Enhancing remote sensing research on global change to improve our understanding on Earth system processes
Suitability mapping of global wetland areas and validation with remotely sensed data
With increasing urbanization and agricultural expansion, large tracts of wetlands have been either disturbed or converted to other uses. To protect wetlands, accurate distribution maps are needed. However, because of the dramatic diversity of wetlands and difficulties in field work, wetland mapping on a large spatial scale is very difficult to do. Until recently there were only a few high resolution global wetland distribution datasets developed for wetland protection and restoration. In this paper, we used hydrologic and climatic variables in combination with Compound Topographic Index (CTI) data in modeling the average annual water table depth at 30 arc-second grids over the continental areas of the world except for Antarctica. The water table depth data were modeled without considering influences of anthropogenic activities. We adopted a relationship between potential wetland distribution and water table depth to develop the global wetland suitability distribution dataset. The modeling results showed that the total area of global wetland reached 3.316×107km2. Remote-sensing-based validation based on a compilation of wetland areas from multiple sources indicates that the overall accuracy of our product is 83.7%. This result can be used as the basis for mapping the actual global wetland distribution. Because the modeling process did not account for the impact of anthropogenic water management such as irrigation and reservoir construction over suitable wetland areas, our result represents the upper bound of wetland areas when compared with some other global wetland datasets. Our method requires relatively fewer datasets and has a higher accuracy than a recently developed global wetland dataset.
A 30 meter land cover mapping of China with an efficient clustering algorithm CBEST
Remote sensing based land cover mapping at large scale is time consuming when using either supervised or unsupervised classification approaches. This article used a fast clustering method—Clustering by Eigen Space Transformation (CBEST) to produce a land cover map for China. Firstly, 508 Landsat TM scenes were collected and processed. Then, TM images were clustered by combining CBEST and K-means in each pre-defined ecological zone (50 in total for China). Finally, the obtained clusters were visually interpreted as land cover types to complete a land cover map. Accuracy evaluation using 2159 test samples indicates an overall accuracy of 71.7% and a Kappa coefficient of 0.64. Comparisons with two global land cover products (i.e., Finer Resolution Observation and Monitoring of Global Land Cover (FROM-GLC) and GlobCover 2009) also indicate that our land cover result using CBEST is superior in both land cover area estimation and visual effect for different land cover types.
High-resolution remote sensing mapping of global land water
Land water, one of the important components of land cover, is the indispensable and important basic information for climate change studies, ecological environment assessment, macro-control analysis, etc. This article describes the overall study on land water in the program of global land cover remote sensing mapping. Through collection and processing of Landsat TM/ETM+, China's HJ-1 satellite image, etc., the program achieves an effective overlay of global multi-spectral image of 30 m resolution for two base years, namely, 2000 and 2010, with the image rectification accuracy meeting the requirements of 1：200000 mapping and the error in registration of images for the two periods being controlled within 1 pixel. The indexes were designed and selected reasonably based on spectral features and geometric shapes of water on the scale of 30 m resolution, the water information was extracted in an elaborate way by combining a simple and easy operation through pixel-based classification method with a comprehensive utilization of various rules and knowledge through the object-oriented classification method, and finally the classification results were further optimized and improved by the human-computer interaction, thus realizing high-resolution remote sensing mapping of global water. The completed global land water data results, including Global Land 30-water 2000 and Global Land 30-water 2010, are the classification results featuring the highest resolution on a global scale, and the overall accuracy of self-assessment is 96%. These data are the important basic data for developing relevant studies, such as analyzing spatial distribution pattern of global land water, revealing regional difference, studying space-time fluctuation law, and diagnosing health of ecological environment.
A multi-resolution global land cover dataset through multisource data aggregation
Recent developments of 30 m global land characterization datasets (e.g., land cover, vegetation continues field) represent the finest spatial resolution inputs for global scale studies. Here, we present results from further improvement to land cover mapping and impact analysis of spatial resolution on area estimation for different land cover types. We proposed a set of methods to aggregate two existing 30 m resolution circa 2010 global land cover maps, namely FROM-GLC (Finer Resolution Observation and Monitoring-Global Land Cover) and FROM-GLC-seg (Segmentation), with two coarser resolution global maps on development, i.e., Nighttime Light Impervious Surface Area (NL-ISA) and MODIS urban extent (MODIS-urban), to produce an improved 30 m global land cover map—FROM-GLC-agg (Aggregation). It was post-processed using additional coarse resolution datasets (i.e., MCD12Q1, GlobCover2009, MOD44W etc.) to reduce land cover type confusion. Around 98.9% pixels remain 30 m resolution after some post-processing to this dataset. Based on this map, majority aggregation and proportion aggregation approaches were employed to create a multi-resolution hierarchy (i.e., 250 m, 500 m, 1 km, 5 km, 10 km, 25 km, 50 km, 100 km) of land cover maps to meet requirements for different resolutions from different applications. Through accuracy assessment, we found that the best overall accuracies for the post-processed base map (at 30 m) and the three maps subsequently aggregated at 250 m, 500 m, 1 km resolutions are 69.50%, 76.65%, 74.65%, and 73.47%, respectively. Our analysis of area-estimation biases for different land cover types at different resolutions suggests that maps at coarser than 5 km resolution contain at least 5% area estimation error for most land cover types. Proportion layers, which contain precise information on land cover percentage, are suggested for use when coarser resolution land cover data are required.
Preliminary analysis of spatiotemporal pattern ofglobal land surface water
Land surface water (LSW) is one of the most important resources for human survival and development, and it is also a main component of global water recycling. A full understanding of the spatial distribution of land surface water and a continuous measuring of its dynamics can support to diagnose the global ecosystem and environment. Based on the Global Land 30-water 2000 and Global Land 30-water 2010 products, this research analyzed the spatial distribution pattern and temporal fluctuation of land surface water under scale-levels of global, latitude and longitude, continents, and climate zones. The Global Land 30-water products were corrected the temporal inconsistency of original remotely sensed data using MODIS time-series data, and then calculated the indices such as water area, water ration and coefficient of spatial variation for further analysis. Results show that total water area of land surface is about 3.68 million km2 (2010), and occupies 2.73% of land area. The spatial distribution of land surface water is extremely uneven and is gathered mainly in mid- to high-latitude area of the Northern Hemisphere and tropic area. The comparison of water ratio between 2000 and 2010 indicates the overall fluctuation is small but spatially differentiated. The Global Land 30-water products and the statistics provided the fundamental information for analyzing the spatial distribution pattern and temporal fluctuation of land surface water and diagnosing the global ecosystem and environment.
Numerical simulation and data assimilation of the water-energy cycle over semiarid northeastern China
The default fractional vegetation cover and terrain height were replaced by the estimated fractional vegetation cover, which was calculated by the Normalized Difference Vegetation Index (NDVI) of Earth Observing System Moderate-Resolution Imaging Spectroradiometer (EOS-MODIS) and the Digital Elevation Model of the Shuttle Radar Topography Mission (SRTM) system. The near-surface meteorological elements over northeastern China were assimilated into the three-dimensional variational data assimilation system (3DVar) module in the Weather Research and Forecasting (WRF) model. The structure and daily variations of air temperature, humidity, wind and energy fields over northeastern China were simulated using the WRF model. Four groups of numerical experiments were performed, and the simulation results were analyzed of latent heat flux, sensible heat flux, and their relationships with changes in the surface energy flux due to soil moisture and precipitation over different surfaces. The simulations were compared with observations of the stations Tongyu, Naiman, Jinzhou, and Miyun from June to August, 2009. The results showed that the WRF model achieves high-quality simulations of the diurnal characteristics of the surface layer temperature, wind direction, net radiation, sensible heat flux, and latent heat flux over semiarid northeastern China in the summer. The simulated near-surface temperature, relative humidity, and wind speed were improved in the data assimilation case (Case 2) compared with control case (Case 1). The simulated sensible heat fluxes and surface heat fluxes were improved by the land surface parameterization case (Case 3) and the combined case (Case 4). The simulated temporal variations in soil moisture over the northeastern arid areas agree well with observations in Case 4, but the simulated precipitation should be improved in the WRF model. This study could improve the land surface parameters by utilizing remote sensing data and could further improve atmospheric elements with a data assimilation system. This work provides an effective attempt at combining multi-source data with different spatial and temporal scales into numerical simulations. The assimilation datasets generated by this work can be applied to research on climate change and environmental monitoring of arid lands, as well as research on the formation and stability of climate over semiarid areas.
Effect of a thermokarst lake on soil physical properties and infiltration processes in the permafrost region of the Qinghai-Tibet Plateau, China
Changes in the hydrological processes in alpine soil constituteone of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typically developing thermokarst lake was chosen as a subject for a study using model simulation based on observations of soil physical properties, infiltration processes, and soil moisture. The results showed that the selected thermokarst lake imposed certain changes on the soil infiltration processes and,with the degree of impact intensifying, the initial infiltration rate decreased. The greatest reduction was achieved in the area of moderate impact. However, the stable infiltration rate and cumulative infiltration gradually increased in the surface layer at a depth of 10and 20cm, both decreasing initially and then increasing, which is correlated significantly with soil textures. Moreover, the cumulative infiltration changed in line with steady infiltration rate. Based on a comparative analysis, the Horton model helps better understand the effect on the soil infiltration processes of the cold alpine meadow close to the chosen thermokarst lake. In conclusion, the formation of the thermokarst lake reduced the water holding capacity of the alpine meadow soil and caused the hydraulic conductivity to increase, resulting in the reduction of runoff capacityin the area of the thermokarst lake.
Spatial distribution of marine chemicals along a transect from Zhongshan Station to the Grove Mountain area,Eastern Antarctica
This study investigates the regional distribution of marine aerosol originated species (Na+, Cl-, nss-SO42- and MSA) in the snow pits (or firn cores) collected along a transect between Zhongshan Station and the Grove Mountain area (450 km inland) on the eastern side of the Lambert Glacier Basin. Concentrations of Na+ and Cl- decrease exponentially with distance from the coast to 100 km inland (i.e., 1500 m a.s.l.). Statistical results demonstrate that distance from the coast inland and elevation affect the concentration of sea-salt originated ions in inland areas significantly. Increase of Cl-/Na+ ratio and higher variability in its standard deviation suggest that there are other sources of ions in addition to sea-salt in inland areas of the Antarctic continent. The concentrations of Na+ and Cl- from nine sampling sites in the Grove Mountain area are relatively higher than those from sites along CHINARE transect, although all sites are at similar distance inland. This phenomenon indicates that the barrier effect of the mountain may be the most important factor influencing ion deposition. In addition, nss-SO42- and MSA vary differently, with nss-SO42- decreasing with distance more significantly. This implies that sources and transporting pathways influence the deposition of the two sulfur compounds considerably, being supported by the spatial pattern of correlation coefficients between the nss-SO42- and MSA.
Modeling the impacts of policy interventions from REDD+ in Southeast Asia：A case study in Indonesia
Reducing Emissions from Deforestation and Forest Degradation (REDD+) and enhancing "removals of greenhouse gas emissions by forests" in developing countries through positive incentives is regarded as an essential component of the post-2012 climate regime for stabilizing greenhouse gas emissions and an important way of engaging developing countries in global mitigation efforts. We aimed to evaluate the potential effectiveness of REDD+ by integrating it into a land use option framework. One of our goals was to develop scenarios for evaluating the impacts of land use changes on carbon and environmental processes. In addition, we aimed to quantify the potential economic benefits to society of compensated reductions and to identify hotspots for applying REDD+. Three land use change scenarios were examined：(I) business as usual (BAU), (II) economic development, and (III) REDD+. A case study in Indonesia was examined using these land use scenarios and policy interventions, evaluating their effects on carbon emissions, socioeconomics, and environmental features of a spatial system using land use models. Significant emissions and water erosion reductions were predicted to be achieved under the REDD+ scenario, due to reduced deforestation of <6% over the next decade; >0.14 Mt CO2e reduction was predicted relative to the BAU scenario. Furthermore, the spatial land use model indicated that REDD+ payments of forest carbon credits in the compliance market would play a key role in compensating rural communities and plantation companies for their opportunity cost in ending deforestation. This study provides an example of integrating land use modeling with a scenario analysis framework to evaluate plausible future forecasts and to evaluate the potential impacts of REDD+.
Sensitivity studies of a high accuracy surface modeling method
The sensitivities of the initial value and the sampling information to the accuracy of a high accuracy surface modeling (HASM) are investigated and the implementations of this new modeling method are modified and enhanced. Based on the fundamental theorem of surface theory, HASM is developed to correct the error produced in geographical information system and ecological modeling process. However, the earlier version of HASM is theoretically incomplete and its initial value must be produced by other surface modeling methods, such as spline, which limit its promotion. In other words, we must use other interpolators to drive HASM. According to the fundamental theorem of surface theory, we modify HASM, namely HASM.MOD, by adding another important nonlinear equation to make it independent of other methods and, at the same time, have a complete and solid theory foundation. Two mathematic surfaces and monthly mean temperature of 1951-2010 are used to validate the effectiveness of the new method. Experiments show that the modified version of HASM is insensitive to the selection of initial value which is particular important for HASM. We analyze the sensitivities of sampling error and sampling ratio to the simulation accuracy of HASM.MOD. It is found that sampling information plays an important role in the simulation accuracy of HASM.MOD. Another feature of the modified version of HASM is that it is theoretically perfect as it considers the third equation of the surface theory which reflects the local warping of the surface. The modified HASM may be useful with a wide range of spatial interpolation as it would no longer rely on other interpolation methods.
The influence of rainfall on PR radar measurement of ocean surface wind speed and its calibration
Rain can significantly degrade the wind vector retrieval from Precipitation Radar (PR) by three mechanisms, namely, two-way rain attenuation, rain volume-backscattering, and ocean surface roughening from the rain splash effect. Here we first derive the radar equation for PR in rainy conditions. Then we use the rain attenuation model for Ku band, volume backscatter model for spherical raindrops and PR-TMI (TRMM Microwave Imager, TMI) matchup datasets from June to August in 2010 to solve the radar equation, and quantitatively analyze the influence of rainfall on PR radar measurement of ocean surface wind speed. Our results show that the significant effect of rain on radar signal is dominated by two-way rain attenuation and rain splash effect, and the effect of rain volume-backscattering is relatively the weakest, which can even be neglected in rain-weak conditions. Moreover, both the two-way rain attenuation and rain splash effect increase with the increasing of integration rain rate and incident angle. Last, we combine volume-backscattering effect and splash effect into a simple phenomenological model for rain calibration and select three typhoon cases from June to August in 2012 to verify the accuracy of this model. Before calibration, the mean difference and mean square error (MSE) between PR-observed б0 and wind-induced б0 are about 2.95 dB and 3.10 dB respectively. However, after calibration, the mean difference and MSE are reduced to 0.64 dB and 1.61 dB respectively. The model yields an accurate calibration for PR near-nadir normalized radar cross section (NRCS) in rainy conditions.
Enhanced modeling of latent heat flux from urban surfaces in the Noah/single-layer urban canopy coupled model
The numerical modeling of the impacts of urban buildings in mesoscale meteorological models has gradually improved in recent years. Correctly representing the latent heat flux from urban surfaces is a key issue in urban land-atmosphere coupling studies but is a common weakness in current urban canopy models. Using the surface energy balance data at a height of 140 m from a 325 m meteorological tower in Beijing, we conducted a 1-year continuous off-line simulation by using a coupled land surface model and a single-layer urban canopy model and found that this model has a relatively large systematic error for simulated latent heat flux. To improve the numerical method for modeling latent heat flux from urban surfaces, we combined observational analysis and urban land surface model to derive an oasis effect coefficient for urban green areas; to develop a temporal variation formula for water availability in urban impervious surfaces; and to specify a diurnal profile and the maximum values of anthropogenic latent heat release for four seasons. These results are directly incorporated into the urban land surface model to improve model performance. In addition, this method serves as a reference for studies in other urban areas.
Design and testing of a global climate prediction system based on a coupled climate model
A global climate prediction system (PCCSM4) was developed based on the Community Climate System Model, version 4.0, developed by the National Center for Atmospheric Research (NCAR), and an initialization scheme was designed by our group. Thirty-year (1981-2010) one-month-lead retrospective summer climate ensemble predictions were carried out and analyzed. The results showed that PCCSM4 can efficiently capture the main characteristics of JJA mean sea surface temperature (SST), sea level pressure (SLP), and precipitation. The prediction skill for SST is high, especially over the central and eastern Pacific where the influence of El Niño-Southern Oscillation (ENSO) is dominant. Temporal correlation coefficients between the predicted Niño3.4 index and observed Niño3.4 index over the 30 years reach 0.7, exceeding the 99% statistical significance level. The prediction of 500-hPa geopotential height, 850-hPa zonal wind and SLP shows greater skill than for precipitation. Overall, the predictability in PCCSM4 is much higher in the tropics than in global terms, or over East Asia. Furthermore, PCCSM4 can simulate the summer climate in typical ENSO years and the interannual variability of the Asian summer monsoon well. These preliminary results suggest that PCCSM4 can be applied to real-time prediction after further testing and improvement.
Second order potential vorticity and its potential applications
A new invariant, the second order potential vorticity (SPV), is derived in this paper. SPV is the dot product of vorticity and the potential vorticity (PV) gradient, and is proven conservative for a compressible, adiabatic and frictionless atmosphere. Research shows that the new invariant may be used to indicate the evolution of PV, because SPV includes all the information that determines PV evolution: the wind field, and the PV gradient. Furthermore, SPV is capable of diagnosing heavy precipitation because of the strong signals it presents in areas of heavy rainfall. SPV also shows great potential as a comprehensive conserved quantity for indicating the dynamical tropopause and baroclinic instability.
A climatic dataset of ocean vertical turbulent mixing coefficient based on real energy sources
Using data on wind stress, significant height of combined wind waves and swell, potential temperature, salinity and seawater velocity, as well as objectively-analyzed in situ temperature and salinity, we established a global ocean dataset of calculated wind- and tide-induced vertical turbulent mixing coefficients. We then examined energy conservation of ocean vertical mixing from the point of view of ocean wind energy inputs, gravitational potential energy change due to mixing (with and without artificially limiting themixing coefficient), and K-theory vertical turbulent parameterization schemes regardless of energy inputs. Our research showed that calculating the mixing coefficient with average data and artificial limiting the mixing coefficient can cause a remarkable lack of energy conservation, with energy losses of up to 90% and changes in the energy oscillation period. The data also show that wind can introduce a huge amount of energy into the upper layers of the Southern Ocean, and that tidesdo so in regions around underwater mountains. We argue that it is necessary to take wind and tidal energy inputs into account forlong-term ocean climate numerical simulations. We believe that using this ocean vertical turbulent mixing coefficient climatic dataset is a fast and efficient method to maintain the ocean energy balance in ocean modeling research.
Using a Lagrangian model to estimate source regions of particles in sediment traps
A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED (Dynamique des Flux Atmosphériques en Méditerranée) station by tracking particles backwards from March 1 to August 31, 2001. The analysis suggests that source regions depend on the flow fields, the settling speed of the particles, and the deployment depths of the traps. Monthly variation is observed in the distribution patterns of source regions, which is caused by the currents. The source regions are located around the traps and up to hundreds of kilometers away. As the settling speed increases with the particle diameters, the distance to the source regions decreases. The vertical flux can be approximately estimated in 1D for the particles with diameters larger than 500μm. Furthermore, traps moored at various depths at the DYFAMED can collect particles that originated from different regions in the Ligurian Sea.
Controlling factors on the submarine canyon system：A case study of the Central Canyon System in the Qiongdongnan Basin, northern South China Sea
Based on an integrated analysis of high-resolution 2D/3D seismic data and drilling results, this study analyzes the tectonic-sedimentary evolution of the Qiongdongnan Basin (QDNB) since the late Miocene, and discusses the controlling factors on the formation and development of the Central Canyon System (CCS). The sediment failures caused by the relative sea level falling might have discharged deposits from the slope to the canyon. The two suits of the infillings, i.e., turbidites and mass transport complex (MTC), were derived from the northwestern source and northern source, respectively. The sediment supplies, which differ significantly among different areas, might have led to the variations observed in the internal architectures. Tectonic transformation around 11.6 Ma had provided the tectonic setting for the CCS and formed an axial sub-basin in the central part of the Changchang Depression, which could be called the rudiment of the CCS. The tectonic activity of the Red River Fault (RRF) at about 5.7 Ma might have strengthened the hydrodynamics of the deposits at the junction of the Yinggehai Basin (YGHB) and the QDNB to trigger a high-energy turbidity current. The MTC from the northern continental slope system might have been constrained by the Southern Uplift, functioning as a barrier for the infillings of the CCS. Thanks to a sufficient sediment supply during the Holocene period and the paleo-seafloor morphology, the relief of modern central canyon with the starving landform in the eastern Changchang Depression might have been accentuated by deposition of sediments and vertical growth along the canyon flanks, where collapse deposits were widely developed. Corresponding to the segmentation of the CCS, the forming mechanisms of the canyon between the three segments would be different. The turbidite channel in the head area had likely been triggered by the abundant sediment supply from the northwestern source together with the fault activity at about 5.7 Ma of the RRF. The formation and evolution of the canyon in the western segment were caused by combined effects of the turbidite channel from the northwestern source, the MTC from the northern continental slope, and the paleo-seafloor geomorphology. In the eastern segment, the canyon was constrained by the tectonic transformation occurring at approximately 11.6 Ma and the insufficient sediment supply from the wide-gentle slope.
Rare earth element and yttrium compositions of the Paleoproterozoic Yuanjiacun BIF in the Lüliang area and their implications for the Great Oxidation Event (GOE)
In China, most Precambrian banded iron formations (BIFs) are situated in the North China Craton. The Yuanjiacun iron deposit, located in the Lüliang area, is arguably the most representative Superior-type BIF. This iron deposit is coherent with the sedimentary rock succession of the Yuanjiacun Formation in the lower Lüliang Group, and was interpreted to be deposited at 2.3-2.1 Ga, based on ages of overlying and underlying volcanic strata. This age overlaps with the time range of the Great Oxidation Event (GOE, 2.4-2.2 Ga). The Yuanjiacun BIF consists mainly of subhedral-xenomorphic magnetite and quartz and rarely other minerals with a lower degree of metamorphism, from greenschist to lower amphibolite facies. The geochemical characteristics of this BIF are similar to those of Superior-type BIFs. Prominent positive La, Y, and Eu anomalies normalized by the Post Archean Australian Shale (PAAS) indicate that the primary chemical precipitate is a result of solutions that represent mixtures of seawater and high-T hydrothermal fluids. The contamination from crustal detritus found is negligible based on low abundances of Al2O3 and TiO2 (<0.5%) and of trace elements such as Th, Hf, Zr, and Sc (<1.5 ppm), as well as the lack of co-variations between Al2O3 and TiO2. In particular, the Yuanjiacun BIF samples do not display significant negative Ce anomalies like those of the Archean iron formations, but rather, the Yuanjiacun BIF samples exhibit prominent positive Ce anomalies, low Y/Ho ratios, and high light to heavy REE ((Pr/Yb)SN) ratios, which are essentially consistent with the late Paleoproterozoic (<2.0 Ga) BIFs around the world. These characteristics of the Yuanjiacun BIF samples imply that the ancient ocean (2.3-2.1 Ga) was redox-stratified from oxic shallow water to deeper anoxic water. The specific redox conditions of the ancient ocean may be related to the GOE, which gave rise to the oxidation of Ce and Mn in the upper water, and to the presence of a Mn oxide shuttle in the ocean, resulting in varying REE patterns due to the precipitation and dissolution of this Mn oxide shuttle under different redox states. Therefore, the Yuanjiacun BIF appears to have formed near the redoxcline and lower-level reduced marine water.
Neogene palynological assemblages in the west slope of Songliao Basin and their geological implications
Abundant palynological fossils are found from the drill core in the west slope of Songliao Basin, the first full coring borehole that drilled throughout the Neogene. Two Palynological assemblages are recognized according to their vertical distributions, i.e., the late early Miocene-middle Miocene assemblage from the Da'an Formation named as Caryapollenites simplex-Momipites coryloides-Celtispollenites sp.-Tsugaepollenites igniculus, and the late Miocene-early Pliocene assemblage from the Taikang Formation named as Artemisiaepollenites minor-Betulaceoipollenites sp.-Carpinipites sp.-Polypodiaceae- sporites sp. On the basis of the composition of each assemblage, we infer that the climate was warm-temperate to sub-tropic during the late early Miocene-middle Miocene and the vegetation was mainly deciduous broadleaved forest and subordinate coniferous and broad-leaved mixed forest with few understory ferns, and probably some shallow fresh water wetlands. The climate then turned cooler and drier in the late Miocene-early Pliocene, represented by the development of xerophytic herbs and temperate plants, although the canopy of the forest remained relatively stable. The results significantly improve the understanding of the Cenozoic palynostratigraphy in the Songliao Basin, and provide new data for both stratigraphical correlation and paleovegetational and paleoclimatical analysis in adjacent area.
The porosity origin of dolostone reservoirs in the Tarim, Sichuan and Ordos basins and its implication to reservoir prediction
Origin of dolostone remained a controversial subject, although numerous dolomitization models had been proposed to date. Because of the dolomitization's potential to be hydrocarbon reservoirs, one debatable issue was the role of dolomitization in porosity construction or destruction. Based upon case studies of dolostone reservoirs in various geological settings such as evaporative tidal flat (Ordos Basin, NW China), evaporative platform (Sichuan Basin, SW China), and burial and hydrothermal diagenesis (Tarim Basin, NW China), here we systematically discuss the origin of porosity in dolostone reservoirs. Contrary to traditional concepts, which regarded dolomitization as a significant mechanism for porosity creation, we found two dominant factors controlling reservoir development in dolostones, i.e., porosity inherited from precursor carbonates and porosity resulted from post-dolomitization dissolution. Actually, dolomitization rarely had a notable effect on porosity creation but rather in many cases destroyed pre-existing porosity such as saddle dolostone precipitation in vugs and fractures. Porosity in dolostones associated with evaporative tidal flat or evaporative platform was generally created by subaerial dissolution of evaporites and/or undolomitized components. Porosity in burial dolostones was inherited mostly from precursor carbonates, which could be enlarged due to subsequent dissolution. Intercrystalline porosity in hydrothermal dolostones was either formed during dolo- mitization or inherited from precursor carbonates, whereas dissolution-enlarged intercrystalline pores and/or vugs were usually interpreted to be the result of hydrothermal alteration. These understandings on dolostone porosity shed light on reservoir prediction. Dolostone reservoirs associated with evaporative tidal flat were laterally distributed as banded or quasi-stratified shapes in evaporite-bearing dolostones, and vertically presented as multi-interval patterns on tops of shallowing-upward cycles. Dolostone reservoirs associated with evaporative platform commonly occurred along epiplatforms or beneath evaporite beds, and vertically presented as multi-interval patterns in dolostones and/or evaporite-bearing dolostones of reef/shoal facies. Constrained by primary sedimentary facies, burial dolostone reservoirs were distributed in dolomitized, porous sediments of reef/shoal facies, and occurred vertically as multi-interval patterns in crystalline dolostones on tops of shallowing-upward cycles. Hydrothermal dolomitization was obviously controlled by conduits (e.g., faults, unconformities), along which lenticular reservoirs could develop.
Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China
Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-14C ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14C dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn't change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12±18.50)×10-5) and δ18O ((1.76±1.03)‰) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11±0.41)×10-5 and δ18O=(-4.82±0.96)‰). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and δ18O ratios than modern Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today's Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ~5% larger than it is today.
An Asian origin for Sinomastodon (Proboscidea, Gomphotheriidae) inferred from a new Upper Miocene specimen from Gansu of China
We report a fossil specimen referable to Sinomastodontinae gen. et sp. indet. from the Neogene strata at Yanghecun locality, Xihe County, Gansu Province, China. The specimen is characterized by a brevirostrine mandible, complete pretrite trefoils, and relatively simple posttrite half lophids, showing typical features of Sinomastodon. It differs from the other known species of Sinomastodon by the following features： relatively short and wide m3 due to fewer lophid numbers, less inflated pretrite accessory central conules, poorly developed secondary trefoils and cementum, and relatively strong cingulid. All of these features indicate a bias towards pleisiomorphies of Sinomastodon, implying that this specimen is more ancestral than any known species of Sinomastodon. The symphysis of the new specimen is relatively long, which differs from the typical brevirostrine Sinomastodon, and thus we consider it a gen. et sp. indet. in the Subfamily Sinomastodontinae. In addition, the horizon in which the present specimen was found probably represents the Upper Miocene because it is lower than Pliocene strata yielding Hipparion (Proboscidipparon) pater. Generally, Sinomastodon is considered to have migrated from North America at about the time of the Miocene/Pliocene boundary, and to have been derived from a certain clade of American gomphotheres. However, the discovery of the Yanghecun specimen verifies that Sinomastodon lived in East Asia during the Late Miocene, and probably derived from Old World gomphotheres (e.g., G. wimani). The similarity between the members of the Subfamilies Sinomastodontinae and those of Cuvieroniinae is suggested to have been the result of parallel evolution.
Rayleigh wave phase velocity tomography and strong earthquake activity on the southeastern front of the Tibetan Plateau
To investigate the relationship between velocity structure and earthquake activity on the southeastern front of the Tibetan Plateau, we make use of continuous observations of seismic ambient noise data obtained at 55 broadband stations from the regional Yunnan Seismic Network. These data are used to compute Rayleigh wave Green's Functions by cross-correlating between two stations, extracting phase velocity dispersion curves, and finally inverting to image Rayleigh wave phase velocity with periods between 5 and 34 s by ambient noise tomography. The results show significant lateral variations in crustal and uppermost mantle structures in the studied region. Phase velocity anomalies at short periods (5-12 s) are closely related to regional tectonic features such as sediment thickness and the depth of the crystalline basement. The Sichuan-Yunnan rhombic block, enclosed by the Honghe, Xiaojiang and Jianchuan faults, emerges as a large range of low-velocity anomalies at periods of 16-26 s, that inverts to high-velocity anomalies at periods of 30-34 s. The phase velocity variation in the vicinity of the Sichuan-Yunnan rhombic block suggests that the low-velocity anomaly area in the middle-lower crust may correspond to lower crustal channelized flow of the Tibetan Plateau. The spatial distribution of strong earthquakes since 1970 reveals that the Yunnan region is inhomogeneous and shows prominent characteristics of block motion. However, earthquakes mostly occur in the upper crust, with the exception of the middle-Yunnan block where earthquakes occur at the interface zone between high and low velocity as well as in the low-velocity zones, with magnitudes being generally less than 7. There are few earthquakes of magnitude 5 at the depths of 15-30 km, where gather earthquakes of magnitude 7 or higher ones which mainly occur in the interface zone between high and low velocities with others extending to the high-velocity abnormal zone.
Ion dynamics associated with substorm dipolarization fronts
We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts (DFs) in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS spacecraft in the near-Earth magnetotail (~-10 Re). We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic (LSK) simulation results. The LSK simulation reproduced the sudden ion energy flux enhancement concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.
A new plasmapause location model based on THEMIS observations
A new empirical model of plasmapause location as functions of magnetic local time and geomagnetic indices has been developed based on the observations from THEMIS mission. We use the two-year data of electron density inferred from spacecraft potential to identify the plasmapause crossings and create a database of plasmapause locations. The database is further used to build up an empirical model of plasmapause related to magnetic local time based on the equation from O'Brien and Moldwin (2003). The new model is compared with previous plasmapause location models. It is found that our newly developed model is the best in predicting plasmapause locations among the existing models. The models based on Kp and Dst indices are better than the model based on AE index, suggesting that the plasmapause location is controlled by large scale convection of the magnetosphere.
The geometric factor of high energy protons detector on FY-3 satellite
Geometric factor is the key parameter for inversion of particle spectrum in space particle detection. Traditional geometric factor is obtained through the method of numerical calculation with the actual structure of the detector as the input condition. The degree of accuracy for data inversion is reduced since traditional geometric factor fails to take into account the physical process of interaction between the particle and substance as well as the influence of factors such as the particle interference between different energy channels on the measurement result. Here we propose an improved geometrical factor calculation method, the concept of which is to conduct actual structural modelling of the detector in the GEANT4 program, consider the process of interaction between the particle and substance, obtain the response function of the detector to particles of different energy channels through the method of Monte Carlo simulation, calculate the influence of contaminated particle on the geometrical factor, and finally get the geometrical factors for different energy channels of the detector. The imrpoved geometrical factor obtained through the method has carried out inversion for the data of high energy protons detector on China's FY-3 satellite, the energy spectrum after which is more in line with the power law distribution recognized by space physics. The comparison with the measured result of POES satellite indicates that the FY-3 satellite data are in good accordance with the satellite data, which shows the method may effectively improve the quality of data inversion.