The role of the terrestrial biosphere in Holocene carbon cycle dynamics

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