Past, present and future biomes in Beringia: Comparison between simulations and pollen analysis

Abstract. Past, present and future biomes in Beringia, a region including Alaska and Eastern Russia, were simulated using an equilibrium vegetation model, BIOME4 and a statistical downscaling method in order to illustrate their geographical and temporal changes. Outputs form five CMIP5 models were utilized to represent the climate for four time periods, i.e., the Last Glacial Maximum (LGM; 21 ka), the mid-Holocene Optimum (6 ka), the modern period, and the near future (the end of this century under a RCP8.5 scenario). Present-day biome simulations were generally consistent with current vegetation observations in the study region. Pollen samples indicate that the Bering Land Bridge was covered almost entirely by cushionforb and graminoid tundra during the LGM, whereas the paleoclimate simulations show large across-model variations in this region. Three out of the five modelsʼ climate data produce evergreen and deciduous taiga at 21 ka in what is now southwestern Alaska and southeastern Bering continental shelf. The 6 ka simulations are in better agreement with pollen-based distributions of biomes. Future simulations show a general northward shift of biomes, including intrusions of cool and warm-temperate mixed, and cool coniferous forests above 60° N, especially in southwest Alaska.