Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2016-24
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Mar 2016
Review status
This discussion paper is a preprint. It has been under review for the journal Climate of the Past (CP). A final paper in CP is not foreseen.
An investigation of carbon cycle dynamics since the Last Glacial Maximum: Complex interactions between the terrestrial biosphere, weathering, ocean alkalinity, and CO2 radiative warming in an Earth system model of intermediate complexity
C. T. Simmons1, L. A. Mysak2, and H. D. Matthews1 1Department of Geography, Planning and Environment, Concordia University, 1445 Boul. de Maisonneuve Ouest, H1255-26, Montréal, Québec, Canada H3G 1M8
2Department of Atmospheric and Oceanic Sciences, McGill University, 805 Rue Sherbrooke Ouest, Montréal, Québec, Canada H3A 0B9
Abstract. Proxy reconstructions and modeling studies of the glacial-interglacial changes in the global carbon cycle have led to a stimulating debate in the paleoclimate literature about the mechanisms leading to a 90–100 ppmv increase in atmospheric CO2. In this paper, we used the University of Victoria Earth System Climate Model v. 2.9 to simulate the carbon cycle response to ice sheet retreat and Milankovitch (insolation) forcing from the Last Glacial Maximum (LGM) to the present. In addition, we conducted sensitivity studies to address the contributions of CO2 radiative forcing, atmospheric carbon content, and weathering rates to climate and carbon cycle changes since 21 kyr BP. The simulations show that ice sheet and orbital changes by themselves do not lead to a notable increase in atmospheric CO2 over the course of deglaciation. However, with the application of CO2 radiative forcing and different weathering rates, the simulated atmospheric CO2 variations ranged over ~ 35 ppmv. Virtually all of the simulated net global vegetation carbon uptake since the LGM is attributable to CO2 fertilization rather than greater land availability or warmer temperatures. Furthermore, the ‘greening’ from CO2 fertilization significantly enhances total deglacial warming (by 0.14°C) and contributes to warmer intermediate and deep ocean temperatures during the interglacial period. We also found that CO2 radiative forcing was the dominant factor allowing for greater outgassing at the ocean surface and an earlier ventilation of deep-ocean DIC. The downwelling of high-alkalinity surface waters stimulated by a stronger, earlier overturning circulation led to greater deep sedimentation (alkalinity removal), which, in turn, permitted CO2 to continue to increase through much of the simulation period.

Citation: Simmons, C. T., Mysak, L. A., and Matthews, H. D.: An investigation of carbon cycle dynamics since the Last Glacial Maximum: Complex interactions between the terrestrial biosphere, weathering, ocean alkalinity, and CO2 radiative warming in an Earth system model of intermediate complexity, Clim. Past Discuss., https://doi.org/10.5194/cp-2016-24, 2016.
C. T. Simmons et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Referee comments', Anonymous Referee #1, 12 Apr 2016 Printer-friendly Version 
 
RC2: 'Good content, poor presentation', Victor Brovkin, 02 May 2016 Printer-friendly Version 
 
AC1: 'Reviewer responses', C. T. Simmons, 10 Jun 2016 Printer-friendly Version 
 
EC1: 'Editor decision', Uwe Mikolajewicz, 16 Jun 2016 Printer-friendly Version 
C. T. Simmons et al.
C. T. Simmons et al.

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