Increased terrestrial carbon storage across the Palaeocene–Eocene boundary

A rapid, short-lived, global warming event at the close of the Palaeocene ca. 55.5 million years ago (Ma) was associated with the addition of massive amounts of carbon to the exogenic carbon cycle and major benthic extinctions. Evaluation of the response of the terrestrial biosphere to this transient ancient ‘greenhouse’ world with a process-based terrestrial carbon cycle model and global palaeoclimate simulations indicates the sequestration of ca. 1112 Gt C into the vegetation and soil carbon pools. A largely independent global carbon isotope mass balance analysis also points to the strong potential for the terrestrial biosphere to sequester substantial amounts of carbon at this time, with the increase being calculated at between 2107 and 3060 Gt C. This analysis suggests that some other feature of global environmental change across the Palaeocene–Eocene boundary may have been forcing terrestrial carbon cycle dynamics at this time. However, even a minimum increase of 1112 Gt C would have been sufficiently large to implicate the response of the terrestrial carbon cycle as a negative feedback mechanism on climate at 55.5 Ma, possibly reducing global temperatures by up to 2.5°C.