Atmospheric pCO2 reconstructed across five early Eocene global warming events

Ying Cui, Brian A. Schubert

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Multiple short-lived global warming events, known as hyperthermals, occurred during the early Eocene (56–52 Ma). Five of these events – the Paleocene–Eocene Thermal Maximum (PETM or ETM1), H1 (or ETM2), H2, I1, and I2 – are marked by a carbon isotope excursion (CIE) within both marine and terrestrial sediments. The magnitude of CIE, which is a function of the amount and isotopic composition of carbon added to the ocean–atmosphere system, varies significantly between marine versus terrestrial substrates. Here we use the increase in carbon isotope fractionation by C3 land plants in response to increased pCO2 to reconcile this difference and reconstruct a range of background pCO2 and peak pCO2 for each CIE, provided two potential carbon sources: methane hydrate destabilization and permafrost-thawing/organic matter oxidation. Although the uncertainty on each pCO2 estimate using this approach is low (e.g., median uncertainty = +23%/−18%), this work highlights the potential for significant systematic bias in the pCO2 estimate resulting from sampling resolution, substrate type, diagenesis, and environmental change. Careful consideration of each of these factors is required especially when applying this approach to a single marine–terrestrial CIE pair. Given these limitations, we provide an upper estimate for background early Eocene pCO2 of 463 +248/−131 ppmv (methane hydrate scenario) to 806 +127/−104 ppmv (permafrost-thawing/organic matter oxidation scenario). These results, which represent the first pCO2 proxy estimates directly tied to the Eocene hyperthermals, demonstrate that early Eocene warmth was supported by background pCO2 less than ∼3.5× preindustrial levels and that pCO2>1000 ppmv may have occurred only briefly, during hyperthermal events.

Original languageEnglish
Pages (from-to)225-233
Number of pages9
JournalEarth and Planetary Science Letters
Volume478
DOIs
StatePublished - 15 Nov 2017

Fingerprint

Carbon Isotopes
carbon isotopes
global warming
Global warming
carbon isotope
Eocene
permafrost
Permafrost
Thawing
Methane
thawing
estimates
Hydrates
hydrates
Biological materials
Carbon
methane
melting
oxidation
organic matter

Keywords

  • C land plant proxy
  • early Eocene
  • hyperthermals
  • pCO

Cite this

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title = "Atmospheric pCO2 reconstructed across five early Eocene global warming events",
abstract = "Multiple short-lived global warming events, known as hyperthermals, occurred during the early Eocene (56–52 Ma). Five of these events – the Paleocene–Eocene Thermal Maximum (PETM or ETM1), H1 (or ETM2), H2, I1, and I2 – are marked by a carbon isotope excursion (CIE) within both marine and terrestrial sediments. The magnitude of CIE, which is a function of the amount and isotopic composition of carbon added to the ocean–atmosphere system, varies significantly between marine versus terrestrial substrates. Here we use the increase in carbon isotope fractionation by C3 land plants in response to increased pCO2 to reconcile this difference and reconstruct a range of background pCO2 and peak pCO2 for each CIE, provided two potential carbon sources: methane hydrate destabilization and permafrost-thawing/organic matter oxidation. Although the uncertainty on each pCO2 estimate using this approach is low (e.g., median uncertainty = +23{\%}/−18{\%}), this work highlights the potential for significant systematic bias in the pCO2 estimate resulting from sampling resolution, substrate type, diagenesis, and environmental change. Careful consideration of each of these factors is required especially when applying this approach to a single marine–terrestrial CIE pair. Given these limitations, we provide an upper estimate for background early Eocene pCO2 of 463 +248/−131 ppmv (methane hydrate scenario) to 806 +127/−104 ppmv (permafrost-thawing/organic matter oxidation scenario). These results, which represent the first pCO2 proxy estimates directly tied to the Eocene hyperthermals, demonstrate that early Eocene warmth was supported by background pCO2 less than ∼3.5× preindustrial levels and that pCO2>1000 ppmv may have occurred only briefly, during hyperthermal events.",
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Atmospheric pCO2 reconstructed across five early Eocene global warming events. / Cui, Ying; Schubert, Brian A.

In: Earth and Planetary Science Letters, Vol. 478, 15.11.2017, p. 225-233.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Atmospheric pCO2 reconstructed across five early Eocene global warming events

AU - Cui, Ying

AU - Schubert, Brian A.

PY - 2017/11/15

Y1 - 2017/11/15

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AB - Multiple short-lived global warming events, known as hyperthermals, occurred during the early Eocene (56–52 Ma). Five of these events – the Paleocene–Eocene Thermal Maximum (PETM or ETM1), H1 (or ETM2), H2, I1, and I2 – are marked by a carbon isotope excursion (CIE) within both marine and terrestrial sediments. The magnitude of CIE, which is a function of the amount and isotopic composition of carbon added to the ocean–atmosphere system, varies significantly between marine versus terrestrial substrates. Here we use the increase in carbon isotope fractionation by C3 land plants in response to increased pCO2 to reconcile this difference and reconstruct a range of background pCO2 and peak pCO2 for each CIE, provided two potential carbon sources: methane hydrate destabilization and permafrost-thawing/organic matter oxidation. Although the uncertainty on each pCO2 estimate using this approach is low (e.g., median uncertainty = +23%/−18%), this work highlights the potential for significant systematic bias in the pCO2 estimate resulting from sampling resolution, substrate type, diagenesis, and environmental change. Careful consideration of each of these factors is required especially when applying this approach to a single marine–terrestrial CIE pair. Given these limitations, we provide an upper estimate for background early Eocene pCO2 of 463 +248/−131 ppmv (methane hydrate scenario) to 806 +127/−104 ppmv (permafrost-thawing/organic matter oxidation scenario). These results, which represent the first pCO2 proxy estimates directly tied to the Eocene hyperthermals, demonstrate that early Eocene warmth was supported by background pCO2 less than ∼3.5× preindustrial levels and that pCO2>1000 ppmv may have occurred only briefly, during hyperthermal events.

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