The role of the terrestrial biosphere in Holocene carbon cycle dynamics

Measurements of atmospheric CO2 concentration, and its stable carbon isotop e composition, from gas samples trapped in ice at Taylor Dome, Antarctica, indicate that the global carbon cycle has not been in steady state during t he Holocene epoch. Inverse carbon cycle modelling has led to the hypothesiz ed cumulative release from the terrestrial biosphere of 195 Gt C between 7 and 1 kyr before present (bp). Here, three independent lines of evidence te sting this hypothesis are critically examined: global reconstructions of te rrestrial carbon reservoirs, vegetation-climate modelling, and high latitud e subfossil plant stable carbon isotope records. Despite inherent uncertain ties associated with each approach, it emerges that none strongly upholds t he suggestion that terrestrial ecosystems released large amounts of carbon between 7 and 1 kyr bp. Consequently, our understanding of the processes in volved in the exchange of CO2 between the atmosphere, oceans and land biota continues to remain incomplete and to require further investigation.