Temperature and atmospheric CO ₂ concentration estimates through the PETM using triple oxygen isotope analysis of mammalian bioapatite

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) is a remarkable climatic and environmental event that occurred 56 Ma ago and has importance for understanding possible future climate change. The Paleocene-Eocene transition is marked by a rapid temperature rise contemporaneous with a large negative carbon isotope excursion (CIE). Both the temperature and the isotopic excursion are well-documented by terrestrial and marine proxies. The CIE was the result of a massive release of carbon into the atmosphere. However, the carbon source and quantities of CO 2 and CH 4 greenhouse gases that contributed to global warming are poorly constrained and highly debated. Here we combine an established oxygen isotope paleothermometer with a newly developed triple oxygen isotope paleo-CO 2 barometer. We attempt to quantify the source of greenhouse gases released during the Paleocene-Eocene transition by analyzing bioapatite of terrestrial mammals. Our results are consistent with previous estimates of PETM temperature change and suggest that not only CO 2 but also massive release of seabed methane was the driver for CIE and PETM.PETM | temperature | CO 2 concentration | mammals

Tracing the oxygen isotope composition of the upper Earth’s atmosphere using cosmic spherules

“…Lower than modern GPP levels would lead to an even higher resolution of calculated CO 2 levels. The reconstruction of CO 2 levels based on 17 O in I-type spherules is therefore considerably more precise than CO 2 reconstruction from 17 O of sulfate1 and reaches far more back into Earth history than 17 O from air inclusions in ice cores42 and fossil mammal bioapatite213. However, to use Δ' 17 O of air oxygen as paleo-CO 2 -barometer the GPP at that time needs to be known14.…”

“…The high δ 18 O of tropospheric O 2 is caused by the Dole effect, whereas the low Δ' 17 O value reflects mass-independent fractionation effects in the stratosphere. The higher the atmospheric CO 2 levels, the lower the Δ' 17 O values1214; a relation that was used as paleo-CO 2 barometer1213.…”

A High‐Fidelity Benthic Stable Isotope Record of Late Cretaceous–Early Eocene Climate Change and Carbon‐Cycling

“…Core photo from Shipboard Scientific Party (). (a) Recalibrated atmospheric p CO 2 data (Anagnostou et al, ; Beerling et al, , ; Cui & Schubert, , ; Demicco et al, ; Fletcher et al, ; Gehler et al, ; Huang et al, ; Koch et al, ; Nordt et al, , ; Royer, , , ; Royer, Berner, et al, ; Royer, Wing, et al, ; Sinha & Stott, ; Steinthorsdottir et al, ; Stott, ; see Figure S2). Horizontal dashed lines indicate pre‐industrial (1), and 2018 (2) levels, along with the most pessimistic emission scenario (RCP8.5) for the year 2100 (3), from Cubasch et al ().…”

“…Cooler global temperatures at this time were likely facilitated by the burial of significant volumes of carbon in either biogenic CH 4 hydrates beneath the continental shelves (Dickens, 2003), lowlatitude peat deposits (Kurtz et al, 2003), or high-latitude permafrost (DeConto et al, 2012), to produce the positive carbon isotope signature of the ocean-atmosphere system that we observe. This period of cool temperatures and carbon sequestration was followed by a long-term warming trend from the Late Paleocene-Early Eocene, triggered by rising atmospheric pCO 2 levels and perhaps an intensification of 10.1029/2019PA003556 (Anagnostou et al, 2016;Beerling et al, 2002Beerling et al, , 2009Cui & Schubert, 2016Demicco et al, 2003;Fletcher et al, 2008;Gehler et al, 2016;Huang et al, 2013;Koch et al, 1992;Nordt et al, 2002Nordt et al, , 2003Royer, 2003Royer, , 2006Royer, , 2014Royer, Wing, et al, 2001;Sinha & Stott, 1994;Steinthorsdottir et al, 2016;Stott, 1992; see Figure S2). Horizontal dashed lines indicate pre-industrial (1), and 2018 (2) levels, along with the most pessimistic emission scenario (RCP8.5) for the year 2100 (3), from Cubasch et al (2013).…”

Sensitivity of the Eocene climate to CO<sub>2</sub> and orbital variability

“…The onset of the PETM, at approximately 55.9 Ma (Westerhold et al, 2009), is recognised as the boundary between the Palaeocene and Eocene epochs (Aubry et al, 2007), and is characterised by a large CIE, indicating large GHG emissions, accompanied by a sudden rise in global temperature (Kennett and Stott, 1991), extensive extinction and origination of nanoplankton (Gibbs et al, 2006) and widespread ocean anoxia (Dickson et al, 2012). There is some evidence from analysis and modelling of the timing and duration of variations in δ 13 C and δ 18 O observed in nanoplankton fossils that some of the GHG emissions were initially in the form of CH 4 (Dickens, 2011;Lunt et al, 2011;Thomas et al, 2002), which is rapidly oxidised in the atmosphere to CO 2 .…”