Zongli Wang

East Asian summer monsoon precipitation variability since the last deglaciation

The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the “present” is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7–7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8–5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5–8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change.

A high-resolution record of Holocene environmental and climatic changes from Lake Balikun (Xinjiang, China): Implications for central Asia

A high-resolution record of Holocene environmental and climatic change in the Balikun area was reconstructed from a sediment core from the Lake Balikun. Multiproxy data show that the climate was extremely arid during the early Holocene (before 8.6 cal. ka BP). Moisture began to increase after 8.6 cal. ka BP and the climate was humid between 7.9 and 4.3 cal. ka BP. A significant dry event occurred around 4.3–3.8 cal. ka BP. The climate became generally wet during the late Holocene (after 3.8 cal. ka BP). The Holocene pollen and geophysical records do not indicate a wet early Holocene, making it evident that there was no early-Holocene humid period associated with peak Asian monsoon strength. Regional comparisons indicate that this region has a different pattern of Holocene environmental and climatic change from the Asian monsoonal area and south Siberia.

Temporal Change of Radiocarbon Reservoir Effect in Sugan Lake, Northwest China during the Late Holocene

Many lacustrine chronology records suffer from radiocarbon reservoir effects. A continuous, accurate varve chronology, in conjunction with accelerator mass spectrometry (AMS) 14 C dating, was used to determine the age of lacustrine sediment and to quantify the past 14 C reservoir effect in Sugan Lake (China). Reservoir age varied from 4340 to 2590 yr due to 14 C-depleted water in the late Holocene. However, during the Little Ice Age (LIA), 14 C reservoir age was relatively stable. According to this study, 14 C reservoir age in the late Holocene may be driven by hydrological and climatic changes of this period. Therefore, special caution should be paid to the correction of the 14 C reservoir effect by a unique 14 C reservoir age in paleoclimatic and paleolimnological study of northwest China.

Vegetation succession and East Asian Summer Monsoon Changes since the last deglaciation inferred from high-resolution pollen record in Gonghai Lake, Shanxi Province, China:

A cal. 20-year-resolution pollen record from Gonghai Lake presented the detailed process of mountain vegetation succession and East Asian Summer Monsoon (EASM) changes since the last deglaciation in Shanxi Province, North China. Modern vegetation distribution and lake surface pollen assemblages suggested that the fossil pollen mainly came from local and surrounding vegetation in Gonghai Lake, which reflected the elevational changes of plant communities in study area. From 14,700 to 11,100 cal. yr BP, open forests and mountain meadows dominated by shrubs and herbaceous species in surrounding area, suggesting a weak EASM with less precipitation. In the period between 11,100 and 7300 cal. yr BP, bushwoods and grasses were gradually replaced by mixed broadleaf-conifer forest, first developed by pioneer species of Betula and Populus and then replaced by Picea, Pinus, and Quercus, implying an enhanced EASM and increased temperature and precipitation. During the period of 7300–5000 cal. yr BP, warm-fitted trees became expanded and widespread, indicating a climax community of mixed broadleaf-conifer forest and warm and humid climate with higher temperature and sufficient precipitation and the strongest period of EASM. From 5000 to 1600 cal. yr BP, Pinus pollen increased, but Quercus pollen decreased, showing the breakup of the climax community and the recession of the EASM. Since 1600 cal. yr BP, under the threats of land reclamation and deforestation, forest cover sharply decreased, and mountain grass lands were developed. The EASM changes inferred from pollen record of Gonghai Lake were asynchronous to the oxygen isotope records of stalagmites from southern China. We suggest that the existence of remnant Northern Hemisphere ice sheets and relative low sea levels might hampered the northward penetration of the EASM in early Holocene, which caused the maximum monsoon precipitation to reach northern China until mid-Holocene.

A late-Holocene pollen record from the western Qilian Mountains and its implications for climate change and human activity along the Silk Road, Northwestern China

The sparsity of long-term reliable climatic records hampers our understanding of human–environment interactions in the semi-arid Hexi Corridor, NW China. Here, we present a late-Holocene pollen record from a small alpine lake, Tian’E, in the western Qilian Mountains. The chronology is provided by nine accelerator mass spectrometry (AMS) 14C dates from terrestrial plant remains. The ratios of Artemisia and Amaranthaceae (A/C) are used to reconstruct the history of regional humidity: An unstable climate occurred during 1530–1270 BC; there were three relatively wet periods, at 1270 BC–AD 400, AD 1200–1350, and AD 1600–present; and there were two dry periods, from AD 400 to 1200 and from AD 1350 to 1600. Comparison with tree-ring data indicates that continuous droughts were responsible for the abandonment of several archaeological sites and ancient cities in the region, including the major city of Dunhuang, which was abandoned in AD 1372 and AD 1524 for nearly 200 years.