Long‐term variability in the global carbon cycle inferred from a high‐precision CO2 and δ13C ice‐core record

The new high precision Law Dome ice core record of CO 2 and δ 13 CO 2 is used with a 1-D global carbon cycle model to investigate natural variability in the carbon cycle and the anthropogenic CO 2 perturbation, focusing on variations on time-scales of centuries. A major feature of the ice core record is the decrease in CO 2 , and increase in δ 13 C, through the ‘‘Little Ice Age’′ period (roughly 1550–1800). We show that this observed decrease in CO 2 is consistent with the effect of decreased temperature on either terrestrial or oceanic exchange, however the increase in δ 13 C favors a terrestrial response to cooling. We perform single deconvolution model calculations which generally give good agreement with observed variations in CO 2 , δ 13 C and Δ 14 C data for different reservoirs and due to both natural and anthropogenic causes. The fit to prebomb Δ 14 C is improved by using an ice core 10 Be record to represent the natural production of 14 C due to cosmic rays, however, the uncertainties in interpreting the 10 Be are as yet too large to use prebomb Δ 14 C to better constrain the model parameters. DOI: 10.1034/j.1600-0889.1999.t01-1-00009.x