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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 10
Clim. Past, 12, 1949–1978, 2016
https://doi.org/10.5194/cp-12-1949-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Clim. Past, 12, 1949–1978, 2016
https://doi.org/10.5194/cp-12-1949-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Oct 2016

Research article | 12 Oct 2016

Ocean carbon cycling during the past 130 000 years – a pilot study on inverse palaeoclimate record modelling

Christoph Heinze1,2,3, Babette A. A. Hoogakker4, and Arne Winguth5 Christoph Heinze et al.
  • 1Geophysical Institute, University of Bergen, Allégaten 70, 5007 Bergen, Norway
  • 2Uni Research Climate, Nygårdsgaten 112, 5008 Bergen, Norway
  • 3Bjerknes Centre for Climate Research, Bergen, Norway
  • 4Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, UK
  • 5Department of Earth and Environmental Sciences, University of Texas Arlington, P.O. Box 19049, Arlington, TX 76019, USA

Abstract. What role did changes in marine carbon cycle processes and calcareous organisms play in glacial–interglacial variation in atmospheric pCO2? In order to answer this question, we explore results from an ocean biogeochemical general circulation model. We attempt to systematically reconcile model results with time-dependent sediment core data from the observations. For this purpose, we fit simulated sensitivities of oceanic tracer concentrations to changes in governing carbon cycle parameters to measured sediment core data. We assume that the time variation in the governing carbon cycle parameters follows the general pattern of the glacial–interglacial deuterium anomaly. Our analysis provides an independent estimate of a maximum mean sea surface temperature drawdown of about 5 °C and a maximum outgassing of the land biosphere by about 430 Pg C at the Last Glacial Maximum as compared to pre-industrial times. The overall fit of modelled palaeoclimate tracers to observations, however, remains quite weak, indicating the potential of more detailed modelling studies to fully exploit the information stored in the palaeoclimatic archive. This study confirms the hypothesis that a decline in ocean temperature and a more efficient biological carbon pump in combination with changes in ocean circulation are the key factors for explaining the glacial CO2 drawdown. The analysis suggests that potential changes in the export rain ratio POC : CaCO3 may not have a substantial imprint on the palaeoclimatic archive. The use of the last glacial as an inverted analogue to potential ocean acidification impacts thus may be quite limited. A strong decrease in CaCO3 export production could potentially contribute to the glacial CO2 decline in the atmosphere, but this remains hypothetical.

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Sensitivities of sediment tracers to changes in carbon cycle parameters were determined with a global ocean model. The sensitivities were combined with sediment and ice core data. The results suggest a drawdown of the sea surface temperature by 5 °C, an outgassing of the land biosphere by 430 Pg C, and a strengthening of the vertical carbon transfer by biological processes at the Last Glacial Maximum. A glacial change in marine calcium carbonate production can neither be proven nor rejected.
Sensitivities of sediment tracers to changes in carbon cycle parameters were determined with a...
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