Internal layer tracing and age‐depth‐accumulation relationships for the northern Greenland ice sheet

Abstract

Abstract. Clues to previous ice sheet structure and long-term glaciological processes are preserved in the internal layering configuration of the Greenland ice sheet. Information about these internal layers has been retrieved over many parts of the ice sheet with the University of Kansas ice-penetrating radar. We report on the coherence of these layers over very large distances, describe a method of tracing these layers along thousands of kilometers of flight line, and do so for one flight during the 1999 Program for Arctic Regional Climate Assessment (PARCA) aircraft campaign. We determine the ages of these layers, based on information at the GRIP ice core site, and extend these ages along the flight line to Camp Century, where they are compared to modeled-derived age estimates. These ages agree with each other to between 2 and 15%, differences that can be substantially reduced with minor changes to the model parameters (accumulation rate and shear layer depth). Finally, we are able to derive estimates of accumulation rates along the flight line by fitting the age-depth data from layer tracing to a Dansgaard-Johnsen model with a minimization technique, providing estimates that match recent accumulation patterns within a few centimeters per year.

Laurentide Ice Sheet basal temperatures during the last glacial cycle as inferred from borehole data

“…While this indicates that basal temperatures near the pressure melting point of ice cannot be solely responsible for ice sheet instability and col-lapse, it demonstrates that they are a key parameter in ice sheet evolution and one that ice sheet evolution models must take into account. Elevated basal temperatures, near or above the pressure melting point of ice, have been recorded in the present-day ice sheets (Fahnestock et al, 2001;Pritchard et al, 2012). Our results indicate that this alone cannot be considered as an indication of ice sheet collapse.…”

A semi-automatic approach for estimating bedrock and surface layers from multichannel coherent radar depth sounder imagery

“…Other studies focused on tracing near surface internal layers in radar imagery. For example, Fahnestock et al 3 developed an algorithm which uses cross-correlation and a peak-following routine, Karlsson and Dahl-Jensen 4 present a ramp function-based approach, and Sime et al 5 developed a technique to obtain layer dip information from two datasets in the Antarctic. For techniques in detecting bedrock and surface layers, Ilisei et al 6 generated a statistical map of the subsurface by exploiting the properties of the radar signal and used a segmentation algorithm for estimating investigated areas, but identifying curves can also be accomplished using image processing and computer vision techniques.…”

Estimating bedrock and surface layer boundaries and confidence intervals in ice sheet radar imagery using MCMC

“…Although our application focuses on detecting bedrock and surface layers, other studies use similar techniques to identify internal layers in radar imagery. Approaches include Fahnestock et al [8], Karlsson and Dahl-Jensen [7], Sime et al [9], Mitchell et al [12], and Panton [13].…”

“…A few recent papers have studied how to use image processing and computer vision techniques to determine layer boundaries automatically or semi-automatically from echograms [2,3,4,5,6,7,8,9,10], but this is a hard problem because of the high degree of noise, the often faint layer boundaries, and confusing linear structures caused by signal reflections and clutter. In fact, even human annotators produce diverging estimates of the boundaries in many cases.…”