The successful reconstruction of past atmospheric CO2 concentrations from Antarctic ice
cores started in the early 1980s. Each newly published record is the product of painstaking
discrete measurements of hand-sized samples from ice cores that can reach more than 3
kilometers of depth. Hence, high-resolution reconstructions of CO2 are usually limited to a
specific window of time of the last 800 thousand years (800 ka). Using the EDC ice core,
we reconstructed atmospheric CO2 concentrations during Marine Isotope Stage 5 (MIS 5;
135–106 ka). The new dataset covers the penultimate deglaciation, the last interglacial, and
the last glacial inception in unprecedented centennial resolution. Our new record shows remarkably stable CO2 concentrations for ten thousand years during MIS 5e. Simultaneously,
a series of worldwide climatic changes took place, such as falling temperatures in the oceans
and over the poles, growing ice sheets, generalized climate instability in the Northern Hemisphere, and changes in the Earth’s orbital parameters. The lack of marked variability in
the CO2 record during this period can be explained by an unusual combination of dynamic
carbon fluxes and the lack of a suitable deep ocean storage reservoir. As enigmatic as the
plateau is the last glacial inception when CO2 suddenly drops from interglacial levels and
resumes its coupling with Antarctic temperature. We propose that a Northern Hemisphere
trigger sourced this threshold-like behavior.

Despite the centennial-scale resolution achieved with the MIS 5 record, we only tentatively interpret submillennial CO2 features. While building the dataset, we realized that
CO2 showed sharp oscillations between neighboring data points, too fast to be fingerprinted
by true atmospheric variability. Much of the ensuing work tackled the understanding of
CO2 fluctuations at the centimeter scale and how they affected our record. We concluded
that while the high resolution allowed the establishment of precisely timed slope changes,
individual fluctuations at the centennial scale were likely the result of fractionation effects
during the bubble enclosure process in the ice core.

The measurement device used to reconstruct CO2 at the University of Bern is the end
product of decades of accumulated knowledge on how to measure CO2 from ancient air
bubbles trapped in polar ice. The centrifugal ice microtome (CIM), continuously developed
and improved since 2008, is a dry-extraction technique with state-of-the-art precision and
high sample throughput. During this Ph.D., the implemented improvements regarding the
CIM related to statistical analysis of different potential sources of error. These finesses
allowed for a deeper understanding of the system’s intricacies and increased confidence when
interpreting its output concentrations.