Applicants

Dr. Johannes Freitag
Alfred-Wegener-Institut
Helmholtz-Zentrum für Polar- und Meeresforschung

Professor Dr. Claudia Redenbach
Technische Universität Kaiserslautern
Fachbereich Mathematik
Arbeitsgruppe Statistik

Project Description

The analysis of air entrapped in bubbles in polar ice cores yields valuable information on the composition of the atmosphere during the last centuries. However, exploitation of this source of information is hampered by the lack of absolute dating tools linking the ice and the observed air to a certain period in time. Recent dating approaches rely on models which require a measure for the cumulated deformation of the ice as input. Up to now, there is no means for obtaining this information directly from an observed ice core. In the proposed project, we suggest using the locations of bubble centres as markers for the deformation. The main goal is to establish methods for the direct estimation of deformation parameters from the point pattern of bubble centres. To this end, our interdisciplinary research group will combine approaches from glaciology and point process statistics.The locations of bubble centres will be measured by means of core-scale X-ray-microfocus computer tomography on ice samples from different deep ice cores (EDC, EDML, Renland). The main idea of our analysis is based on the assumption that deformation introduces an anisotropy in the bubble centre patterns. Hence, estimates for the main axes and the degree of anisotropy may provide information on the main deformation directions and the strength of deformation. Although point process statistics is an active field of current research, suitably general methods for the anisotropy analysis of 3D point patterns are not available up to now. Hence, the glaciological problems posed in this project ask for advancements in the field of spatial statistics. In particular, methods for the estimation of preferred directions and deformation parameters in 3D point processes have to be found. Additionally, the presence of noise bubbles forming during relaxation of the ice must be taken into account. Using the estimated deformation parameters, models from glaciology for prediction of deformation parameters and dating of the ice will be validated and improved. The measured cumulated strain will give insights to the potential effect of microstructure (grain size, texture and fabric, impurity content) on the deformation behaviour of ice. The analysis of bubbly ice from the Renland ice core will provide information on deformation close to bedrock of a polar icecap for the first time.

DFG Programme: Infrastructure Priority Programmes

International Connection: Sweden

Cooperation partner: Professor Dr. Aila Särkkä

Term since 2015