Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
doi:10.5194/cp-2016-108
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
08 Nov 2016
Review status
This discussion paper is under review for the journal Climate of the Past (CP).
Response of the carbon cycle to the different orbital configurations of the last 9 interglacials
Nathaelle Bouttes1, Didier Swingedouw1, Didier Roche2,3, Maria Sanchez-Goni1,4, and Xavier Crosta1 1Univ. Bordeaux, EPOC, UMR 5805, F-33615 Pessac, France
2Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris - Saclay, F-91191 Gif-sur-Yvette, France
3Earth and Climate Cluster, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
4EPHE, PSL Research University, F-33615 Pessac, France
Abstract. Atmospheric CO2 levels during interglacials prior to the Mid Bruhnes Event (MBE, ~ 430 ka BP) have lower values of around 40 ppm than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to differences in external forcing before and after the MBE, might have increased the ocean carbon storage and thus explained the lower CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings and atmospheric CO2 concentrations over the nine last interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few ppm. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 is slightly smaller in these pre-MBE simulated interglacials including ice sheet variations, but the magnitude is still far too small. These results suggest a possible mis-representation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, that could explain the lower atmospheric CO2 concentrations during pre-MBE interglacials.

Citation: Bouttes, N., Swingedouw, D., Roche, D., Sanchez-Goni, M., and Crosta, X.: Response of the carbon cycle to the different orbital configurations of the last 9 interglacials, Clim. Past Discuss., doi:10.5194/cp-2016-108, in review, 2016.
Nathaelle Bouttes et al.
Nathaelle Bouttes et al.
Nathaelle Bouttes et al.

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Short summary
Atmospheric CO2 is key for climate change. CO2 is lower during the oldest warm period of the last million years, the interglacials, than during the most recent ones (since 430,000 years ago). This difference has not been explained yet, but could be due to changes of ocean circulation. We test this hypothesis and the role of vegetation and ice sheets using an intermediate complexity model. We show that only small changes of CO2 can be obtained, underlying missing feedbacks or mechanisms.
Atmospheric CO2 is key for climate change. CO2 is lower during the oldest warm period of the...
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