Master Thesis Defense by Josephine Yolanda Lindsey-Clark

Title: Experimental Techniques in Ice Core Physics

Ice, firn and snow cores contain records of past climate variables. Through continuous flow analysis, impurities within the ice and snow can be measured. The concentration of some impurities in the ice show seasonally dependent variation, enabling annual layer counting. This technique can be used to constrain accumulation rates for surface mass balance models used to calculate future sea level rise. The Light-weight In Situ Analysis box, (the LISA box), was developed at the department for Physics of Ice, Climate and Earth at the Niels Bohr Institute in 2017, as a fully portable system to measure multiple shallow snow anywhere on the ice. In the summers of 2017-2019, the LISA box was taken to different sites across Greenland, providing estimates of annual layer thickness with high accuracy, and reconstruction of regional snow accumulation patterns for 2015-2018. This has proven the LISA box to be an excellent novel method for obtaining accumulation rates at different locations, with sub-annual resolution necessary for validating model outputs. 

The objective of this was to make optimisations to the LISA box, improving its capabilities in the field. Based on previous use in the field and recommendations for future improvement, optimisations were made to the system, including the installation of a new debubbler, design of a melthead stand, electronic core depth registration, minimisation of the wastewater pump, and enhancements to the Labview interface and data saving. Results from the LISA box were intended to be coupled with atmospheric model simulations to establish the source locations of aerosols deposited at the proposed Müller ice-core drill site, using NCEP/NCAR reanalysis data with the Hybrid Single-Particle Lagrangian Integrated Trajectory. The main source was established to be the Arctic Ocean, accounting for up to 50\% of the back-trajectory origin points in the summer. 

The LISA box was prepared to be shipped to the Müller ice cap, where it would be used to measure several shallow cores at different locations around the proposed drill site. After this, the box was intended to go to East Greenland Ice-core Project (EastGRIP), to obtain additional recent accumulation studies. However, an issue with the shipment meant that the LISA box never arrived at Müller or EastGRIP. In lieu of the intended fieldwork with the LISA box, an alternative project was worked on at the EastGRIP: an active-sonar system to measure drill liquid level in the borehole, originally proposed and designed by Aslak Grinsted. The system was successfully installed and measured the drill liquid level depth as the ice core drill reached the bottom of the ice sheet, where no change in liquid level was registered. After drilling had concluded, a drill liquid level rise of half a meter was observed by the system, possibly linked to a porous connection with water underneath the ice. 

Supervisor: Helle Astrid Kjær
Censor: Andreas Peter Ahlstrøm (GEUS)