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

• Published in: Climate of the Past
• Main Authors: M. Guillermic, S. Misra, R. Eagle, A. Tripati
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: geo; envir; Pacific; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-18-183-2022; https://cp.copernicus.org/articles/18/183/2022/cp-18-183-2022.pdf; https://doaj.org/article/e56e07c0b30d45e1976c7a5f64a92a7f

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.