An Extraction System for Radiocarbon Microanalysis of Dissolved Organic Carbon in Glacier Ice

• Main Author: Schindler, Johannes
• Other Authors: Schwikowski, Margit
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: 570 Life sciences; biology; 540 Chemistry; ice core
• Online Access: https://boris.unibe.ch/99695/1/17schindler_j.pdf; https://boris.unibe.ch/99695/

Alpine glaciers situated in mid- and low latitudes are valuable archives for paleoclimatology. They offer a continuous record of recent local climatic conditions in regions where the majority of humankind lived and still lives. For meaningful interpretation of an ice core from such an archive, accurate dating is essential. Usually, several complementary approaches are used to establish a depth-age relationship. The oldest part of the ice at the bottom of the ice core suffers annual layer thinning and is influenced by small-scale bedrock geometry, which limits the use of annual layer counting or the assignment of reference horizons for dating. Nuclear dating techniques overcome this restriction since they do not rely on the preservation of a resolvable stratigraphy by using the continuous record of the respective radioisotope. Radiocarbon is especially powerful for dating alpine glaciers because its half-life of 5730 years suitably allows it to cover the typical age range of these archives. Most important, glacier ice does contain minute amounts of carbon. While macrofossils can only be found by coincidence, organic aerosols deposited on the glacier offer the best source of contemporary carbon in glacier ice. Despite a large part of its chemical composition being unknown, organic carbon found in an ice sample can be operationally classified into a particulate fraction (POC) and a dissolved fraction (DOC). Radiocarbon dating of POC has proven to be very successful and is a routine application by now. The major limitation of this technique is the low POC concentration found especially in pre-industrial and polar ice samples. Therefore, the DOC fraction promises even better suitability for dating thanks to its by a factor of 5 to 10 higher concentrations. Nevertheless, a straightforward analysis of DOC is hampered by its vulnerability to contamination. DOC consists in large part of mono- and dicarboxylic acids - compounds that can easily be taken up from the surrounding gas phase during sample preparation or which ...