Long-term variability in the global carbon cycle inferred from a high-precision CO2 and delta C-13 ice-core record

The new high precision Law Dome ice core record of CO2 and delta(13)CO(2) i sused with a 1-D global carbon cycle model to investigate natural variabili ty in the carbon cycle and the anthropogenic CO2 perturbation, focusing on variations on time-scales of centuries. A major feature of the ice core rec ord is the decrease in CO2, and increase in delta(13)C, through the "Little Ice Age" period (roughly 1550-1800). We show that this observed decrease i n CO2 is consistent with the effect of decreased temperature on either terr estrial or oceanic exchange, however the increase in delta(13)C favors a te rrestrial response to cooling. We perform single deconvolution model calcul ations which generally give good agreement with observed variations in CO2, delta(13)C and Delta(14)C data for different reservoirs and due to both na tural and anthropogenic causes. The fit to prebomb Delta(14)C is improved b y using an ice core Be-10 record to represent the natural production of C-1 4 due to cosmic rays, however the uncertainties in interpreting the Be-10 a re as yet too large to use pre-bomb Delta(14)C to better constrain the mode l parameters.