Estimates of late middle Eocene &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; based on stomatal density of modern and fossil &amp;lt;i&amp;gt;Nageia&amp;lt;/i&amp;gt; leaves

Liu, Xiaoyan; Gao, Qi; Meng, Han; Jin, Jianhua

doi:10.5194/cp-12-241-2016

Cited by 11 publications

(13 citation statements)

References 75 publications

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“…Stomatal proxy pCO 2 reconstructions currently offer the highest-resolution record of Eocene pCO 2 , with almost 50 data points, compared to ∼10 each derived from marine alkenone and boron isotopes, and ∼20 from paleosols. The numerous studies, using various fossil angiosperms as well as the fossil gymnosperms Ginkgo and Metasequoia, in the three stomatal proxy methods currently in use mostly agree that the Eocene pCO 2 was more moderately elevated compared to what marine proxies and climate modeling suggest (McElwain, 1998;Kürschner et al, 2001;Royer et al, 2001;Greenwood et al, 2003b;Retallack, 2009;Smith et al, 2010;Doria et al, 2011;Grein et al, 2011;Roth-Nebelsick et al, 2012;Franks et al, 2014;Maxbauer et al, 2014;Liu et al, 2016;Steinthorsdottir et al, 2016;Wolfe et al, 2017). The discrepancy between the marine isotope and stomatal proxy pCO 2 results is considerable, with the marine isotopes recording pCO 2 currently assumed to be more consistent with the elevated Eocene temperatures recorded by numerous proxies and the workings of the Earth's climate system (Cramwinckel et al, 2018).…”

Section: Comparison To Existing Pco 2 Records and Implicationsmentioning

confidence: 99%

Moderate levels of Eocene pCO2 indicated by Southern Hemisphere fossil plant stomata

Steinthorsdottir

Vajda

Pole³

et al. 2019

Geology

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Reducing the uncertainty in predictions of future climate change is one of today’s greatest scientific challenges, with many significant problems unsolved, including the relationship between pCO2 and global temperature. To better constrain these forecasts, it is meaningful to study past time intervals of global warmth, such as the Eocene (56.0–33.9 Ma), serving as climatic analogues for the future. Here we reconstructed pCO2 using the stomatal densities of a large fossil Lauraceae (laurel) leaf database from ten sites across the Eocene of Australia and New Zealand. We show that mostly moderate pCO2 levels of ∼450–600 ppm prevailed throughout the Eocene, levels that are considerably lower than the pCO2 forcing currently needed to recreate Eocene temperatures in climate models. Our data record significantly lower pCO2 than inferred from marine isotopes, but concur with previously published Northern Hemisphere Eocene stomatal proxy pCO2. We argue that the now globally consistent stomatal proxy pCO2 record for the Eocene is robust and that climate sensitivity was elevated and/or that additional climate forcings operated more powerfully than previously assumed.

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Section: Comparison To Existing Pco 2 Records and Implicationsmentioning

confidence: 99%

Moderate levels of Eocene pCO2 indicated by Southern Hemisphere fossil plant stomata

Steinthorsdottir

Vajda

Pole³

et al. 2019

Geology

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“…In order to clarify the definition of two key stratigraphic features, we recommend using the following terms: (i) for the basal Oligocene δ 18 O increase we suggest the term "earliest Oligocene oxygen isotope step" (EOIS) to denote the large isotope step that occurs well after the EOB and within the lower part of chron C13n (Fig. 1); (ii) we suggest the term "early Oligocene glacial maximum" (EOGM; Liu et al, 2004;Fig. 1) to denote the peak-to-peak isotope stratigraphic interval, corresponding to most of chron C13n (starting at the top of the EOIS).…”

Section: Terminology Of the Eocene-oligocene Transitionmentioning

confidence: 99%

“…Summary of Eocene Oligocene terminology and approximate timings of events, as interpreted at the time of writing. Timescales referred to are GTS2012 (Gradstein et al, 2012) and CK95 (Cande and Kent, 1995 Liu et al (2004). The end of the EOGM may correspond to a second δ 18 O peak, sometimes referred to as Oi-1b…”

Section: Terminology Of the Eocene-oligocene Transitionmentioning

confidence: 99%

The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons

et al. 2021

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Abstract. The Eocene–Oligocene transition (EOT) was a climate shift from a largely ice-free greenhouse world to an icehouse climate, involving the first major glaciation of Antarctica and global cooling occurring ∼34 million years ago (Ma) and lasting ∼790 kyr. The change is marked by a global shift in deep-sea δ18O representing a combination of deep-ocean cooling and growth in land ice volume. At the same time, multiple independent proxies for ocean temperature indicate sea surface cooling, and major changes in global fauna and flora record a shift toward more cold-climate-adapted species. The two principal suggested explanations of this transition are a decline in atmospheric CO2 and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. Here we review and synthesise proxy evidence of palaeogeography, temperature, ice sheets, ocean circulation and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of climate model simulations of temperature change across the EOT. The simulations compare three forcing mechanisms across the EOT: CO2 decrease, palaeogeographic changes and ice sheet growth. Our model ensemble results demonstrate the need for a global cooling mechanism beyond the imposition of an ice sheet or palaeogeographic changes. We find that CO2 forcing involving a large decrease in CO2 of ca. 40 % (∼325 ppm drop) provides the best fit to the available proxy evidence, with ice sheet and palaeogeographic changes playing a secondary role. While this large decrease is consistent with some CO2 proxy records (the extreme endmember of decrease), the positive feedback mechanisms on ice growth are so strong that a modest CO2 decrease beyond a critical threshold for ice sheet initiation is well capable of triggering rapid ice sheet growth. Thus, the amplitude of CO2 decrease signalled by our data–model comparison should be considered an upper estimate and perhaps artificially large, not least because the current generation of climate models do not include dynamic ice sheets and in some cases may be under-sensitive to CO2 forcing. The model ensemble also cannot exclude the possibility that palaeogeographic changes could have triggered a reduction in CO2.

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“…Two studies with restricted temporal ranges reconstructed pCO2 in the Bartonian, indicating 400-500 ppm using Metasequoia from Canada (Maxbauer et al, 2014) and ~390 ppm using the podocarp conifer Nageia maomigensis from China (Liu et al, 2016).…”

Section: Terrestrial Proxiesmentioning

confidence: 99%

The Eocene-Oligocene transition: a review of marine and terrestrial proxy data, models and model-data comparisons

Hutchinson¹,

Coxall²,

Lunt³

et al. 2020

Preprint

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Abstract. The Eocene-Oligocene transition (EOT) from a largely ice-free greenhouse world to an icehouse climate with the first major glaciation of Antarctica was a phase of major climate and environmental change occurring ~34 million years ago (Ma) and lasting ~500 kyr. The change is marked by a global shift in deep sea δ18O representing a combination of deep-ocean cooling and global ice sheet growth. At the same time, multiple independent proxies for sea surface temperature indicate a surface ocean cooling, and major changes in global fauna and flora record a shift toward more cold-climate adapted species. The major explanations of this transition that have been suggested are a decline in atmospheric CO2, and changes to ocean gateways, while orbital forcing likely influenced the precise timing of the glaciation. This work reviews and synthesises proxy evidence of paleogeography, temperature, ice sheets, ocean circulation, and CO2 change from the marine and terrestrial realms. Furthermore, we quantitatively compare proxy records of change to an ensemble of model simulations of temperature change across the EOT. The model simulations compare three forcing mechanisms across the EOT: CO2 decrease, paleogeographic changes, and ice sheet growth. We find that CO2 forcing provides by far the best explanation of the combined proxy evidence, and based on our model ensemble, we estimate that a CO2 decrease of about 1.6× across the EOT (e.g. from 910 to 560 ppmv) achieves the best fit to the temperature change recorded in the proxies. This model-derived CO2 decrease is consistent with proxy estimates of CO2 decline at the EOT.

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Estimates of late middle Eocene <i>p</i>CO<sub>2</sub> based on stomatal density of modern and fossil <i>Nageia</i> leaves

Cited by 11 publications

References 75 publications

Moderate levels of Eocene pCO2 indicated by Southern Hemisphere fossil plant stomata

Moderate levels of Eocene pCO2 indicated by Southern Hemisphere fossil plant stomata

The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons

The Eocene-Oligocene transition: a review of marine and terrestrial proxy data, models and model-data comparisons

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