Masters´ thesis defense by Sonja Wahl

Title: "Holocene Climate and Ice Flow of the Renland Ice Cap"

Abstract: Measured ice core borehole temperatures contain valuable information about climatic conditions of the past. Numerical borehole temperature models are the tool for extracting this information, allowing the reconstruction of past temperatures. Profound knowledge about the ice flow is required when developing a borehole temperature model.

This thesis aims to reconstruct the Holocene temperature history of the Eastern Greenlandic peninsula Renland which is of use for estimating the future Greenland Ice Sheet behaviour in a changing climate.

Borehole temperature models were set up for two ice core drill sites located in close proximity to each other on the Renland Ice Cap. The models reproduce the observed ice cap temperature profiles within an accuracy of 0.03°C. A new concept referred to as step-model was introduced to describe the ice flow at the two locations. It is supported by comparing model results with observed annual layer thicknesses and ice age markers. Surface temperature reconstruction was performed using temperature records from remote weather stations as well as δ¹⁸O isotope proxy data. Both methods calculate similar temperatures for the 20^th-century, revealing a mid-century warming and a steep increase in temperatures since 1980. Holocene temperatures were reconstructed by calibrating an isotope paleothermometer. The resulting temperature estimates agree in their overall pattern and indicate a climatic optimum around 9ky b2k with an apparent and mostly steady cooling trend thereafter.

The developed borehole temperature models are limited in their temporal validity, but demonstrate the feasibility to model temperature profiles of the Renland Ice Cap. They can be further modified to extend their validity into the glacial, allowing temperature reconstructions of the entire ice core record, dating back into the Eemian.