Preprints
https://doi.org/10.5194/cp-2020-158
https://doi.org/10.5194/cp-2020-158

  08 Feb 2021

08 Feb 2021

Review status: this preprint is currently under review for the journal CP.

Atmospheric CO2 estimates for the Miocene to Pleistocene based on foraminiferal δ11B at Ocean Drilling Program Sites 806 and 807 in the Western Equatorial Pacific

Maxence Guillermic1,2, Sambuddha Misra3,4, Robert Eagle1,2, and Aradhna Tripati1,2 Maxence Guillermic et al.
  • 1Department of Atmospheric and Oceanic Sciences, Department of Earth, Planetary, and Space Sciences, Center for Diverse Leadership in Science, Institute of the Environment and Sustainability, University of California – Los Angeles, Los Angeles, CA 90095 USA
  • 2Laboratoire Géosciences Océan UMR6538, UBO, Institut Universitaire Européen de la Mer, Rue Dumont d'Urville, 29280, Plouzané, France
  • 3The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, UK
  • 4Indian Institute of Science, Centre for Earth Sciences, Bengaluru, Karnataka 560012, India

Abstract. Constraints on the evolution of atmospheric CO2 levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, estimates of past CO2 levels do not always converge and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO2 values across major climate transitions over the past 17 million years using the boron isotopic composition (δ11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807. These sites are in a region that today is in equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We use high-precision multi-collector inductively-coupled plasma mass spectrometry and show that data from these sites can reproduce the ice core record. Estimates of early Miocene pCO2 are generally higher than published reconstructions from other sites, while values for the Pliocene and Pleistocene are more similar to other datasets. We find evidence for reductions in pCO2 of ~280 µatm during the Middle Miocene Climate Transition, ~270 µatm during Pliocene Glacial Intensification, and ~50 µatm during the Mid-Pleistocene Climate Transition. There is possible evidence for a larger reduction in glacial pCO2 during the Mid-Pleistocene Transition compared to interglacial pCO2, and a minimum in pCO2 during glacial MIS 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion throughout the past 17 million years.

Maxence Guillermic et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2020-158', Thomas Chalk, 22 Mar 2021
    • AC1: 'Reply on RC1', Maxence Guillermic, 16 Jun 2021
  • RC2: 'Comment on cp-2020-158', Anonymous Referee #2, 10 Apr 2021
    • AC2: 'Reply on RC2', Maxence Guillermic, 16 Jun 2021

Maxence Guillermic et al.

Maxence Guillermic et al.

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Short summary
Here we reconstruct atmospheric CO2 values across major climate transitions over the past 17 million years (Myrs) from two sites in the West Pacific Warm Pool and using a pH proxy on surface dwellers foraminifera. We are able to accurately reproduce pCO2 data from ice cores, therefore we apply the same framework to older samples to create a long-term pH and pCO2 reconstruction. We give quantitative constraints on pH and pCO2 changes over the main climate transitions of the last 17 Myrs.