Origin of englacial stratigraphy at three deep ice core sites of the Greenland Ice Sheet by synthetic radar modelling

Seyedhamidreza Mojtabavi,Jan Eichler,Ilka Weikusat,John Paden,Olaf Eisen,Frank Wilhelms,Steven Franke,Daniel Steinhage,Dorthe Dahl-Jensen,Daniela Jansen

doi:10.1017/jog.2021.137

Abstract

AbstractDuring the past 20 years, multi-channel radar emerged as a key tool for deciphering an ice sheet's internal architecture. To assign ages to radar reflections and connect them over large areas in the ice sheet, the layer genesis has to be understood on a microphysical scale. Synthetic radar trace modelling based on the dielectric profile of ice cores allows for the assignation of observed physical properties’ variations on the decimetre scale to radar reflectors extending from the coring site to a regional or even whole-ice-sheet scale. In this paper we rely on the available dielectric profiling data of the northern Greenland deep ice cores: NGRIP, NEEM and EGRIP. The three records are well suited for assigning an age model to the stratigraphic radar-mapped layers, and linking up the reflector properties to observations in the cores. Our modelling results show that the internal reflections are mainly due to conductivity changes. Furthermore, we deduce fabric characteristics at the EGRIP drill site from two-way-travel-time differences of along and across-flow polarized radarwave reflections of selected horizons (below 980 m). These indicate in deeper parts of the ice column an across-flow concentratedc-axis fabric.

Highlights

The ice sheets are the biggest freshwater reservoirs of the earth system and are a significant factor for the future evolution of sea level (Stocker and others, 2013; Shepherd and others, 2019; Tapley and others, 2019; Edwards and others, 2021)
To accomplish our goal to identify the physical origin of a certain internal reflection horizons (IRHs), and determine ages for those reflections which can be identified as IRHs, we used single-trace ‘A-scopes’ (e.g. Figs 2, 5) and radargrams for the comparison between synthetic radar and airborne Radio-echo sounding (RES) data over larger regions
In order to understand physical processes that cause the IRH and identify ages for the reflectors causing the layers, we rely on the airborne radar measurements and modelling of synthetic radar traces that were fed by conductivity and permittivity data from East Greenland deep Ice-core Project (EGRIP), North Greenland Eemian (NEEM) and NGRIP2 ice cores in Greenland

Summary

Introduction

The ice sheets are the biggest freshwater reservoirs of the earth system and are a significant factor for the future evolution of sea level (Stocker and others, 2013; Shepherd and others, 2019; Tapley and others, 2019; Edwards and others, 2021). Understanding the behaviour of the ice sheets in response to changes in climate is essential for improving predictions for the future projections. Radio-echo sounding (RES) of ice and the mapping of internal reflections can provide valuable insights into the history of ice streams, accumulation patterns and the physical properties of internal layers in Greenland and Antarctica Investigating physical properties of ice sheets and understanding complex ice flow behaviours (e.g. effects from anisotropy) can provide more insights to acquire missing process knowledge of ice stream dynamics in the ice sheet and glacier models. Most ice-sheet and glacier models assume the ice to be isotropic. Understanding ice flow behaviours can reduce model uncertainty and increase prediction accuracy for the future behaviour of sea level projections

Methods

Discussion

Conclusion