Yuansheng Li

Comprehensive assessment of toxic metals in urban and suburban street deposited sediments (SDSs) in the biggest metropolitan area of China

A set of toxic metals, i.e. As, Hg, Pb, Cd, Cu, Zn, Ni and Cr, in urban and suburban SDSs were investigated comparatively in the biggest metropolitan area of China, Shanghai. Results showed that all of the metals except As were accumulated greatly, much higher than background values. Geo-accumulation index indicated that metal contamination in urban SDSs was generally heavier than that in suburban SDSs. Potential ecological risk index demonstrated that overall risks caused by metals were considerable. Cd contributed 52% to the overall risk. Multivariate statistical analysis revealed that in urban SDSs, Zn, Ni, Cd, Pb, Cu and Cr were related to traffic and industry; coal combustion led to elevated levels of Hg; soil parent materials controlled As contents. In suburban SDSs, Pb, Cu, As and Cd largely originated from traffic pollution; Zn, Ni and Cr were associated with industrial contaminants; Hg was mainly from domestic solid waste.

S‐velocity model and inferred Moho topography beneath the Antarctic Plate from Rayleigh waves

Since 2007/2008, seismographs were deployed in many new locations across much of Antarctica. Using the records from 122 broadband seismic stations, over 10,000 Rayleigh wave fundamental-mode dispersion curves have been retrieved from earthquake waveforms and from ambient noise. Using the processed data set, a 3-D S-velocity model for the Antarctic lithosphere was constructed using a single-step surface wave tomographic method, and a Moho depth map was estimated from the model. Using the derived crustal thicknesses, the average ratio of lithospheric mantle and crustal densities of Antarctica was calculated. The calculated density ratio indicates that the average crustal density for Antarctica is much higher than the average values for continental crust or the average density of lithospheric mantle is so low as to be equal to low-density bound of Archean lithosphere. The latter implies that the lithospheric mantle in much of Antarctica should be old and of Archean age. The East Antarctic Mountain Ranges (EAMOR) represent a thick crustal belt, with the thickest crust (~60 km) located close to Dome A. Very high velocities can be found at depths greater than 200 km beneath parts of East Antarctica, demonstrating that the continental lithosphere extends deeper than 200 km. The very thick crust beneath the EAMOR may represent the collision suture of East Gondwana with Indo-Antarctica and West Gondwana during the Pan-African orogeny.

Fluxes, variability and sources of cadmium, lead, arsenic and mercury in dry atmospheric depositions in urban, suburban and rural areas

In Chinas largest city, Shanghai, dry deposition fluxes of Cd, Pb, As and Hg were 137, 19354, 2897 and 9.4 μgm(-2)a(-1), respectively in an urban area, intermediate in a suburban area, and 51.7, 5311, 1703 and 7.3 μgm(-2)a(-1), respectively in a rural area. Enrichment factors were Cd>Pb>As>Hg. Seasonal variations of metals differed: Pb and As were dominated by fossil fuel combustion, Cd was related to industrial pollution, and natural source controlled Hg levels.

Temperature, lithosphere‐asthenosphere boundary, and heat flux beneath the Antarctic Plate inferred from seismic velocities

We estimate the upper-mantle temperature of the Antarctic Plate based on the thermoelastic properties of mantle minerals and S velocities using a new 3-D shear velocity model, AN1-S [An et al., 2015, JGR]. Crustal temperatures and surface heat fluxes are then calculated from the upper-mantle temperature assuming steady-state thermal conduction. The temperature at the top of the asthenosphere beneath the oceanic region and West Antarctica is higher than the dry mantle solidus, indicating the presence of melt. From the temperature values, we generate depth maps of the lithosphere–asthenosphere boundary and the Curie-temperature isotherm. The maps show that East Antarctica has a thick lithosphere similar to that of other stable cratons, with the thickest lithosphere (~250 km) between Domes A and C. The thin crust and lithosphere beneath West Antarctica are similar to those of modern subduction-related rift systems in East Asia. A cold region beneath the Antarctic Peninsula is similar in spatial extent to that of a flat-subducted slab beneath the southern Andes, indicating a possible remnant of the Phoenix Plate, which was subducted prior to 10 Ma. The oceanic lithosphere generally thickens with increasing age, and the age–thickness correlation depends on the spreading rate of the ridge that formed the lithosphere. Significant flattening of the age–thickness curves is not observed for the mature oceanic lithosphere of the Antarctic Plate.

Large-scale spatial variability of major ions in the atmospheric wet deposition along the China Antarctica transect (31°N~69°S)

ABSTRACT Twenty-two atmospheric wet deposition samples were collected along the large-scale transect from China to Antarctica, and the major ion components as well as their sources were analysed. It is the first time that chemical composition variation of precipitation has been investigated on such a large-scale transect. The results show that the precipitations exhibit near-neutral pH on the average. On the whole, ionic levels on an equivalent basis are presented as Cl−>Na+>Mg2+> >Ca2+>K+> > , and ionic contents of rainfall are generally higher compared with values of snowfall. Ionic concentrations vary greatly on the study transect, and the values of the Northern Hemisphere are relatively higher. Both enrichment factor and principal component analyses reveal that Cl−, Na+, K+ and Mg2+ are mainly related to sea salt, namely, the marine source. The good correlations between marine-sourced ions and wind speed indicate that seawater sprays are important sources of precipitation ions. Land-based sources, for example, human activities, are the primary sources of , and Ca2+. partly originates from sea salt, but anthropogenic and biogenic sources are also important contributors. Backward trajectories illustrate well the different main sources and transport routes of the precipitation ions.

Antarctic ice velocities from GPS locations logged by seismic stations

Abstract In 2007–08, seismologists began deploying passive seismic stations over much of the Antarctic ice sheet. These stations routinely log their position by navigation-grade global positioning system (GPS) receivers. This location data can be used to track the stations situated on moving ice. For stations along the traverse from Zhongshan station to Dome A in East Antarctica and at the West Antarctic Ice Sheet divide the estimated velocities of the ice surface based on positions recorded by navigation-grade GPS are consistent with those obtained by high-accuracy geodetic GPS. Most of the estimated velocities have an angle difference of <28° with the steepest downhill vector of the ice surface slope at the stations. These results indicate that navigation-grade GPS measurements over several months provide reliable information on ice sheet movement of ≥1 m yr-1. With an uncertainty of ~0.3–1 m yr-1, this method is able to resolve both very slow ice velocities near Dome A and velocities of >100 m yr-1 on Thwaites Glacier. Information on ice velocity at three locations for which no data from satellite-based interferometric synthetic aperture radar are available have also been provided using this method.

Metals and metalloids in precipitation collected during CHINARE campaign from Shanghai, China, to Zhongshan Station, Antarctica: Spatial variability and source identification

Metals and metalloids in continental precipitation have been widely observed, but the data over open oceans are still very limited. Investigation of metals and metalloids in marine precipitation is of great significance to understand global transport of these elements in the atmosphere and their input fluxes to the oceans. So shipboard sampling of precipitation was conducted during a Chinese National Antarctic Research Expedition campaign from Shanghai, China, to Zhongshan Station, East Antarctica, and 22 samples (including 17 rainfall and 5 snowfall events) were collected and analyzed for concentrations of Pb, Ni, Cr, Cu, Co, Hg, As, Cd, Sb, Se, Zn, Mn, and Ti. Results show that concentrations of both metals and metalloids vary considerably along the cruise, with higher concentrations at coastal sites and lower values on the south Indian Ocean. Although only soluble fractions were determined for elements, concentrations in this study are generally comparable to the reported values of marine rain. Enrichment factor analysis shows that most of metals and metalloids are enriched versus crustal sources, even in the samples collected from remote south Indian Ocean. In addition, metals and metalloids in precipitation are also very enriched above sea-salt abundance, indicating that impacts of sea-salt aerosols on their concentrations are negligible. Main sources of metals and metalloids were explored with the aid of multivariate statistical analyses. The results show that human emissions have far-reaching distribution, which may exert an important influence on the solubility of elements in precipitation. This investigation provides valuable information on spatial variation and possible sources of trace elements in precipitation over the open oceans corresponding to understudied region.

Chinese First Deep Ice-Core Drilling Project DK-1 at Dome A, Antarctica (2011-2013): progress and performance

Abstract The Chinese First Deep Ice-Core Drilling Project DK-1 has commenced at Kunlun station in the Dome A region, the highest plateau in Antarctica. During the first season, within the 28th Chinese National Antarctic Research Expedition (CHINARE) 2011/12 the pilot hole was drilled and reamed in order to install a 100 m deep fiberglass casing. In the next season, 29th CHINARE 2012/13, the deep ice-core drilling system was installed, and all the auxiliary equipment was connected and commissioned. After filling the hole with drilling fluid (n-butyl acetate), three runs of ‘wet’ ice-core drilling were carried out and a depth of 131.24 m was reached. Drilling to the bedrock at the target depth of ∼3100 m is planned to be completed during a further four seasons. We describe the work in progress and the status of equipment for the Dome A drilling project.

Nitrate deposition and preservation in the snowpack along a traverse from coast to the ice sheet summit (Dome A) in East Antarctica

Antarctic ice core nitrate (NO−3 ) can provide a unique record of the atmospheric reactive nitrogen cycle. However, the factors influencing the deposition and preservation of NO−3 at the ice sheet surface must first be understood. Therefore, an intensive program of snow and atmospheric sampling was made on a traverse from the coast to the ice sheet summit, Dome A, East Antarctica. Snow samples in this observation include 120 surface snow samples (top ∼ 3 cm), 20 snow pits with depths of 150 to 300 cm, and 6 crystal ice samples (the topmost needle-like layer on Dome A plateau). The main purpose of this investigation is to characterize the distribution pattern and preservation of NO−3 concentrations in the snow in different environments. Results show that an increasing trend of NO−3 concentrations with distance inland is present in surface snow, and NO−3 is extremely enriched in the topmost crystal ice (with a maximum of 16.1 μeq L−1). NO−3 concentration profiles for snow pits vary between coastal and inland sites. On the coast, the deposited NO−3 was largely preserved, and the archived NO−3 fluxes are dominated by snow accumulation. The relationship between the archived NO−3 and snow accumulation rate can be depicted well by a linear model, suggesting a homogeneity of atmospheric NO−3 levels. It is estimated that dry deposition contributes 27–44 % of the archived NO−3 fluxes, and the dry deposition velocity and scavenging ratio for NO−3 were relatively constant near the coast. Compared to the coast, the inland snow shows a relatively weak correlation between archived NO−3 and snow accumulation, and the archived NO−3 fluxes were more dependent on concentration. The relationship between NO−3 and coexisting ions (nssSO2− 4 , Na + and Cl) was also investigated, and the results show a correlation between nssSO2− 4 (fine aerosol particles) and NO−3 in surface snow, while the correlation between NO−3 and Na + (mainly associated with coarse aerosol particles) is not significant. In inland snow, there were no significant relationships found between NO−3 and the coexisting ions, suggesting a dominant role of NO−3 recycling in determining the concentrations.

Ex Situ Culturing Experiments Revealed Psychrophilic Hydrogentrophic Methanogenesis Being the Potential Dominant Methane-Producing Pathway in Subglacial Sediment in Larsemann Hills, Antarctic

It was recognized only recently that subglacial ecosystems support considerable methanogenic activity, thus significantly contributing the global methane production. However, only limited knowledge is available on the physiological characteristics of this kind of methanogenic community because of the technical constraints associated with sampling and cultivation under corresponding environmental conditions. To elucidate methanogenesis beneath the glacial margin in East Antarctic Ice Sheet, we took an integrated approach that included cultivation of microbes associated with the sediment samples in the lab and analysis of mcrA gene therein. After 7 months of incubation, the highest rate of methanogenesis [398 (pmol/day)/gram] was observed at 1°C on a supply of H2. The rates of methanogenesis were lower on acetate or unamended substrate than on H2. The rates on these two substrates increased when the temperature was raised. Methanomicrobiales predominated before and after prolonged incubation, regardless whether H2, acetate, or unamended substrate were the energy source. Therefore, it was inferred that psychrophilic hydrogenotrophic methanogenesis was the primary methane-producing pathway in the subglacial ecosystem we sampled. These findings highlight the effects of temperature and substrate on potential methanogenesis in the subglacial sediment of this area, and may help us for a better estimation on the Antarctica methane production in a changing climate.