Liangcheng Tan

Centennial- to decadal-scale monsoon precipitation variability in the semi-humid region, northern China during the last 1860 years: Records from stalagmites in Huangye Cave

We developed a composite oxygen isotopic record of cave calcite for the last 1860 years based on three stalagmites from the Huangye Cave in eastern Gansu Province, northern China. The δ18O values reflect monsoon precipitation changes, with lower δ18O values representing higher precipitation and vice versa. Three intervals of high precipitation were identified at AD 138—450, AD 730—1200, and AD 1860—1960. Two intervals of low precipitation occurred at AD 1320—1410 and AD 1530—1860. The reconstructed monsoon precipitation variations correlate well with other records further east in the eastern Yellow River Basin, suggesting synchronous precipitation changes during the late Holocene in the semi-humid region of northern China on decadal to centennial scales. Peak periods of warfare in dynastic transition times, such as at AD 391—420, AD 601—630, AD 1111—1140, AD 1351—1380, and AD 1621—1650, correspond to sharp declines in precipitation or temperature in semi-humid northern China, indicating a strong connection between climatic and societal changes. Our study suggests that climatic deterioration in semi-humid northern China has played an important role in Chinese societal evolution.

Variability of stalagmite-inferred Indian monsoon precipitation over the past 252,000 y

Significance This paper presents a new long speleothem δ18O time series from Xiaobailong cave in southwest China that characterizes changes in a major branch of Indian summer monsoon precipitation over the last 252 kyrs. This record shows not only 23-kyr precessional cycles punctuated by prominent millennial-scale weak monsoon events synchronous with Heinrich events in the North Atlantic, but also clear glacial–interglacial variations that are consistent with marine records but different from the cave records in East China. The speleothem records of Xiaobailong and other caves in East China show that the relationship between the Indian and the East Asian summer monsoon precipitation is not invariant, but rather varies on different timescales depending on the nature and magnitude of the climate forcing. A speleothem δ18O record from Xiaobailong cave in southwest China characterizes changes in summer monsoon precipitation in Northeastern India, the Himalayan foothills, Bangladesh, and northern Indochina over the last 252 kyr. This record is dominated by 23-kyr precessional cycles punctuated by prominent millennial-scale oscillations that are synchronous with Heinrich events in the North Atlantic. It also shows clear glacial–interglacial variations that are consistent with marine and other terrestrial proxies but are different from the cave records in East China. Corroborated by isotope-enabled global circulation modeling, we hypothesize that this disparity reflects differing changes in atmospheric circulation and moisture trajectories associated with climate forcing as well as with associated topographic changes during glacial periods, in particular redistribution of air mass above the growing ice sheets and the exposure of the “land bridge” in the Maritime continents in the western equatorial Pacific.

Large variations of oxygen isotopes in precipitation over south-central Tibet during Marine Isotope Stage 5

Oxygen isotope (δ 18 O) records of two stalagmites from Tianmen Cave, on the south-central Tibetan Plateau, grew during much of Marine Isotope Stage 5. The Tianmen record, the fi rst cave record from the Tibetan Plateau, characterizes a precipitation δ 18 O history larger in amplitude but similar in structure to Asian Monsoon records from the adjacent regions, providing essential evidence that the Asian Monsoon system, including the East Asian and Indian Monsoon subsystems, responds largely to changes in Northern Hemisphere summer insolation. Extremely low δ 18 O values during Marine Isotope Stages 5a, 5c, and 5e suggest that precipitation, rather than temperature, was a major factor controlling δ 18 O in precipitation on orbital time scales in the south-central Tibetan Plateau. The Tianmen record may help in the interpretation of regional ice core δ 18 O records. The large range of orbital-scale shifts in meteoric δ 18 O (>9‰) raises important considerations related to reconstructing the uplift history of the plateau.

Profiling bacterial diversity in a limestone cave of the western Loess Plateau of China

Bacteria and archaea sustain subsurface cave ecosystems by dominating primary production and fueling biogeochemical cyclings, despite the permanent darkness and shortage of nutrients. However, the heterogeneity and underlying mechanism of microbial diversity in caves, in particular those well connect to surface environment are largely unexplored. In this study, we examined the bacterial abundance and composition in Jinjia Cave, a small and shallow limestone cave located on the western Loess Plateau of China, by enumerating and pyrosequencing small subunit rRNA genes. The results clearly reveal the contrasting bacterial community compositions in relation to cave habitat types, i.e., rock wall deposit, aquatic sediment, and sinkhole soil, which are differentially connected to the surface environment. The deposits on the cave walls were dominated by putative cave-specific bacterial lineages within the γ-Proteobacteria or Actinobacteria that are routinely found on cave rocks around the world. In addition, sequence identity with known functional groups suggests enrichments of chemolithotrophic bacteria potentially involved in autotrophic C fixation and inorganic N transformation on rock surfaces. By contrast, bacterial communities in aquatic sediments were more closely related to those in the overlying soils. This is consistent with the similarity in elemental composition between the cave sediment and the overlying soil, implicating the influence of mineral chemistry on cave microhabitat and bacterial composition. These findings provide compelling molecular evidence of the bacterial community heterogeneity in an East Asian cave, which might be controlled by both subsurface and surface environments.

Cyclic precipitation variation on the western Loess Plateau of China during the past four centuries

Precipitation variation on the Loess Plateau (LP) of China is not only important for rain-fed agriculture in this environmentally sensitive region, but also critical for the water and life securities over the whole Yellow River basin. Here we reconstruct high resolution precipitation variation on the western LP during the past 370 years by using two replicated, annually-laminated stalagmites. Spatial analysis suggests that the reconstruction can be also representative for the whole LP region. The precipitation variations show a significant quasi-50 year periodicity during the last 370 years, and have an important role in determining the runoff of the middle Yellow River. The main factor controlling the decadal scale variations and long-term trend in precipitation over this region is southerly water vapour transport associated with the Asian summer monsoon. The Pacific Decadal Oscillation is also an important influence on precipitation variation in this region, as it can affect the East Asian summer monsoon and the West Pacific Subtropical High.

A Chinese cave links climate change, social impacts, and human adaptation over the last 500 years

The collapse of some pre-historical and historical cultures, including Chinese dynasties were presumably linked to widespread droughts, on the basis of synchronicities of societal crises and proxy-based climate events. Here, we present a comparison of ancient inscriptions in Dayu Cave from Qinling Mountains, central China, which described accurate times and detailed impacts of seven drought events during the period of 1520–1920 CE, with high-resolution speleothem records from the same cave. The comparable results provide unique and robust tests on relationships among speleothem δ18O changes, drought events, and societal unrest. With direct historical evidences, our results suggest that droughts and even modest events interrupting otherwise wet intervals can cause serious social crises. Modeling results of speleothem δ18O series suggest that future precipitation in central China may be below the average of the past 500 years. As Qinling Mountain is the main recharge area of two large water transfer projects and habitats of many endangered species, it is imperative to explore an adaptive strategy for the decline in precipitation and/or drought events.

Late Cenozoic Climate Change in Monsoon-Arid Asia and Global Changes

Based on the geological and biological findings, and climate model simulations, current understanding of the Asian monsoon-arid environment has been synthesized here. This chapter addresses the evolution of the Asian monsoon-arid environment and how it is related to the growth of the Tibetan Plateau (TP), and global environmental change since the Cenozoic. Asian monsoon appearance may begin in the late Eocene. The basic structure of the monsoon-arid environment was established by late Oligocene, and the modern pattern of the monsoon-arid environment developed in the late Pliocene. Conceptual models for Asian monsoon-arid environmental change mechanisms at various time scales are proposed here. The occurrence of great Northern hemisphere glaciation has been discussed. Differentiation of the natural background and anthropogenic signals are examined. Policies and countermeasures for sustainable development on the Loess Plateau and arid areas are proposed for future reference.

The East Asian summer monsoon variability over the last 145 years inferred from the Shihua Cave record, North China

The precipitation variability associated with the East Asian summer monsoon (EASM) has profound societal implications. Here, we use precisely dated and seasonally-resolved stalagmite oxygen isotope (δ18O) records from Shihua Cave, North China to reconstruct the EASM variability over the last 145 years. Our record shows a remarkable weakening of the EASM strength since the 1880s, which may be causally linked to the warming of the tropical Pacific and Indian Oceans. The δ18O record also exhibits a significant ~30-year periodicity, consistent with the instrumental, historical and proxy-based rainfall records from North China, plausibly driven by the Pacific Decadal Oscillation (PDO). Together, these observations imply that ~30-year periodicity is a persistent feature of the EASM, which remains significant with or without anthropogenic forcing. If indeed, the EASM rainfall in North China might decline significantly in the near future, which may affect millions of people in this region.

Climate change and soil erosion in a small alpine lake basin on the Loess Plateau, China

We employed multi-proxy indices retrieved from sediments in Lake Chaonaqiu, an alpine lake on the western Loess Plateau (LP) of China, to reconstruct a precipitation history over the last ~300 years. The results correlate well with records from tree rings and historical documents in neighboring regions. We show that the lake oscillated between two states, i.e., wetter climatic conditions, which favored denser vegetation cover, and promoted weaker catchment soil erosion; and drier climatic conditions, which lead to less vegetation coverage, correlate with stronger surface soil erosion. Several intensive soil erosion events were identified in the sediment cores, and most of these occurred during decadal/multi-decadal dry periods, and correlate well with flood events documented in historical literature. The results of this study show that soil erosion by flood events is particularly intense during dry periods, and further highlights the role of vegetation cover in the conservation of water and soil in small lake basins on the Chinese LP. This article is protected by copyright. All rights reserved.

Asian Monsoon Variability Recorded in Other Archives

This chapter provides an extensive review of paleomonsoon variability on millennial- to decadal time scales in various archives other than loess, including speleothems, lake sediments, peat deposits, desert deposits, marine sediments, corals, ice cores, tree rings, pollen archives and historical documents. Case studies will be presented to introduce the major proxy indices associated with these archives, and the reconstructed history of Asian monsoon variability. Advances in the study of monsoon variability and the peculiarity of different archives will also be introduced in this chapter.