Paleogene temperature gradient, seasonal variation and climate evolution of northeast China

Continental Paleogene climates have been well studied in Europe and North America, but very little is known from Asia because paleoclimatic results have only been reported from particular geological intervals. Here, based on 29 plant assemblages from 8 well age-controlled fossiliferous sites, we quantitatively reconstruct the climates through most of the Paleogene of northeast China and discuss related seasonal variations. Our results demonstrate that the mean annual temperature (MAT) gradient was fairly shallow (0.27 degrees C/1 degrees latitude) during the Paleocene throughout this region. In the Eocene, seasonality was high in the region, indicated by marked differences in both temperature and precipitation between winters and summers of the sites. The paleo-East Asian monsoon must have had intensified at least in the late mid Eocene, shown by apparent differences in annual precipitation distribution at all the sites. Regarding the Paleogene climatic evolution of northeast China, our quantitative results suggest that MAT overall declined from warm in the Paleocene and Eocene to moderate in the Oligocene, generally consistent with the trend of marine records but with some distinctions. Two significant cooling events are recognized in the early and mid Eocene with MAT 3.4 degrees C and 3.8 degrees C lower, and winter temperature 5.8 degrees C and 4.7 degrees C lower, respectively, in similar magnitudes to corresponding variations in Europe and North America. Furthermore, the present results show that MAT rebounded in the late mid Eocene and then decreased until the Oligocene, a similar pattern demonstrated in Europe during the mid Eocene to Oligocene interval. (C) 2011 Elsevier B.V. All rights reserved.