Grimmer, Markus Ron (2023). Reconstructing past mean ocean temperature using noble-gas ratios in the EDC ice core. (Thesis). Universität Bern, Bern
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Abstract
Throughout the Quaternary, Earth’s climate system has repeatedly undergone major reorganisations. Glacial terminations, the transitions of the climate system from its cold glacial to its warmer interglacial state, represent the largest natural reorganisations in this period. As the climate shifts from glacial to interglacial state, the planet takes up vast amounts of energy. This energy is largely split up between Earth’s two dominant surface energy reservoirs on glacial–interglacial timescale: the ocean and the latent heat used to melt continental ice sheets. The extent of continental ice sheets can be inferred from sea level reconstructions, whereas the energy stored in the ocean is described by the ocean heat content, which through the heat capacity of water is directly linked to mean ocean temperature (MOT). Thus, global sea level and MOT are the two key metrics for determining Earth’s energy imbalance during the Quaternary. Ratios of noble gases and N2 trapped in polar ice cores are a novel proxy for MOT. Since noble gases are inert, their atmospheric abundances on glacial-interglacial timescale are solely dependent on their well understood temperature-dependent solubilities in ocean water. As the atmosphere is well-mixed, a single ice core sample is sufficient to obtain a snapshot of the global ocean’s noble gas content, and, through the temperature-dependent solubilities, its heat content. Thanks to high precision mass spectrometry, the 1σ uncertainty for reconstructing MOT in Bern is on the order of 0.3 °C. Consequently, MOT has proven to be a novel powerful proxy for the past climate. The aims of this PhD-project were twofold. The first aim was to further improve the analytical procedure used to reconstruct MOT here at the University of Bern. This was achieved by improving the extraction system’s capacity for capturing drilling fluid, which caused problems in previous measurement campaigns; by increasing the analytical precision for measuring noble-gas ratios through introducing new mass spectrometry corrections and updating established ones; and by establishing a fully data-based correction routine for firn fractionation processes, thereby reducing systematic uncertainties of the routine. The second aim was to produce a new MOT dataset, making use of the improved procedure. This was achieved by measuring 72 EPICA Dome C ice core samples, which span Terminations II, III, and IV, and their subsequent interglacials. This new dataset greatly expands on the existing MOT data and for the first time allows for studying the past four glacial–interglacial transitions and their subsequent interglacials from an OHC perspective. The dataset reveals consistent influence of ocean overturning circulation on the evolution of deglacial and early interglacial MOT evolution.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 29 November 2023 |
| Subjects: | 500 Science > 530 Physics |
| Institute / Center: | 08 Faculty of Science > Physics Institute |
| Depositing User: | Hammer Igor |
| Date Deposited: | 03 Jul 2025 06:49 |
| Last Modified: | 03 Jul 2025 22:25 |
| URI: | https://boristheses.unibe.ch/id/eprint/6356 |
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