A new study in Nature Geoscience finds that during the Palaeocene-Eocene Thermal Maximum (PETM) roughly 56 million years ago, the burial of terrestrial organic carbon in coastal marine sediments increased dramatically. Using biomarker records from five global sites, researchers show that vascular plant and soil carbon made up 40-95% of total organic carbon in shallow marine sediments during the PETM, compared to just 12-20% in modern sediments. Burial fluxes increased 10 to 50 times due to enhanced erosion and higher sedimentation rates. This means the marine burial of terrestrial organic carbon acted as a significant negative feedback, sequestering excess carbon released during the PETM and helping the Earth system recover over timescales longer than 10,000 years. The authors note that current palaeoclimate model simulations do not account for this carbon sink, suggesting they underestimate the Earth's natural capacity to draw down atmospheric CO2 during warming events. The findings have implications for understanding long-term carbon cycle recovery and natural climate stabilization mechanisms.
