Pingzhong Zhang

A Test of Climate, Sun, and Culture Relationships from an 1810-Year Chinese Cave Record

A record from Wanxiang Cave, China, characterizes Asian Monsoon (AM) history over the past 1810 years. The summer monsoon correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes. It was generally strong during Europes Medieval Warm Period and weak during Europes Little Ice Age, as well as during the final decades of the Tang, Yuan, and Ming Dynasties, all times that were characterized by popular unrest. It was strong during the first several decades of the Northern Song Dynasty, a period of increased rice cultivation and dramatic population increase. The sign of the correlation between the AM and temperature switches around 1960, suggesting that anthropogenic forcing superseded natural forcing as the major driver of AM changes in the late 20th century.

An 800 ky proxy record of climate from lake sediments of the Zoige Basin, eastern Tibetan Plateau

Abstract We present the results of magnetic susceptibility, geochemical and pollen analyses of a 120-m-long core of lacustrine and fluvial sediments from the Zoige Basin, eastern Tibetan Plateau. Palaeomagnetic dating indicates that the sediment sequence spans the last ca. 800 ky. The magnetic susceptibility record appears to be related to global ice volume over this period and this relationship is used to produce a tentative revised chronology for the sediment sequence. The various climate proxies show a pattern of periodic variations over the last 800 ky BP. The date of 500 ky BP is a significant boundary: prior to this date, the climate proxies show a pattern of more frequent variability; after 500 ky BP the variations are of lower frequency and higher amplitude. The results also indicate that marine oxygen isotope stage 13 was an unusually intense interglacial in the eastern Tibetan Plateau and Chinese Loess Plateau areas.

1400-year cold/warm fluctuations reflected by environmental magnetism of a lake sediment core from the Chen Co, southern Tibet, China

Lake Chen Co, situated at 90°33–39′E, 28°53–59′N with a lake level of 4420 m asl, is an enclosed lake with 148 km2 of catchment area and 40 km2 of lake surface. It is mainly supplied by glacier melt water either from surface inflow or groundwater. Atmospheric precipitation is mainly concentrated in June–September. A 216-cm long lake sediment core was obtained at a site with 8 m of water depth, 800 m from the lakeshore and 1.5% of the bottom slope in this lake. The sediment core was taken by a piston sampler and was sliced with an interval of 1 cm each. 210Pb dating measurement suggested that the average sedimentary rate was 0.16 cm yr−1, which also was confirmed by 137Cs peak occurrence. Magnetic analyses included low-frequency dependent susceptibility (χLF), susceptibility of anhysteretic remanent magnetism (χARM), the saturation isothermal remanent magnetism (SIRM), the isothermal remanent magnetism (IRM) reverse and ‘Soft’ and ‘Hard’ contents were performed for the sediment core. Results showed that χLF was an index for reflecting the environmental conditions, but was not sufficient to reveal details of magnetic features. This had been proved by measurements of IRM Reverse percentage and ‘Soft’ and ‘Hard’ magnetic minerals values. The log(SIRM/χLF) had much more information to reveal environmental changes. The χARM/χLF might be more sensitive to the local environmental conditions because it was well able to indicate the grain-size variations of magnetic particles. In the past ca. 1400 years, the warm stages were ca. 620–740 AD, 1120–1370 AD and since ca. 1900 AD. After an intensively cold stage during ca. 1550–1690 AD, a cold-humid stage from ca. 1690–1900 AD and a warm-dry stage since ca. 1900 AD followed. Among these stages, the warmest one occurred in ca. 1120–1370 AD and the coldest stage was between ca. 1550 and 1690 AD. This result might be compared with many other research results from lake cores, ice cores and the Chinese historical documents.

The climate variability in northern Levant over the past 20,000 years

The Levant constitutes an important region for assessing linkages between climate and societal changes throughout the course of human history. However, large uncertainties remain in our understanding of the regions hydroclimate variability under varying boundary conditions. Here we present a new high-resolution, precisely dated speleothem oxygen-carbon isotope and Sr/Ca records, spanning the last 20 ka from Jeita Cave, northern Levant. Our record reveals a higher (lower) precipitation-evaporation (P-E) balance during the Last Glacial Maximum and Bolling interstadial (Heinrich stadial 1). The early-middle Holocene is characterized by a trend toward higher P-E state, culminating between similar to 7 and 6 ka. The middle-late Holocene is characterized by two millennial-length drier periods during 5.3-4.2 and 2.8-1.4 ka. On submillennial time scale, the northern Levant climate variability is dominated by 500 year periodicity. Comparisons with the regional proxy records suggest persistent out-of-phase climate variability between the northern and southern Levant on a wide range of timescales.

Seasonality of westerly moisture transport in the East Asian summer monsoon and its implications for interpreting precipitation δ18O

East Asian summer monsoon (EASM) rainfall impacts the worlds most populous regions. Accurate EASM rainfall prediction necessitates robust paleoclimate reconstructions from proxy data and quantitative linkage to modern climatic conditions. Many precisely dated oxygen isotope records from Chinese stalagmites have been interpreted as directly reflecting past EASM rainfall amount variability, but recent research suggests that such records instead integrate multiple hydroclimatic processes. Using a Lagrangian precipitation moisture source diagnostic, we demonstrate that EASM rainfall is primarily derived from the Indian Ocean. Conversely, Pacific Ocean moisture export peaks during winter, and the moisture uptake area does not differ significantly between summer and winter and is thus a minor contributor to monsoonal precipitation. Our results are substantiated by an accurate reproduction of summer and winter spatial rainfall distributions across China. We also correlate modern EASM rainfall oxygen isotope ratios with instrumental rainfall amount and our moisture source data. This analysis reveals that the strength of the source effect is geographically variable, and differences in atmospheric moisture transport may significantly impact the isotopic signature of EASM rainfall at the Hulu, Dongge, and Wanxiang Cave sites. These results improve our ability to isolate the rainfall amount signal in paleomonsoon reconstructions and indicate that precipitation across central and eastern China will directly respond to variability in Indian Ocean moisture supply.

The uplifting and environmental change of Qinghai-Xizang (Tibetan) Plateau in the past 0.9 Ma inferred from core RM of Zoige Basin

According to the synthetic multi-disciplinary study on the lake sediments from core RM of Zoige Basin, i.e. the deepest wholly-collected core in Tibetan Plateau, the palaeoclimate and palaeoenvironment for the basin in the past 0.9 Ma have been reconstructed. The analytical results suggest that there distinctively exist 3 accelerated uplifting periods for the east Plateau in the past 0.9 Ma, i.e. 800, 360 and 160 kaB.P., with the study on the sedimentary characteristics, the texture of sedimentary cycles and variations of depositional rates, in conjunction with the environment features of cold/warm to dry/wet combination. The paper also probes into the environmental effect under the 3 accelerated tectonic-upliftings on the background of global change.

A 14 000-year record of paleoenvironmental change in the western basin of China's third largest lake, Lake Taihu

The longest vertical profile from the western basin of Taihu Lake ever taken was nearly 4 m (396 cm) in length and represented a time period of over 14 000 years. The core was analyzed for the following proxies, magnetic susceptibility, organic carbon isotope, total organic carbon, total nitrogen, total pigments, saturated hydrocarbons, carbon 14, thermolytic hydrogen (the hydrogen index, HI) and foraminifera. Results from the west Taihu lake core indicate that ca. 14 300–13 400 a B.P., the lake was relatively shallow and the climate was likely to have been quite arid. From 13 400 to 12 400 a B.P., the environment became less arid and the depth of the water in Lake Taihu increased. Marine incursions occurred during this period as indicated by the presence of numerous marine foraminifera. From ca. 12 400 to 10 900 a B.P., the climate became wetter, warmer and more variable. A cold dry period occurred around ca. 11 500 a B.P., causing the lake to become more shallow. From 10 900 to 10 000 a B.P., a warm and wet period reasserted itself and water depth again increased. A cold dry period reoccurred from 10 000 to 9500 a B. P. From 9500 to 7200 a B.P., the climate was quite variable. By 7200–5700 a B.P., the climate again turned warmer and wetter. Some of the major sediment proxies used in this study changed dramatically at ca. 5050 a B.P., reflecting changes in material source and a probable interruption of sedimentation. The modern environment (4900 aB.P.-present) was characterized by a well oxidized sediment layer and thriving algae. The lake is presently very eutrophic and is characterized by cyanobacteria, primarily Microcystis aeruginosa, the dominant primary producer in the lake. This is the first study to use a variety of organic geochemical proxies to infer paleoenvironmental changes in Taihu Lake.

Climate variations of Central Asia on orbital to millennial timescales

The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia’s hydroclimate variability from Tonnel’naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel’naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.

The 5400 a BP extreme weakening event of the Asian summer monsoon and cultural evolution

We explored a time series of the Asian summer monsoon (ASM) variability during the transition period from the middle to the late Holocene in the marginal Asian monsoon region. We used an absolutely dated 230Th record with only a ~20-year dating error, and oxygen isotope data with an 8-year average temporal resolution from the top 22-mm segment of stalagmite WXB07-4 from Wanxiang Cave, western Loess Plateau. The ASM intensity weakened gradually from 6420 to 4920 a BP, which was mainly characterized by three phases: (1) a strengthening phase with a higher precipitation amount between 6420 and 6170 a BP; (2) a smooth fluctuating interval during 6170–5700 a BP; and (3) a sudden extreme weakening period from 5700 to 4920 a BP. Interestingly, the extreme weakening interval of the ASM occurred during the period between 5700 and 4920 a BP, an abrupt change dated at 5430 a BP, which is known as the 5400 a BP, or 5.4 ka BP, event. The period included 290 years of gradual weakening, and 350 years of slow strengthening. This was synchronous with some cave records from the Asian monsoon region within dating errors. Comparing with Chinese archaeological archives over the past 7000 years, the early decline of the Yangshao Culture in the Yellow River Basin and the Hongshan Culture in the West Liao River Basin occurred during the period of gradual decrease of ASM precipitation. The dramatic decline in precipitation, caused by the extreme weakening of the ASM at 5400 a BP, may have been partly related to the decline of the Miaodigou Culture at the Yangguanzhai site in the Weihe River valley; the middle Yangshao Culture in western Henan in the Yellow River Basin; the early Dawenkou Culture on the lower reaches of the Yellow River; and the middle Hongshan Culture in the west of the Liaohe River valley. During the later period of the 5400 a BP event (5430–4920 a BP), a small amplitude increase and a subsequent sharp decrease of ASM precipitation may have also been linked to the contemporaneous prosperity and disappearance of the late Yangshao and Hongshan cultures; the disappearance of the late Yangshao Culture represented by the Yangguanzhai site in the Guanzhong basin on the Weihe River; the fourth phase of the late Yangshao Culture on the upstream Dadiwan site; the beginning of the middle Dawenkou Culture, the formation of its late stage, and the rise of the Longshan culture; and the rise of the Qujialing and Liangzhu cultures on the lower Yangtze River. Compared with the stalagmite precipitation records on the Qinghai-Tibetan Plateau, the rise and expansion of the Majiayao Culture in the upper Yellow River valley at 5300 a BP may have also been connected to the more dramatic increase of the summer monsoon precipitation at higher, rather than lower, altitudes during the late 5400 a BP event.