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Improving the <I>Ginkgo</I> CO<SUB>2</SUB> barometer: Implications for the early Cenozoic atmosphere

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dc.contributor.author Barclay, Richard S. en
dc.contributor.author Wing, Scott L. en
dc.date.accessioned 2016-09-20T22:35:56Z
dc.date.available 2016-09-20T22:35:56Z
dc.date.issued 2016
dc.identifier.citation Barclay, Richard S. and Wing, Scott L. 2016. "<a href="https://repository.si.edu/handle/10088/29508">Improving the Ginkgo CO2 barometer: Implications for the early Cenozoic atmosphere</a>." <em>Earth and Planetary Science Letters</em>. 439:158&ndash;171. <a href="https://doi.org/10.1016/j.epsl.2016.01.012">https://doi.org/10.1016/j.epsl.2016.01.012</a> en
dc.identifier.issn 0012-821X
dc.identifier.uri https://hdl.handle.net/10088/29508
dc.description.abstract Stomatal properties of fossil Ginkgo have been used widely to infer the atmospheric concentration of CO2 in the geological past (paleo-pCO2). Many of these estimates of paleo-pCO2 have relied on the inverse correlation between pCO2 and stomatal index (SI the proportion of epidermal cells that are stomata) observed in recent Ginkgo biloba, and therefore depend on the accuracy of this relationship. The SI - p CO2 relationship in G. biloba has not been well documented, however. Here we present new measurements of SI for leaves of G. biloba that grew under pCO2 from 290 to 430 ppm. We prepared and imaged all specimens using a consistent procedure and photo-documented each count. As in prior studies, we found a significant inverse relationship between SI and pCO2, however, the relationship is more linear, has a shallower slope, and a lower correlation coefficient than previously reported. We examined leaves of G. biloba grown under pCO2 of 1500 ppm, but found they had highly variable SI and a large proportion of malformed stomata. We also measured stomatal dimensions, stomatal density, and the carbon isotope composition of G. biloba leaves in order to test a mechanistic model for inferring pCO2. This model overestimated observed pCO2, performing less well than the SI method between 290 and 430 ppm. We used our revised SI-pCO2 response curve, and new observations of selected fossils, to estimate late Cretaceous and Cenozoic pCO2 from fossil Ginkgo adiantoides. All but one of the new estimates is below 800 ppm, and together they show little long-term change in pCO2 or relation to global temperature. The low Paleogene pCO2 levels indicated by the Ginkgo SI proxy are not consistent with the high pCO2 inferred by some climate and carbon cycle models. We cannot currently resolve the discrepancy, but greater agreement between proxy data and models may come from a better understanding of the stomatal response of G. biloba to elevated pCO2, better counts and measurements of fossil Ginkgo, or models that can simulate greenhouse climates at lower pCO2. en
dc.relation.ispartof Earth and Planetary Science Letters en
dc.title Improving the <I>Ginkgo</I> CO<SUB>2</SUB> barometer: Implications for the early Cenozoic atmosphere en
dc.type Journal Article en
dc.identifier.srbnumber 139073
dc.identifier.doi 10.1016/j.epsl.2016.01.012
rft.jtitle Earth and Planetary Science Letters
rft.volume 439
rft.spage 158
rft.epage 171
dc.description.SIUnit NH-Paleobiology en
dc.description.SIUnit NMNH en
dc.description.SIUnit Peer-reviewed en
dc.citation.spage 158
dc.citation.epage 171

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