No Evidence for a Large Atmospheric CO<sub>2</sub> Spike Across the Cretaceous‐Paleogene Boundary

Milligan, Joseph; Royer, Dana L.; Franks, Peter J.; Upchurch, Garland R.; McKee, Melissa L.

doi:10.1029/2018gl081215

Cited by 34 publications

(35 citation statements)

References 100 publications

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“…We can also assess the roles of different initial atmospheric pCO 2 concentrations and equilibrium climate sensitivity values. In the early Paleocene, background pCO 2 is estimated to be ~300–600 ppm (Milligan et al, 2019), and equilibrium climate sensitivity in the ice‐free early Paleocene is estimated to be 3°C per pCO 2 doubling (Royer, 2016).…”

Section: Discussionmentioning

confidence: 99%

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From⁴⁰Ar/³⁹Ar Dates, Magnetostratigraphy, and Biostratigraphy

Fendley

Sprain

Renne

et al. 2020

Geochem Geophys Geosyst

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Deccan Traps flood basalt volcanism affected ecosystems spanning the end‐Cretaceous mass extinction, with the most significant environmental effects hypothesized to be a consequence of the largest eruptions. The Rajahmundry Traps are the farthest exposures (~1,000 km) of Deccan basalt from the putative eruptive centers in the Western Ghats and hence represent some of the largest volume Deccan eruptions. Although the three subaerial Rajahmundry lava flows have been geochemically correlated to the Wai Subgroup of the Deccan Traps, poor precision associated with previous radioisotopic age constraints has prevented detailed comparison with potential climate effects. In this study, we use new 40Ar/39Ar dates, paleomagnetic and volcanological analyses, and biostratigraphic constraints for the Rajahmundry lava flows to ascertain the timing and style of their emplacement. We find that the lower and middle flows (65.92 ± 0.25 and 65.67 ± 0.08 Ma, ±1σ systematic uncertainty) were erupted within magnetochron C29r and were a part of the Ambenali Formation of the Deccan Traps. By contrast, the uppermost flow (65.27 ± 0.08 Ma) was erupted in C29n as part of the Mahabaleshwar Formation. Given these age constraints, the Rajahmundry flows were not involved in the end‐Cretaceous extinction as previously hypothesized. To determine whether the emplacement of the Rajahmundry flows could have affected global climate, we estimated their eruptive CO2 release and corresponding climate change using scalings from the LOSCAR carbon cycle model. We find that the eruptive gas emissions of these flows were insufficient to directly cause multi‐degree warming; hence, a causal relationship with significant climate warming requires additional Earth system feedbacks.

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Section: Discussionmentioning

confidence: 99%

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From⁴⁰Ar/³⁹Ar Dates, Magnetostratigraphy, and Biostratigraphy

Fendley

Sprain

Renne

et al. 2020

Geochem Geophys Geosyst

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“…SI is less affected than SD by additional environmental and physiological factors besides p CO 2 , such as irradiance levels, moisture, and leaf expansion (Salisbury, 1927). The stomatal proxy methods are by now well‐established in the paleoclimate literature, having been applied to a plethora of plant taxa from a wide variety of geological, ecological, and climatological backgrounds to reconstruct paleo‐ p CO 2 from the Paleozoic until today, generally showing remarkable intermethod consistency (e.g., Barclay & Wing, 2016; Grein et al, 2013; Kürschner et al, 2008; Li et al, 2019; Londoño et al, 2018; Mays et al, 2015; McElwain & Steinthorsdottir, 2017; Milligan et al, 2019; Montañez et al, 2016; Reichgelt et al, 2013; Royer et al, 2001; Steinthorsdottir et al, 2011, 2013; Steinthorsdottir, Porter, et al, 2016; Steinthorsdottir, Vajda, Pole, & Holdgate, 2019; Steinthorsdottir, Vajda, & Pole, 2019; Steinthorsdottir & Vajda, 2015; Tesfamichael et al, 2017; Wagner et al, 1996; Zhou et al, 2020) and are considered one of four most useful proxies for paleo‐ p CO 2 (Beerling & Royer, 2011).…”

Section: Methodsmentioning

confidence: 99%

Near‐Future pCO₂ During the Hot Miocene Climatic Optimum

Steinthorsdottir

Jardine

Rember

2021

Paleoceanog and Paleoclimatol

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To improve future predictions of anthropogenic climate change, a better understanding of the relationship between global temperature and atmospheric concentrations of CO2 (pCO2), or climate sensitivity, is urgently required. Analyzing proxy data from climate change episodes in the past is necessary to achieve this goal, with certain geologic periods, such as the Miocene climatic optimum (MCO), a transient period of global warming with global temperatures up to ~7°C higher than today, increasingly viewed as good analogues to future climate under present emission scenarios. However, a problem remains that climate models cannot reproduce MCO temperatures with less than ~800 ppm pCO2, while most previously published proxies record pCO2 < 450 ppm. Here, we reconstructed MCO pCO2 with a multitaxon fossil leaf database from the well‐dated MCO Lagerstätte deposits of Clarkia, Idaho, USA, using four current methods of pCO2 reconstructions. The methods are principally based on either stomatal densities, carbon isotopes, or a combination of both—thus offering independent results. The total of six reconstructions mostly record pCO2 of ~450–550 ppm. Although slightly higher than previously reconstructed pCO2, the discrepancy with the ~800 ppm required by climate models remains. We conclude that climate sensitivity was heightened during MCO, indicating that highly elevated temperatures can occur at relatively moderate pCO2. Ever higher climate sensitivity with rising temperatures should be very seriously considered in future predictions of climate change.

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“…This was a key message sent by the associated "News and Views" piece in the same issue of Science (Burgess, 2019), and the notion that the U−Pb and 40 Ar/ 39 Ar datasets disagreed substantially has been propagated by subsequent discussion and news coverage on Sci-enceMag.org (Kerr and Ward, 2019;Voosen, 2019). Authors of subsequent papers (Henehan et al, 2019;Hull et al, 2020;Linzmeier et al, 2020;Milligan et al, 2019;Montanari and Coccioni, 2019;Sepúlveda et al, 2019) also seem to conclude that the datasets do not agree on the eruption rates of the Deccan Traps and/or that the dataset of Sprain et al (2019) suggests an inflection in eruption rates of Deccan Traps at the KPB.…”

Section: Introductionmentioning

confidence: 99%

An evaluation of Deccan Traps eruption rates using geochronologic data

et al. 2021

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Abstract. Recent attempts to establish the eruptive history of the Deccan Traps large igneous province have used both U−Pb (Schoene et al., 2019) and 40Ar/39Ar (Sprain et al., 2019) geochronology. Both of these studies report dates with high precision and unprecedented coverage for a large igneous province and agree that the main phase of eruptions began near the C30n–C29r magnetic reversal and waned shortly after the C29r–C29n reversal, totaling ∼ 700–800 kyr duration. These datasets can be analyzed in finer detail to determine eruption rates, which are critical for connecting volcanism, associated volatile emissions, and any potential effects on the Earth's climate before and after the Cretaceous–Paleogene boundary (KPB). It is our observation that the community has frequently misinterpreted how the eruption rates derived from these two datasets vary across the KPB. The U−Pb dataset of Schoene et al. (2019) was interpreted by those authors to indicate four major eruptive pulses before and after the KPB. The 40Ar/39Ar dataset did not identify such pulses and has been largely interpreted by the community to indicate an increase in eruption rates coincident with the Chicxulub impact (Renne et al., 2015; Richards et al., 2015). Although the overall agreement in eruption duration is an achievement for geochronology, it is important to clarify the limitations in comparing the two datasets and to highlight paths toward achieving higher-resolution eruption models for the Deccan Traps and for other large igneous provinces. Here, we generate chronostratigraphic models for both datasets using the same statistical techniques and show that the two datasets agree very well. More specifically, we infer that (1) age modeling of the 40Ar/39Ar dataset results in constant eruption rates with relatively large uncertainties through the duration of the Deccan Traps eruptions and provides no support for (or evidence against) the pulses identified by the U−Pb data, (2) the stratigraphic positions of the Chicxulub impact using the 40Ar/39Ar and U−Pb datasets do not agree within their uncertainties, and (3) neither dataset supports the notion of an increase in eruption rate as a result of the Chicxulub impact. We then discuss the importance of systematic uncertainties between the dating methods that challenge direct comparisons between them, and we highlight the geologic uncertainties, such as regional stratigraphic correlations, that need to be tested to ensure the accuracy of eruption models. While the production of precise and accurate geochronologic data is of course essential to studies of Earth history, our analysis underscores that the accuracy of a final result is also critically dependent on how such data are interpreted and presented to the broader community of geoscientists.

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No Evidence for a Large Atmospheric CO₂ Spike Across the Cretaceous‐Paleogene Boundary

Cited by 34 publications

References 100 publications

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From⁴⁰Ar/³⁹Ar Dates, Magnetostratigraphy, and Biostratigraphy

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From⁴⁰Ar/³⁹Ar Dates, Magnetostratigraphy, and Biostratigraphy

Near‐Future pCO₂ During the Hot Miocene Climatic Optimum

An evaluation of Deccan Traps eruption rates using geochronologic data

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No Evidence for a Large Atmospheric CO2 Spike Across the Cretaceous‐Paleogene Boundary

Cited by 34 publications

References 100 publications

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy

Near‐Future pCO2 During the Hot Miocene Climatic Optimum

An evaluation of Deccan Traps eruption rates using geochronologic data

Contact Info

Product

Resources

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No Evidence for a Large Atmospheric CO₂ Spike Across the Cretaceous‐Paleogene Boundary

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From⁴⁰Ar/³⁹Ar Dates, Magnetostratigraphy, and Biostratigraphy

No Cretaceous‐Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From⁴⁰Ar/³⁹Ar Dates, Magnetostratigraphy, and Biostratigraphy

Near‐Future pCO₂ During the Hot Miocene Climatic Optimum