ALBERT

Description: In this study we present dissolved and particulate 230Th and 232Th results, as well as particulate 234Th data, obtained as part of the GEOTRACES central Arctic Ocean sections GN04 (2015) and IPY11 (2007). Samples were analyzed following GEOTRACES methods, and compared to previous results from 1991. We observe significant decreases in 230Th concentrations in the deep waters of the Nansen Basin. We ascribe this non-steady state removal process to a variable release and scavenging of trace metals near an ultra-slow spreading ridge. This finding demonstrates that hydrothermal scavenging in the deep-sea may vary on annual time scales and highlights the importance of repeated GEOTRACES sections

Description: Most lakes in the interior Tibetan Plateau have expanded rapidly since the late 1990s. Because of a lack of observations, lake water balances and their changes are far from well understood. Evaporation is a component of the lake water balance, and this study quantifies its magnitude, decadal change, and its contribution to the water balance changes in Lake Nam Co, one of the largest lakes on the Tibetan Plateau (with an area of approximately 2000 km 2 and a mean depth of approximately 40 m). The lake temperature and the evaporation are simulated by the Flake model. The simulation results are validated against observed lake temperature profile from 2013 and MODIS lake surface temperature data from 2000-2014. The simulated latent heat flux and sensible heat flux are validated against Bowen ratio-derived estimates for 2013. Based on the validated simulation results, the long-term mean annual evaporation is approximately 832 ± 69 mm, and this value is much less than the potential evaporation estimated using the Penman-Monteith equation. The annual evaporation from 1980-2014 displays a complex decadal oscillation, mainly due to the changes in energy-related terms (air temperature and radiation). The mean lake evaporation since the late 1990s is greater than previous periods; thus, this change in evaporation has suppressed the recent expansion of Nam Co.

Description: Abstract Dynamic changes in soil organic carbon (SOC) have become a popular topic in global research on organic carbon as part of the increasing attention being paid to food security and reducing greenhouse gas emissions. In this paper, the semiarid regions of China were selected as a research focus, and SOC data from 1980–2015 were analyzed using IBM SPSS Statistics 20.0 software. SOC in farmland varied according to cultivated land type, mulching material type, and planting method in the studied regions. The SOC content is 10.3–10.8 g/kg in supplementally irrigated land and flat dry land, 7.1–8.7 g/kg in terraced dry land and river beach land, and 6.2–6.4 g/kg in sloping dry land. The SOC content increased to 16.1–17.4 g/kg when crop stalks were used as mulch. The increase was only 11.5‐13.5 g/kg in soils mulched with film or sandstone. The SOC value in wheat, maize, and potatoes sown on single or double ridges was 2.4–3.2%, 35.7–36.4% and 4.4–4.8%, respectively, which are higher than the values for wheat, maize, and potatoes sown using the flat planting method. The SOC sequestering potential also varied according to the previously noted factors and was improved from 224.1–383.8% depending on cultivated land type, from 96.5–182.3% depending on mulching material type, and from 96.1–191.3% depending on planting method. The SOC sequestering potential can be improved by 453.2–757.4% with the integration of the optimal cultivated land type, mulching material type, and planting method. Thus, there is substantial soil carbon sequestration potential in China's semiarid regions. This article is protected by copyright. All rights reserved.

Description: Abstract In this work, we report a lead‐free piezoelectric ceramic of (0.9‐x)NaNbO3‐0.1BaTiO3‐xBaZrO3, and the effects of BaZrO3 on the phase structure, microstructure, electrical properties and temperature stability are investigated. A morphotropic phase boundary‐like region consisting of rhombohedral (R) and tetragonal (T) phases is constructed in the compositions with x = 0.035‐0.04. More importantly, in situ temperature independence of the piezoelectric effect {piezoelectric constant (d33) and strain} can be achieved below the Curie temperature (Tc). Intriguingly, the electric field‐induced strain is still observed at T ≥ Tc due to the combined actions of the electrostrictive effect and the electric field‐induced phase transition. We believe that NaNbO3‐based ceramics of this type have potential for applications in actuators and sensors.

Description: Independent measurements of the volumetric and elastic properties of Columbia River basalt glass were made up to 5.5 GPa by high-pressure X-ray microtomography and GHz-ultrasonic interferometry, respectively. The Columbia River basalt displays P- and S-wave velocity minima at 4.5 and 5 GPa, respectively, violating Birch's Law. These data constrain the pressure dependence of the density and elastic moduli at high pressure, which cannot be modeled through usual equations of state nor determined by step-wise integrating the bulk sound velocity as is common practice. We propose a systematic variation in compression behavior of silicate glasses that is dependent on the degree of polymerization and arises from the flexibility of the aluminosilicate network. This behavior likely persists into the liquid state for basaltic melts resulting in weak pressure dependence for P-wave velocities perhaps to depths of the transition zone. Modeling the effect of partial melt on P-wave velocity reductions suggest that melt fraction determined by seismic velocity variations may be significantly overestimated in the crust and upper mantle.

Description: Abstract Although the impact of El Niño–Southern Oscillation on the Tibetan Plateau (TP) is reflected through stable isotopes of precipitation and ice cores, the hydroclimate response of TP lakes to El Niño–Southern Oscillation is seldom investigated. Here we show that significant lake water deficit occurred on the central TP (CTP) due to a dramatic decrease in precipitation 2016 El Ni/2016 El Niño event, followed by extreme lake water surplus in 2016 and 2017 over most of the TP (except the eastern CTP). Similar but weaker lake shrinkage and afterward expansion can also be found during historical El Niño events. Further exploration reveals that the CTP dry anomaly during El Niño events tends to bridge the dry anomalies over India and northern China, thereby forming a dry zone along the northwestern edge of the Asian monsoon domain. This study may shed light on the prediction of lake level changes on the TP.

Description: ABSTRACT Numerical simulation in coupled elastic and poroelastic media is important in oil and gas exploration. However, the interface between elastic and poroelastic media is a challenge to handle. In order to deal with the coupled model, the first‐order velocity–stress wave equations are used to unify the elastic and poroelastic wave equations. In addition, an arbitrary high‐order discontinuous Galerkin method is used to simulate the wave propagation in coupled elastic–poroelastic media, which achieves same order accuracy in time and space domain simultaneously. The interfaces between the two media are explicitly tackled by the Godunov numerical flux. The proposed forms of numerical flux can be used efficiently and conveniently to simulate the wave propagation at the interfaces of the coupled model and handle the absorbing boundary conditions properly. Numerical results on coupled elastic–poroelastic media with straight and curved interfaces are compared with those from a software that is based on finite element method and the interfaces are handled by boundary conditions, demonstrating the feasibility of the proposed scheme in dealing with coupled elastic–poroelastic media. In addition, the proposed method is used to simulate a more complex coupled model. The numerical results show that the proposed method is feasible to simulate the wave propagation in such a media and is easy to implement.

Description: The elasticity of Al-bearing stishovite with 1.0, 3.3 and 4.5 wt.% Al 2 O 3 were investigated in the multi-anvil apparatus at high pressures and temperatures up to 21 GPa and 1700 K, by ultrasonic interferometry in conjunction with in situ X-ray techniques. The moduli K S and G are found to decrease with increasing Al 2 O 3 content, while their pressure and temperature derivatives do not change in a significant manner for 1.0 and 3.3 wt.% Al 2 O 3 . The temperature derivatives for 4.5 wt.% Al 2 O 3 , however, are larger, which may result from a change in the Al substitution mechanism at high Al 2 O 3 content. It is shown that acoustic velocities of any Mid-Ocean Ridge Basalt are lower by -0.4 % than those calculated from pure stishovite data. Velocity perturbations up to -3.4 % ( V P ) and -4.2 % ( V S ) in subducted slabs are explained by the combination of the thermal equilibration ( ΔT ~600 K) of the slab and Al-enrichment in stishovite.

Description: The relationships between cover and AGB for the dominant and widely distributed alpine grasslands on the northern Tibetan Plateau is still not fully examined. The objectives of this study are to answer the following question: (1) How does aboveground biomass (AGB) of alpine grassland relate to plant cover at different spatial scales? (2) What are the major biotic and abiotic factors influencing on AGB–cover relationship? A community survey (species, cover, height, and abundance) was conducted within 1 m × 1 m plots in 70 sites along a precipitation gradient of 50–600 m. Ordinary linear regression was employed to examine AGB–cover relationships of both community and species levels at regional scale of entire grassland and landscape scale of alpine meadow, alpine steppe, and desert steppe. Hierarchical partitioning was employed to estimate independent contributions of biotic and abiotic factors to AGB and cover at both scales. Partial correlation analyses were used to discriminate the effects of biotic and abiotic factors on AGB–cover relationships at two spatial scales. AGB and community cover both exponentially increased along the precipitation gradient. At community level, AGB was positively and linearly correlated with cover for all grasslands except for alpine meadow. AGB was also linearly correlated with cover of species level at both regional and landscape scales. Contributions of biotic and abiotic factors to the relationship between AGB and cover significantly depended on spatial scales. Cover of cushions, forbs, legumes and sedges, species richness, MAP, and soil bulk density were important factors that influenced the AGB–cover relationship at either regional or landscape scale. This study indicated generally positive and linear relationships between AGB and cover are at both regional and landscape scales. Spatial scale may affect ranges of cover and modify the contribution of cover to AGB. AGB–cover relationships were influenced mainly by species composition of different functional groups. Therefore, in deriving AGB patterns at different spatial scales, community composition should be considered to obtain acceptable accuracy. This study indicated generally positive and linear relationships between AGB and cover are at both regional and landscape scales, and suggested that in deriving AGB patterns at different spatial scales, community composition and related environmental factors should be considered to obtain acceptable accuracy.

Description: ABSTRACT Effects of climate change on vegetation greenness have attracted considerable attention in the context of global change; however, the dependence of such climatic effects on elevation remains poorly understood. In this study, we examine the relationship between vegetation greenness change and climate change and, in particular, characterize how this relationship changes with elevation in the high mountains of southwest China by using the remotely sensed normalized difference vegetation index (NDVI), and observed temperature and precipitation data sets for the period of 1982–2013. The results show that vegetation exhibited a greening trend (slope: 0.0008 year −1 , p  〈 0.01) under climate warming (slope: 0.04 °C year −1 , p  〈 0.01) and drying (slope: −2.47 mm year −1 , p  〉 0.05). The vegetation greening and climate warming trends were stronger in the higher elevation plateaus than in the lower elevation mountains. Statistical analysis showed that temperature was the main driving factor on vegetation greening, and the driving effect was elevation-dependent. A substantially more significant correlation between climate warming and vegetation greening was found in the higher elevation plateaus, which reveals a higher temperature sensitivity of these plateaus. In addition, a significant correlation between inter-annual standard deviations of NDVI and precipitation during 1982–2013 was tracked over the entire study area. Map of the high mountains of southwest China showing the elevation pattern, landform distributions (a) and different vegetation types (b). The simple hatch indicates elevation below 1000 m above sea level.