scholarly journals Glaciological characteristics in the Dome Fuji region and new assessment for 1.5 Ma old ice

2017 ◽  
Author(s):  
Nanna B. Karlsson ◽  
Tobias Binder ◽  
Graeme Eagles ◽  
Veit Helm ◽  
Frank Pattyn ◽  
...  
Keyword(s):  
Ice Core ◽  
Radar Data ◽  
Initial Assessment ◽  
Airborne Radar ◽  
Depth Information ◽  
Viable Option ◽  
Geothermal Heat ◽  
Ice Core Record ◽  
Complex Landscape ◽  
The Antarctic

Abstract. A key objective in palaeo-climatology is the retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma. The identification of a suitable Antarctic site requires sufficient knowledge of the subglacial landscape beneath the Antarctic Ice Sheet. Here, we present new ice thickness information from the Dome Fuji region, East Antarctica, based on airborne radar surveys conducted during the 2014/15 and 2016/17 southern summers. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results for obtaining an old ice core show that especially the region immediately south of Dome Fuji station persists as a good candidate site. An initial assessment of basal conditions revealed the existence several wet-based areas. Further radar data analysis shows overall high continuity of layer stratigraphy in the region. This indicates that extending the age-depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option.

scholarly journals Glaciological characteristics in the Dome Fuji region and new assessment for “Oldest Ice”

2018 ◽  
Vol 12 (7) ◽  
pp. 2413-2424 ◽  
Author(s):  
Nanna B. Karlsson ◽  
Tobias Binder ◽  
Graeme Eagles ◽  
Veit Helm ◽  
Frank Pattyn ◽  
...  
Keyword(s):  
Ice Core ◽  
Radar Data ◽  
Initial Assessment ◽  
Airborne Radar ◽  
Depth Information ◽  
Geothermal Heat ◽  
Ice Core Record ◽  
Complex Landscape ◽  
Subglacial Lakes ◽  
The Antarctic

Abstract. A key objective in palaeo-climatology is the retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma. The identification of a suitable Antarctic site requires sufficient knowledge of the subglacial landscape beneath the Antarctic Ice Sheet. Here, we present new ice thickness information from the Dome Fuji region, East Antarctica, based on airborne radar surveys conducted during the 2014/15 and 2016/17 southern summers. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results show that especially the region immediately south of Dome Fuji station persists as a good candidate site for obtaining an old ice core. An initial assessment of basal conditions revealed the existence of what appears to be subglacial lakes. Further radar data analysis shows overall high continuity of layer stratigraphy in the region. This indicates that extending the age–depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option.

scholarly journals Antarctic firn compaction rates from repeat-track airborne radar data: II. Firn model evaluation

2015 ◽  
Vol 56 (70) ◽  
pp. 167-174 ◽  
Author(s):  
S.R.M. Ligtenberg ◽  
B. Medley ◽  
M.R. Van Den Broeke ◽  
P. Kuipers Munneke
Keyword(s):  
Ice Sheet ◽  
Radar Data ◽  
Airborne Radar ◽  
Model Resolution ◽  
West Antarctica ◽  
Volume Changes ◽  
Layer Depth ◽  
Direct Measurements ◽  
Ice Sheet Mass Balance ◽  
The Antarctic

AbstractThe thickness and density of the Antarctic firn layer vary considerably in time and space, thereby contributing to ice-sheet volume and mass changes. Distinguishing between these mass and volume changes is important for ice-sheet mass-balance studies. Evolution of firn layer depth and density is often modeled, because direct measurements are scarce. Here we directly compare modeled firn compaction rates with observed rates obtained from repeat-track airborne radar data over a 2 year interval (2009–11) in West Antarctica. Spatially, the observed compaction rates exhibit significant variability, but when averaged to scales comparable to the model resolution (20–50 km), the measurements and model results qualitatively agree. A colder and drier period preceding the 2009 survey led to lower compaction rates during the 2009–10 interval, when compared to 2010–11, which is partly captured by the firn model. Spatially, higher compaction rates are observed and modeled in warmer regions with higher accumulation.

scholarly journals Potential mechanisms for anisotropy in ice-penetrating radar data

2012 ◽  
Vol 58 (209) ◽  
pp. 613-624 ◽  
Author(s):  
R. Drews ◽  
O. Eisen ◽  
D. Steinhage ◽  
I. Weikusat ◽  
S. Kipfstuhl ◽  
...  
Keyword(s):  
Ice Core ◽  
Impurity Content ◽  
Radar Data ◽  
Surface Strain ◽  
Center Frequency ◽  
Dronning Maud Land ◽  
Principal Directions ◽  
Drilling Site ◽  
Antenna Polarization ◽  
The Antarctic

AbstractRadar data (center frequency 150 MHz) collected on the Antarctic plateau near the EPICA deep-drilling site in Dronning Maud Land vary systematically in backscattered power, depending on the azimuth antenna orientation. Backscatter extrema are aligned with the principal directions of surface strain rates and change with depth. In the upper 900m, backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression, while below 900 m the maxima shift by 90° pointing towards the lateral flow dilatation. We investigate the backscatter from elongated air bubbles and a vertically varying crystal-orientation fabric (COF) using different scattering models in combination with ice-core data. We hypothesize that short-scale variations in COF are the primary mechanism for the observed anisotropy, and the 900 m boundary between the two regimes is caused by ice with varying impurity content. Observations of this kind allow the deduction of COF variations with depth and are potentially also suited to map the transition between Holocene and glacial ice.

scholarly journals Basal conditions of two Transantarctic Mountains outlet glaciers from observation-constrained diagnostic modelling

2014 ◽  
Vol 60 (223) ◽  
pp. 855-866 ◽  
Author(s):  
Nicholas R. Golledge ◽  
Oliver J. Marsh ◽  
Wolfgang Rack ◽  
David Braaten ◽  
R. Selwyn Jones
Keyword(s):  
Satellite Images ◽  
Radar Data ◽  
Airborne Radar ◽  
Rate Parameter ◽  
Geothermal Heat ◽  
Ice Surface ◽  
Grounding Line ◽  
Modelling Procedure ◽  
Basal Sliding ◽  
Glacier Flow

AbstractWe present a diagnostic glacier flowline model parameterized and constrained by new velocity data from ice-surface GPS installations and speckle tracking of TerraSAR-X satellite images, newly acquired airborne-radar data, and continental gridded datasets of topography and geothermal heat flux, in order to better understand two outlet glaciers of the East Antarctic ice sheet. Our observational data are employed as primary inputs to a modelling procedure that first calculates the basal thermal regime of each glacier, then iterates the basal sliding coefficient and deformation rate parameter until the fit of simulated to observed surface velocities is optimized. We find that the two glaciers have both frozen and thawed areas at their beds, facilitating partial sliding. Glacier flow arises from a balance between sliding and deformation that fluctuates along the length of each glacier, with the amount of sliding typically varying by up to two orders of magnitude but with deformation rates far more constant. Beardmore Glacier is warmer and faster-flowing than Skelton Glacier, but an up-glacier deepening bed at the grounding line, coupled with ice thicknesses close to flotation, lead us to infer a greater vulnerability of Skelton Glacier to grounding-line recession if affected by ocean-forced thinning and concomitant acceleration.

scholarly journals High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys conducted over 30 years

2021 ◽  
Author(s):  
Shun Tsutaki ◽  
Shuji Fujita ◽  
Kenji Kawamura ◽  
Ayako Abe-Ouchi ◽  
Kotaro Fukui ◽  
...  
Keyword(s):  
Ice Core ◽  
Radar Data ◽  
High Gain ◽  
Ice Thickness ◽  
Important Challenge ◽  
Complex Landscape ◽  
Beam Directivity ◽  
Subglacial Topography ◽  
Antarctic Research ◽  
The Difference

Abstract. The retrieval of continuous ice core records of more than 1 Myr is an important challenge in palaeo-climatology. For identifying suitable sites for drilling such ice, the knowledge of the subglacial topography and englacial layering is crucial. For this purpose, extensive ground-based ice radar surveys were done over Dome Fuji in the East Antarctic plateau during the 2017–2018 and 2018–2019 austral summers by the Japanese Antarctic Research Expedition, on the basis of ground-based radar surveys conducted over the previous ~ 30 years. High-gain Yagi antennae were used to improve the antenna beam directivity and thus attain a significant decrease in hyperbolic features in the echoes from mountainous ice-bedrock interfaces. We combined the new ice thickness data with the previous ground-based data, recorded since the 1980s, to generate an accurate high-spatial-resolution (up to 0.5 km between survey lines) ice thickness map. This map revealed a complex landscape composed of networks of subglacial valleys and highlands, which sets substantial constraints for identifying possible locations for new drilling. In addition, our map was compared with a few bed maps compiled by earlier independent efforts based on airborne radar data to examine the difference in features between sets of the data.

scholarly journals Constraining the geothermal heat flux in Greenland at regions of radar-detected basal water

2019 ◽  
Vol 65 (254) ◽  
pp. 1023-1034 ◽  
Author(s):  
Soroush Rezvanbehbahani ◽  
Leigh A. Stearns ◽  
C. J. van der Veen ◽  
Gordon K. A. Oswald ◽  
Ralf Greve
Keyword(s):  
Heat Flux ◽  
Water Distribution ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
Geothermal Heat ◽  
Community Effort ◽  
Pressure Melting

AbstractThe spatial distribution of basal water critically impacts the evolution of ice sheets. Current estimates of basal water distribution beneath the Greenland Ice Sheet (GrIS) contain large uncertainties due to poorly constrained boundary conditions, primarily from geothermal heat flux (GHF). The existing GHF models often contradict each other and implementing them in numerical ice-sheet models cannot reproduce the measured temperatures at ice core locations. Here we utilize two datasets of radar-detected basal water in Greenland to constrain the GHF at regions with a thawed bed. Using the three-dimensional ice-sheet model SICOPOLIS, we iteratively adjust the GHF to find the minimum GHF required to reach the bed to the pressure melting point, GHFpmp, at locations of radar-detected basal water. We identify parts of the central-east, south and northwest Greenland with significantly high GHFpmp. Conversely, we find that the majority of low-elevation regions of west Greenland and parts of northeast have very low GHFpmp. We compare the estimated constraints with the available GHF models for Greenland and show that GHF models often do not honor the estimated constraints. Our results highlight the need for community effort to reconcile the discrepancies between radar data, GHF models, and ice core information.

scholarly journals Accumulation Variability in the Antarctic Peninsula: The Role of Large-Scale Atmospheric Oscillations and Their Interactions*

2016 ◽  
Vol 29 (7) ◽  
pp. 2579-2596 ◽  
Author(s):  
Bradley P. Goodwin ◽  
Ellen Mosley-Thompson ◽  
Aaron B. Wilson ◽  
Stacy E. Porter ◽  
M. Roxana Sierra-Hernandez
Keyword(s):  
Antarctic Peninsula ◽  
Large Scale ◽  
Southern Oscillation ◽  
Accumulation Rate ◽  
Ice Core ◽  
Southern Annular Mode ◽  
Phase Changes ◽  
High Temporal Resolution ◽  
Ice Core Record ◽  
The Antarctic

Abstract A new ice core drilled in 2010 to bedrock from the Bruce Plateau (BP) on the Antarctic Peninsula (AP) provides a high temporal resolution record of environmental conditions in this region. The extremely high annual accumulation rate at this site facilitates analysis of the relationships between annual net accumulation An on the BP and large-scale atmospheric oscillations. Over the last ~45 years, An on the BP has been positively correlated with both the southern annular mode (SAM) and Southern Oscillation index (SOI). Extending this analysis back to 1900 reveals that these relationships are not temporally stable, and they exhibit major shifts in the late-1940s and the mid-1970s that are contemporaneous with phase changes in the Pacific decadal oscillation (PDO). These varying multidecadal characteristics of the An–oscillation relationships are not apparent when only data from the post-1970s era are employed. Analysis of the longer ice core record reveals that the influence of the SAM on An depends not only on the phase of the SAM and SOI but also on the phase of the PDO. When the SAM’s influence on BP An is reduced, such as under negative PDO conditions, BP An is modulated by variability in the tropical and subtropical atmosphere through its impacts on the strength and position of the circumpolar westerlies in the AP region. These results demonstrate the importance of using longer-term ice core–derived proxy records to test conventional views of atmospheric circulation variability in the AP region.

scholarly journals Modelling the Antarctic Ice Sheet across the Mid Pleistocene Transition – Implications for Oldest Ice

2019 ◽  
Author(s):  
Johannes Sutter ◽  
Hubertus Fischer ◽  
Klaus Grosfeld ◽  
Nanna B. Karlsson ◽  
Thomas Kleiner ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Ice Core ◽  
Ice Sheet ◽  
Middle Pleistocene ◽  
Climate Modelling ◽  
Geothermal Heat ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Pleistocene Climate ◽  
The Antarctic

Abstract. The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3D continental ice sheet modelling. To this end, we present an ensemble of ice sheet simulations spanning the last 2 Myr and employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the effects of changing climate conditions, sea level and geothermal heat flux boundary conditions on the mass balance and ice dynamics of the Antarctic Ice Sheet. Our modelling results show a range of configurational ice sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate re-organisation and associated ice-dynamic changes we identify several regions conducive to conditions maintaining 1.5 Myr old ice, particularly around Dome Fuji, Dome C and Ridge B, in agreement to previous studies. This finding strengthens the notion that old ice exists in previously identified regions, while providing a dynamic continental ice sheet context.

Evidence for an early Holocene climatic optimum in the Antarctic deep ice-core record

1992 ◽  
Vol 6 (3-4) ◽  
pp. 169-177 ◽  
Author(s):  
P Ciais ◽  
J R Petit ◽  
J Jouzel ◽  
C Lorius ◽  
N I Barkov ◽  
...  
Keyword(s):  
Ice Core ◽  
Early Holocene ◽  
Holocene Climatic Optimum ◽  
Ice Core Record ◽  
Climatic Optimum ◽  
The Antarctic

scholarly journals A comparison of automated approaches to extracting englacial-layer geometry from radar data across ice sheets

2020 ◽  
Vol 61 (81) ◽  
pp. 234-241 ◽  
Author(s):  
Richard Delf ◽  
Dustin M. Schroeder ◽  
Andrew Curtis ◽  
Antonios Giannopoulos ◽  
Robert G. Bingham
Keyword(s):  
Ice Core ◽  
Accurate Determination ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Radar Data ◽  
Test Case ◽  
Estimation Algorithms ◽  
Ice Sheet Dynamics ◽  
The Antarctic

AbstractRadar surveys across ice sheets typically measure numerous englacial layers that can often be regarded as isochrones. Such layers are valuable for extrapolating age–depth relationships away from ice-core locations, reconstructing palaeoaccumulation variability, and investigating past ice-sheet dynamics. However, the use of englacial layers in Antarctica has been hampered by underdeveloped techniques for characterising layer continuity and geometry over large distances, with techniques developed independently and little opportunity for inter-comparison of results. In this paper, we present a methodology to assess the performance of automated layer-tracking and layer-dip-estimation algorithms through their ability to propagate a correct age–depth model. We use this to assess isochrone-tracking techniques applied to two test case datasets, selected from CreSIS MCoRDS data over Antarctica from a range of environments including low-dip, continuous layers and layers with terminations. We find that dip-estimation techniques are generally successful in tracking englacial dip but break down in the upper and lower regions of the ice sheet. The results of testing two previously published layer-tracking algorithms show that further development is required to attain a good constraint of age–depth relationships away from dated ice cores. We recommend that auto-tracking techniques focus on improved linking of picked stratigraphy across signal disruptions to enable accurate determination of the Antarctic-wide age–depth structure.

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