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Warm tropical sea surface temperatures in the Late Cretaceous and Eocene epochs

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TLDR
New data from exceptionally well preserved foraminifer shells extracted from impermeable clay-rich sediments indicate that for the intervals studied, tropical sea surface temperatures were at least 28–32 °C, more in line with the understanding of the geographical distributions of temperature-sensitive fossil organisms and the results of climate models with increased CO2 levels.
Abstract
Climate models with increased levels of carbon dioxide predict that global warming causes heating in the tropics, but investigations of ancient climates based on palaeodata have generally indicated cool tropical temperatures during supposed greenhouse episodes. For example, in the Late Cretaceous and Eocene epochs there is abundant geological evidence for warm, mostly ice-free poles, but tropical sea surface temperatures are generally estimated to be only 15-23 degrees C, based on oxygen isotope palaeothermometry of surface-dwelling planktonic foraminifer shells. Here we question the validity of most such data on the grounds of poor preservation and diagenetic alteration. We present new data from exceptionally well preserved foraminifer shells extracted from impermeable clay-rich sediments, which indicate that for the intervals studied, tropical sea surface temperatures were at least 28-32 degrees C. These warm temperatures are more in line with our understanding of the geographical distributions of temperature-sensitive fossil organisms and the results of climate models with increased CO2 levels.

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Marked Decline in Atmospheric Carbon Dioxide Concentrations During the Paleogene

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Oceanic anoxic events and plankton evolution: Biotic response to tectonic forcing during the mid-Cretaceous

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CO2-forced climate thresholds during the Phanerozoic

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References
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Journal ArticleDOI

Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

TL;DR: This work focuses primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records.
Journal ArticleDOI

Atmospheric carbon dioxide concentrations over the past 60 million years

TL;DR: The boron-isotope ratios of ancient planktonic foraminifer shells are used to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations.
Book

Modern Planktonic Foraminifera

TL;DR: This chapter discusses the taxonomy and Species Features of Spinose Planktonic Foraminifera, and the development of Symbiosis, Commensalism and Parasitism, as well as the relationships between Symbiont Morphology and Host Physiological Interactions.
Journal ArticleDOI

Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes

TL;DR: In this paper, the authors reported experimental measurements on living symbiotic and non-symbiotic plankton foraminifera (Orbulina universa and Globigerina bulloides respectively) showing that the 13C/12C and 18O/16O ratios of the calcite shells decrease with increasing seawater [CO32−].
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