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The increasing atmospheric carbon dioxide (CO2) is the most important factor forcing climate change. However, due to lack of observation data about large-scale range-resolved CO2, there remains substantial uncertainty in current global atmospheric CO2 budget, which hinders giving insight into CO2 cycle and modeling its forcing to climate change. Space-based range-resolved differential absorption lidar (range-resolved DIAL), is a promising and powerful means for obtaining large-scale range-resolved CO2 data, but has been rarely studied. Prior to developing spaceborne range-resolved DIAL, a preliminary study on optimization of on/off-line wavelengths must be performed to ensure high signal-to-noise (SNR), high sensitivity to near surface region and minimize the interference of atmospheric factors. This study aims to find the optimum wavelength scenarios in terms of random errors determined by SNR, weighting functions used to assess sensitivity to near-surface region, and systematic errors affected by atmospheric factors. Firstly, we find the optimal on/off-line wavelengths at 1.57μm and 2.05μm, which are widely used and show good results for measuring CO2 concentration, after estimating on-line and off-line wavenumbers separately using evaluation indexes called and . Furthermore, we get the optimum wavelength scenarios of spaceborne range-resolved DIAL by comparing the random, systematic errors and weighting functions of optimal on-line and off-line wavelengths at 1.57μm and 2.05μm. Results show that the wavelength scenario at 2.05μm is the optimal for spaceborne range-resolved CO2 detection. To satisfy the requirement that the relative random errors are smaller than 0.01 (

Little attention has been paid to climate change in the marginal regions of the Asian summer monsoon (ASM) domain since Marine Isotope Stage (MIS) 3 (60-27 cal kyr BP). Here, based on the mineralogy and grain size of a 24-m-long sediment core retrieved from Jilantai Salt Lake, we provide a paleolake evolution record from a marginal region of the ASM domain over the past 47 kyr. Our results indicate that the lake was a brackish or saline lake and that the region was relatively humid during 47–43 cal kyr BP. From 43 to 27.5 cal kyr BP, the lake salinity increased and the climate began to deteriorate. From 27.5 to 11.8 cal kyr BP, aeolian activity intensified and the climate was arid. From 11.8 to 5.6 cal kyr BP, the lake salinity continuously increased, and the climate was persistently arid. After 5.6 cal kyr BP, the lake salinity dramatically increased, the lake became a salt lake, and the climate was extremely arid. In general, the climate was semihumid in mid-late MIS 3, arid in MIS 2 (27–11.7 cal kyr BP), and hyperarid in the Holocene. This climate change pattern is apparently different from that in the regions influenced by the Asian monsoon and westerlies, indicating that the enhanced Asian monsoon or westerlies were not the main forcing mechanism driving climate change in the marginal regions of the ASM domain. Enhanced ice-albedo feedback caused by the expanded Northern Hemisphere ice volume during MIS 3 would have resulted in less net incoming solar radiation and relatively low temperatures in the mid-high-latitudes. The relatively low temperatures might have weakened the evaporation capacity of Jilantai Basin and increased south-north temperature gradients, resulting in an increase in local precipitation. Therefore, the climate was semihumid in mid-late MIS 3. The lowest Northern Hemisphere summer insolation (NHSI) combined with significantly increased ice-albedo feedback associated with the largest Northern Hemisphere ice volume would have led to a remarkable reduction in temperature, resulting in the reorganization of major atmospheric and hydrological systems in the Northern Hemisphere and an arid climate in MIS 2. Subsequently, the Northern Hemisphere ice volume nearly vanished, and the rising NHSI enhanced evaporation, thereby generating a hyperarid climate in the Holocene.

The enhanced Arctic sea ice melting under global warming has improved the accessibility potential of the northeast passage (NP). However, the variations of navigability of this passage under the changing sea ice conditions remain unclear. Here, we investigated the past changes and future trends of sea ice conditions and navigability in the NP waters during the period from 2011 to 2050 based on the satellite-observed sea ice products and model simulations. The AMSR-E and AMSR-E2 ASI sea ice concentration and SMOS sea ice thickness datasets from 2011 to 2020, as well as the simulations during 2021 and 2050 provided by the Coupled Model Inter-comparison Project Phase 6 (CMIP6), were used to quantify the navigation risk of different type of vessels according to the International Maritime Organization (IMO) Polar Operational Limit Assessment Risk Indexing System (POLARIS) navigation risk assessment model. An optimal path algorithm was applied to determine the routes based on the navigation risks. The results showed the extended navigable periods and variations in the optimal paths under the future emission scenarios. This study could benefit the usage of satellite-observed sea ice products in the navigation aid of the vessels.

Facing the major scientific issues of the global carbon cycle and the monitoring demand for carbon emission reduction all over the world, this paper researches and develops a new calculation method for space-based remote sensing detection of greenhouse gas-flux based on the atmospheric boundary layer turbulence transport theory and the active detection of coherent differential absorption lidar system. By obtaining the atmospheric wind profile information, gas concentration profile information and the new calculation method for space-based gas-flux proposed in this paper, the near-surface gas-flux information in the detected area can be directly obtained. So it can innovatively realize the space-based active and direct remote sensing of the atmospheric boundary layer gas-flux. The method in this paper not only can make up the blank in the space-based active detection of greenhouse gas-flux, but also can realize the high spatial and temporal resolution measurement of the three-dimensional atmospheric motion. It reduces assumptions and errors of the existing model based on the column concentration assimilation inversion method, so it can realize a direct and active observation of global multi-scale, high-quality, long-sequence gas-flux.

With the increasing computations in power system simulations, high-performance and cost-effective power system simulator is highly required. In this paper, a cloud-computing based power system simulator, namely CloudPSS, is designed. Based on an open service integrating framework, a self-developed electromagnetic transients (EMT) simulator with an automatic code generator is provided to accelerate EMT simulations using heterogeneous computing devices in the cloud, such as CPU and GPU. Test results show that the CloudPSS platform can achieve significant speedups for both large-scale simulation tasks and multi-scenario tasks. Moreover, benefit from the time-sharing of cloud computing resources, the computational cost can be greatly reduced.

The input-output method (IOM) is one of the most popular methods of estimating the ice sheet mass balance (MB), with a significant advantage in presenting the dynamics response of ice to climate change. Assessing the uncertainties of the MB estimation using the IOM is crucial to gaining a clear understanding of the Antarctic ice-sheet mass budget. Here, we introduce a framework for assessing the uncertainties in the MB estimation due to the methodological differences in the IOM, the impact of the parameterization and scale effect on the modeled surface mass balance (SMB, input), and the impact of the uncertainties of ice thickness, ice velocity, and grounding line data on ice discharge (D, output). For the assessment of the D’s uncertainty, we present D at a fine scale. Compared with the goal of determining the Antarctic MB within an uncertainty of 15 Gt yr−1, we found that the different strategies employed in the methods cause considerable uncertainties in the annual MB estimation. The uncertainty of the RACMO2.3 SMB caused by its parameterization can reach 20.4 Gt yr−1, while that due to the scale effect is up to 216.7 Gt yr−1. The observation precisions of the MEaSUREs InSAR-based velocity (1–17 m yr−1), the airborne radio-echo sounder thickness (±100 m), and the MEaSUREs InSAR-based grounding line (±100 m) contribute uncertainties of 17.1 Gt yr−1, 10.5 ± 2.7 Gt yr−1 and 8.0~27.8 Gt yr−1 to the D, respectively. However, the D’s uncertainty due to the remarkable ice thickness data gap, which is represented by the thickness difference between the BEDMAP2 and the BedMachine reaches 101.7 Gt yr−1, which indicates its dominant cause of the future D’s uncertainty. In addition, the interannual variability of D caused by the annual changes in the ice velocity and ice thickness are considerable compared with the target uncertainty of 15 Gt yr−1, which cannot be ignored in annual MB estimations.

Topaz-II is a space nuclear reactor developed by the Former Soviet Union. It is a thermal-neutron reactor with UO2 ceramics as fuel. Electricity is generated based on the principle of thermoelectric conversion. The reactivity is controlled by several groups control drums. Its lifetime can be three years and its reactivity feedback and further dynamic characteristics are varying with its lifetime. The positive reactivity feedback characteristics and different dynamic characteristics in different lifetime make it changeling to design a suitable control system for Topaz-II. All-coefficient adaptive control is a single-input single-output adaptive control method applied to a parameter unknown, linear time invariant or slowly varying object. In some specific conditions, it is also suitable for the non-linear systems. In this method, the model where the sum of coefficients is equal to one is reconstructed based on the original dynamic model. All coefficients in this model can be identified. Therefore, it is possible to realize the optimal control. Firstly, the model of Topaz-II nuclear reactor system is built. It includes point-reactor kinetics model with six groups delayed neutrons, a one-dimensional lumped transient thermal model of the nuclear fuel element and the moderator, a thermionic model of the converters, a control drum drive model. The reactivity feedbacks with fuel temperature and moderator are considered. Based on the model, the dynamic characteristics are analyzed. Then, with the nonlinear model of Topaz-II nuclear reactor system, the transfer functions are obtained and analyzed. Based on the transfer functions, the model where the sum of coefficients is equal to one is built by using the all-coefficient adaptive control method. After dealing with the parameter and analyzing the error, the all-coefficient adaptive control systems are designed. To evaluate the performance of the control systems, power maneuvering events including a 30%FP (Full Power) step change and a reactivity disturbance of 0.0065 are simulated. The responses with traditional and proposed control methods are evaluated and compared. The simulation results show that the all-coefficient adaptive control system has a better performance in settling time and overshoot compared with those with traditional PID controller.

Excessive exchangeable sodium and high soil pH result in structural destabilization of sodic soil. The long-term application of cattle manure is an important management practice that can affect the physical properties of sodic soil. Experiments were carried out using a randomized complete block design comprising five treatments according to the cattle manure application history: corn (Zea mays L.) fields with annual manure application since 2011 (M2011), 2006 (M2006), 2001 (M2001) and 1995 (M1995) were used as the experimental treatments; manure was applied at a rate of 10,000 kg ha−1 yr−1 on an oven-dry weight basis, and corn without manure application was used as the control. The results indicated that long-term application of manure to sodic soil resulted in significant increases in soil porosity, water-holding capacity, and saturated hydraulic conductivity (Ks) and a decrease in bulk density in comparison to the control treatment. In addition, manure application significantly increased macro-aggregate formation and the mean weight diameter (MWD). Based on stepwise regression analysis, the dominant independent variable that affected aggregate stability was water-stable aggregates (WSAs) of 0.5–1 mm, and the dominant independent variable that affected both capillary porosity (ƒc) and non-capillary porosity (ƒn) was WSAs of 0.25–0.5 mm. MWD, ƒn and especially soil organic matter (SOM) were the dominant attributes that affected Ks. It was concluded that improved soil physical properties are related to soil aggregation, resulting mainly from macro-aggregate formation, particularly WSAs of 0.25–0.5 and 0.5–1 mm. This is due to binding-agent production and increased SOM from annual manure application.

The climate conditions during Marine Isotope Stage (MIS) 3 were similar to present-day conditions, but whether humidity then exceeded present levels is debated, and the driving mechanisms of palaeoclimate evolution since MIS 3 remain unclear. Here, we use pollen data from Wulagai Lake, Inner Mongolia, to reconstruct vegetation and climate changes since the middle MIS 3. The steppe biome is reconstructed as the first dominant biome and the desert biome as the second, and the results show that the vegetation was steppe over the last 43,800 years. Poaceae, Artemisia, Caryophyllaceae and Humulus were abundant from middle to late MIS 3, indicating humid climate conditions. As drought-tolerant species such as Hippophae, Nitraria and Chenopodiaceae spread during MIS 2, the climate became arid. The Holocene is characterized by the dominance of steppe with mixed coniferous-broadleaved forests in the Greater Hinggan Range, and the desert biome retains high affinity scores, indicating that the climate was semi-arid. The climate from middle to late MIS 3 was wetter than in the Holocene; this shift was related to changes in the Northern Hemisphere's solar insolation and ice volume. The humid conditions during MIS 3 were attributed to strong ice–albedo feedback, which led to evaporation that was less than the precipitation. The enhanced evaporation caused by increased solar insolation and decreased ice volume might have exceeded the precipitation during the Holocene and resulted in low effective humidity in the Wulagai Lake basin.

Wind power generation and multilevel converter are two of the most rapidly developing and promising technologies in recent years. This paper concentrates on the multi-scale transients modeling methods of the doubly fed induction generator (DFIG) based wind power generation system using back-to-back three-level neutral point clamped (NPC) converter. The averaged model and switching function model of the NPC converter are proposed to deal with the large-scale simulation of the wind power system. In addition, the overall control strategies is proposed to drive these models. The simulation results show the good accuracy and efficiency of the proposed average model and switching function model compared with the detailed model, and verify the effectiveness of the proposed control strategies.

The Flux information based on momentum, energy and matter is an important link between different components of the earth system. Flux observation is of great significance for understanding the energy and matter exchange in each circle of the earth system, revealing the carbon cycle process at the same time. Fluxes between the atmosphere and the Earth's surface must pass through the atmospheric boundary layer and have considerable influence on the state of the atmospheric boundary layer. Therefore, the observation and analysis of vertical turbulent flux in the atmospheric boundary layer has become a hot topic of atmospheric research. Based on the development of turbulence theory, the method of calculating gas-flux in the atmospheric boundary layer is constantly improved. In recent years, with the development of lidar detection system, doppler lidar system and differential absorption lidar system have also been effectively used to measure the mean wind speed and small-scale dynamic turbulence parameters, which can be applied to directly detect gas flux of the atmospheric boundary layer. For major scientific issues in the global carbon cycle and carbon emission reduction monitoring needs, this paper has developed a new method of gas-flux calculation of atmospheric boundary layer, while obtaining the wind profile information and gas concentration profile information at the same time and at the same place by the detection of lidar system. This method calculates flux takes into account the atmospheric stability judgment, surface friction velocity and the Monin-Obukhov stability parameter based on the turbulent transport theory of atmospheric boundary layer. It can quickly and effectively realize the active remote sensing detection of the gas flux information of atmospheric boundary layer under different atmospheric stability conditions，which has been proved to be effective and accurate by comparing with other gas-flux data.

Since an increasing number of global gross primary productivity (GPP) products have become available and been applied in climate change research, there is an urgent need to compare their performance in capturing spatial and temporal variability, especially in the regions where the number of training data is limited or model parameters are of relatively larger uncertainty. Here, we investigated the spatial patterns of interannual trends and variations, and seasonal-cycle amplitudes of GPP in the arctic and boreal zones, and explored the differences across various GPP products during the overlapping period (2000−2010). We compared three main types of state-of-the-art GPP products, including simulations derived from terrestrial biosphere models of the Multi-scale Synthesis and Terrestrial Model Intercomparison Project using drivers under different scenarios, 3 datasets up-scaled from FLUXNET eddy covariance measurements based on machine-learning algorithms, and 2 semi-empirical or empirical remotely sensed products based on different satellite data. We also examined the differences of GPP variability across the main ecosystem types, mainly including tundra and taiga, and assessed the contributions of different ecosystems to the temporal variations of total GPP in this zone. The results showed all the products could capture the interannual and seasonal variability of GPP, but the spatial patterns varied largely, which was in-deep discussed. This study will benefit the usage of the GPP products in the carbon cycle research for the arctic and boreal ecosystems.

Quantifying changes in Earth’s ice sheets and identifying the climate drivers are central to improving sea level projections. But it is a pity that the future sea level is difficult to predicted. Space observation can provide global multiscale long-term continuous monitoring data. And it is very important for understanding intrinsic mechanisms, improve models and projections and analyze the impacts on human civilization.Several satellites are applied for Global Cryosphere Watch, including sea ice extent and concentration, ice sheet elevation, glacier area and velocity. Although there are many variable can be measured by satellite sensors. But several variables need to improve the observing capability and developing new methods. Such as snow depth on ice, ice sheets thickness, and permafrost parameters. China has established high-resolution earth observation system to realize stereopsis and dynamic monitoring of the lands, the oceans and the atmosphere.Currently, Qian Xuesen Laboratory working together with Sun Yat-sen University, is trying to design a new space observation system to support Three Poles Environment and Climate Changes project. We are conceptualizing two series satellites including FluxSats and BingSats for carbon/water cycle and cryosphere observations, respectively. To clarify the mechanism of the cryosphere carbon release and carbon sink effects of the oceans and ecosystems. We are developing a new lidar system for detecting the concentration and wind speed, and then atmospheric boundary layer flux exchange can be estimated. To understand the rapid change of the sea ice, such as drift, fragmentation and freeze. We need a short revisit and wide swath system capabilities. InSAR technology gives the digitial elevation of the ice surface. And temporal difference InSAR (DInSAR) shows the changes of elevation. BingSAT-Tomographic Observation of Polar Ice Sheets (TOPIS) achieves the tomographic observation of polar ice sheets with a wide swath and short revisit time. Over the polar regions, the CubeSats form a large cross-track baseline with the master satellite to realize the high two-dimensional spatial resolution with the along-track synthetic aperture. The MirrorSAR technology is utilized in BingSat-TOPIS to achieve time and phase synchronization more economically than the traditional bistatic radar. Sparse array and digital beamforming are also considered to significantly reduce the number of microsatellites, and achieve tomographic images of polar ice sheets.

A high resolution mangrove map (e.g., 10-m), which can identify mangrove patches with small size (< 1 ha), is a central component to quantify ecosystem functions and help government take effective steps to protect mangroves, because the increasing small mangrove patches, due to artificial destruction and plantation of new mangrove trees, are vulnerable to climate change and sea level rise, and important for estimating mangrove habitat connectivity with adjacent coastal ecosystems as well as reducing the uncertainty of carbon storage estimation. However, latest national scale mangrove forest maps mainly derived from Landsat imagery with 30-m resolution are relatively coarse to accurately characterize the distribution of mangrove forests, especially those of small size (area < 1 ha). Sentinel imagery with 10-m resolution provide the opportunity for identifying these small mangrove patches and generating high-resolution mangrove forest maps. Here, we used spectral/backscatter-temporal variability metrics (quantiles) derived from Sentinel-1 SAR (Synthetic Aperture Radar) and sentinel-2 MSI (Multispectral Instrument) time-series imagery as input features for random forest to classify mangroves in China. We found that Sentinel-2 imagery is more effective than Sentinel-1 in mangrove extraction, and a combination of SAR and MSI imagery can get a better accuracy (F1-score of 0.94) than using them separately (F1-score of 0.88 using Sentinel-1 only and 0.895 using Sentinel-2 only). The 10-m mangrove map derived by combining SAR and MSI data identified 20,003 ha mangroves in China and the areas of small mangrove patches (< 1 ha) was 1741 ha, occupying 8.7% of the whole mangrove area. The largest area (819 ha) of small mangrove patches is located in Guangdong Province, and in Fujian the percentage of small mangrove patches in total mangrove area is the highest (11.4%). A comparison with existing 30-m mangrove products showed noticeable disagreement, indicating the necessity for generating mangrove extent product with 10-m resolution. This study demonstrates the significant potential of using Sentinel-1 and Sentinel-2 images to produce an accurate and high-resolution mangrove forest map with Google Earth Engine (GEE). The mangrove forest maps are expected to provide critical information to conservation managers, scientists, and other stakeholders in monitoring the dynamics of mangrove forest.

The freshwater flux from icebergs into the Southern Ocean plays an important role in the global climate through its impact on the deep-water formation. Large uncertainties exist in the ice volume transported by Southern Ocean icebergs due to the sparse spatial and temporal coverage of observations, especially observations of ice thickness. The iceberg freeboard is a critical geometric parameter for measuring the thickness of an iceberg and then estimating its volume. This study developed a new, highly efficient shadow-height method to precisely measure the freeboard of various icebergs surrounded by sea ice using Landsat-8 Operational Land Imager 15-m bi-temporal panchromatic image shadows at low-solar-elevation angles. We evaluated and validated shadow length precision according to bi-temporal measurements and comparison with the measurements from the unmanned aerial vehicle. We determined freeboard precision according to shadow length precision and solar elevation angle. In our case study area, 4832 available freeboard measuring points with shadow length precision better than 2 pixels covered 376 icebergs with sizes ranging from 0.002 to 0.7 km² and with freeboard ranging from 2.3 to 83.4 m. At the solar elevation angles of 5.2°, the freeboard precision of 64.1% data could reach 1 m and 86.9% could reach 2 m. Our proposed method effectively filled in the data gap of existing freeboard measurement methods.

Iceberg calving is the main process that facilitates the dynamic mass loss of ice sheets into the ocean, which accounts for approximately half of the net mass loss of all Antarctic ice shelves. Fine-scale calving variability observations can help reveal the involved calving mechanisms and identify the principal processes that influence how the changing climate affects the mass loss of ice sheets. Iceberg calving from specific ice shelves or regions has been monitored before, but there is still a lack of consistent, long-term and high-precision records on independent calving events for all Antarctic ice shelves. In this study, we developed a circum-Antarctic annual iceberg calving product measuring every independent calving event larger than 1 km2 that occurred from August 2005 to August 2019. We first simulated the expansion of the coastline according to ice velocity, and then manually delineated the calved areas, which are considered to be the differences between the simulated coastline and the actual coastline derived from the corresponding satellite imagery, based on 15 years of continuous multisource optical and synthetic aperture radar images. This product provides detailed information on each calving event, including the associated year of occurrence, area, size, average thickness, mass, recurrence interval, type, and measurement uncertainties. In total, 1786 annual calving events occurred on the Antarctic ice shelves from August 2005 to August 2019. The average annual calving area was measured as 3411.4 km2 with an uncertainty value of 17.1 km2, and the average calving rate was measured as 771.1 Gt/yr with an uncertainty value of 10.2 Gt/yr. The calving frequency, area, and mass fluctuated moderately during the first decade, followed by a dramatic increase from 2015/16 to 2018/19. During the dataset period, large ice shelves, such as the Ronne-Filchner, Ross and Amery Ice Shelves, advanced with low calving frequency, while small and medium-sized ice shelves retreated and calved more frequently. Iceberg calving is most prevalent in West Antarctica, followed by the Antarctic Peninsula and Wilkes Land in East Antarctica. The annual circum-Antarctic iceberg calving dataset provides consistent and precise calving observations with the longest time coverage. The dataset provides multidimensional variables for each independent calving event that can be used to study detailed spatiotemporal variations in Antarctic iceberg calving. The dataset can also be used to study ice sheet mass balance, calving mechanisms and the responses of iceberg calving to climate change. The dataset is shared via Global Change Data Repository (href="http://www.geodoi.ac.cn/WebEn/doi.aspx?Id=1516), and entitled Annual iceberg calving dataset of the Antarctic ice shelves (2005–2019) with DOI: https://doi.org/10.3974/geodb.2020.04.09.V1.

Mangrove forest is considered as one of the pivotal ecosystems to near-shore environment health, adjacent terrestrial ecosystems and even global climate change migration. However, for past two decades, they are declining rapidly. In order to take effective steps to prevent the extinction of mangroves, high spatial resolution information of large-scale mangrove distribution is urgent. Recent study has indicated that a suitable pixel size for extracting mangroves should be at least equal to 10 m. Hence, Sentinel imagery (Sentinel-1 C-band synthetic aperture radar (SAR) and Sentinel-2 Multi-Spectral Instrument (MSI) imagery) whose spatial resolution is 10 m may hold great potentials to achieve this goal, but there are limited researches investigating it. Therefore, in this study, we will explore the potential of Sentinel imagery to extract mangrove forests in China on the Google Earth Engine platform. Specifically, our study was mainly conducted around 3 questions: (1) Which Sentinel imagery provides a higher accuracy for mangrove forest mapping, Sentinel-1 SAR data or Sentinel-2 multi-spectral data? (2) which combination of features from Sentinel imagery provides the most accurate mangrove forest map? (3) Compared to 30-m resolution mangrove products derived from Landsat imagery, how does 10-m resolution map improve our knowledge about the distribution of mangrove forest in China? Our results show that: (1) The highest producer’s accuracies (the reason why using producer’s accuracy as an accuracy evaluation indicator here is that the omission errors in mangrove forest extent map are much larger than commission errors) of mangrove forest maps derived from Sentinel-1 and Sentinel-2 imagery are 91.76% and 90.39%, respectively, which means that the contributions of Sentinel-1 SAR and Sentinel-2 MSI imagery to mangrove mapping are similar; (2) The highest producer’s accuracy of mangrove forest map at 10-m resolution is 95.4%. The mangrove forest map with the highest accuracy is obtained by combining quantiles of spectral and backscatter bands, spectral index, and texture index derived from time series of Sentinel-1 and Sentinel-2 imagery, indicating that the combination of Sentinel-1 SAR and Sentinel-2 MSI imagery is more useful in mangrove forest mapping than using them separately; (3) In China, the total area of mangrove forest extent at 10-m resolution is similar to that at 30-m resolution (20003 ha vs. 19220 ha). However, compared to 30-m resolution mangrove products, the 10-m resolution mangrove map identifies 1741 ha (occupying 8.7% of total mangrove forest area in China) mangrove forests in size smaller than 1 ha, which are especially important to low-lying coastal zone. This study demonstrates the feasibility of Sentinel imagery in large-scale mangrove forest mapping and gives guidance to map global mangrove forest at 10-m resolution in the future.

Studying the carbon dynamics of estuarine sediment is crucial to understanding of carbon cycle in the coastal ocean. This study is designed to investigate the spatial variability of organic (TOC) and inorganic carbon (TIC), and to explore the mechanisms regulating their dynamics in the Yellow River Estuary (YRE) and Liao River Estuary (LRE). Based on data of the surface sediment cores, we found that TIC (6.3-20.1 g kg-1) was much higher than TOC (0.2-4.4 g kg-1) in the YRE, but TIC (0.4 - 4.2 g kg-1) much lower than TOC (0.1 - 8.7 g kg-1) in the LRE. Both TOC and TIC were generally higher to the north than to the south in the YRE, and higher offshore than nearshore in the LRE, primarily due to the differences in kinetic energy level (i.e., higher to the south and nearshore). The ranges of C:N and δ13Corg were smaller in the YRE (2.1 - 10.1 and -24.26‰ ~ -22.66‰) than in the LRE (0.8 - 13.4 and -27.80‰ ~ -22.12‰). Our analysis suggested that TOC was mainly from marine sources in the YER, except in the southern shallow bay where approximately 75% of TOC was terrigenous. The contribution of terrestrial sources TOC was much higher in the nearshore area than in the offshore area in the LRE. The overall low levels of TOC were due to profound resuspension that could cause enhanced decomposition. On the other hand, high levels of TIC resulted partly from higher rates of biological production, and partly from decomposition of TOC associated with sediment resuspension. The isotopic signiture in TIC seems to imply that the latter is dominant in forming more TIC in both the YRE and LRE, and there may be transfer of OC to IC in the water column. Further studies with integrative and quantitative approaches are needed not only to assess the spatial and temporal variations of major carbon forms in the water column and sediments, but also to quantify the contributions of various sources and transformations among the different carbon pools, which aims to better understand the carbon cycle in northern China in a changing climate.

Soil salt accumulation and salt leaching are very important issues for a long-term irrigation-dominated oasis with shallow groundwater in arid land. The critical ratio of drainage to irrigation (CRDI) was defined and determined to help the guide drainage and irrigation practices and maintain sustainable oasis agricultural development. This study aimed to identify the soil salinity evolution under long-term irrigation and to determine the threshold of irrigation to drainage with land-use change and groundwater depth by regression, water and salt balance, and geostatistical analysis. The results showed that the soil salinity in 0–20 cm soil depth has decreased greatly in the Weigan Oasis over the past 60 years, with an annual average decrease of 0.68 g·kg−1 in the Weigan Oasis. The soil salt content generally increases from inside to outside of the region and varies from the upperstream to downstream. In the past 30 years, land-use change has caused a sharp reduction in the salinity in the region, and the process of irrigation and drainage has made a decrease in the total salt of the irrigated district of 207.38 × 105 t. Meanwhile, shallow groundwater depth and salinity are the main factors influencing soil salinization in this fluvial oasis. A CRDI is determined to be 8.20% in the Weigan Oasis. In conclusion, our study provides scientific support for the prevention and control of regional soil salinization, as well as a managerial basis for the rational allocation of water resources in long-term irrigation-dominated oasis.

As more generators and loads are integrated by power electronic converters with complicated controls, electromagnetic transients (EMTs) simulation becomes an important tool for studying dynamic characteristics of large-scale power systems. To accelerate system-level EMT simulations, a fine-grained parallel algorithm on graphics processing units (GPU) is proposed. By decomposing the computational models of the EMT simulation into heterogeneous, homogeneous and network solution computations, the simulations are mapped into three unified GPU kernels. To incorporate control signals and non-linear features of electrical components, heterogeneous computations are formulated as layered direct acyclic graphs (LDAG) of primitive operations. An LDAG kernel is designed to carry out theses primitive operations efficiently by grouped threads. Then, homogeneous computations for state updates of electrical components are modelled as sets of fused multiply-add (FMA) operations, which are concurrently processed by an FMA kernel. Moreover, a hybrid network solution kernel is designed to solve the network equations, which can adaptively select dense or sparse solvers. Large-scale test systems are created and simulated on an NVIDIA K20x GPU. The results show that the proposed GPU-based EMT simulations are accurate and achieve 10x speedups over the CPU-based ones.

Simulation of heating network has important significance for running state prediction, production planning and control strategy making. In past decades, a series of studies are focusing on heating network modeling and simulation. In this paper, we proposed an improved hydraulic-thermal decoupling method for heating network simulation, which is based on steady-state model. The improvement is mainly reflected in the aspect of thermal model solution, where a recursive search method is presented, and about 35% performance improvement is achieved. In addition, we implemented the improved method on CloudPSS, an open cloud computing platform developed by our team. Finally, some numerical experiments were conducted on the platform to analyze the operation characteristics of the heating network.

The large number of switching devices in high-frequency power conversion systems have lead to a computational challenge for electromagnetic transients (EMT) simulation programs, as it can significantly increase the simulation time. Based on the half-bridge sub-circuit, this paper analyses the possible parasitic switching events of adjacent switches on the same bridge arm, and a fast switching status combination judgement algorithm is proposed. This algorithm does not have the process of iterative detection when searching for stable switch combination, thus it can effectively reduce the simulation time. Different testing cases are simulated in both the proposed-algorithm-embedded cloud power system simulation platform (CloudPSS) and the PSCAD, which shows a desirable accuracy of the proposed algorithm.

Lake sediment is an important carbon reservoir, and thus may play an important role in the terrestrial carbon cycle. Bosten Lake is the largest inland freshwater lake in China, which has been influenced by both climate change and human activity especially since 1950. In this study, two short sediment cores were collected from Bosten Lake. Grain size and total organic carbon (TOC) and inorganic carbon (TIC) were determined. We also analyzed isotopic compositions of TOC (δ 13 C org ) and carbonate (δ 13 C carb and δ 18 O carb ), and 137 Cs and 210 Pb. We found that the TIC burial rate (38.7–51.8 g C m − 2 year − 1 ) was much greater than for TOC (17.7–20.1 g C m − 2 year − 1 ) over the past century. The TOC burial rate increased from 1.6–4.2 g C m − 2 year − 1 in the 1900s, to 9.7–10.1 g C m − 2 year − 1 in the 1950s, and then to 43.7–44.7 g C m − 2 year − 1 during the 2000s. The TIC burial rate increased from 5.3–9.2 g C m − 2 year − 1 in the 1900s, to 22.5–36.2 g C m − 2 year − 1 in the 1950s, to 69.4–111.8 g C m − 2 year − 1 in the 1990s, and then decreased to 76.1–87.6 g C m − 2 year − 1 in the 2000s. The pronounced increasing trend in the burial rate of TOC (TIC) during 1950–2012 (1950–2002) was attributable to warming and/or increased human activities; the sharp decrease in TIC during 2002–2012 was caused by reduced biological activity, less evaporation and a rapid decline in lake level. Our study points out that climate change and human disturbance have significantly altered carbon burial in Bosten Lake over the last century.

There is evidence of higher levels of pedogenic carbonate (PIC) than soil organic carbon (SOC) in cropland, and a positive relationship between PIC and SOC in salt-affected soils of arid and semi-arid regions. This study is designed to test the hypothesis that PIC is influenced by intensive cropping and salinization in semi-humid regions, in which soil carbonate (SIC) often exceeds SOC. We select a typical cropland with a maize-wheat rotation in the North China Plain, which covers two distinct regions, i.e. the Hebei Plain (HBP) under intensive cropping and the Yellow River Delta (YRD) under soil salinization. Our data show large variations in soil carbon stocks, with slightly higher values for PIC (3.9–14.5 kg C m−2) relative to those of SOC (2.2–9.2 kg C m−2) in the top 1 m. On average, SOC stock is 5.65 kg C m−2 in the YRD, which is slightly lower than in the HBP (6.21 kg C m−2); SIC is significantly higher in the YRD (16.9 kg C m−2) relative to the HBP (13.7 kg C m−2). However, PIC stock is smaller in the YRD (8.67 kg C m−2) relative to the HBP (9.41 kg C m−2). Despite no clear SIC-SOC relationship, there exists a significant positive correlation (P

Two sediment cores from the Changjiang (Yangtze) River estuary and its adjacent East China Sea were collected and studied for eutrophication history using paleoecological records of environmental changes over the last century. A multiproxy approach by using biological and geochemical analyses revealed changes in diatom assemblages, total organic carbon (TOC), total nitrogen (TN) and biogenic silica (BSi) and give an indication of nutrient in status and trends in Changjiang River estuary and its adjacent East China Sea. The diatom assemblages in the two cores generally increased gradually from the 1970s, and accelerated from the 1990s until now, reflecting the increased eutrophication and causing large algae blooms/red tides. The TOC, TN and BSi showing the similar trends, supported the interpretation of the eutrophication process indicated by diatom analyses. The two cores were located in different sea areas of the East China Sea, and we discuss their relative changes based on their environment characteristics. We also discuss the potential effect of anthropogenic influences and ongoing projects on eutrophication in the Changjiang River and its adjacent East China Sea.

The Yellow-Bohai Sea (YBS) is a typical marginal sea in the Northwest Pacific Ocean; however, little is known about the dynamics of particulate organic carbon (POC) and underlying mechanisms. Here, we analyze the spatial and temporal variations of surface POC derived from MODIS-Aqua during 2002–2016. Overall, POC is higher in the Bohai Sea (315–588 mg m−3) than in the Yellow Sea (181–492 mg m−3), and higher in the nearshore than in the offshore. Surface POC is highest in spring in the YBS, and lowest in winter (summer) in the Bohai Sea (the Yellow Sea). The spatial and seasonal patterns of POC are due to combined influences of primary productivity, water exchange, sediment resuspension and terrestrial inputs. Surface POC shows an overall decreasing trend prior to 2012 followed by an upward trend until 2015 in the YBS, which is almost opposite to chlorophyll; the decrease (increase) may result from strengthened (weakened) water exchange with the East China Sea through the Yellow Sea Warm Current. Declined terrestrial runoff is also partly responsible for the decrease prior to 2012. Our study suggests that water exchange and sediment resuspension are dominant factors regulating the spatial and temporal variability of POC in the YBS.

Lake sediment is a vital carbon reservoir, which is affected by biogeochemical and hydrological processes in the watershed. To study the dynamics of organic carbon in surface sediment of the Bosten Lake, we analyzed total organic carbon (TOC) and its stable carbon isotopic composition (δ13Corg), total nitrogen (TN), and grain size in the surface (0–2 cm) sediment. Our data showed that there was a large spatial variability in both TOC (2.1–4.2%) and δ13Corg (−26.65 to −24.13‰) in surface sediment of the Bosten Lake. By using a three end member mixing model, we estimated that 54–90% of TOC was from autochthonous source. We found higher TOC concentration (>3.7%) near the mouth of the Kaidu River, in the central-north section and in the east section, which was attributable to autochthonous, autochthonous plus allochthonous, and allochthonous sources, respectively. The lowest TOC was seen in the mid-west section, which might mainly be due to the high kinetic energy levels. Our analyses suggested that the magnitude and spatial distribution of TOC in the surface sediment of Bosten Lake were influenced by complex processes and regulated by multiple factors.

Lake sediment is an important carbon reservoir. However, little is known on the dynamics and sources of sediment organic carbon in Bosten Lake. We collected 13 surface (0–2 cm) sediment samples in Bosten Lake and analyzed total organic carbon (TOC), total nitrogen (TN), stable carbon isotopic composition in TOC (δ13Corg), and grain size. We found a large spatial variability in TOC content (1.8–4.4 %) and δ 13Corg value (−26.77 to −23.98 ‰). Using a three-end-member mixing model with measured TOC : TN ratio and δ13Corg, we estimated that 54–90 % of TOC was from autochthonous sources. Higher TOC content (> 3.7 %) was found in the east and central-north sections and near the mouth of the Kaidu River, which was attributable to allochthonous, autochthonous plus allochthonous, and autochthonous sources, respectively. The lowest TOC content was found in the mid-west section, which might be a result of high kinetic energy levels. Our study indicated that the spatial distribution of sediment TOC in the Bosten Lake was influenced by multiple and complex processes.

Estuarine sediment is an important carbon reservoir, and thus may play an important role in the global carbon cycle. The Yellow River Estuary is a large estuary in northern China, having implications for the Bohai Sea's carbon cycle. However, little is known about carbon dynamics in the sediment of the transitional zone near the river mouth. In this study, we collected 15 short sediment cores from the Yellow River Estuary, and measured grain size, total nitrogen (TN), total organic carbon (TOC) and inorganic carbon (TIC) and the isotopic compositions of TOC (δ13Corg) and carbonate (δ13Ccarb and δ18Ocarb). We found that TIC concentration (6.3–20.1 g kg−1) was much higher than TOC (0.2–4.4 g kg−1) in the surface sediment. Both TOC and TIC were higher to the north (2.6 and 14.5 g kg−1) than to the south (1.6 and 12.2 g kg−1), except in the southern bay where TOC and TIC reached 2.7 and 15.4 g kg−1, respectively. The δ13Corg value ranged narrowly from −24.26 ‰ to −22.66 ‰, indicating that TOC might be mainly autochthonous. However, C : N ratio varied from 2.1 to 10.1, with higher ratio found in the southern bay. We estimated that 60.8 % of TOC might be from terrigenous OC in the southern bay. The lower TOC values in the south section were due to relatively higher kinetic energy level whereas the higher values in the bay was attributable to terrigenous matters accumulation and lower kinetic energy level. There was a significantly positive correlation between TIC and TOC, indicating that TIC was primarily from autogenic carbonate. However, the southern bay revealed the most negative δ13Corg and δ13Ccarb, suggesting that there might exist some transfer of OC to IC in the section. Our study points out that the dynamics of sedimentary carbon in the Yellow River Estuary is influenced by multiple and complex processes, and highlights the importance of carbonate in carbon sequestration.