Physical Modeling of Firn — Densification, Temperature, Grain Growth, and Water Retention

• Main Author: Schultz, Timm
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2024
• Subjects: Antarctic; Greenland; Antarc*; glacier
• Online Access: http://tuprints.ulb.tu-darmstadt.de/27894/; https://tuprints.ulb.tu-darmstadt.de/27894/1/DissertationTimmSchultz.pdf; https://doi.org/10.26083/tuprints-00027894

The Greenland and Antarctic ice sheets are covered with snow. Over time, this snow becomes glacier ice due to continuous compaction. The intermediate product between seasonal snow and glacier ice is called firn. The process of this transition is called firn densification. Modeling this process has been a subject of glaciology for many decades, as it has the potential to provide the density distribution over the entire extent of ice sheets. Knowing the density of the firn body is not only crucial for determining the mass balance of the ice sheets, but also allows for better reconstructions of past climate using ice cores. Another issue related to firn densification, which has become more relevant in the recent past due to changing climate conditions on the ice sheets, is the simulation of surface meltwater infiltration into the firn. This thesis aims to consider the modeling of firn compaction in the context of continuum mechanics. After establishing some basic concepts of continuum mechanics, three different approaches to modeling the densification of firn are reviewed in detail. A novel approach, based on an extensive firn core dataset, is developed to further optimize the so-called cell model approach. The firn body can be considered as a system in which different processes influence each other. The densification of the firn is only one of these processes and depends, among other phenomena, on the evolution of the temperature. Therefore, the simulation of the densification process requires the modeling of additional properties, such as the temperature, thermal conductivity, heat capacity, and the mean grain radius. Model concepts for a comprehensive simulation of firn are presented. In addition, meltwater flow through firn is modeled using Richards’ Equation, which describes unsaturated flow through porous media. Numerical concepts are presented to implement and couple the model concepts presented. This includes the description of a one-dimensional Lagrangian model approach and the discretization of the ...