Highly resolved d13C measurements on CO2 in air from Antarctic ice cores

Eyer, Marc (2004). Highly resolved d13C measurements on CO2 in air from Antarctic ice cores (Unpublished). (Dissertation, Universität Bern, Philosophisch–naturwissenschaftliche Fakultät, Physikalisches Institut, Abteilung für Klima– und Umweltphysik)

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This work deals with highly resolved measurements of the stable 13C isotope on CO2 from air of Antarctic ice cores. The motivation to do this bases on highly resolved atmospheric CO2 reconstructions available since about five years, reaching back to the last glacial. The detailed evolution of the CO2, as presented in the records of Indermühle et al., 1999; Indermühle et al., 2000; Monnin et al., 2001; Flückiger et al., 2002 are mostly unexplained.
δ13C measurements on CO2 have the potential to decrypt the processes leading to CO2 concentration changes in the atmosphere. The main CO2 sources, the ocean and the biosphere have different δ13C signatures. The admixed or removed CO2 in or from the atmosphere can be allocated to its source by analyzing the changes in the δ13C signature. As an example this was tried by Indermühle et al. [1999] for the Holocene with data from the Taylor Dome ice core. In the conclusions they attribute the CO2 concentration re–increase in the mid Holocene to a decrease in the terrestrial biosphere. The few δ13C data which were available to support his scenario left room for speculations. Two years later Broecker et al. [2001] challenged the Indermühle–scenario and presented an alternative, based on ocean carbonate data showing strong carbonate changes in the ocean. This alternative scenario attributed the atmospheric CO2 increase in the second halve of the Holocene to this ocean carbon reorganization.
A new measuring system allows us to produce δ13C results in the same resolution as for the CO2. We measured the δ13C at two different Antarctic ice cores, both drilled in the frame work of the European Project for Ice Core drilling in Antarctica (EPICA). The first core was drilled at Concordia Station (EDC) in Est–Antarctica, the second at Kohnen Station (EDML) in Dronning Maud Land.
At the EDC ice core we produced a record covering the past 18’000 years. Additionally 15 samples were measured in the glacial with ages between 20’000 and 40’000 years. The results show a reaction of the atmospheric δ13C on the main changes in the carbon cycle. These changes are supposed to be subject to changes in the ocean circulation for the last glacial and the last termination. In the early Holocene in contrary the growing terrestrial and/or marine biosphere seems to contribute dominantly to the atmospheric δ13C changes. In the younger Holocene the ocean plays a major role again. The results of the second core EDML show a much larger scatter, why a interpretation is much more delicate. Potentially fractionation effects at the enclosure process of the air in the ice are responsible for this low reproducibility. The higher accumulation rate at the EDML site and the small sample size of our system leads to a subseasonal time resolution. The enclosure fractionation thus is not smoothed and scatters the data.

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