Nils Weitzel , Andreas Hense, Ulrike Herzschuh, Thomas Böhmer, Xianyong Cao, Kira Rehfeld

The Last Glacial Maximum (LGM, ~21.000 years before present) was a period with significantly lower global mean temperature, large Northern Hemisphere ice sheets, and low CO2 concentrations. Unlike other high-latitude areas, Siberia was not covered by a terrestrial ice sheet. Climate simulations with LGM boundary conditions show large inter-model differences especially in Northern Siberia, which impede a direct analysis of Siberian LGM climate from simulations. Thus, constraints from proxy data are needed.
Here, we reconstruct summer temperature and moisture availability from a network of Siberian pollen records using statistical transfer functions. The estimates are corrected for the lower CO2 concentrations during the LGM with an a posteriori method.
Using a Bayesian framework, we combine the pollen-based reconstructions with climate simulations to obtain the first regional state estimate of LGM climate constrained by proxies from Central and Eastern Siberia. Our reconstruction shows higher summer temperature anomalies than most high-latitude areas and simulations. Reconstructed moisture availability is similar to present-day values, consistent with most simulations. Analyses of the simulations show that anomalous circulation patterns and reduced cloud cover contribute particularly to the relatively high summer temperatures, supporting previous studies based solely on climate simulations. Our data-constrained state estimate is well-suited for future analyses of Siberian LGM climate such as investigations of the reasons for the absence of a Siberian ice sheet during the LGM.