Preprints
https://doi.org/10.5194/egusphere-2022-574
https://doi.org/10.5194/egusphere-2022-574
 
14 Jul 2022
14 Jul 2022
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

Predicting trends in atmospheric CO2 across the Mid-Pleistocene Transition using existing climate archives

Jordan R. W. Martin1, Joel Pedro2,3, and Tessa R. Vance3 Jordan R. W. Martin et al.
  • 1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7004, Australia
  • 2Australian Antarctic Division, Kingston, 7050, Australia
  • 3Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, 7004, Australia

Abstract. During the Mid-Pleistocene Transition (MPT), ca. 1250–800 kya, the Earth’s glacial cycles changed from 41 ky to 100 ky periodicity. The emergence of this longer ice-age periodicity was accompanied by higher global ice volume in glacial periods and lower global ice volume in interglacial periods. Since there is no known change in external orbital forcing across the MPT, it is generally agreed that the cause of this transition is internal to the earth system. Resolving the climate–carbon cycle–cryosphere dynamics processes responsible for the MPT remains a major challenge in ice core and climate science. To address this challenge, the international ice core community has prioritized recovery of an ice core record spanning the MPT interval. The results from such ‘oldest ice’ projects are still several years away. Our objective here it to make an advanced prediction of atmospheric CO2 out to 1.5 my. Our prediction utilizes existing records of atmospheric carbon dioxide (CO2) from Antarctic ice cores spanning the past 800 ky along with the existing benthic water stable isotope (ẟ18O) record from marine sediment cores. Our predictions assume that the relationship between CO2 and benthic ẟ18O over the past 800 thousand years can be extended over the last one and a half million years. The implied null hypothesis is that there has been no fundamental change in the global climate–carbon cycle–cryosphere feedback systems across the MPT. We find that our predicted CO2 record is significantly lower during glacial intervals than the existing blue-ice and boron isotope-based estimates of CO2 that pre-date the continuous 800 ky CO2 record. Our predicted glacial CO2 concentrations are ~9 ppm below glacial CO2 concentrations observed in blue ice data at ca. 1 mya and ~19 ppm below glacial CO2 concentrations reconstructed from boron isotopic data over ca ~1.1–1.25 mya. These results support rejection of our null hypothesis and provide quantitative evidence of a fundamental shift in the global climate–carbon cycle–cryosphere feedback systems across the MPT. However, the definitive test of the various theories explaining the MPT will be comparison of our predicted records with the forthcoming oldest ice core records.

Jordan R. W. Martin et al.

Status: open (until 08 Sep 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-574: Very simple analysis', Anonymous Referee #1, 12 Aug 2022 reply
  • RC2: 'Comment on egusphere-2022-574', Anonymous Referee #2, 16 Aug 2022 reply
  • CC1: 'Comment on egusphere-2022-574', Peter Köhler, 18 Aug 2022 reply

Jordan R. W. Martin et al.

Jordan R. W. Martin et al.

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Short summary
This study uses existing paleo-climate archive and simple statistical modelling to predict atmospheric trends across the Mid-Pleistocene Transition, and ahead of the global efforts to retrieve the oldest ice from Antarctica. We find evidence to suggest a change in the global carbon-climate feedback system over this time that supports theories to the cause of the transition. The change is characterised by glacial stage reduction of carbon dioxide from 1250–750 thousand years ago.