HOW THE EVOLUTION OF GRASSES AND DIATOMS IN THE CENOZOIC INFLUENCED THE GLOBAL CARBON CYCLE

Following the late Paleocene thermal maximum, C3 grasses began to rapidly radiate. Whether the radiation was in response to fires brought on by aridity associated with the LPTM, or was stimulated by the evolution of grazing mammals with higher hypsodontic indices remains unclear. However, the rise of grasses and their associated high silicate requirements appears to have accelerated silicate weathering and influenced both riverine and aeolian silicon fluxes from the continents to the ocean. The accelerated silicon fluxes appear to correspond with a radiation in diatoms that continues to present time. The rise of diatoms in oceanic ecosystems appears to have further accelerated the sedimentation and subsequent burial of organic carbon, especially along continental margins. The burial is reflected in an increase in 13C in carbonates. We suggest these two factors, namely the radiation of diatoms and the corresponding burial of organic matter, have been critical factors that have led to the long term depletion of CO2 in the mobile pools, and ultimately led to the resurgence of permanent high latitude ice in the latter half of the Cenozoic eon.