Oxygen isotope signatures of quartz from major Asian dust sources: Implications for changes in the provenance of Chinese loess

We present a systematic investigation of the oxygen isotopic composition of quartz in both fine and coarse fractions (&lt;16 and 16-63 mu m) from major dust source regions in East Asia, including the Mongolian Gobi, the northern Chinese deserts, the Taklimakan desert, and the Qaidam Basin. The results demonstrate that the quartz oxygen isotope ratios of the Taklimakan desert and the Mongolian Gobi are more heterogeneous compared with the other areas. The quartz delta O-18 values of both the fine and coarse fractions from the various sources are overlapped to varying degrees, thus making it difficult to differentiate them. Nevertheless, the quartz delta O-18 values of both fractions exhibit an increasing trend from the Mongolian Gobi, to the northern Chinese deserts, and then to the Taklimakan desert. This implies that the geological settings of the source areas are different, which in turn results in differing contributions of high-temperature igneous rocks. The combination of quartz delta O-18 results with other quartz-based provenance tracers can clearly differentiate the three major source areas, i.e., the Taklimakan desert, the Mongolian Gobi, and the northern Chinese deserts. In addition, comparison of our results with previous delta O-18 measurements of fine-grained quartz from the Luochuan loess sequence suggests the likely glacial interglacial fluctuations in dust provenance. Finally, we suggest that the combination of quartz delta O-18 signatures and other dust provenance tracers can potentially improve the recognition of long-term fluctuations in the provenance of Chinese loess-red clay deposits.</p

Provenance fluctuations of aeolian deposits on the Chinese Loess Plateausince the Miocene

The evolution of the provenance of aeolian deposits on the Chinese Loess Plateau (CLP) is closely linked to changes in source aridity and dust transport dynamics. Although previous studies have revealed that the provenance of Chinese aeolian deposits may have fluctuated on tectonic timescales, the exact timing and cause of the provenance shifts remain poorly constrained due to limitations of the isotopic and mineralogical tracers used. Here we report the results of electron spin resonance (ESR) signal intensity and crystallinity index (CI) of fine-grained (<16 lm) quartz isolated from two aeolian sequences on the CLP, in order to address tectonic-scale shifts in dust provenance over the last 23.5 Ma. The ESR–CI results spanning the interval 7–5 Ma for two aeolian sequences are comparable, implying a broadly similar provenance of dust deposits over the entire CLP. The ESR–CI values are lower after 7 Ma than before 9.5 Ma, indicating that a significant provenance shift occurred during 9.5–7 Ma. Comparison of the ESR–CI results for fine-grained quartz in desert surface samples and for the loess and Red Clay sequences indicates that the provenance shift may have been caused by increased dust input from the Mongolian Gobi and western China (i.e., the Taklimakan desert) since the late Miocene. The combination of our results with regional tectonic evidence and global climate record suggests that tectonically-driven climate changes in the dust sources may have played a dominant role in driving the late Miocene provenance shift

Molecular composition and size distribution of sugars, sugar-alcohols and carboxylic acids in airborne particles during a severe urban haze event caused by wheat straw burning

Molecular compositions and size distributions of water-soluble organic compounds (WSOC, i.e., sugars, sugar-alcohols and carboxylic acids) in particles from urban air of Nanjing, China during a severe haze event caused by field burning of wheat straw were characterized and compared with those in the summer and autumn non-haze periods. During the haze event levoglucosan (4030 ng m(-3)) was the most abundant compound among the measured WSOC, followed by succinic acid, malic acid, glycerol, arabitol and glucose, being different from those in the non-haze samples, in which sucrose or azelaic acid showed a second highest concentration, although levoglucosan was the highest. The measured WSOC in the haze event were 2-20 times more than those in the non-hazy days. Size distribution results showed that there was no significant change in the compound peaks in coarse mode (&gt;2.1 mu m) with respect to the haze and non-haze samples, but a large difference in the fine fraction (&lt;2.1 mu m) was found with a sharp increase during the hazy days mostly due to the increased emissions of wheat straw burning. Molecular compositions of organic compounds in the fresh smoke particles from wheat straw burning demonstrate that sharply increased concentrations of glycerol and succinic and malic acids in the fine particles during the haze event were mainly derived from the field burning of wheat straw, although the sources of glucose and related sugar-alcohols whose concentrations significantly increased in the fine haze samples are unclear. Compared to that in the fresh smoke particles of wheat straw burning an increase in relative abundance of succinic acid to levoglucosan during the haze event suggests a significant production of secondary organic aerosols during transport of the smoke plumes.</p

Magnetostratigraphy and luminescence dating on a sedimentary sequence from northern East China Sea: Constraints on evolutionary history of eastern marginal seas of China since the Early Pleistocene

Owing to the large and increasing population density in low-lying coastal regions, even small changes in sea level can have substantial societal and economic impacts. Alternations of terrestrial and marine sediments deposited in coastal areas or continental shelves are important and effective indicators of sea-level changes, and thus, have been widely studied in the marginal seas of China over the past 30 years. However, sea-level change results from not only eustatic factors but also tectonic activity. The Zhe-Min (or Zhejiang-Fujian) Uplift (ZMU) was such an important factor in geomorphology, and formed a barrier preventing entry of sea water into the northern marginal seas of China, but its Quaternary history is poorly known. In this study, a new borehole (ECS-DZ1) was drilled in the Zhoushan Islands, northern East China Sea to obtain information on the evolution of the ZMU during the Quaternary. Information from paleomagnetic and luminescence dating was combined with data on sedimentary changes. The main results are: (1) constrained by luminescence ages, the upper sedimentary units were extrapolated to have been deposited since similar to 0.2 Ma; (2) paleomagnetic results suggest that the ECS-DZ1 borehole sequence spans from the pre-Olduvai Matuyama reverse chron to the Brunhes normal chron, approximately constraining the age of the basal sedimentary unit to similar to 2.0 Ma; (3) a significant hiatus or erosion between two major sedimentary units possibly occurred between the late Early Pleistocene and Middle Pleistocene. As the Zhoushan Islands are within the ZMU and considering previous transgression studies around this region, it is inferred that the ZMU subsided at similar to 2.0 Ma, allowing seawater to invade northward in the Yellow Sea basin. The ZMU might have been uplifted again no later than 1.0 Ma, causing a sedimentary hiatus or lacustrine development. After similar to 0.2 Ma, the ZMU subsided completely, allowing large transgressions to develop across the northern marginal seas of China in the context of global sea-level changes.</p

Paleo-megalake termination in the Quaternary: Paleomagnetic andwater-level evidence from south Bohai Sea, China

Asian marginal seas play an important role in moderating material and energy flux linkages between Asia and the Northwest Pacific, and thus have profound climatic and environmental effects. In this study, by combining paleomagnetic study with sediment grain-size analysis on the Lz908 borehole sedimentary sequence from the southern Bohai Sea, new insights into regional geomorphological process since the late early Pleistocene are obtained. The main results are as follows. (1) Paleomagnetic findings suggest that the sequence recorded the Brunhes normal chron and the late Matuyama reverse chron, including the Jaramillo normal subchron. (2) The sedimentary processes in the study area since 1327 ka show a three-stage pattern, with depositional rates of 4.3, 17 and 107 cm/ka during 1327–260 ka (later part of the early and middle Pleistocene), 260–10 ka (late middle and late Pleistocene), and the Holocene, respectively. (3) The sedimentary basin was a part of the Bohai Paleolakes (BHPL) prior to 260 ka, whose water levels were consistently higher than 3 m above the present-day level. After 260 ka, seawater entered the Bohai basin, and relative sea level cyclically fluctuated with global sea-level changes. We therefore infer that the Miaodao Islands, which were the natural barrier of the BHPL blocking seawater entry, had partially subsided before 260 ka, only allowing seawater to enter the basin during a global sea-level maximum. The BHPL terminated around 260 ka, and the “barrier” subsided completely around ~ 130 ka, causing the Bohai basin to become an inner shelf sea

Global Survey of Antibiotic Resistance Genes in Air

Despite its emerging significant public health concern, the presence of antibiotic resistance genes (ARGs) in urban air has not received significant attention. Here, we profiled relative abundances (as a fraction, normalized by 16S rRNA gene) of 30 ARG subtypes resistant to seven common classes of antibiotics, which are quinolones, &beta;-lactams, macrolides, tetracyclines, sulfonamides, aminoglycosides, and vancomycins, in ambient total particulate matter (PM) using a novel protocol across 19 world cities. In addition, their longitudinal changes in PM2.5 samples in Xi&rsquo;an, China as an example were also studied. Geographically, the ARGs were detected to vary by nearly 100-fold in their abundances, for example, from 0.07 (Bandung, Indonesia) to 5.6 (San Francisco, USA). The &beta;-lactam resistance gene blaTEM was found to be most abundant, seconded by quinolone resistance gene qepA; and their corresponding relative abundances have increased by 178% and 26%, respectively, from 2004 to 2014 in Xi&rsquo;an. Independent of cities, gene network analysis indicates that airborne ARGs were differentially contributed by bacterial taxa. Results here reveal that urban air is being polluted by ARGs, and different cities are challenged with varying health risks associated with airborne ARG exposure. This work highlights the threat of urban airborne transmission of ARGs and the need of redefining our current air quality standards in terms with public health.</p

Gamma-ray astronomy and cosmic-ray physics with ARGO-YBJ

The ARGO-YBJ detector, located 4300 m a.s.l. on the Tibet plateau, is a ground-based, full- coverage array of Resistive Plate Chambers (RPCs) covering a surface of 78×74 m2, surrounded by a guard ring of RPCs enclosing a total surface of about 11000 m2. ARGO-YBJ was designed to detect extensive air showers generated by cosmic rays and gamma rays with primary energy greater than few hundred GeV, in order to study the region of the cosmic-ray spectrum out of the reach of both satellite-based experiments and traditional ground-based arrays. The experiment has been running with its complete layout since November 2007, collecting over 2:5×1011 events. The main results obtained by ARGO-YBJ will be presented here, and specifically: the monitoring of astronomical gamma-ray sources, such as the Crab nebula and the MRK 421 AGN, the moon shadow, the medium-scale anisotropy map, the proton-proton inelastic cross section at center-of- mass energy between 70 and 500 GeV where no accelerator data are available

Gamma-ray astronomy with ARGO-YBJ

ARGO-YBJ is a full coverage air shower array located at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm2) recording data with a duty cycle ≥85% and an energy threshold of a few hundred GeV. In this paper the latest results in Gamma-Ray Astronomy are summarized