Abstract
The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state.
Highlights
The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago
Our Hg records provide evidence that the onset of the PETM was triggered by volcanic activity, but we find at least one other carbon reservoir must have subsequently been released as Hg and Hg/total organic carbon (TOC) decline in the second part of the PETM onset
Average shale Hg over the Phanerozoic has been estimated as 62 ppb, and average Hg/TOC as 71.9 ppb/ wt%, these datasets are skewed towards studies of Large Igneous Province volcanism and may be above overall average shale background
Summary
The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. We report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. 1234567890():,; The relative geological rapidity of warming and CO2 release at the Paleocene–Eocene Thermal Maximum (PETM), and the potential activation of feedbacks between warming and organic carbon reservoirs ~56 million years ago[1], have relevance to understanding future Earth system responses to ongoing anthropogenic perturbation[2]. Plausible carbon sources include peatlands and permafrost[3], methane hydrates[8], sedimentary marine organic matter[9,10], and the mantle[5], while proposed hypotheses for the PETM trigger include changes in orbital insolation[1,3,11], volcanic activity of the North Atlantic Igneous Province (NAIP, Fig. 1)[12,13], and an extra-terrestrial impact[14]. To constrain the timing of pulsed volcanism across the PETM and help elucidate its role as a trigger, we present the first high-resolution records of Hg from sediment cores 22/10a−4 (ref. 26) and E−8X (~100–500 years per sample; Figs. 1 and 2)
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