Abstract
The early Eocene (c. 56 - 48 million years ago) experienced some of the highest global temperatures in Earth’s history since the Mesozoic, with no polar ice. Reports of contradictory ice-rafted erratics and cold water glendonites in the higher latitudes have been largely dismissed due to ambiguity of the significance of these purported cold-climate indicators. Here we apply clumped isotope paleothermometry to a traditionally qualitative abiotic proxy, glendonite calcite, to generate quantitative temperature estimates for northern mid-latitude bottom waters. Our data show that the glendonites of the Danish Basin formed in waters below 5 °C, at water depths of <300 m. Such near-freezing temperatures have not previously been reconstructed from proxy data for anywhere on the early Eocene Earth, and these data therefore suggest that regionalised cool episodes punctuated the background warmth of the early Eocene, likely linked to eruptive phases of the North Atlantic Igneous Province.
Highlights
The early Eocene (c. 56 - 48 million years ago) experienced some of the highest global temperatures in Earth’s history since the Mesozoic, with no polar ice
The characterisation of the glendonites is based on Scanning Electron Microscopy (SEM), cathodoluminescence (CL) and light microscopy (Fig. 3), stable isotope (Fig. 4) and minor element analysis (Table 1), clumped isotope thermometry (Table 1), and organic biomarker extraction (Table 2 and Fig. 5), with details of the analyses in the Methods section
10% from dissolved inorganic carbon (DIC), or c. 50% was from methane and 50% from DIC (Fig. 4)
Summary
The early Eocene (c. 56 - 48 million years ago) experienced some of the highest global temperatures in Earth’s history since the Mesozoic, with no polar ice. Despite a large body of evidence for globally warm background conditions throughout the early Eocene[2,3], there are reports of glacial sediments and glendonites from the high latitudes, suggesting that episodic cooler intervals may have interrupted the Eocene warmth[4,5,6]. Glendonites are traditionally considered cold-climate indicators, due to the temperature-dependency of their parent ikaite in natural settings, and the fact that they are found in paleo-high latitude sediments frequently associated with glacial deposits[13]. Their presence in early- and mid-Eocene deposits from North America[14] Quantitative temperature reconstructions for the glendonites are needed to test if the glendonites of early Eocene Denmark are indicative of very low temperatures (≤4 °C8)
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