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 Surface topography and ice flow in the vicinity of the EDML deep-drilling site, Antarctica

2007 ◽  
Vol 53 (182) ◽  
pp. 442-448 ◽  
Author(s):  
Christine Wesche ◽  
Olaf Eisen ◽  
Hans Oerter ◽  
Daniel Schulte ◽  
Daniel Steinhage
Keyword(s):  
Surface Topography ◽  
Ice Core ◽  
Surface Strain ◽  
Mean Velocity ◽  
Velocity Magnitude ◽  
Digital Elevation ◽  
Dronning Maud Land ◽  
Drilling Site ◽  
Flow Compression ◽  
Elevation Model

AbstractInterpretation of ice-core records requires accurate knowledge of the past and present surface topography and stress–strain fields. The European Project for Ice Coring in Antarctica (EPICA) drilling site (75.0025° S, 0.0684° E; 2891.7 m) in Dronning Maud Land, Antarctica, is located in the immediate vicinity of a transient and forking ice divide. A digital elevation model is determined from the combination of kinematic GPS measurements with the GLAS12 datasets from the ICESat. Based on a network of stakes, surveyed with static GPS, the velocity field around the drilling site is calculated. The annual mean velocity magnitude of 12 survey points amounts to 0.74 m a–1. Flow directions mainly vary according to their distance from the ice divide. Surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site. The strain field is characterized by along-flow compression, lateral dilatation and vertical layer thinning.

scholarly journals Characterizing the glaciological conditions at Halvfarryggen ice dome, Dronning Maud Land, Antarctica

2013 ◽  
Vol 59 (213) ◽  
pp. 9-20 ◽  
Author(s):  
Reinhard Drews ◽  
Carlos Martín ◽  
Daniel Steinhage ◽  
Olaf Eisen
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Cores ◽  
Radar Data ◽  
Ice Thickness ◽  
Atmospheric Conditions ◽  
Ice Flow ◽  
International Partnerships ◽  
Drill Site ◽  
Dronning Maud Land

AbstractWe present a comprehensive approach (including field data, remote sensing and an anisotropic ice-flow model) to characterize Halvfarryggen ice dome in coastal Dronning Maud Land, Antarctica. This is a potential drill site for the International Partnerships in Ice Core Sciences, which has identified the need for ice cores covering atmospheric conditions during the last few millennia. We derive the surface topography, the ice stratigraphy from radar data, and accumulation rates which vary from 400 to 1670 kg m−2 a−1 due to preferred wind directions and changing surface slope. The stratigraphy shows anticlines and synclines beneath the divides. We transfer Dansgaard–Johnsen age–depth scales from the flanks along isochrones to the divide in the upper 20–50% of the ice thickness and show that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts (1) 11 ka BP ice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years, (3) basal temperatures below the melting point (−12°C to −5°C) and (4) a highly developed crystal orientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic COF and ice flow.

scholarly journals Simulation of the Antarctic ice sheet with a three-dimensional polythermal ice-sheet model, in support of the EPICA project

1998 ◽  
Vol 27 ◽  
pp. 201-206 ◽  
Author(s):  
R. Calov ◽  
A. Savvin ◽  
R. Greve ◽  
I. Hansen ◽  
K. Hutter
Keyword(s):  
Shear Deformation ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Drilling Process ◽  
Antarctic Ice Sheet ◽  
Atlantic Sector ◽  
Dronning Maud Land ◽  
The Antarctic

The three-dimensional polythermal ice-sheet model SICOPOLIS is applied to the entire Antarctic ice sheet in support of the European Project for Ice Coring in Antartica (EPICA). in this study, we focus on the deep ice core to be drilled in Dronning Maud Land (Atlantic sector of East Antarctica) as part of EPICA. It has not yel been decided where the exact drill-site will be situated. Our objective is to support EPICA during its planning phase as well as during the actual drilling process. We discuss a transient simulation with a climate forcing derived from the Vostok ice core and the SPECMAP sea-level record. This simulation shows the range of accumulation, basal temperature, age and shear deformation to be expected in the region of Dronning Maud Land. Based on these results, a possible coring position is proposed, and the distribution of temperature, age, horizontal velocity and shear deformation is shown for this column.

Synoptic situations causing high precipitation rates on the Antarctic plateau: observations from Kohnen Station, Dronning Maud Land

2006 ◽  
Vol 18 (2) ◽  
pp. 279-288 ◽  
Author(s):  
Gerit Birnbaum ◽  
Ralf Brauner ◽  
Hinnerk Ries
Keyword(s):  
Large Scale ◽  
Ice Core ◽  
Mean Value ◽  
Cloud Formation ◽  
Heavy Snowfall ◽  
Greenwich Meridian ◽  
Dronning Maud Land ◽  
High Precipitation ◽  
The Antarctic

Kohnen Station (75°S, 0°E, 2892 m) is one of the two drilling sites of the European Project for Ice Coring in Antarctica. Snow falls at Kohnen only a few times a year with comparatively high precipitation rates of 1 mm to over 5 mm water equivalent per event. These events contribute considerably to the total annual accumulation of which the long-term mean value is 62 mm water equivalent per year. For ice core interpretation, it is important to understand synoptic processes leading to such high precipitation rates. Our investigation is based on visually observed periods of heavy snowfall at Kohnen during summer campaigns since 2001/2002. The corresponding synoptic situations can be grouped into three categories. Category I is where occluding fronts of eastward-moving low pressure systems reach the plateau, a fairly frequent occurrence. Category II is where lows or secondary lows formed east of the Greenwich Meridian move to the west (retrograde movement), and frontal clouds influence the plateau. In Category III, large-scale lifting processes (due to an upper air low west of Kohnen Station) lead to cloud formation over the plateau of Dronning Maud Land.

scholarly journals Neumayer III and Kohnen Station in Antarctica operated by the Alfred Wegener Institute

2016 ◽  
Vol 2 ◽  
Author(s):  
Christine Wesche ◽  
Rolf Weller ◽  
Gert König-Langlo ◽  
Tanja Fromm ◽  
Alfons Eckstaller ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Shelf ◽  
Deep Drilling ◽  
Research Activities ◽  
Starting Point ◽  
Air Chemistry ◽  
Dronning Maud Land ◽  
Core Project ◽  
The Antarctic

The Alfred Wegener Institute operates two stations in Dronning Maud Land, Antarctica. The German overwintering station Neumayer III is located on the Ekström Ice Shelf at 70°40’S and 08°16’W and is the logistics base for three long-term observatories (meteorology, air chemistry and geophysics) and nearby research activities. Due to the vicinity to the coast (ca. 20 km from the ice shelf edge), the Neumayer III Station is the junction for many German Antarctic expeditions, especially as the starting point for the supply traverse for the second German station Kohnen.The summer station Kohnen is located about 600 km from the coast and 750 km from Neumayer III Station on the Antarctic plateau at 75°S and 00°04’E. It was erected as the base for the deep-drilling ice core project, which took place between 2001 and 2006. Since then Kohnen Station is used as a logistics base for different research projects.

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 Identifying isochrones in GPR profiles from DEP-based forward modeling

2003 ◽  
Vol 37 ◽  
pp. 344-350 ◽  
Author(s):  
Olaf Eisen ◽  
Frank Wilhelms ◽  
Uwe Nixdorf ◽  
Heinrich Miller
Keyword(s):  
Ice Core ◽  
Forward Modeling ◽  
Radar Data ◽  
Minor Importance ◽  
Volcanic Event ◽  
Complex Reflection Coefficient ◽  
Core Property ◽  
Dronning Maud Land ◽  
Modeling Data ◽  
Ground Penetrating

AbstractIsochronic continuous horizons between 20 and 90 m depth in a ground-penetrating radar (GPR) profile, recorded in Dronning Maud Land, Antarctica, are identified by comparison of synthetic and measured single radar traces. The measured radar-gram is derived from a stacked GPR profile; the synthetic radargram is computed by convolution of the complex reflection coefficient profile, based on dielectric profiling (DEP) data of a 150 m ice core, with a depth-invariant wavelet. It reproduces prominent reflections of the measured radargram to a considerable degree. Analyzing matching peaks in both radargrams enables us to identify isochronic reflections and transfer individual volcanic-event datings to the GPR profile. Reflections are primarily caused by changes in permittivity; changes in conductivity are of minor importance. However, several peaks in permittivity andconductivity show a good correlation and indicate that some reflections are related to acidic layers. The results demonstrate the possibility of reproducing radargrams from ice-core property profiles, a necessary step for the interpretation of remotely sensed radar data and the general significance of connecting ice-core and radar data for correct interpretations. Problems related to forward modeling, data gaps, origin of permittivity peaks, and GPR profiles used for comparison, are discussed.

scholarly journals Layer disturbances and the radio-echo free zone in ice sheets

2009 ◽  
Vol 3 (1) ◽  
pp. 307-321 ◽  
Author(s):  
R. Drews ◽  
O. Eisen ◽  
I. Hamann ◽  
S. Kipfstuhl ◽  
A. Lambrecht ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Depth Range ◽  
Free Zone ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Dronning Maud Land ◽  
Ice Sheet Dynamics ◽  
Dielectrical Properties ◽  
The Antarctic

Abstract. Radio-echo sounding of the Antarctic and Greenlandic ice sheets often reveals a layer in the lowest hundreds of meters above bedrock more or less free of radio echoes, known as the echo-free zone (EFZ). The cause of this feature is unclear, so far lacking direct evidence for its origin. We compare echoes around the EPICA drill site in Dronning Maud Land, Antarctica, with the microstructural and dielectrical properties of the EPICA-DML ice core. We find that echoes disappear in the depth range, where the coherency of the layers is lost due to disturbances caused by the ice flow. At the drill site, the EFZ onset at ~2100 m marks a boundary, below which the ice core may have experienced flow induced disturbances on various scales. The dating of the climate record becomes increasingly difficult below 1900 m, until correlation with the Dome C record is lost below 2417 m depth. The onset also indicates changing rheology which needs to be accounted for in the modeling of ice sheet dynamics.

scholarly journals Dating of a Dome Fuji (Antarctica) shallow ice core by volcanic signal synchronization with B32 and EDML1 chronologies

2014 ◽  
Vol 8 (1) ◽  
pp. 769-804 ◽  
Author(s):  
Y. Motizuki ◽  
Y. Nakai ◽  
K. Takahashi ◽  
M. Igarashi ◽  
H. Motoyama ◽  
...  
Keyword(s):  
Volcanic Eruption ◽  
Accumulation Rate ◽  
Ice Core ◽  
Volcanic Eruptions ◽  
Annual Layer ◽  
Signature Matching ◽  
Dronning Maud Land ◽  
Signal Synchronization ◽  
The Mean ◽  
Drilling Site

Abstract. We found extremely good synchronization of volcanic eruption signals between a shallow ice core drilled at Dome Fuji in 2001 (DF01 core) and the B32 shallow ice core from Dronning Maud Land, East Antarctica. We then applied volcanic signature matching to transfer the B32 chronology constructed by annual layer counting to a portion of the DF01 core for which annual layer counting was difficult because of the low precipitation rate. Matching was done by careful comparison of non-sea-salt sulfate (nssSO42−) data, which have a temporal resolution of about 1 yr, between the DF01 and B32 cores. The newly obtained chronology is called DFS1 (Dome Fuji Shallow ice core 1). In total, 31 volcanic eruptions were synchronized from AD 1900 back to AD 187, the earliest volcanic eruption date in the B32 core. The mean accumulation rate between synchronized volcanic horizons of the Dome Fuji core relative to rates at the B32 core drilling site did not differ significantly between these dates, increasing our confidence in this matching approach. We also used the B32-correlated EDML1/EDC3 chronology obtained from the top part of the EPICA Dronning Maud Land (DML) deep ice core to date a portion of the DF01 core. This new chronology, called DFS2 (Dome Fuji Shallow ice core 2), uses the correlations between B32 and EDML1/EDC3 ages to date the DF01 core from AD 1900 back to AD 199; moreover, four volcanic eruption dates from the EDML1/EDC3 chronology were used to date the interval from AD 199 back to AD 1. Because the EDML1/EDC3 ages were determined by adopting the B32 chronology back to AD 1170, DFS1 and DFS2 dates are identical between AD 1170 and 1900. These two methods enabled us to obtain a detailed chronology of the DF01 core, in particular the part before the last millennium, which has been difficult before this. We also present the absolute mean accumulation rates at Dome Fuji between AD 1 and 1900, based on the DFS1 and DFS2 chronologies.

scholarly journals Core-scale radioscopic imaging: a new method reveals density–calcium link in Antarctic firn

2013 ◽  
Vol 59 (218) ◽  
pp. 1009-1014 ◽  
Author(s):  
Johannes Freitag ◽  
Sepp Kipfstuhl ◽  
Thomas Laepple
Keyword(s):  
Calcium Ion ◽  
Ice Core ◽  
Ion Concentration ◽  
Impurity Density ◽  
Universal Feature ◽  
Density Relationship ◽  
Dronning Maud Land ◽  
Calcium Ion Concentration ◽  
Improved Accuracy ◽  
The Antarctic

AbstractA new radioscopic imaging technique has been developed to measure firn density in unprecedented resolution and accuracy even when the porosity is low or the geometry of a core or piece of core is not perfect. The technique is based on an X-ray microfocus computer tomograph (ICE-CT) designed especially for ice-core applications. Applied on an archive piece of the Antarctic firn core B32 drilled in Dronning Maud Land in 1998, the obtained density profile shows a strong correlation with the calcium ion concentration as found previously in Greenland. Given the impurity–density relationship found previously in Greenland, our result suggests both improved accuracy of the new density measurements and an impurity–density relationship with a similar magnitude in Greenland to that on the Antarctic plateau. Our measurements provide first evidence that the impurity–density relationship is a universal feature of polar firn and that the calcium ion concentration can serve as a proxy to describe quantitatively the effect of the impurities on densification.

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