sizes are. However, when NH summer occurs at aphelion, there is a threshold in the ice volume beyond which the wave train is not induced anymore. Therefore, below this threshold, the wave train effect is dominant and the ice sheets reinforce precipitation over East China. Beyond this threshold, the ice sheets reduce the precipitation mainly through reducing the land/ocean thermal contrast.

scholarly journals Individual and combined effects of ice sheets and precession on MIS-13 climate

2009 ◽  
Vol 5 (1) ◽  
pp. 557-593
Author(s):  
Q. Z. Yin ◽  
A. Berger ◽  
M. Crucifix
Keyword(s):  
Northern Hemisphere ◽  
Asian Summer Monsoon ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Summer Precipitation ◽  
East China ◽  
Asian Summer ◽  
The Last Glacial

Abstract. Simulations with an Earth System Model of Intermediate Complexity are made to investigate the role of insolation and the size of ice sheets on the regional and global climate for marine isotope stage (MIS) 13. The astronomical forcing is selected at two dates with opposite precession, one when Northern Hemisphere summer (NHS) occurs at perihelion (at 506 ka BP) and the other when it occurs at aphelion (at 495 ka BP). Experiments with five different volumes of the Eurasian and North American ice sheets (ranging from 0 to the Last Glacial Maximum one) are done under these two astronomical conditions. When NHS is at perihelion, the Earth is warmer, the seasonal contrast in Northern (Southern) Hemisphere is larger (smaller) and summer precipitation in Northern Hemisphere monsoon regions is more abundant than when it is at aphelion. The global cooling due to the ice sheets is mainly related to the ice sheet area, little to their height. The regional cooling and warming anomalies caused by the ice sheets get intensified with increasing ice sheet size. The cooling is different whether the NHS occurs at aphelion or at perihelion. Precipitation over different monsoon regions responds differently to the size of the ice sheets. Over North Africa, the ice sheets always reduce precipitation, larger the size less the precipitation. Over East China, when NHS is at perihelion, the ice sheets reinforce the summer precipitation whatever their sizes. But when NHS is at aphelion, there is a threshold in the ice volume beyond which the ice sheets start to reduce the precipitation over East China. This underlies the importance of insolation in shaping the ice sheet impact on the precipitation over the East Asian Summer Monsoon (EASM) region.

scholarly journals Ice-sheet mass balance at the Last Glacial Maximum from the GENESIS version 2 global climate model

1997 ◽  
Vol 25 ◽  
pp. 250-258 ◽  
Author(s):  
Starley L. Thompson ◽  
David Pollard
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Mass ◽  
Ice Sheet Mass Balance ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractAt the Last Glacial Maximum (LGM) about 21000 years ago (21 ka BP), the overall mass balance of the Laurentide and Eurasian ice sheets should have been close to zero, since their rate of change of total ice volume was approximately zero at that time. The surface mass balance should have been zero or positive to balance any iceberg/iceshelf discharge and basal melting, but could not have been strongly negative. In principle this can be tested by global climate model (GCM) simulations with prescribed ice-sheet extents and topography.We describe results from a suite of 21 ka BP simulations using a new GCM (GENESIS version 2.0.a), with sea-surface temperatures (SSTs) prescribed from GLIMAP (1981) and predicted by a mixed-layer ocean model, and with ice sheets prescribed from both the ICE-4G (Peltier, 1994) and CLIMAP (1981) reconstructions. This GCM is well suited for ice-sheet mass-balance studies because (i) the surface can be represented at a finer resolution than the atmospheric GCM, (ii) an elevation correction accounts for spectral distortions of the atmospheric GCM topography, (iii) a simple post-processing correction for the refreezing of meltwater is applied, and (iv) the model's precipitation and mass balances for present-day Greenland and Antarctica are realistic. However, for all reasonable combinations of SSTs and ice-sheet configurations, the predicted annual surface mass balances of the LGM Laurentide and Eurasian ice sheets are implausibly negative. Possible reasons for this discrepancy are discussed, including increased ice-age aerosols, higher CLIMAP-like ice-sheet profiles in the few thousand years preceding the LGM, and a surface of the southern Laurentide just before the LGM to produce fleetingly the ICE-4G profile at 21 ka BP.

Exploring the complex uncertainties in coupled climate-ice simulations of the Last Glacial Maximum

2021 ◽  
Author(s):  
Lauren Gregoire ◽  
Niall Gandy ◽  
Lachlan Astfalck ◽  
Robin Smith ◽  
Ruza Ivanovic ◽  
...  
Keyword(s):  
Mass Balance ◽  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Sea Surface ◽  
Surface Mass ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Simulating the co-evolution of climate and ice-sheets during the Quaternary is key to understanding some of the major abrupt changes in climate, ice and sea level. Indeed, events such as the Meltwater pulse 1a rapid sea level rise and Heinrich, Dansgaard–Oeschger and the 8.2 kyr climatic events all involve the interplay between ice sheets, the atmosphere and the ocean. Unfortunately, it is challenging to simulate the coupled Climate-Ice sheet system because small biases, errors or uncertainties in parts of the models are strongly amplified by the powerful interactions between the atmosphere and ice (e.g. ice-albedo and height-mass balance feedbacks). This leads to inaccurate or even unrealistic simulations of ice sheet extent and surface climate. To overcome this issue we need some methods to effectively explore the uncertainty in the complex Climate-Ice sheet system and reduce model biases. Here we present our approach to produce ensemble of coupled Climate-Ice sheet simulations of the Last Glacial maximum that explore the uncertainties in climate and ice sheet processes.</p><p>We use the FAMOUS-ICE earth system model, which comprises a coarse-resolution and fast general circulation model coupled to the Glimmer-CISM ice sheet model. We prescribe sea surface temperature and sea ice concentrations in order to control and reduce biases in polar climate, which strongly affect the surface mass balance and simulated extent of the northern hemisphere ice sheets. We develop and apply a method to reconstruct and sample a range of realistic sea surface temperature and sea-ice concentration spatio-temporal field. These are created by merging information from PMIP3/4 climate simulations and proxy-data for sea surface temperatures at the Last Glacial Maximum with Bayes linear analysis. We then use these to generate ensembles of FAMOUS-ice simulations of the Last Glacial maximum following the PMIP4 protocol, with the Greenland and North American ice sheets interactively simulated. In addition to exploring a range of sea surface conditions, we also vary key parameters that control the surface mass balance and flow of ice sheets. We thus produce ensembles of simulations that will later be used to emulate ice sheet surface mass balance.  </p>

scholarly journals Ice-sheet mass balance during the last glacial maximum

1997 ◽  
Vol 25 ◽  
pp. 145-152 ◽  
Author(s):  
Gilles Ramstein ◽  
Adeline Fabre ◽  
Sophie Pinot ◽  
Catherine Ritz ◽  
Sylvie Joussaume
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
General Circulation Models ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Intercomparison Project ◽  
The Last Glacial Maximum ◽  
The Last Glacial

In the framework of the Paleoclimate Modelling Intercomparison Project (PMIP), simulations of the Last Glacial Maximum (LGM) have- been performed. More than 10 different atmospheric general circulation models (AGCMs) have been used with the same boundary conditions: sea-surface temperatures prescribed by CLIMAP (1981), ice-sheet reconstruction provided by Peltier (1994), change in insolation, and reduced CO2 content. One of the major questions is to investigate whether the simulations of the LGM are in equilibrium with the prescribed ice-sheet reconstruction. To answer this question, we have used two different approaches. First, we analyze the results of a sel of LGM simulations performed with different versions of the Laboratoire de Meteorolo-gie Dynamique (LMD) AGCM and study the hydrologic and snow- budgets over the Laurcntide and Fennoscandian ice sheets. Second, we use the AGCM outputs to force an ice-sheet model in order to investigate its ability to maintain the ice sheets as reconstructed by CLIMAP (1981) or Peltier (1994).

scholarly journals A three-dimensional climate—ice-sheet model applied to the Last Glacial Maximum

1997 ◽  
Vol 25 ◽  
pp. 333-339 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’siobbel
Keyword(s):  
Last Glacial Maximum ◽  
Northern Hemisphere ◽  
Climate Model ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A quasi-three-dimensional (3-D) climate model (Sellers, 1983) was used to simulate the climate of the Last Glacial Maximum (LGM) in order to provide climatic input for the modelling of the Northern Hemisphere ice sheets. The climate model is basically a coarse-gridded general circulation (GCM) with simplified dynamics, and was subject to appropriate boundary conditions for ice-sheet elevation, atmospheric CO2concentration and orbital parameters. When compared with the present-daysimulation, the simulated climate at the Last Glacial Maximum is characterized by a global annual cooling of 3.5°C and a reduction in global annualprecipitation of 7.5%, which agrees well with results from other, more complex GCMs. Also the patterns of temperature change compare fairly with mostother GCM results, except for a smaller cooling over the North Atlantic and the larger cooling predicted for the summer rather than for the winter over Eurasia.The climate model is able to simulate changes in Northern Hemisphere tropospheric circulation, yielding enhanced westerlies in the vicinity of the Laurentide and Eurasian ice sheets. However, the simulated precipitation patterns are less convincing, and show a distinct mean precipitation increase over the Laurentide ice sheet. Nevertheless, when using the mean-monthly fields of LGM minus present-day anomalies of temperature and precipitation rate to drive a three-dimensional thermomechanical ice-sheet model, it was demonstrated that within realistic bounds of the ice-flow and mass-balance parameters, veryreasonable reconstructions of the Last Glacial Maximum ice sheets could be obtained.

Water vapour, CO 2 and insolation over the last glacial-interglacial cycles

1993 ◽  
Vol 341 (1297) ◽  
pp. 253-261 ◽  
Keyword(s):  
Water Vapour ◽  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Last Glacial ◽  
Ice Volume ◽  
Water Vapour Feedback ◽  
Astronomical Forcing ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A two-dimensional model which links the atmosphere, the mixed layer of the ocean, the sea ice, the continents, the ice sheets and their underlying bedrock has been used to test the Milankovitch theory over the last two glacial-interglacial cycles. A series of sensitivity analyses have allowed us to understand better the internal mechanisms which drive the simulated climate system and in particular the feedbacks related to surface albedo and water vapour. It was found that orbital variations alone can induce, in such a system, feedbacks sufficient to generate the low frequency p art of the climatic variations over the last 122 ka. These simulated variations at the astronomical timescale are broadly in agreement with reconstructions of ice-sheet volume and of sea level independently obtained from geological data. Imperfections in the stimulated climate were the insufficient southward extent of the ice sheets and the too small hemispheric cooling at the last glacial maximum . These deficiencies were partly remedied in a further experiment by using the time-dependent atmospheric CO2 concentration given by the Vostok ice core in addition to the astronomical forcing. In this transient simulation, 70% of the Northern Hemisphere ice volume is related to the astronomical forcing and the related changes in the albedo, the rem aining 30% being due to the CO 2 changes. Analysis of the processes involved shows that variations of ablation are more important for the ice-sheet response than are variations of snow precipitation. A key mechanism in the deglaciation after the last glacial maxim um appears to be the ‘ageing’ of snow which significantly decreases its albedo. The other factors which play an important role are ice-sheet altitude, insolation, taiga cover, ice-albedo feedback, ice-sheet configuration (‘continentality’ and ‘desert’ effect), isostatic rebound, CO 2 changes and tem perature-water vapour feedback. Numerical experiments have also been carried out with a one-dimensional radiative-convective model in order to quantify the influence of the CO 2 changes and of the water vapour feedback on the climate evolution of the Northern Hemisphere over the last 122 ka. Results of these experiments indicate that 67% of the simulated cooling at the last glacial maximum can be attributed to the astronomical forcing and the subsequent surface albedo increase, the remaining 33% being associated with the reduced CO 2 concentration. Moreover, the water vapour feedback explains 40% of the simulated cooling in all the experiments done. The transient response of the clim ate system to both the astronomical and CO 2 forcing was also simulated by the LLN (Louvain-la-Neuve) 2.5-dimensional model over the two last glacial-interglacial cycles. It is particularly significant that spectral analysis of the simulated Northern Hemisphere global ice volume variations reproduces correctly the relative intensity of the peaks at the orbital frequencies. Except for variations with timescales shorter than 5 ka, the simulated long-term variations of total ice volume are comparable to that reconstructed from deep sea cores. For example, the model simulates glacial maxima of similar amplitudes at 134 ka BP and 15 ka BP, followed by abrupt deglaciations. The complete deglaciation of the three main Northern Hemisphere ice sheets, which is simulated around 122 ka BP, is in partial disagreement with reconstructions indicating that the Greenland ice sheet survived during the Eemian interglacial. The continental ice volume variations during the last 122 ka of the 200 ka simulation are, however, not significantly affected by this shortcoming.

scholarly journals Ice-sheet mass balance during the last glacial maximum

1997 ◽  
Vol 25 ◽  
pp. 145-152 ◽  
Author(s):  
Gilles Ramstein ◽  
Adeline Fabre ◽  
Sophie Pinot ◽  
Catherine Ritz ◽  
Sylvie Joussaume
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
General Circulation Models ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Intercomparison Project ◽  
The Last Glacial Maximum ◽  
The Last Glacial

In the framework of the Paleoclimate Modelling Intercomparison Project (PMIP), simulations of the Last Glacial Maximum (LGM) have- been performed. More than 10 different atmospheric general circulation models (AGCMs) have been used with the same boundary conditions: sea-surface temperatures prescribed by CLIMAP (1981), ice-sheet reconstruction provided by Peltier (1994), change in insolation, and reduced CO2 content. One of the major questions is to investigate whether the simulations of the LGM are in equilibrium with the prescribed ice-sheet reconstruction. To answer this question, we have used two different approaches. First, we analyze the results of a sel of LGM simulations performed with different versions of the Laboratoire de Meteorolo-gie Dynamique (LMD) AGCM and study the hydrologic and snow- budgets over the Laurcntide and Fennoscandian ice sheets. Second, we use the AGCM outputs to force an ice-sheet model in order to investigate its ability to maintain the ice sheets as reconstructed by CLIMAP (1981) or Peltier (1994).

scholarly journals Exploring the impact of atmospheric forcing and basal boundary conditions on the simulation of the Antarctic ice sheet at the Last Glacial Maximum

2020 ◽  
Author(s):  
Javier Blasco ◽  
Jorge Alvarez-Solas ◽  
Alexander Robinson ◽  
Marisa Montoya
Keyword(s):  
Boundary Conditions ◽  
Continental Shelf ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Volume ◽  
Basal Friction ◽  
The Antarctic ◽  
Continental Shelf Break ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Little is known about the distribution of ice in the Antarctic ice sheet (AIS) during the Last Glacial Maximum (LGM). Whereas marine and terrestrial geological data indicate that the grounded ice advanced to a position close to the continental-shelf break, the total ice volume is unclear. Glacial boundary conditions are potentially important sources of uncertainty, in particular basal friction and climatic boundary conditions. Basal friction exerts a strong control on the large-scale dynamics of the ice sheet and thus affects its size, and is not well constrained. Glacial climatic boundary conditions determine the net accumulation and ice temperature, and are also poorly known. Here we explore the effect of the uncertainty in both features on the total simulated ice storage of the AIS at the LGM. For this purpose we use a hybrid ice-sheet-shelf model that is forced with different basal-drag choices and glacial background climatic conditions obtained from the LGM ensemble climate simulations of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). For a wide range of plausible basal friction configurations, the simulated ice dynamics vary widely but all simulations produce fully extended ice sheets towards the continental-shelf break. More dynamically active ice sheets correspond to lower ice volumes, while they remain consistent with the available constraints on ice extent. Thus, this work points to the possibility of an AIS with very active ice streams during the LGM. In addition, we find that the surface boundary temperature field plays a crucial role in determining the ice extent through its effect on viscosity. For ice sheets of a similar extent and comparable dynamics, we find that the precipitation field determines the total AIS volume. However, precipitation is deeply uncertain. Climatic fields simulated by climate models show more precipitation in coastal regions than a spatially uniform anomaly, which can lead to larger ice volumes. We strongly support using these paleoclimatic fields to simulate and study the LGM and potentially other time periods like the Last Interglacial. However, their accuracy must be assessed as well, as differences between climate model forcing lead to a range in the simulated ice volume and extension of about 6 m sea-level equivalent and one million km2.

scholarly journals Climate response to freshwater perturbations in Northern or Southern Hemispheres at the last glacial inception, the last glacial maximum and the present-day

2010 ◽  
Vol 6 (3) ◽  
pp. 1077-1110
Author(s):  
G. Philippon-Berthier ◽  
G. Ramstein ◽  
S. Charbit ◽  
C. Ritz
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Freshwater Inputs ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Freshwater inputs in North Atlantic due to huge surge of icebergs coming from ice sheets might be responsible for drastic regional and global abrupt climatic transitions. To quantify the sensitivity of climate system to these freshwater inputs, we use a model of intermediate complexity coupled to ice-sheet models for both Northern and Southern Hemispheres. We mimic the Dansgaard-Oeschger and Heinrich Events by forcing the model with appropriate freshwater perturbations. The originality of this study is to investigate with such a global model, the response of the coupled system to freshwater discharges for three different climate contexts, the Last Glacial Maximum (LGM), the Last Glacial Inception (LGI) and the present-day (PD) climates. We first show that in all climate contexts, the North Atlantic circulation is more sensitive to freshwater flux when ice sheets are present. Secondly, the "seesaw" mechanism occurs mostly for the North Atlantic freshwater perturbation whereas it remains very weak for the Southern Ocean freshwater release. Moreover, this seesaw is generally enhanced when ice sheets are interactive. The most striking result is that the freshwater perturbation amplifies the inception of the North American ice sheet at LGI the sea-level drop associated is significantly increased and in a much better agreement with data.

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