Abstract
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, records vary in their temporal and spatial coverage and 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 16 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, measured using high-precision multi-collector inductively coupled plasma mass spectrometry. We compare our results to published data from ODP Site 872, also in the Western Equatorial Pacific, that goes back to 22 million years ago. These sites are in a region that today is near equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We show that δ11B data from this region are consistent with other boron-based studies. The data show evidence for elevated pCO2 during the Middle Miocene and Early to Middle Pliocene, and reductions in pCO2 of ∼200 ppm during the Middle Miocene Climate Transition, ∼250 ppm during Pliocene Glacial Intensification and ∼50 ppm during the Mid-Pleistocene Climate Transition. During the Mid-Pleistocene Transition there is a minimum pCO2 at marine isotopic stage (MIS) 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion from the Miocene to the late Quaternary.
Highlights
Due to concerns about the long-term consequences of anthropogenic emissions and associated climate change (IPCC, 2014, 2018), efforts have been made to quantify past atmo-Published by Copernicus Publications on behalf of the European Geosciences Union.M
The record we generated does not overlap with Site 872, they are 1 million years (Myr) apart (15.7 and 16.7 Ma); there is a good correspondence between our Mg/Ca data and the published Mg/Ca record from T. trilobus at Site 872 (Sosdian et al, 2018)
Comparison with Site 872 data that are part of the compilation from Sosdian et al (2018) shows that their δ11B data are in line with our dataset (Fig. 2b), and all sites examined in the Western Equatorial Pacific (WEP) (Sites 806, 807, and 872) are above the lysocline (Shipboard Scientific Party, 1991)
Summary
M. Guillermic et al.: Atmospheric CO2 estimates for the Miocene to Pleistocene spheric CO2 and examine past relationships between CO2 and temperature. Guillermic et al.: Atmospheric CO2 estimates for the Miocene to Pleistocene spheric CO2 and examine past relationships between CO2 and temperature Such data are critical for constraining Earth-system sensitivity (Lea, 2004; Lunt et al, 2010; Pagani et al, 2010; Hansen et al, 2012, 2013; Foster and Rohling, 2013; Schmittner et al, 2011; Tierney et al, 2020), but are of broad interest for contextualizing the evolution of climate and geological systems throughout Earth’s history (Tripati et al, 2011; Foster et al, 2017; Tripati and Darby, 2018). There remains a pressing need for robust and higher-resolution atmospheric CO2 records
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