Dynamics of Ecological Recovery from the Cretaceous-Paleogene Event

The K/T mass extinction precipitated a ~15 million year recovery phase that has been subdivided into a ~3 my period of low diversity with unusually low carbon isotope gradients in the oceans, and a late recovery phase of rising taxonomic diversity that lasts ~10-12 my. The low carbon isotope gradients between the surface and the deep ocean have traditionally been interpreted in terms of either a prolonged low productivity “Strangelove Ocean” or a ocean dominated by reduced export productivity due to extinction of zooplankton.

New geochemical records demonstrate that the bulk of the early Danian radiation of planktic foraminifera was initiated by thermocline-dwelling species. Carbon gradients between the thermocline and the abyss are naturally very low (or even inverted) throughout the Paleocene and even in the modern ocean so the low gradients in the early Danian do not require unusually low productivity in contrast to the established model but instead partly reflect the lack of a surface ocean proxy record. The low carbon isotope gradients are also due to the extinction of photosymbiotic clades which do not recover until the re-evolution of this ecology nearly 4 million years after the K/T boundary. Our data suggest that the basic processes of carbon export recovered much faster than is suggested by current models.