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Radiostratigraphy and age structure of the Greenland Ice Sheet.

MacGregor JA, Fahnestock MA, Catania GA, Paden JD, Prasad Gogineni S, Young SK, Rybarski SC, Mabrey AN, Wagman BM, Morlighem M - J Geophys Res Earth Surf (2015)

Bottom Line: 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.Phase 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.

View Article: PubMed Central - PubMed

Affiliation: Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA.

ABSTRACT

: 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 points: Phase 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.

No MeSH data available.


Related in: MedlinePlus

Airborne ice-penetrating radar surveys collected over the GrIS by KU between 1993 and 2013. Transects are color-coded by (a) campaign and (b) maximum number of reflections traced within 1 km segments along track. Portions of transects shown as black lines indicate no reflections were traced in those segments. Triangle denotes deep ice core sites. Ice, land, and ocean masks are from Bamber et al. [2013].
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fig01: Airborne ice-penetrating radar surveys collected over the GrIS by KU between 1993 and 2013. Transects are color-coded by (a) campaign and (b) maximum number of reflections traced within 1 km segments along track. Portions of transects shown as black lines indicate no reflections were traced in those segments. Triangle denotes deep ice core sites. Ice, land, and ocean masks are from Bamber et al. [2013].

Mentions: We examined the 479,595 km of 150 and 195 MHz ice-penetrating radar data collected over the GrIS using several airborne platforms by KU between 1993 and 2013 (Table 1 and Figure 1). These data include 512 transects of varying lengths (6–3965 km; median 530 km). Note that many sorties (individual flights) are split into multiple transects (also known as segments). The system designs, acquisition parameters, and processing techniques applied to these data are described in detail elsewhere (Table 1). The nominal vertical range resolution in ice of these data is 2.5–4.4 m and their along-track horizontal resolution varies between 15 and 150 m, depending on the system used and whether the data were focused using synthetic aperture radar (SAR) techniques [Leuschen et al., 2000; Legarsky et al., 2001].


Radiostratigraphy and age structure of the Greenland Ice Sheet.

MacGregor JA, Fahnestock MA, Catania GA, Paden JD, Prasad Gogineni S, Young SK, Rybarski SC, Mabrey AN, Wagman BM, Morlighem M - J Geophys Res Earth Surf (2015)

Airborne ice-penetrating radar surveys collected over the GrIS by KU between 1993 and 2013. Transects are color-coded by (a) campaign and (b) maximum number of reflections traced within 1 km segments along track. Portions of transects shown as black lines indicate no reflections were traced in those segments. Triangle denotes deep ice core sites. Ice, land, and ocean masks are from Bamber et al. [2013].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508962&req=5

fig01: Airborne ice-penetrating radar surveys collected over the GrIS by KU between 1993 and 2013. Transects are color-coded by (a) campaign and (b) maximum number of reflections traced within 1 km segments along track. Portions of transects shown as black lines indicate no reflections were traced in those segments. Triangle denotes deep ice core sites. Ice, land, and ocean masks are from Bamber et al. [2013].
Mentions: We examined the 479,595 km of 150 and 195 MHz ice-penetrating radar data collected over the GrIS using several airborne platforms by KU between 1993 and 2013 (Table 1 and Figure 1). These data include 512 transects of varying lengths (6–3965 km; median 530 km). Note that many sorties (individual flights) are split into multiple transects (also known as segments). The system designs, acquisition parameters, and processing techniques applied to these data are described in detail elsewhere (Table 1). The nominal vertical range resolution in ice of these data is 2.5–4.4 m and their along-track horizontal resolution varies between 15 and 150 m, depending on the system used and whether the data were focused using synthetic aperture radar (SAR) techniques [Leuschen et al., 2000; Legarsky et al., 2001].

Bottom Line: 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.Phase 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.

View Article: PubMed Central - PubMed

Affiliation: Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA.

ABSTRACT

: 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 points: Phase 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.

No MeSH data available.


Related in: MedlinePlus