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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 10 | Copyright
Clim. Past, 14, 1515-1527, 2018
https://doi.org/10.5194/cp-14-1515-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 22 Oct 2018

Research article | 22 Oct 2018

Reduced carbon cycle resilience across the Palaeocene–Eocene Thermal Maximum

David I. Armstrong McKay1,2 and Timothy M. Lenton3 David I. Armstrong McKay and Timothy M. Lenton
  • 1Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton, SO14 3ZY, UK
  • 2Stockholm Resilience Centre, Stockholm University, Kräftriket 2B, 10691 Stockholm, Sweden
  • 3Earth System Science group, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4QE, UK

Abstract. Several past episodes of rapid carbon cycle and climate change are hypothesised to be the result of the Earth system reaching a tipping point beyond which an abrupt transition to a new state occurs. At the Palaeocene–Eocene Thermal Maximum (PETM) at  ∼ 56Ma and at subsequent hyperthermal events, hypothesised tipping points involve the abrupt transfer of carbon from surface reservoirs to the atmosphere. Theory suggests that tipping points in complex dynamical systems should be preceded by critical slowing down of their dynamics, including increasing temporal autocorrelation and variability. However, reliably detecting these indicators in palaeorecords is challenging, with issues of data quality, false positives, and parameter selection potentially affecting reliability. Here we show that in a sufficiently long, high-resolution palaeorecord there is consistent evidence of destabilisation of the carbon cycle in the  ∼ 1.5Myr prior to the PETM, elevated carbon cycle and climate instability following both the PETM and Eocene Thermal Maximum 2 (ETM2), and different drivers of carbon cycle dynamics preceding the PETM and ETM2 events. Our results indicate a loss of resilience (weakened stabilising negative feedbacks and greater sensitivity to small shocks) in the carbon cycle before the PETM and in the carbon–climate system following it. This pre-PETM carbon cycle destabilisation may reflect gradual forcing by the contemporaneous North Atlantic Volcanic Province eruptions, with volcanism-driven warming potentially weakening the organic carbon burial feedback. Our results are consistent with but cannot prove the existence of a tipping point for abrupt carbon release, e.g. from methane hydrate or terrestrial organic carbon reservoirs, whereas we find no support for a tipping point in deep ocean temperature.

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This study uses statistical analyses to look for signs of declining resilience (i.e. greater sensitivity to small shocks) in the global carbon cycle and climate system across the Palaeocene–Eocene Thermal Maximum (PETM), a global warming event 56 Myr ago driven by rapid carbon release. Our main finding is that carbon cycle resilience declined in the 1.5 Myr beforehand (a time of significant volcanic emissions), which is consistent with but not proof of a carbon release tipping point at the PETM.
This study uses statistical analyses to look for signs of declining resilience (i.e. greater...
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