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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

Depth of synthetic isochrones of ages (a) 11.7 ka (beginning of the Holocene epoch), (b) 29 ka (approximately the Last Glacial Maximum; end of Marine Isotope Stage (MIS) 3) [Lisiecki and Raymo, 2005], (c) 57 ka (beginning of MIS 3), and (d) 115 ka (end of the Eemian period) across the GrIS. (e–h) Uncertainty in the depth of the 11.7, 29, 57, and 115 ka isochrones, respectively.
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fig09: Depth of synthetic isochrones of ages (a) 11.7 ka (beginning of the Holocene epoch), (b) 29 ka (approximately the Last Glacial Maximum; end of Marine Isotope Stage (MIS) 3) [Lisiecki and Raymo, 2005], (c) 57 ka (beginning of MIS 3), and (d) 115 ka (end of the Eemian period) across the GrIS. (e–h) Uncertainty in the depth of the 11.7, 29, 57, and 115 ka isochrones, respectively.

Mentions: Throughout the ice sheet, we observe a pattern of age that is consistent with what is already known of the age structure of the GrIS [Fahnestock et al., 2001a; Karlsson et al., 2013; Sime et al., 2014] and its long-term and modern patterns of accumulation rate [Fahnestock et al., 2001b; Ettema et al., 2009]. Shallower Holocene-aged ice, whose present depth is more strongly influenced by the long-term pattern of accumulation rate, is more downwarped west of the central ice divide, toward the south, and toward the ice sheet margins (Figures8 and 9 and Animation S2). Although our ability to map the age structure within the southern reaches of the ice sheet is limited, our results suggest that most of the ice sheet south of Jakobshavn Isbræ (∼69°N) is Holocene aged. The effect of NEGIS upon the age structure is evident as a prominent northeast trending change in the depth-age relationship that originates north of GRIP and GISP2.


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)

Depth of synthetic isochrones of ages (a) 11.7 ka (beginning of the Holocene epoch), (b) 29 ka (approximately the Last Glacial Maximum; end of Marine Isotope Stage (MIS) 3) [Lisiecki and Raymo, 2005], (c) 57 ka (beginning of MIS 3), and (d) 115 ka (end of the Eemian period) across the GrIS. (e–h) Uncertainty in the depth of the 11.7, 29, 57, and 115 ka isochrones, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig09: Depth of synthetic isochrones of ages (a) 11.7 ka (beginning of the Holocene epoch), (b) 29 ka (approximately the Last Glacial Maximum; end of Marine Isotope Stage (MIS) 3) [Lisiecki and Raymo, 2005], (c) 57 ka (beginning of MIS 3), and (d) 115 ka (end of the Eemian period) across the GrIS. (e–h) Uncertainty in the depth of the 11.7, 29, 57, and 115 ka isochrones, respectively.
Mentions: Throughout the ice sheet, we observe a pattern of age that is consistent with what is already known of the age structure of the GrIS [Fahnestock et al., 2001a; Karlsson et al., 2013; Sime et al., 2014] and its long-term and modern patterns of accumulation rate [Fahnestock et al., 2001b; Ettema et al., 2009]. Shallower Holocene-aged ice, whose present depth is more strongly influenced by the long-term pattern of accumulation rate, is more downwarped west of the central ice divide, toward the south, and toward the ice sheet margins (Figures8 and 9 and Animation S2). Although our ability to map the age structure within the southern reaches of the ice sheet is limited, our results suggest that most of the ice sheet south of Jakobshavn Isbræ (∼69°N) is Holocene aged. The effect of NEGIS upon the age structure is evident as a prominent northeast trending change in the depth-age relationship that originates north of GRIP and GISP2.

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