Xulong Wang

Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka

Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely records the variability of both the Westerlies and the ASM since 32 ka, reflecting the interplay of these two systems. These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales. During the last glaciation, the influence of the Westerlies dominated; prominent dust-rich intervals, correlated with Heinrich events, reflect intensified Westerlies linked to northern high-latitude climate. During the Holocene, the dominant ASM circulation, punctuated by weak events, indicates linkages of the ASM to orbital forcing, North Atlantic abrupt events, and perhaps solar activity changes.

Wet climate during the ‘Little Ice Age’ in the arid Tarim Basin, northwestern China:

A relatively cold period, the ‘Little Ice Age’ (LIA), just prior to the current warm period, has been documented from many regions of the globe. However, hydrological changes (wet/dry conditions) during the LIA appear to be very different across different climatic regimes, suggesting that the position, strength and/or pattern of atmospheric circulation could have changed significantly in the past. Therefore, paleohydrological studies may have some implications for potential future hydrological changes in an anticipated warming world. In this study, we investigated hydrological changes over the last ~800 years in the arid Tarim Basin, northwestern China. We used carbon isotopes of plant remains (mainly leaves) from a 10.5 m long aeolian sand sediment section to evaluate changes in dry/wet conditions. The average value of carbon isotopes of plant remains during the LIA period (~AD 1490 to 1890) is −26.0‰, ranging from −28.2‰ to −23.6‰, much lower than values before (average of −24.3‰, from −25.5‰ to −22.4‰)...A relatively cold period, the ‘Little Ice Age’ (LIA), just prior to the current warm period, has been documented from many regions of the globe. However, hydrological changes (wet/dry conditions) during the LIA appear to be very different across different climatic regimes, suggesting that the position, strength and/or pattern of atmospheric circulation could have changed significantly in the past. Therefore, paleohydrological studies may have some implications for potential future hydrological changes in an anticipated warming world. In this study, we investigated hydrological changes over the last ~800 years in the arid Tarim Basin, northwestern China. We used carbon isotopes of plant remains (mainly leaves) from a 10.5 m long aeolian sand sediment section to evaluate changes in dry/wet conditions. The average value of carbon isotopes of plant remains during the LIA period (~AD 1490 to 1890) is −26.0‰, ranging from −28.2‰ to −23.6‰, much lower than values before (average of −24.3‰, from −25.5‰ to −22.4‰) and after this period (average of −22.8‰, −24.6‰ to −21.6‰). Although other environmental factors could also affect carbon isotopes to some degree, such consistent, large negative isotopic excursions of up to 6‰ strongly suggest a wetter climatic condition in the study area at that time, which is also consistent with two silty clay layers, indicating a wet depositional environment, found around AD 1560 and AD 1625 during the LIA period. This inference is consistent with previous studies suggesting a relatively wet period during the LIA in the Tarim Basin and possibly extending to the western central Asia region, but appears to be opposite to hydrological changes in regions that are today dominated by Asian monsoon systems. This pattern of regional hydrological changes may be related to possible changes in the trajectory or strength of the westerlies and/or the orographic effect in this region, as previous studies suggested.

Structural properties and photoluminescence of ZnO nanowalls prepared by two-step growth with oxygen-plasma-assisted molecular beam epitaxy

Low dimensional (nanowall) ZnO structures were prepared by a two-step growth method with oxygen-plasma-assisted molecular beam epitaxy, where the as-grown film was first engraved on a porous template using the oxygen plasma and then the ZnO nanowalls were grown on the template. The resonance Raman spectra showed the surface mode. A morphology model was proposed on the basis of the scanning electron microscopy patterns and this mode. The room and low temperature photoluminescence showed that the nanowalls had intense ultraviolet emission properties, which benefited from the low dimensional structure with few defects.

Late Palaeozoic corals of Tibet (Xizang) and West Yunnan, Southwest China: successions and palaeobiogeography

Abstract A dynamic pattern of coral faunal provincialism in the Carboniferous to Permian sequence is preserved in Tibet–West Yunnan. During the Early Carboniferous, an undifferentiated Eurasian province was present, containing the Kueichouphyllum , Keyserlingophyllum - Siphonophyllia , and Cyathaxonia faunas, that reflect major environmental differences relative to previous interpretations. During the Late Carboniferous–Early Permian, the Indoralian province and the Cathaysian province can be distinguished. The former is recognised by an absence of Late Carboniferous–Asselian corals and by the presence of the Sakmarian–Artinskian Cyathaxonia fauna. The latter contains the Late Carboniferous and Early Permian compound corals Nephelophyllum and Kepingophyllum . As many blocks drifted northward beginning in the late Early Permian, the Indoralian province had evolved into two discrete provinces: the Himalayan and Cimmerian provinces. The Himalayan province as a relic of the Indoralian province was in the northern margin of Gondwanaland. The Cimmerian province between the Himalayan and the Cathaysian provinces consists of the present tectonic blocks: Lhasa, Qiangtang, Tengchong, and Baoshan in Tibet and West Yunnan. It is characterised by Roadian non-dissepimental solitary corals and Wordian–Capitanian compound Waagenophyllidae, as well as some endemic Cimmerian taxa such as Thomasiphyllum and Wentzellophyllum persicum . The Cathaysian province is dominated by Szechuanophyllum and Ipciphyllum . During the Late Permian, the Himalayan province and the Cathaysian province can be recognised. The former contains only small solitary corals, referred to as the Lytvolasma fauna, and the latter is identified by Liangshanophyllum , a fasciculate waagenophyllid.

Permian coral faunas of the eastern Cimmerian Continent and their biogeographical implications

Abstract Because of a depositional hiatus, Late Carboniferous corals are unknown from the eastern Cimmerian Continent. Early Permian (Asselian to Artinskian) corals are characterized by non-dissepimented solitary forms, and the absence of Kepingophyllidae and Waagenophyllidae, forms common in the Cathaysian biotic province. Roadian faunas in most areas of the eastern Cimmerian Continent are dominated by small solitary corals. These faunas are quite different from those of the Cathaysian area, where abundant large solitary and compound corals occur. By the Wordian, and into the Capitanian, large solitary and massive Waagenophyllidae, with a Cathaysian aspect, were well developed and widespread in the Cimmerian Continent. However, some endemic taxa, like Thomasiphyllum, also occur. Late Permian corals consist only of Cathaysian elements. Therefore, paleobiogeographically, the coral faunas in the eastern Cimmerian Continent reveal the following changes: (1) a Peri-Gondwanan affinity during the Early Permian to early Middle Permian, (2) an endemic Cimmerian–Cathaysian affinity during the late Middle Permian, and (3) a true Cathaysian fauna during the Late Permian. These changes may be related to the rifting of the Cimmerian Continent from Gondwanaland in the Late Early Permian and its subsequent northward drift.

Evolution of magnetic behaviour in the graphitization process of glassy carbon

We have carried out DC magnetization measurements on spherical glassy carbon exposed to high temperatures and high pressures. The observed magnetic signals clearly depend on the sintering temperature. On the basis of the graphitization temperature (around 1400oC), the behaviour can be classified into three regions: (1) paramagnetism in the no-graphitization region; (2) ferromagnetism in the near-graphitization region; (3) diamagnetic behaviour after graphitization. The magnetic transitions associated with the process of graphitization are discussed.

Seismically enhanced solute fluxes in the Yangtze River headwaters following the A.D. 2008 Wenchuan earthquake

Large earthquakes alter physical and chemical processes at Earths surface, triggering landslides, fracturing rock, changing large-scale permeability, and influencing hydrologic pathways. The resulting effects on global chemical cycles are not fully known. Here we show changes in the dissolved chemistry of the Min Jiang, a river in the Yangtze River (China) headwaters, following the A.D. 2008 M w 7.9 Wenchuan earthquake. Total solute fluxes transported by the Min Jiang increased after the earthquake, accompanied by an ∼4× increase in Na*/Ca ratios (where Na* is Na+ corrected for atmospheric and evaporite contributions) and a 0.000644 ± 0.000146 increase in 87Sr/86Sr isotopic ratios. These changes are consistent with enhanced contribution from silicate sources. We infer that the CO2 consumption rate via silicate-derived alkalinity increased 4.3 ± 0.4 times. If similar changes are associated with other large earthquakes, enhanced solute export could directly link tectonic activity with weathering and alkalinity fluxes that supply nutrients to ecosystems, influence seawater chemistry evolution, and steer Earths long-term carbon cycle and climate.

Chinese Loess and the East Asian Monsoon

This chapter offers a comprehensive review of loess studies on the Loess Plateau, and how they provide evidence for past monsoon variability. The chronological framework that has been established for the Loess Plateau with the use of multiple chronometers is explained in detail. Sedimentological, paleomagnetic and geochemical climate proxies are also discussed, and the history,variability and dynamics of the paleomonsoon is described at tectonic, orbital and millennial time scales.

Hydroclimatic contrasts over Asian monsoon areas and linkages to tropical Pacific SSTs.

Knowledge of spatial and temporal hydroclimatic differences is critical in understanding climatic mechanisms. Here we show striking hydroclimatic contrasts between northern and southern parts of the eastern margin of the Tibetan Plateau (ETP), and those between East Asian summer monsoon (EASM) and Indian summer monsoon (ISM) areas during the past ~2,000 years. During the Medieval Period, and the last 100 to 200 years, the southern ETP (S-ETP) area was generally dry (on average), while the northern ETP (N-ETP) area was wet. During the Little Ice Age (LIA), hydroclimate over S-ETP areas was wet, while that over N-ETP area was dry (on average). Such hydroclimatic contrasts can be broadly extended to ISM and EASM areas. We contend that changes in sea surface temperatures (SSTs) of the tropical Pacific Ocean could have played important roles in producing these hydroclimatic contrasts, by forcing the north-south movement of the Intertropical Convergence Zone (ITCZ) and intensification/slowdown of Walker circulation. The results of sensitivity experiments also support such a proposition.

The unusual morphology, structure, and magnetic property evolution of glassy carbon upon high pressure treatment

Glassy carbon (GC) has been high-pressure high-temperature treated. An interesting morphology evolution from the pristine sample to the high pressure products was observed. It is found that GC can be graphitized under pressure at a temperature much lower than that at ambient condition. Furthermore the inisitu structure and electrical measurements of GC and graphitized glassy carbon (GGC) under high temperature and high pressure have been investigated up to 30 GPa. We particularly emphasize the unusual magnetic properties of GC treated under high pressures and high temperatures. A paramagnetic to ferromagnetic-like, and then to superconducting (a diamagnetic signal with hysteresis magnetic response) -like behavior, which can be observed at temperatures as high as 80 K, appears as a successive evolution from the initial GC to GGC in accordance with three regions distinguished by the graphitization temperature. This interesting evolution of magnetic properties probably evokes the new understanding of carbon element.