scholarly journals Thermally induced icequakes detected on blue ice areas of the East Antarctic ice sheet

2019 ◽  
Vol 60 (79) ◽  
pp. 45-56 ◽  
Author(s):  
Denis Lombardi ◽  
Irina Gorodetskaya ◽  
Guilhem Barruol ◽  
Thierry Camelbeeck
Keyword(s):  
Thermal State ◽  
Seismic Station ◽  
Ice Sheet ◽  
Leeward Side ◽  
Surface Cooling ◽  
Thermally Induced ◽  
Seismic Waveform ◽  
Dronning Maud Land ◽  
Temporal Occurrence ◽  
Waveform Pattern

ABSTRACTOver a year of seismic observations, ~5000 short duration icequakes were detected by a permanent broadband station installed at the Princess Elisabeth base, located ~180 km inland in eastern Dronning Maud Land, East-Antarctica. Icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events, totalizing ~1500 icequakes. The corresponding icequake locations point towards two distinct zones of outcropping blue ice areas (BIAs) located respectively at 4 and 1 km from the seismic station, both on the leeward side of a nunatak protruding through the ice sheet. The temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled, in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes. Further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change. Besides providing information on the ice fracture mechanics and rheology, investigations of thermal icequakes may be regarded as a ground-based proxy for the monitoring of the thermal state of BIAs, and characterization of ice-sheet ablation zones.

The effect of geothermal heat flux on the deglacial evolution of the Greenland ice sheet

2021 ◽  
Author(s):  
Parviz Ajourlou ◽  
François PH Lapointe ◽  
Glenn A Milne ◽  
Yasmina Martos
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Thermal State ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Sampling Procedure ◽  
Geophysical Research ◽  
Geothermal Heat ◽  
Input Field ◽  
Uncertainty Estimates

<p>Geothermal heat flux (GHF) is known to be an important control on the basal thermal state of an ice sheet which, in turn, is a key factor in governing how the ice sheet will evolve in response to a given climate forcing. In recent years, several studies have estimated GHF beneath the Greenland ice sheet using different approaches (e.g. Rezvanbehbahani et al., Geophysical Research Letters, 2017; Martos et al., Geophysical Research Letters, 2018; Greve, Polar Data Journal, 2019). Comparing these different estimates indicates poor agreement and thus large uncertainty in our knowledge of this important boundary condition for modelling the ice sheet. The primary aim of this study is to quantify the influence of this uncertainty on modelling the past evolution of the ice sheet with a focus on the most recent deglaciation. We build on past work that considered three GHF models (Rogozhina et al., 2011) by considering over 100 different realizations of this input field. We use the uncertainty estimates from Martos et al. (Geophysical Research Letters, 2018) to generate GHF realisations via a statistical sampling procedure. A sensitivity analysis using these realisations and the Parallel Ice Sheet Model (PISM, Bueler and Brown, Journal of Geophysical Research, 2009) indicates that uncertainty in GHF has a dramatic impact on both the volume and spatial distribution of ice since the last glacial maximum, indicating that more precise constraints on this boundary condition are required to improve our understanding of past ice sheet evolution and, consequently, reduce uncertainty in future projections.</p>

scholarly journals The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere–sea-ice–ocean model

2013 ◽  
Vol 9 (4) ◽  
pp. 1629-1643 ◽  
Author(s):  
M. Blaschek ◽  
H. Renssen
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Early Holocene ◽  
Surface Cooling ◽  
Holocene Climate ◽  
Nordic Seas ◽  
The Holocene ◽  
Holocene Thermal Maximum ◽  
Thermal Maximum ◽  
The Impact

Abstract. The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

scholarly journals A Numerical Study of Plane Ice-Sheet Flow

1986 ◽  
Vol 32 (111) ◽  
pp. 139-160 ◽  
Author(s):  
K. Hutter ◽  
S. Yakowitz ◽  
F. Szidarovszky
Keyword(s):  
Surface Temperature ◽  
Thermal State ◽  
Numerical Study ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Tangential Velocity ◽  
Rigid Base ◽  
Geothermal Heat ◽  
Functional Relations ◽  
External Forcings

AbstractThe plane steady flow of a grounded ice sheet is numerically analysed using the approximate model of Morland or Hutter. In this, the ice behaves as a non-linear viscous fluid with a strongly temperature-dependent rate factor, and ice sheets are assumed to be long and shallow. The climate is assumed to be prescribed via the accumulation/ablation distribution and the surface temperature, both of which are functions of position and unknown height. The rigid base exerts external forcings via the normal heat flow, the geothermal heat, and a given basal sliding condition connecting the tangential velocity, tangential traction, and normal traction. The functional relations are those of Morland (1984) or motivated by his work. We use equations in his notation.The governing equations and boundary conditions in dimensionless form are briefly stated and dimensionless variables are related to their physical counterparts. The thermo-mechanical parabolic boundary-value problem, found to depend on physical scales, constitutive properties, and external forcing functions, has been numerically solved. For reasons of stability, the numerical integration must proceed from the ice divide towards the margin, which requires a special analysis of the ice divide. We present this analysis and then describe the versatility and limitations of the constructed computer code.Results of extensive computations are shown. In particular, we prove that the Morland–Hutter model for ice sheets is only applicable when sliding is sufficiently large (satisfying inequality (30)). In the range of the validity of this inequality, it is then demonstrated that of all physical scaling parameters only a single π-product influences the geometry and the flow within the ice sheet. We analyse the role played by advection, diffusion, and dissipation in the temperature distribution, and discuss the significance of the rheological non-linearities. Variations of the external forcings, such as accumulation/ablation conditions, free surface temperature, and geothermal heat, demonstrate the sensitivity of the ice-sheet geometry to accumulation conditions and the robustness of the flow to variations in the thermal state. We end with a summary of results and a critical review of the model.

scholarly journals Does a difference in ice sheets between Marine Isotope Stages 3 and 5a affect the duration of stadials?

2021 ◽  
Author(s):  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Akira Oka ◽  
Takahito Mitsui ◽  
Fuyuki Saito
Keyword(s):  
Sea Ice ◽  
Recovery Time ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Surface Cooling ◽  
Glacial Ice ◽  
Formation Region ◽  
Background Climate ◽  
The Impact

Abstract. Glacial periods undergo frequent climate shifts between warm interstadials and cold stadials on a millennial time-scale. Recent studies have shown that the duration of these climate modes varies with the background climate; a colder background climate and lower CO2 generally results in a shorter interstadial and a longer stadial through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, the duration of stadials was shorter during the Marine Isotope Stage 3 (MIS3) compared with MIS5, despite the colder climate in MIS3, suggesting potential control from other climate factors on the duration of stadials. In this study, we investigated the role of glacial ice sheets. For this purpose, freshwater hosing experiments were conducted with an atmosphere–ocean general circulation model under MIS5a, MIS3 and MIS3 with MIS5a ice sheet conditions. The impact of ice sheet differences on the duration of the stadials was evaluated by comparing recovery times of the AMOC after freshwater forcing was reduced. Hosing experiments showed a slightly shorter recovery time of the AMOC in MIS3 compared with MIS5a, which was consistent with ice core data. We found that larger glacial ice sheets in MIS3 shortened the recovery time. Sensitivity experiments showed that stronger surface winds over the North Atlantic shortened the recovery time by increasing the surface salinity and decreasing the sea ice amount in the deepwater formation region, which set favourable conditions for oceanic convection. In contrast, we also found that surface cooling by larger ice sheets tended to increase the recovery time of the AMOC by increasing the sea ice thickness over the deepwater formation region. Thus, this study suggests that the larger ice sheet in MIS3 compared with MIS5a could have contributed to the shortening of stadials in MIS3, despite the climate being colder than that of MIS5a, when the effect of surface wind played a larger role.

scholarly journals Late Weichselian thermal state at the base of the Scandinavian Ice Sheet

2019 ◽  
Author(s):  
Dmitry Y. Demezhko ◽  
Anastasia A. Gornostaeva ◽  
Alexander N. Antipin
Keyword(s):  
Thermal State ◽  
Ice Sheet ◽  
Ground Surface ◽  
Substantial Part ◽  
Temperature Pattern ◽  
Glacial Cycle ◽  
Surface Temperatures ◽  
Scandinavian Ice Sheet ◽  
Late Weichselian ◽  
The Last Glacial

Abstract. Geothermal estimates of the ground surface temperatures for the last glacial cycle in Northern Europe has been analyzed. During the Middle and Late Weichselian (55–12 kyr BP) a substantial part of this area was covered by the Scandinavian Ice Sheet. The analysis of geothermal data has allowed reconstructing limits of the ice sheet extension and its basal thermal state in the Late Weichselian. Ground surface temperatures outside the ice sheet were extremely low (from −8 to −18 °C). Within the ice sheet, there were both thawed and frozen zones. The revealed temperature pattern is generally consistent with the modern one for the ground surface temperatures in Greenland that makes it possible to consider these ice sheets as analogues. The anomalous climatically induced surface heat flux and orbital insolation of the Earth varied consistently outside the glaciation and independently within the limits of the ice sheet.

scholarly journals Impact of mid-glacial ice sheets on deep ocean circulation and global climate: Role of surface cooling on the AMOC

2020 ◽  
Author(s):  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Akira Oka
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Global Climate ◽  
Surface Wind ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Strengthening Effect ◽  
Surface Cooling ◽  
Glacial Ice

Abstract. This study explores the effect of southward expansion of mid-glacial ice sheets on the global climate and the Atlantic meridional overturning circulation (AMOC), as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 and 5a are performed with an atmosphere-ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 °C and 2.2 °C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3 % in MIS3, whereas it is enhanced by 16 % in MIS5a, both of which are consistent with a reconstruction. Sensitivity experiments extracting the effect of the expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 °C, contributing to about 40 % of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 °C over the Southern Ocean as a result of colder North Atlantic deep water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles, and hence compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by the two competing effects, surface wind and surface cooling. The relative strength of surface wind and surface cooling depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.

scholarly journals Distribution of Reflected Power From the Bed by Radio Echo-Sounding in the Shirase Glacier Drainage Area, East Dronning Maud Land, Antarctica

1989 ◽  
Vol 12 ◽  
pp. 124-126
Author(s):  
Hirokazu Ohmae ◽  
Fumihiko Nishio ◽  
Shinji Mae
Keyword(s):  
Drainage Basin ◽  
Ice Sheet ◽  
Ice Flow ◽  
Boundary Area ◽  
Radio Echo Sounding ◽  
Dronning Maud Land ◽  
Reflected Power ◽  
Basal Shear ◽  
Reflection Intensity ◽  
Echo Sounding

A large part of the area of the Shirase Glacier drainage basin has been surveyed by airborne (operating frequency: 179 MHz) and ground-based (60 MHz) radio echo-sounding to define the bedrock topography and to investigate the condition of bed/ice interface since 1982.It is shown that the reflection intensity from the bed, which is corrected for attenuation in the ice sheet, has a higher value for reflection intensity in the down-stream area of Shirase Glacier than in the up-stream area. The area of strongest intensity of reflection from the bed coincides with the area for which the calculated temperature at the bed is above −1°C. The boundary area between the highest and lowest values of corrected reflected intensity corresponds to the area of decreasing basal shear stress. It is found that the distribution of high corrected reflection intensity corresponds to the area of thinning of the ice sheet, which has been measured by ice-flow observation in the Shirase Glacier drainage basin.

scholarly journals Investigating Controls on the Formation and Distribution of Wintertime Storage of Water in Supraglacial Lakes

2020 ◽  
Vol 8 ◽  
Author(s):  
Derrick Julius Lampkin ◽  
Lora Koenig ◽  
Casey Joseph ◽  
Jason Eric Box
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lake Area ◽  
Channel Networks ◽  
Supraglacial Lakes ◽  
Lake Model ◽  
Temporal Occurrence ◽  
Atmospheric Factors ◽  
And Behavior ◽  
Percolation Zone

Supraglacial lakes over the Greenland Ice Sheet can demonstrate multi-model drainage states. Lakes can demonstrate incomplete drainage, where residual melt can become buried under ice and snow and survive throughout the winter. We evaluate atmospheric factors that influence the propensity for the formation of buried lakes over the ice sheet. We examine the spatial and temporal occurrence and behavior of buried lakes over the Jakobshavn Isbrae and Zachariae Isstrøm outlet basins and assess the magnitude of insolation necessary to preserve melt water using a numerical lake model from 2009 to 2012. Buried lakes tend to occur at higher elevations within the ablation zone and those present at elevations > 1000 m tend to reoccur over several seasons. Lakes without buried water are relatively small (∼1 km2), whereas lakes with buried water are larger (∼6–10 km2). Lake area is correlated with the number of seasons sub-surface water persists. Buried lakes are relatively deep and associated with complex supraglacial channel networks. Winter stored water could be a precursor to the formation of supraglacial channels. Simulations of the insulation potential of accumulated snow and ice on the surface of lakes indicate substantial regional differences and inter-annual variability. With the possibility of inland migration of supraglacial lakes, buried lakes could be important in the evolution of ablation/percolation zone hydrology.

scholarly journals Simulation of the Antarctic ice sheet with a three-dimensional polythermal ice-sheet model, in support of the EPICA project. II. Nested high-resolution treatment of Dronning Maud Land, Antarctica

2000 ◽  
Vol 30 ◽  
pp. 69-75 ◽  
Author(s):  
A. Savvin ◽  
R. Greve ◽  
R. Calov ◽  
B. Mügge ◽  
K. Hutter
Keyword(s):  
High Resolution ◽  
Shear Deformation ◽  
Ice Core ◽  
Geographic Origin ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Climate History ◽  
Antarctic Ice Sheet ◽  
Drill Site ◽  
Dronning Maud Land

AbstractThe modern dynamic and thermodynamic state of the entire Antarctic ice sheet is computed for a 242 200 year paleoclimatic simulation with the three-dimensional polythermal ice-sheet model SICOPOLIS. The simulation is driven by a climate history derived from the Vostok ice core and the SPECMAP sea-level record. In a 872 km × 436 km region in western Dronning Maud Land (DML), where a deep ice core is planned for EPICA, new high-resolution ice-thickness data are used to compute an improved bedrock topography and a locally refined numerical grid is applied which extends earlier work (Calov and others, 1998). The computed fields of basal temperature, age and shear deformation, together with the measured accumulation rates, give valuable information for the selection of a drill site suitable for obtaining a high-resolution climate record for the last glacial cycle. Based on these results, a possible drill site at 73°59′ S, 00°00′ E is discussed, for which the computed depth profiles of temperature, age, velocity and shear deformation are presented. The geographic origin of the ice column at this position extends 320 km upstream and therefore does not leave the DML region.

scholarly journals Climate and the Initiation of Maritime Ice Sheets

1990 ◽  
Vol 14 ◽  
pp. 232-237 ◽  
Author(s):  
Antony Payne ◽  
David Sugden
Keyword(s):  
Regional Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Lower Latitude ◽  
Atmospheric Moisture ◽  
Glacial Cycle ◽  
Surface Cooling ◽  
Loch Lomond ◽  
Westerly Winds ◽  
Comparison Of The Results

The lower latitude extension of polar water during Quaternary glaciations has two opposing effects on the mass balances of adjacent maritime ice sheets. Cooler air temperatures reduce ablation and increase the fraction of precipitation falling as snow, but also lead to reduced atmospheric moisture content and reduced precipitation. The effects of these contrasting processes on ice-sheet initiation are investigated using a coupled ice-sheet-atmospheric moisture model of the Loch Lomond ice sheet in Scotland (10 000 a B.P.). There is a delicate balance between the degree of cooling required to initiate ice accumulation and that which restricts the flow of moisture over the area. At the regional scale of Scotland, the combined effects of orographic enhancement and the inherent feedback between the rising ice-surface elevation and increasing mass balance are dominant, and ice-sheet growth accelerates. Comparison of the results from models using different wind directions suggests that south-westerly winds were prevalent during the Loch Lomond glaciation in contrast to the dominant westerly winds of the present day. The modelling experiments demonstrate the sensitivity and complexity of the links between ocean surface cooling and ice-sheet growth, particularly at the early stages of a glacial cycle.

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