Megacycles of climate and vegetation in East Asia since 3 Ma

Abstract

Although there are numerous long-term terrestrial climate records based on biological and other indicators spanning the last 3 Myr in Asia, there are few studies on the vegetation evolution on a continental scale. Here we present a long (∼3 Myr) pollen record from core LN-1 from the North China Plain. The record shows that during the interval of 3.0–1.2 Ma, prior to the Mid-Pleistocene transition, the vegetation of the North China Plain was mainly open deciduous broadleaved forest, and that there were five cool and dry phases when conifers and herbs expanded: during 2.7–2.6 Ma, 2.2–2.1 Ma, 1.75–1.85 Ma, 1.5–1.6 Ma, and 1.3–1.4 Ma. Comparison with other pollen records from the East Asian monsoon region reveals a similar series of cool and dry intervals. These extended cool and dry intervals occurred during a period of high Earth orbital eccentricity, and were most likely related to the status of the global ocean carbon reservoir, under eccentricity forcing. We suggest that feedback from the terrestrial vegetation may have interrupted the dominant 41-kyr climatic cyclicity associated with middle and high latitudes of the Northern Hemisphere that had persisted since the Late Pliocene. After 1.2 Ma, the vegetation of the North China Plain changed to steppe and shrub steppe, while at the same time grassland expansion and forest recession occurred in northern China. The associated global cooling led to decreases in ocean temperatures, land-sea exchanges, and monsoon precipitation, which together drove the aridification of the Asian interior. We combined our data with eight published pollen records, and the zonal vegetation maps for East Asia since 3 Ma were generated.