High-resolution study of layering within the percolation and soaked facies of the Greenland ice sheet

• Published in: Annals of Glaciology
• Main Authors: Brown, Joel, Harper, Joel T., Pfeffer, W. Tad, Humphrey, Neil, Bradford, John H.
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2011
• Subjects: Earth Sciences; Glaciology; Greenland; Ice Sheet
• Online Access: https://scholarworks.umt.edu/geosci_pubs/32; https://doi.org/10.3189/172756411799096286; https://scholarworks.umt.edu/context/geosci_pubs/article/1026/viewcontent/High_resolution_study_of_layering_within_the_percolation_and.pdf

Within the percolation and soaked facies of the Greenland ice sheet, the relationship between radar-derived internal reflection horizons and the layered structure of the firm column is unclear. We conducted two small-scale ground-penetrating radar (GPR) surveys in conjunction with 10 m firm cores that we colleced within the percolation and soaked facies of the Greenland ice sheet. The two surveys were separated by the distance of about 50 km and about 340 m of elevation leading to about 40 days of difference in the duration of average annual melt. At the higher site (about 1997 ma.s.l.), which receives less melt, we found that internal reflection horizons identified in GPR data were largely laterally continuous over the grid; however, stratigraphic layers identified in cores could not be traced betweencores over any distance from 1.5 to 14.0 m. Thus, we found no correlation between firn core stratigraphy observed directly and radar-derived internal reflection horizons. At the lower site (about 1660 m a.s.l.), which receives more melt, we found massive ice layers less than 0.5 m thick and stratigraphic boundaries that span less than 15 m horizontally. Some ice layers and stratigraphic boundaries correlate well with internal reflection horizons that are laterally continuous over the area of the radar grid. Internal reflection horizons identified at about 1997 m a.s.l. are likely annual isochrones, but the reflection horizons identified at about 1660 m a.s.l. are likely multi-annual features. We find that mapping accumulation rates over long distances by tying core stratigraphy to radar horizons may lead to ambiguous results because: (1) there is no stratigraphic correlation between firn cores at the 1997 m location; and (2) the reflection horizons at the 1660 m location are multi-annual features.