North Sea mercury evidence of a volcanic trigger for Paleocene/Eocene carbon feedbacks

The PalaeoceneEocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago, and investigation of its trigger can provide insight into thresholds and feedbacks within the climate system. Although both modelling and proxy records suggest volcanic carbon release occurred around this time, identifying the PETM trigger, and the potential contribution of other carbon cycle feedbacks, has proved challenging. To investigate the role of volcanism we report sedimentary mercury records from new North Sea boreholes showing exceptional preservation over the PETM onset. We find elevated levels of mercury occurring directly before and within the early PETM, signifying that pulsed volcanism from the North Atlantic Igneous Province could have provided the trigger and subsequently sustained elevated greenhouse gas levels. However, the PETM onset itself coincides with falling mercury levels, which suggests another carbon reservoir released significant quantities of carbon in response to the initial warming. We inform a series of Earth system model experiments to investigate these plausible carbon sources. The triggering of strong carbon-climate feedbacks by initial volcanic-induced global warming illustrates the existence of tipping points in Earths climate system.