Pollen record of precipitation changes during the Younger Dryas and Early Holocene in the North China Plain

Abstract

The Younger Dryas event, which was the most recent millennial-scale cold event, had a major impact on the global environment. However, there were substantial regional differences in precipitation during the Younger Dryas. Ningjinpo Lake was formed at the end of Late Pleistocene and was formerly the largest lake in the North China Plain. Its sedimentary record is well suited for studying environmental changes during the Younger Dryas. We used pollen and grain-size analyses of 69 lake sediment samples, combined with 1190 modern surface samples and a radiocarbon chronology, to characterize the processes of vegetation succession and precipitation change during the Younger Dryas and Early Holocene in the Ningjinpo area of North China Plain. The results show that during the Younger Dryas the sediments were relatively coarse-grained and the pollen assemblages were dominated by herb taxa such as Poaceae, Artemisia, and Asteraceae, indicating that the vegetation was mainly meadow steppe or forest meadow, and that the climate was generally dry. The annual average precipitation was ~510 mm, which was ~100 mm lower than today. However, four events of enhanced centennial-scale precipitation are evident in the record, characterized by increases in tree pollen representation: during 12,350–12,250, 12,200–12,100, 11.900–11,800 and 12,650–12,550 cal yr B.P. During these events, precipitation was ~50 mm higher than before and afterwards. In the late part of the Younger Dryas (after 12,100 cal yr B.P.), the representation of tree pollen increased, indicating an increase in forest dominated by Pinus and Betula, and precipitation increased to ~560 mm. After 11,440 cal yr B.P., at the beginning of the Holocene, the arboreal pollen percentages exceeded 60%, indicating that the regional vegetation was dominated by Pinus, Ulmus and Quercus forest, and the annual average precipitation was ~620 mm, which was close to that of today.