A stable cadmium isotope perspective on organic carbon burial trends during the Palaeocene-Eocene Thermal Maximum

Biogeochemical models, such as COPSE and cGENIE, have been used to predict the carbon cycle response to emissions into the atmosphere under various forcing scenarios. However, there is still significant uncertainty over model predictions of the magnitude of organic carbon burial into ocean sediments. This limits our understanding of C cycle feedbacks during periods considered to be potentially analogous to current anthropogenic induced climate change.

Stable cadmium isotopes (ẟ¹¹⁴Cd) have potential as a palaeoproxy for organic carbon burial in marine settings, due to the fractionation of Cd during burial in association with organic carbon. Therefore, the generation and evaluation of ẟ¹¹⁴Cd records in organic-rich shale sections encompassing periods of climatic and/or environmental change in the geological past is likely to be a useful tool in tracking and quantifying organic carbon burial trends during such events.

Here we present stable cadmium isotope records from four sections of organic-rich shales covering the Palaeocene-Eocene Thermal Maximum (PETM) occurring around 55.9 Ma, which is both the most recent and most analogous interval of rapid climate fluctuations in the geological record to modern-day climate change. We evaluate these records in terms of their organic carbon burial signals (and so carbon removal from the Earth system) during the lead-up to, onset, peak and recovery of the PETM event, as an initial assessment of the ability of stable cadmium isotopes to trace this process. Better quantification of organic carbon burial will enable the responses of the Earth System to rapid climate change to be better understood.