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The causes of changes in the carbon cycle since the last glacial maximum (LGM, 21ka BP) remain poorly understood. Results from model simulations indicate that variations in its sources and sinks seem to account for the observed LGM methane decrease, but estimates of past changes in land carbon storage are still highly variable. More detailed knowledge of palaeo-wetlands, vegetation composition, plant ecophysiology and biomass burning is required for reliable model validation.
QUEST-Deglaciation is a nested project within the UK NERC QUEST research programme. A major aim of the project is to develop data syntheses suitable for testing a hierarchy of earth-system models. This involves extending existing databases of pollen, plant macrofossils, wetland extent and fire regimes (from charcoal), and creating a new global database of the reconstructed δ13C values of terrestrial vegetation.
The δ13C values of plants have a strong physiological basis that relates closely to photosynthetic pathway, climatic conditions (solar radiation, water stress) during growth and ambient CO2 levels. Model-simulated δ13C values of specific plant functional types can be evaluated quantitatively using palaeodata sources.
δ13C data sources include faunal remains such as bones, teeth and eggshells; soil organic matter and carbonate; terrestrial biomarkers in lake sediments; peat and charcoal. In contrast to pollen and macrofossil data, δ13C values are largely taxonomically independent and do not require biomisation. Our pilot study was focused on the Australasian region, in collaboration with the QUAVIDA (Quaternary Fire, Vegetation and Climate Change in Australasia) research group. Here, we map the current global synthesis of δ13C data from 21ka to present and report time series of δ13C variations in terrestrial biomass in key regions.
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