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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

Example traced radargram (same transection as Figures3 and 4 from 6 May 2011). Radiostratigraphy is color coded using a set of 15 distinct colors that have no physical meaning. This transect's closest intersections with three ice cores are shown as vertical magenta dashed lines. Radar traces are displayed vertically in terms of (a) elevation and (b) a self-consistent flattened projection, i.e., depth at the reference trace. Vertical white dashed line is the trace with the most reflections, to which the flattening is referenced. The region where flattening was not possible is blanked out. (c) Map showing transect location in Greenland. Green (red) dot represents the start (end) of the transect as shown in Figures5a and 5b. Blue dots represent 100 km intervals. This transect ascends the central ice divide and then reverses course, following a parallel track.
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fig05: Example traced radargram (same transection as Figures3 and 4 from 6 May 2011). Radiostratigraphy is color coded using a set of 15 distinct colors that have no physical meaning. This transect's closest intersections with three ice cores are shown as vertical magenta dashed lines. Radar traces are displayed vertically in terms of (a) elevation and (b) a self-consistent flattened projection, i.e., depth at the reference trace. Vertical white dashed line is the trace with the most reflections, to which the flattening is referenced. The region where flattening was not possible is blanked out. (c) Map showing transect location in Greenland. Green (red) dot represents the start (end) of the transect as shown in Figures5a and 5b. Blue dots represent 100 km intervals. This transect ascends the central ice divide and then reverses course, following a parallel track.

Mentions: Figure 5 illustrates the value of flattening radar data using one of the most densely traced transects from the KU data set from central northern Greenland. When displayed in terms of elevation, it is difficult to verify continuity between the traced reflections, particularly those that are discontinuous. After flattening, it is easier to verify that discontinuous reflections are matched self-consistently. After dating the radiostratigraphy, the entire data set can be evaluated in a similar manner (Animation S1 in the supporting information).


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)

Example traced radargram (same transection as Figures3 and 4 from 6 May 2011). Radiostratigraphy is color coded using a set of 15 distinct colors that have no physical meaning. This transect's closest intersections with three ice cores are shown as vertical magenta dashed lines. Radar traces are displayed vertically in terms of (a) elevation and (b) a self-consistent flattened projection, i.e., depth at the reference trace. Vertical white dashed line is the trace with the most reflections, to which the flattening is referenced. The region where flattening was not possible is blanked out. (c) Map showing transect location in Greenland. Green (red) dot represents the start (end) of the transect as shown in Figures5a and 5b. Blue dots represent 100 km intervals. This transect ascends the central ice divide and then reverses course, following a parallel track.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig05: Example traced radargram (same transection as Figures3 and 4 from 6 May 2011). Radiostratigraphy is color coded using a set of 15 distinct colors that have no physical meaning. This transect's closest intersections with three ice cores are shown as vertical magenta dashed lines. Radar traces are displayed vertically in terms of (a) elevation and (b) a self-consistent flattened projection, i.e., depth at the reference trace. Vertical white dashed line is the trace with the most reflections, to which the flattening is referenced. The region where flattening was not possible is blanked out. (c) Map showing transect location in Greenland. Green (red) dot represents the start (end) of the transect as shown in Figures5a and 5b. Blue dots represent 100 km intervals. This transect ascends the central ice divide and then reverses course, following a parallel track.
Mentions: Figure 5 illustrates the value of flattening radar data using one of the most densely traced transects from the KU data set from central northern Greenland. When displayed in terms of elevation, it is difficult to verify continuity between the traced reflections, particularly those that are discontinuous. After flattening, it is easier to verify that discontinuous reflections are matched self-consistently. After dating the radiostratigraphy, the entire data set can be evaluated in a similar manner (Animation S1 in the supporting information).

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