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Climate of the Past An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 Apr 2019

Submitted as: research article | 23 Apr 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).

Carbon isotopes and Pa / Th response to forced circulation changes: a model perspective

Lise Missiaen1,2, Nathaelle Bouttes1, Didier M. Roche1,3, Jean-Claude Dutay1, Aurélien Quiquet1,4, Claire Waelbroeck1, Sylvain Pichat5,6, and Jean-Yves Peterschmitt1 Lise Missiaen et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ-Université Paris-Saclay, F-91198 Gif-sur-Yvette, France
  • 2Climate Change Research Centre, University of New South Wales, Sydney, Australia
  • 3Vrije Universiteit Amsterdam, Faculty of Science, Cluster Earth and Climate, de Boelelaan 1085, 1081HV Amsterdam, the Netherlands
  • 4Institut Louis Bachelier, Chair Energy and Prosperity, Paris, 75002, France
  • 5Université de Lyon, ENS de Lyon, Laboratoire de Géologie de Lyon (LGL-TPE), F-69007 Lyon, France
  • 6Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. Understanding the ocean circulation changes associated with last glacial abrupt climate events is key to better assess climate variability and understand its different natural modes. Sedimentary Pa / Th, benthic δ13C and Δ14C are common proxies used to reconstruct past circulation flow rate and ventilation. To overcome the limitations of each proxy taken separately, a better approach is to produce multi-proxy measurements on a single sediment core. Yet, different proxies can provide conflicting information about past ocean circulation. Thus, modelling them in a consistent physical framework has become necessary to assess the geographical pattern, the timing and sequence of the multi-proxy response to abrupt circulation changes.

We have implemented a representation of the 231Pa and 230Th tracers into the model of intermediate complexity iLOVECLIM, which already included δ13C and Δ14C. We have further evaluated the response of these three ocean circulation proxies to a classical abrupt circulation reduction obtained by freshwater addition in the Nordic seas under preindustrial boundary conditions. Without a priori guess, the proxy response is shown to cluster in modes that resemble the modern Atlantic water masses. The clearest and most coherent response is obtained in the deep (> 2,000 m) Northwest Atlantic, where δ13C and Δ14C significantly decrease while Pa / Th increases. This is consistent with observational data across millennial scale events of the last glacial. Interestingly, while in marine records, except in rare instances, the phase relationship between these proxies remains unclear due to large dating uncertainties, in the model the bottom water carbon isotopes (δ13C and Δ14C) response lags the sedimentary Pa / Th response by a few hundred years.

Lise Missiaen et al.
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Lise Missiaen et al.
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