Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream

Keisling, B. A.; Christianson, Knut; Alley, Richard B.; Peters, L. E.; Christian, John E.; Anandakrishnan, S.; Riverman, K. L.; Muto, Atsuhiro; Jacobel, R. W.

doi:10.3189/2014aog67a090

Cited by 45 publications

(80 citation statements)

References 70 publications

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“…As noted by Keisling et al (2014), the layer continuity index is uniformly high in this region except in the ice stream shear margins, with numerous bright internal layers traceable for several hundred kilometres through the central portion of the ice sheet, allowing confident layer tracing. Internal layers were identified in and propagated through RES profiles using a semi-automatic algorithm that identifies the peak of the radar wavelet nearest an initial user-identified peak, then automatically selects the flanking changes in concavity, and finally follows this wavelet along a radar profile.…”

Section: Core Chronology and Annual Layer Counting Techniquesmentioning

confidence: 66%

“…Although the deepest continuous layer traceable from NGRIP to NEGIS is only ∼ 51 kyr, there is ∼ 600 m of additional ice present at NEGIS with many additional coherent internal layers present ( Fig. 6; Keisling et al, 2014). Thus, the ice here is likely to be considerably older than ∼ 51 kyr.…”

Section: Core Chronology and Annual Layer Counting Techniquesmentioning

confidence: 93%

“…Two other publications Keisling et al, 2014) more fully discuss the geophysical data and resulting interpretations, including additional details on the basal interface and the distribution of internal layers both regionally and in the vicinity of the shallow core site. Christianson et al (2014) directly examine the basal interface and its influence on ice dynamics using several geophysical techniques.…”

Section: Surface Geophysical Surveysmentioning

confidence: 99%

“…Christianson et al (2014) directly examine the basal interface and its influence on ice dynamics using several geophysical techniques. Keisling et al (2014) trace radar layers from NGRIP to NEGIS and infer variations in basal conditions from radar internal stratigraphy.…”

Section: Surface Geophysical Surveysmentioning

confidence: 99%

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Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

et al. 2014

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Abstract. The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75 • 37.61 N, 35 • 56.49 W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations.Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flowrelated changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet.

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Section: Core Chronology and Annual Layer Counting Techniquesmentioning

confidence: 66%

Section: Core Chronology and Annual Layer Counting Techniquesmentioning

confidence: 93%

Section: Surface Geophysical Surveysmentioning

confidence: 99%

Section: Surface Geophysical Surveysmentioning

confidence: 99%

See 2 more Smart Citations

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

et al. 2014

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“…Evans and Smith, 1969;Harrison, 1973;Robin and others, 1977;Drewry and Meldrum, 1978;Dahl-Jensen and others, 1997;Lythe and others, 2001;Paden and others, 2010;Bamber and others, 2013;Keisling and others, 2014;MacGregor and others, 2015) and revealing insights into their past and present flow dynamics (e.g. King and others, 2009;Sime and others, 2014;Bingham and others, 2015;MacGregor and others, 2015;Winter and others, 2015;Cavitte and others, 2016;Christianson and others, 2016).…”

Section: Introductionmentioning

confidence: 99%

Resolving the internal and basal geometry of ice masses using imaging phase-sensitive radar

et al. 2018

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ABSTRACT. The phase-sensitive radio-echo sounder (pRES) is a powerful new instrument that can measure the depth of internal layers and the glacier bed to millimetre accuracy. We use a stationary 16-antenna pRES array on Store Glacier in West Greenland to measure the three-dimensional orientation of dipping internal reflectors, extending the capabilities of pRES beyond conventional depth sounding. This novel technique portrays the effectiveness of pRES in deriving the orientation of dipping internal layers that may complement profiles obtained through other geophysical surveying methods. Deriving ice vertical strain rates from changes in layer depth as measured by a sequence of pRES observations assumes that the internal reflections come from vertically beneath the antenna. By revealing the orientation of internal reflectors and the potential deviation from nadir of their associated reflections, the use of an antenna array can correct this assumption. While the array configuration was able to resolve the geometry of englacial layers, the same configuration could not be used to accurately image the glacier bed. Here, we use simulations of the performance of different array geometries to identify configurations that can be tailored to study different types of basal geometry for future deployments.

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Radiostratigraphy and age structure of the Greenland Ice Sheet

et al. 2015

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Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.Key PointsPhase information predicts reflection slope and simplifies reflection tracingReflections can be dated away from ice cores using a simple ice flow modelRadiostratigraphy is often disrupted near the onset of fast ice flow

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Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream

Abstract: ABSTRACT. We analyze the internal stratigraphy in radio-echo sounding data of the northeast Greenland ice stream to infer past and present ice dynamics. In the upper reaches of the ice stream, we propose that shear-margin steady-state folds in internal reflecting horizons (

Cited by 45 publications

References 70 publications

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

Resolving the internal and basal geometry of ice masses using imaging phase-sensitive radar

Radiostratigraphy and age structure of the Greenland Ice Sheet

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