A cadmium-based quantification of marine organic carbon burial during the PETM

The Paleocene-Eocene Thermal Maximum (PETM, ~ 56 Ma) was driven by rapid, large-scale carbon release into the oceans and atmosphere. Environmental recovery post-PETM must have been associated with climate feedback mechanisms to remove carbon from Earth’s surface reservoirs, including silicate weathering and organic carbon burial. However, the amount of carbon removed by organic matter burial has been difficult to quantify due to ambiguity in many carbon-cycle proxies, thus limiting accurate paleoclimate modelling. We have measured the isotopic composition of cadmium (δ ¹¹⁴ Cd), a novel proxy for organic carbon burial, in sedimentary rocks deposited across the PETM in four separate marine basins. A ~ 0.2‰ positive excursion in δ ¹¹⁴ Cd _sw is interpreted to reflect a global-scale increase in organic cadmium burial in marine sediments. We simulate the global cadmium cycle using a box model to quantify the marine organic carbon burial flux required to drive this isotopic shift. Our median estimate of ~ 40,000 ± 15,500 Pg C total excess organic carbon burial across the PETM suggests that organic carbon burial was highly important in balancing the PETM carbon cycle budget.