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Objectives Globally, the mass proliferation of phytoplankton driven by climate change has emerged as a significant societal issue. This study analyzes over two decades of long-term hydraulic, hydrological, and water quality data collected from the lower Nakdong River, along with changes in phytoplankton community biomass. The aim is to evaluate long-term trends in water quality and the ecological changes occurring in this region. Methods The monitoring site in the lower Nakdong River is Mulgeum, where samples were collected weekly from January 2000 to December 2021 for the analysis of physicochemical water quality characteristics, as well as phytoplankton abundance and species composition. The hydrological status was assessed using flow rate data from the Jin-dong (Haman) station of the Nakdong River, along with rainfall data from the Korea Meteorological Administration for eight regions influencing the lower Nakdong River. Results and Discussion Analysis of the annual average concentration changes of water quality parameters at the Mulgeum intake site in the lower Nakdong River found that water quality has generally improved since the construction period (2009-2012) of the weir. This improvement is attributed to the strengthening of T-P water quality standards for sewage treatment plant discharges in 2012, which resulted in enhanced phosphorus treatment at wastewater facilities in the river's middle and upper regions. Consequently, significant reductions were observed in the annual average concentrations of BOD, NO3-N, T-N, and T-P. Evaluating long-term changes in flow rate and rainfall, it was found that both annual average rainfall and flow rate decreased after the weir was installed, particularly from May to September when temperatures rise. Rainfall decreased by approximately 8% to 38%, while flow rate decreased by 46% to 62%. Long-term temperature changes indicated that summer temperatures increased by 0.9oC to 1.4oC, and winter temperatures rose by 1.6oC to 2.0oC, resulting in an overall annual average increase of about 1.3oC. An analysis of long-term changes in phytoplankton biomass and community composition revealed an increase in average biomass from 3,639 cells/mL before the weir was installed to 4,034 cells/mL afterward, representing an increase of about 11%. In winter, the dominance period and biomass of diatoms decreased, while in summer, the biomass and dominance period of cyanobacteria increased. Notably, in August, biomass increased approximately 7.5 times, rising from 2,009 cells/mL before the dam to 15,059 cells/mL afterward. This significant increase was identified as a key factor in the overall rise in phytoplankton biomass following the weir's installation. Conclusion Recent climate change impacts, such as rising average temperatures and shifting rainfall patterns, have become increasingly evident in South Korea. This study utilizes over 20 years of long-term data to demonstrate that, in the lower Nakdong River, there has been a gradual decline in both rainfall and flow rates, accompanied by an increase in average temperatures. Consequently, the dominance period and biomass of diatoms have decreased. In contrast, cyanobacteria, which thrive in warmer conditions, have experienced an extended dominance period into early spring and late autumn as a result of rising temperatures, leading to an overall increase in cyanobacterial biomass.

Turbidity, as a key indicator of water quality linked to underwater light attenuation, is crucial for evaluating water quality. Control in high-turbidity water environments plays a critical role in navigable rivers. For this purpose, our study proposed a framework for analyzing the spatio-temporal variation of turbidity and its driving factors in a navigable and turbid river using in situ measurement data, satellite data, socioeconomic data, a power index function model, and correlation analysis. The results show that the proposed model is feasible for quantitative turbidity monitoring of the Xitiaoxi River. Its upstream turbidity is lower than downstream, with seasonal averages for spring, summer, autumn, and winter of 93.9, 111.3, 113.5, and 120.9 NTU, respectively. Furthermore, the turbidity in the middle and lower reaches of the Xitiaoxi River continuously increased before 2005 and began to decline after 2005 due to the policy of mining moratorium. This trend is especially noticeable at monitoring points along the main stream of the Xitiaoxi River, such as downstream of the Xitiaoxi River (S1), Gangkou station (S2), middle reaches of the Xitiaoxi River (S4), Hengtangcun station (S6), upper stream of the Xitiaoxi River (S7), and Huxi River (S8). Mining and shipping have significantly contributed to the turbidity of the target river. This framework offers a practical approach for assessing the environmental impacts of both natural and anthropogenic factors, thereby providing valuable insights for river management practices. [ABSTRACT FROM AUTHOR]

Bohai Bay is an important spawning and nursery habitat for a variety of economically important fish inhabiting the Yellow and Bohai seas. Based on a meta-analysis of historical data spanning 40 years, combined with a field survey of current fish habitat conditions conducted in Bohai Bay, a long-term dataset containing early life resource surveys (including 53 voyages, from 1982 to 2021) of marine Osteichthyes was built. Based on statistical analyses, long-term trends in ichthyoplankton assemblage structure, biodiversity, and synchrony were interpreted. The results indicate that ichthyoplankton assemblage structure and the center of gravity for spawning and nursery habitats in Bohai Bay are currently experiencing continuous replacement. Seasonal variations in ichthyoplankton assemblage structure, abundance index, predominant taxa, and species diversity levels are evident. Spawning and nursery habitats are concentrated in the central and inner part of Bohai Bay west of 118º30'E. Compared with survey results from the 1980s, the taxonomic composition and abundance of the ichthyoplankton assemblage structure have changed considerably. The function of Bohai Bay as a spawning and nursery habitat for traditionally economically important fish has declined significantly. The abundance index and taxon number of ichthyoplankton in Bohai Bay fell to a historic low in the early 2010s, then rebounded significantly. The taxa number of ichthyoplankton decreased from 39 in the 1980s to 31 in the early 1990s, 34 in the late 1990s, and 22 in the 2000s to pre-2010s, then further decreased to 21 in the early 2010s. From the middle 2010s, it recovered to a certain degree, increasing to 40 species just prior to 2020. The current number of pelagic egg taxa is 22, 80% of the number in the 1980s, and 88% of the abundance in the 1980s. The current (2020—2021) number of larval fish taxa is 26, almost identical to that in the 1980s, with an abundance 1.33 times greater than that in the 1980s. Interannual and interdecadal variations in fish egg and larvae species diversity fluctuated drastically. Interannual taxon substitution was noticeable. However, the substitution rate has increased significantly in recent years. Spawning, habitat, and temperature adaptation studies of breeding stock indicate that the number of taxa first decreased, then increased. The annual proportion of the number of taxa to pelagic eggs decreased, while the proportion of the number of taxa to adhesive eggs and eggs with egg membrane filaments increased. The annual proportion of continental shelf pelagic-neritic fish taxa increased, while the continental shelf demersal and benthopelagic taxa decreased. The ecological density of numbers in the early life history (EDN-ELH) of Konosirus punctatus, Sardinella zunasi, Larimichthys polyactis, Trichiurus japonicus, Lateolabrax maculatus, and Cynoglossus semilaevis decreased significantly, whereas the EDN-ELH of Engraulis japonicus, Scomberomorus niphonius, Thryssa kammalensis, and Sillago japonica increased. Ichthyoplankton abundance in Bohai Bay mainly depends on environmental conditions in the spawning habitat, fishing intensity, and the degree of damage to the early life stages of fish resources. The temporal variation and succession of the ichthyoplankton assemblage structure in Bohai Bay were the specific manifestations of the multidimensional niche disturbance and structural performance deterioration of the fishery resources under the dual disturbance of global warming and overfishing.

Based on the MODIS (moderate-resolution imaging spectroradiometer) AOD (aerosol optical depth) and MEIC (multi-resolution emission inventory for China) in Northeast China from 2003 to 2022, the spatial distribution and interannual trend of AOD in Northeast China are analyzed. Effects of meteorological factors and anthropogenic emissions on AOD changes in Northeast China are discussed. Results show that the AOD maximum in central Liaoning is 0.6, followed by an average AOD of 0.4 in western Jilin and 0.3 in Heilongjiang. The average AOD in Northeast China is lower than that in north China, Yangtze River Delta and other frequent pollution areas. High AOD occurs in spring and summer in Northeast China, and it decreases spatially in autumn while increases in winter. The summer AOD in Liaoning is significantly higher than that in other regions, when the average value in central Liaoning and the Bohai Rim increases to 0.6. The highest values of AOD in different seasons occur in Liaoning, followed by Jilin and Heilongjiang. The increase of AOD in summer is mainly related to environmental humidity, and adverse meteorological conditions and local emissions have certain effects on near-surface atmospheric extinction in winter. The annual occurrence frequency of AOD in the range of [0.1, 0.2) and [0.2, 0.3) in Liaoning is up to 50%, the annual occurrence frequency of AOD in the range of [0.1, 0.2) in Jilin and Heilongjiang is up to 25%-30%, and the annual occurrence frequency of extreme clean condition in Heilongjiang is up to 15%. Affected by dust events in spring, the occurrence frequency of AOD [0.2, 0.3) and AOD [0.3, 0.4) in Northeast China is 25%. The regional average value of AOD in Northeast China is higher in 2003 and 2014, which is mainly influenced by boundary layer meteorological elements and anthropogenic emission of SO2, PM2.5, organic carbon (OC) and NO2. In Northeast China, AOD is negatively correlated with boundary layer height and average wind speed, and positively correlated with anthropogenic emissions. The correlation coefficient between AOD and anthropogenic emissions of SO2, PM2.5 and OC is the highest in Liaoning. From 2003 to 2022, AOD in Liaoning shows a weak negative growth trend (about-0.1 per decade), while the AOD in Jilin and Heilongjiang shows little change trend. From the perspective of seasonal interannual trend, there is a transition from a negative increasing trend in spring to a positive increasing trend in summer before 2012. After 2013, the summer AOD in Northeast China shows a negative growth trend (-0.3 per decade), which confirms that the contribution of summer aerosol to atmospheric extinction in Northeast China is decreasing in the past 10 years.

Based on data from the Gurbantunggut Desert, the largest fixed/semi-fixed desert in China, and ERA5-Land reanalysis data, the long-term variations and spatial surface heat source (SHS) differences in the Gurbantunggut Desert are discussed herein. The results show the following: (1) The hourly SHS at the Kelameili station during the 2013–2021 period was a weak heat source at night; contrastingly, it was a strong heat source during the day. The duration of the hourly SHS increased gradually from January to July, but it decreased gradually from July to December. The daily SHS showed obvious seasonal variation, reaching the maximum in summer and the minimum in winter. The ERA5-Land reanalysis can reproduce all the variation characteristics of the SHS well. (2) The climatology (i.e., multi-year mean) of the monthly SHS intensity was lower than 50 W/m2 during the January–March and September–December periods in the Gurbantunggut Desert, indicating a weak heat source. On the other hand, the climatology recorded in April–August was higher than 50 W/m2, with a strong heat source. From the perspective of spatial distribution, the eastern and western regions of the Gurbantunggut Desert show strong heat sources, while the central region shows weak heat sources. The spatial distribution of the first and second modes of the empirical orthogonal function (EOF) decomposition reflected the consistent spatial variability and a north–south (or east–west) polarity variation of the monthly SHS in the Gurbantunggut Desert, respectively. (3) The yearly SHS showed negative anomalies during the 1950–1954, 1964–1982 and 2004–2015 periods, and positive anomalies during the 1955–1963, 1983–2003 and 2016–2021 periods in the Gurbantunggut Desert. Additionally, the time series of the SHS anomalies was positively correlated with the Interdecadal Pacific Oscillation (IPO) index. During the negative IPO phase, the yearly SHS showed a negative anomaly in the Gurbantunggut Desert, while the yearly SHS showed a positive anomaly during the positive IPO phase in most regions of the Gurbantunggut Desert. [ABSTRACT FROM AUTHOR]

Long-term variations in precipitation during the major rainy periods in Japan--the Baiu (June-July) and Akisame (September-October) seasons--are investigated using precipitation records from 44 weather stations in western to eastern Japan over the past 120 years (1901 - 2020). The total amount of Baiu precipitation has increased over the 1901 - 2020 period, mainly during the mid-late stages of the season (late June-July) over regions on the Sea of Japan side of the country. Conversely, the precipitation amount during the Akisame season has decreased, mainly during the mid-stage (late September-early October) over all regions. The frequency and intensity of heavy precipitation have generally increased in both seasons, but the trends are much stronger for the Baiu season than for the Akisame season. A prominent positive trend, 23.5 % (100 yr)-1 (18.1 % °C-1), which is much higher than the Clausius-Clapeyron rate (approximately 7 % °C-1), is observed for the Sea of Japan side of western Japan for the seasonal maximum one-day precipitation total during the Baiu season. It may be noteworthy that the observed long-term trends differ greatly between the Baiu and Akisame seasons even though the statistical significances of the trends are not so high, because similar differences between the two rainy seasons are found in the results of global warming simulations. [ABSTRACT FROM AUTHOR]

Study of Air Quality Objectives (AQOs) and long-term changes of air pollution plays a decisive role in formulating and refining pollution control strategies. In this study, 10-year variations of six major air pollutants were analyzed at seven monitoring sites in Hong Kong. The continuous decrease of annual averaged concentrations of NO 2 , SO 2 , CO, PM 2.5 and PM 10 and numbers of days with severe pollution conditions validated the efficiency of the series of air pollution control schemes implemented by the Hong Kong government. However, there is still a big gap to meet the ultimate targets described by the World Health Organization. Besides, the concentration of O 3 at roadside and urban stations increased by 135% ± 25% and 37% ± 18% from 2011 to 2020, respectively, meanwhile the highest 8 hr averaged O 3 concentration was observed as 294 µg/m3 at background station in 2020, which pointed out the increasing ozone pollution in Hong Kong. There was a great decrease in the annual times of air quality health index (AQHI) laying in "high", "very high" and "serious" categories from 2011 to 2020 with the decrease rate of 89.70%, 91.30% and 89.74% at roadside stations, and 79.03%, 95.98% and 72.73% at urban stations, respectively. Nevertheless, the number of days categorized as "high" or above at roadside station was twice more than that in the urban station during the past ten years. Thus, more policies and attentions should be given to the roadside air quality and its adverse health effect to pedestrians on street. [Display omitted] [ABSTRACT FROM AUTHOR]

Vulnerability of each stock in the catches from trawl fisheries in the Gulf of Thailand was assessed by productivity susceptibility analysis. Separate assessments were made based on type of trawler (otter-board, pair and beam) and vessel size (SS, S, M, L and XL, according to gross tonnage). Catches were distinctly different among trawler types and were dominated by demersal fishes, pelagic fishes and shrimps in the otter-board, pair and beam trawlers, respectively. The stocks of over 200 taxa were included in the study; high-vulnerability taxa were found for all trawl types and sizes, except the beam trawler size S. Only seven (7) taxa were classified as high vulnerability, including four (4) teleost taxa, namely Saurida elongata, Plotosus spp., Gymnothorax spp. and Sphyraena spp., and three (3) elasmobranch taxa, namely Carcharhinus spp., Brevitrygon heterura and Neotrygon kuhlii. Meanwhile, as many as 26 high-medium vulnerability taxa were found in catches by otter-board trawler size L, which included not only fishes but also cephalopods. Trends and variation in fish landings of 20 high and high-medium vulnerability taxa were analyzed. Eighteen (18) taxa showed monotonic trends, both continuous and discontinuous, in their time series of annual landings, but not Muraenesox spp. nor Uroteuthis spp. The long-term variations in fish landings ranged mostly between 40% and 50%. The short-term variations showed positive absolute and relative skewness, i.e., mostly between 10% and 20%. Results of this study highlight the taxa that require a precautionary approach for fishery management and warrant comprehensive fish stock assessment. Such data will allow more accurate determination of their status compared to the reference points and facilitate better management of trawl fisheries in the Gulf of Thailand. [ABSTRACT FROM AUTHOR]

• Enhanced Kuroshio looping path across the Luzon Strait is observed during 1993–2020. • Eddy Kinetic Energy shows long-term increasing in the Northeastern South China Sea. • Energy from baroclinic instability is dominant for the EKE long-term increasing. The seasonal to interannual variability of eddy kinetic energy (EKE) in the Northeastern South China Sea (NE-SCS) has been widely studied and it is recognized that they are strongly related to the state of the Kuroshio pathway in the Luzon Strait. While, due to the lack of long-term observations and high-resolution simulations, the decadal change of EKE in NE-SCS remains unexplored. In this study, we show the EKE trend in the past ∼ 30 years in the NE-SCS by using satellite observation and global HYbrid Coordinate Ocean Model reanalysis with the Navy Coupled Ocean Data Assimilation. It is found that due to the weakening of the Kuroshio in the Luzon Strait since 1990 s, the Kuroshio shows an enhanced looping path in the NE-SCS, inducing stronger EKE in this region. Further analysis confirms that the energy transfer by baroclinic instability is dominant for the increasing of EKE, when the Kuroshio intrudes into the NE-SCS and brings more potential energy inside the circulation. The Kuroshio state along the Luzon Strait is the key for modulating the EKE in the NE-SCS. Furthermore, the long-term weakening of Kuroshio current along the Luzon strait during 1993–2020 is determined by the decreasing of subtropical mode water, corresponding to the positive phase of the Atlantic Multidecadal Oscillation. This study provides insight into the interaction between marginal sea (i.e., the SCS) and the open ocean (i.e., the western Pacific Ocean), finally linking to the global climate change. [ABSTRACT FROM AUTHOR]

Sandstorm is a disastrous weather phenomenon that often occurs in arid and semi-arid areas, endangering the ecological environment and affecting people's lives and property safety seriously. Since the 21st century, the sandstorm weather in the Yellow River Basin has ameliorated obviously. However, the causes of the long-term trends in sandstorms during 21st century were still unknown. In this study, fifteen influencing factors from five aspects: ecology, meteorology, hydrology, geography and man-made were selected to comprehensively analyze the driving mechanism of sandstorm activities in the Yellow River Basin since the 21st century, and the effect of each influencing factor on sandstorm weather was quantified. The results indicated that ecological, meteorological and geographical factors had dominant impacts on the spatio-temporal variation of sandstorms during 2000–2021, while hydrological and human factors played little role in the long-term variation of sandstorms. Sandstorms frequently occurred in semi-desert or grassland or non-high vegetation covered areas in spring. Vegetation coverage, precipitation, surface pressure, surface roughness, and soil moisture content were negatively correlated with sandstorms, while wind speed, friction velocity, evaporation, and soil temperature were positively correlated with sandstorms. Precipitation, runoff, evaporation, soil moisture content, soil temperature, and surface temperature indirectly acted on normalized brightness temperature dust index (NBTDI) and sandstorms by changing soil texture. Normalized Vegetation Index (NDVI) had direct negative effects on NBTDI, while wind speed 10 m (WS10m), slope of sub-gridscale orography (SOSGO), and forecast surface roughness (FSR) had direct positive effects on NBTDI. This study comprehensively revealed the dominant factors and their driving mechanism of sandstorm weather in the Yellow River Basin since the 21st century, which had practical application value for the prevention of sandstorms. [Display omitted] • Spatial heterogeneity existed in sandstorms drives across different regions during 2000–2021. • Precipitation, runoff, evaporation, soil moisture, and temperature indirectly affect sandstorms through soil texture. • SP, NDVI, ST, E, R and WS10m on the long-term change of sandstorm were more important. • Vegetation, evaporation, runoff, slope negatively affect sandstorms; wind, temperature positively. [ABSTRACT FROM AUTHOR]

In recent decades, global oceanic dissolved oxygen (DO) levels have been consistently declining, leading to a notable increase in hypoxic zones. However, comprehensive information on the current trends of DO in Jinhae Bay remains scarce. This study investigated the long-term variations in bottom dissolved oxygen (DO) in Jinhae Bay, specifically focusing on recurring occurrences of oxygen-deficient water (ODW) in August, coinciding with the lowest average DO levels with the most stratified water. ODW events predominantly manifested in the inner bay, while the outer bay exhibited fewer instances due to robust water exchange processes. Analysis of the Low DO group revealed higher surface temperature and salinity, indicating diminished oxygen solubility compared to the High DO group. Lower Chemical oxygen demand (COD) and chlorophyll- a (Chl- a) values in the Low DO group suggested enhanced bacterial decomposition and subdued photosynthesis, in contrast to the High DO group. Over the last 25 years, Jinhae Bay has experienced a discernible decline in bottom DO concentrations. Contrastingly, surface temperature has exhibited a consistent upward trend, notably accelerating in the last 12 years, indicating reduced oxygen solubility. Notably, a substantial reduction in bottom DO levels was observed in the outer bay, previously considered less susceptible to hypoxic conditions. Furthermore, a concurrent decrease in pH highlights the urgency for a comprehensive investigation encompassing both summer hypoxia and seawater acidification, crucial for protecting Jinhae Bay's ecosystem from further deterioration. [Display omitted] • DO in Jinhae Bay declined significantly over 25 years, particularly in August. • Increasing surface temperature accelerated oxygen inventory decrease. • A second sharp DO drop occurred in less hypoxia-prone open area. • pH decrease paralleled long-term DO reduction over 25 years. [ABSTRACT FROM AUTHOR]

Based on data from the Gurbantunggut Desert, the largest fixed/semi-fixed desert in China, and ERA5-Land reanalysis data, the long-term variations and spatial surface heat source (SHS) differences in the Gurbantunggut Desert are discussed herein. The results show the following: (1) The hourly SHS at the Kelameili station during the 2013–2021 period was a weak heat source at night; contrastingly, it was a strong heat source during the day. The duration of the hourly SHS increased gradually from January to July, but it decreased gradually from July to December. The daily SHS showed obvious seasonal variation, reaching the maximum in summer and the minimum in winter. The ERA5-Land reanalysis can reproduce all the variation characteristics of the SHS well. (2) The climatology (i.e., multi-year mean) of the monthly SHS intensity was lower than 50 W/m2 during the January–March and September–December periods in the Gurbantunggut Desert, indicating a weak heat source. On the other hand, the climatology recorded in April–August was higher than 50 W/m2, with a strong heat source. From the perspective of spatial distribution, the eastern and western regions of the Gurbantunggut Desert show strong heat sources, while the central region shows weak heat sources. The spatial distribution of the first and second modes of the empirical orthogonal function (EOF) decomposition reflected the consistent spatial variability and a north–south (or east–west) polarity variation of the monthly SHS in the Gurbantunggut Desert, respectively. (3) The yearly SHS showed negative anomalies during the 1950–1954, 1964–1982 and 2004–2015 periods, and positive anomalies during the 1955–1963, 1983–2003 and 2016–2021 periods in the Gurbantunggut Desert. Additionally, the time series of the SHS anomalies was positively correlated with the Interdecadal Pacific Oscillation (IPO) index. During the negative IPO phase, the yearly SHS showed a negative anomaly in the Gurbantunggut Desert, while the yearly SHS showed a positive anomaly during the positive IPO phase in most regions of the Gurbantunggut Desert.

In Jupiter's magnetosphere, the electric current system within the "current sheet" generates a magnetic field, which is comparable to or dominating the Jovian intrinsic field in the magnetosphere. However, updates of an existing model of the magnetospheric field by Khurana (1997, https://doi.org/10.1029/97JA00563) using newly acquired data by Galileo and Juno has never been conducted since it was first formulated. Here we used the data by Voyager 1/2, Galileo, and Juno to revise the current sheet shape model parameters as well as those of the magnetospheric field based on each spacecraft data. We derived fits that reproduced each data well, and revealed long‐term variations of both current sheet and magnetospheric field parameters over several decades. The updated model parameters are useful for detecting dynamic events in the magnetosphere such as magnetopause deformation and plasmoid generation. They can also be used as external fields necessary for probing into the Galilean icy moons by electromagnetic induction methods. Plain Language Summary: Above Jupiter's atmosphere and ionosphere, there is a vast region coined "magnetosphere" where magnetic fields govern physical phenomena. The magnetic fields in the magnetosphere are divided mainly into two components: one arising from inside Jupiter, and the other generated by electric currents flowing in a current sheet in the magnetosphere. Although both had been modeled so far, the models are, as usual, not perfect and should be updated on arrival of new datasets. Unfortunately, the magnetospheric field model is especially outdated compared with the intrinsic field. In this study, we focused on the magnetospheric field and its associated current sheet shape models using three datasets by four spacecraft, pre‐Galileo (Voyager 1 and Voyager 2), Galileo, and Juno. By updating the model parameters for each dataset, we determined three sets of models for current sheet shape and magnetospheric field that showed long‐term variations of Jupiter's magnetosphere over nearly half a century. The three sets of models are useful to detect dynamic events in the Jovian magnetosphere such as temporal changes of its shape and coherent plasma releases, and for probing deep into the Galilean icy moons that are thought to be possible cradles of extraterrestrial life. Key Points: We updated existing models of both current sheet and magnetic field in the Jovian magnetosphere using pre‐Galileo, Galileo, and Juno dataDifferences among the updated model parameters may represent long‐term variations of the current system in the Jovian magnetosphereThe new parameters are useful for study on magnetospheric dynamics and prediction of external magnetic variations for Galilean moons [ABSTRACT FROM AUTHOR]

We present a study on the long‐term variation of lunar semidiurnal (LSD) tides in the mesosphere and lower thermosphere (MLT). The study is based on a meteor radar chain along ∼120°E meridian, which consists of five stations located at Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), Wuhan (WH, 30.5°N, 114.6°E), Sanya (SY, 18.3°N, 109.6°E), and Ledong (LD, 18.4°N, 109.0°E), respectively. Using the Lomb‐Scargle spectral analysis and least squares fitting method, strong quarter‐annual oscillations in the LSD are found at the three midlatitude stations and their magnitudes are comparable. The LSD magnitudes exhibit clear seasonal and latitudinal differences. The monthly mean magnitudes of LSD reach the maximum in January at all five stations but in other seasons they behave differently at different stations. Besides, the effects of polar vortex weakening (PVW) and quasi‐biennial oscillation (QBO) phases on the LSD are discussed. Based on the 12 PVW events, our study observes that the enhancement of the LSD is not always related to the commencements of PVW events. The enhancements of the LSD during the easterly QBO phase are generally stronger than those enhancements during the westerly QBO phase in the MLT region. The easterly QBO phase could modulate the mesospheric zonal mean zonal winds at low latitudes during the PVWs, which is in favor of amplifying the LSD. Our results suggest that the QBO phase is an important factor in enhancing the LSD in the MLT region during PVW events. Key Points: Seasonal and latitudinal variations of lunar semidiurnal (LSD) tidal magnitudes are revealed via long‐term observations by meteor radarsThe quasi‐biennial oscillation phases are associated with the enhancement of the LSD during polar vortex weakening eventsA strong quarter‐annual oscillation is observed in the LSD magnitudes in the mesosphere and lower thermosphere region [ABSTRACT FROM AUTHOR]

Upland forest soil is an important CH4 sink that plays a key role in climate change mitigation. China features large areas of various types of forest, but spatiotemporal variation in CH4 flux has not yet been clarified. Here, we analyzed variation in CH4 flux and the effects of environmental variables on the CH4 flux of forest in China using in situ observational data. Upland forest soil absorbed CH4 at a rate of 0.24 ± 0.02 g m−2 yr−1. The CH4 uptake rate (0.46 ± 0.10 g m−2 yr−1) of warm temperate deciduous broad-leaved forest was the highest. Soil alkali-hydrolyzable nitrogen was the only factor significantly correlated with CH4 uptake variation among vegetation zones. A break point in CH4 uptake over the study period (from 1997 to 2020) was detected in 2015. CH4 uptake slightly decreased until 2015 and increased after 2015. The mean CH4 uptake of the period after 2015 (0.44 ± 0.07 g m−2 yr−1) was significantly higher than that before 2015 (0.20 ± 0.02 g m−2 yr−1). Atmospheric nitrogen deposition was negatively related to interannual CH4 uptake. Our findings suggest that the CH4 uptake of upland forest soil will continue to increase over the next few decades as China accelerates efforts to achieve its carbon neutrality goal, and this would result in continuous decreases in nitrogen deposition through various pathways. [ABSTRACT FROM AUTHOR]

Regional variations in atmospheric moisture residence time (RT) highlight the need to obtain independent observation indexes to constrain different model-based estimates. Stable isotopes of oxygen and hydrogen naturally exist in water molecules that can provide such observational constraints. We analyzed the relationship between RT and precipitation isotopes (δ2H and δ18O) across different climatic zones in Eurasia from 1980 to 2020. Our analysis reveals that: (1) Both precipitation isotopes and RT showed significant increasing trends during 1980–2020. The increase in RT corresponds to weakened net isotopic distillation over Eurasia, suggesting reduced atmospheric circulation intensity under warming conditions. (2) The spatial patterns of RT and precipitation isotopes vary significantly among different moisture source regions, reflecting distinct moisture transport and precipitation formation processes. (3) On long-term scales, RT generally shows positive correlations with precipitation isotopes, except in plateau regions. The RT-δ18O relationship exhibits latitude-dependent variations, with similar slopes in regions sharing common moisture sources. These findings enhance our understanding of the long-term controls on precipitation isotopic composition and atmospheric moisture cycling patterns across Eurasia. • The relationship between RT and δ18O varies obviously with latitude. • RT and precipitation isotopes vary with moisture source regions rather than simple inland-monsoon division. • Long-term increases in RT indicate weakening atmospheric circulation over Eurasia. [ABSTRACT FROM AUTHOR]

The influence of snow cover on the dynamics of soil temperature in the modern climatic conditions of the Eurasian Subarctic was investigated through a quantitative assessment of the features of the seasonal and long-term variation of parameters. Seasonal and long-term values of soil temperature for stable snow period decrease from west to east: a decrease of snow thickness and air temperature from west to east of Eurasia leads to a weakening of the heat-insulating properties of the snow cover with a significant decrease in regional air temperatures. With the emergence of a stable snow cover, the soil temperature seasonal and long-term standard deviation sharply decreases compared to the autumn and spring periods. With the appearance of snow cover, the soil temperature standard deviation drops sharply compared to the autumn and spring periods. An exception is the northeast of Siberia: here, a relatively small thickness of snow determines a noticeable dependence of the course of soil temperature on the dynamics of surface air temperature. There are no significant long-term trends in soil temperature due to its low variability during winter period. Analysis of the course of the studied characteristics anomalies showed an insignificant and non-systematic number of their coincidences. Currently, we have not found similar research results for large regions. The revealed patterns can be used in the analysis of the results of monitoring the state of the land surface, in the development of remote sensing algorithms, in the refinement of predictive scenarios of environmental changes.

Biodiversity in the Bohai Sea is threatened by climate change and human activities. An analysis based on decadal macrobenthic community data was conducted to assess the ecological health. These findings revealed the temporal and spatial variations in species composition and biodiversity, which were primarily influenced by depth, temperature and dissolved oxygen content. The community structure in 2014 exhibited a 70 % dissimilarity compared to other years, and biodiversity was lower in 2014. The dominant species showed a trend towards miniaturization. Abundance-biomass comparison curves indicated that community disturbance improved by implementing various policies. Overall, communities in the Bohai Sea remained stable, except in the Bohai Strait (BH), where synchronous fluctuations with an increasing trend were observed. Enhancing biodiversity and addressing the risks associated with losing single species are essential for maintaining community stability. The community also displayed synchronous tendencies in Laizhou Bay, emphasizing the need for continued long-term monitoring. • Depth, temperature, and DO content were the main factors affecting biodiversity. • The dominant species tended to miniaturize due to overfishing. • The community had a recovery trend because marine management efforts increased. • Asynchrony and competition significantly influenced interspecific relationships. • The community in Bohai Strait needed long-term monitoring and management. [ABSTRACT FROM AUTHOR]

The shipboard measurements over approximately 55 years in the southwestern part of the East Sea (Sea of Japan) demonstrate a remarkable basin-wide, interannual-interdecadal variability in the temperature-based thickness of the East Sea Intermediate Water (ESIW) whose temporal variability shows strong correlation with the density-based thickness (r = 0.97). Relevant to the long-term variability of the ESIW thickness, clear changes in horizonal and vertical features have been observed at the intermediate layer in the mid-1990s, such as 1) increases in vertical temperature gradient in the thermocline by shoaling of 2°C–5°C isotherms, 2) relatively high correlations among isotherms in the interdecadal timescale, 3) appearance of zonal phase difference in the ESIW thickness variability after the mid-1990s, and 4) correlation phase change between the Arctic Oscillation Index and the ESIW thickness. The ESIW thickness could be smaller when its formation is weaker and when the formation of deep-water mass below it becomes stronger. Based on the features observed, we hypothesized on the regime shift concerning the East Sea meridional overturning circulation; before the mid-1990s, active deep-water formation mainly controlled the ESIW layer variability, but after the mid-1990s, the ESIW formation rate predominantly affected its own thickness variability.

The concentration and structure of nutrients play a key role in sustaining marine ecosystems. In recent decades, the change in nutrient input from land has led to significant changes in nutrient concentration and structure in the marginal sea and has had an important impact on the coastal ecosystem. Based on historical data from 1984 to 2016, the long-term variations in nutrients and their potential influencing factors, were analyzed in the Changjiang River Estuary. The concentration of dissolved inorganic nitrogen (DIN) increased gradually from 1984 to 2003, but after 2003 the concentration began to decrease. Compared with DIN, the change in dissolved inorganic phosphate (DIP) had a delayed effect and has exhibited a slow downward trend since 2005. The decreases in DIN and DIP are mainly due to the improvement of wastewater treatment efforts and chemical fertilizer use efficiency in recent years. The retention of nutrients by the Three Gorges Reservoir (TGR) has been another important factor since its completion in 2003, especially because the large amount of particulate phosphorus retained by the TGR has led to a significant decrease in the total phosphorus flux into the sea, which is the main reason for the decrease in DIP. The vatiations of DIP and DIN have been instrumental in causing the observed changes of phytoplankton community in the Changjiang River Estuary.

Atmospheric compositions and acid rain are closely related to atmospheric environment, weather, and climate change. In this study, the concentration levels and long-term trends of CO2, CH4, O3, PM2.5, PM10, and acid rain were presented at the Mt. Waliguan global baseline station in Qinghai, Shangdianzi and Lin'an regional background stations in the North China Plain (NCP) and the Yangtze River Delta region (YRD) of China based on the data observed until 2018. Significant increasing trends of CO2 were found at all of these stations. At Mt. Waliguan, the concentration levels and growth rate were consistent with the average values in the Northern Hemisphere (NH) and those observed at the Mauna Loa station in Hawaii. The CH4 also showed a upward tendency similar to that observed in NH. Compared with the observations at Mt. Waliguan global baseline station, the CO2 and CH4 mole fractions were higher at Shangdianzi and Lin'an regional background stations, indicating the important contributions of anthropogenic activities to the regional background level of CO2 and CH4. The annual averaged surface ozone showed increasing trends at Mt. Waliguan and Shangdianzi stations, whereas no clear trend was found at Lin'an station. Similar variations in the patterns of aerosol concentrations at Shangdianzi and Lin'an were found according to the PM2.5 or PM10 observations. Overall, the aerosol concentrations at both stations shown declining trends since the observations. However, two periods of high particle concentrations occurred in 2006–2007 and 2013–2014. The annual mean aerosol concentrations have continuously decreased after 2013–2014, indicating the effectiveness of pollution control in the NCP and YRD, especially since the implementation of the ‘Action Plan for Prevention and Control of Air Pollution’ in September 2013. Comparative analysis of aerosol with acid rain showed that the period with high concentrations of aerosols in the early years was consistent with that of severe acid rain pollution, suggesting that both aerosol pollution and severe acid rain are closely related to coal combustion emissions in China. As a result of the control of coal combustion emissions for acid and SO2, NOx emissions have contributed more substantially to aerosols due to the rapid growth of vehicle ownership. A comparison of the trends of aerosols with the maximum daily 8-h average of surface ozone (MDA8) at Shangdianzi and Lin'an stations revealed the complicated relationship between aerosol reduction and ozone production, i.e., together with the continuous improvement of particulate pollution in the NCP and YRD, the MDA8 at both stations showed a decreasing trend at first but subsequently increased after 2014 with aerosols remaining reduced. Such different variation patterns of the MDA8 with PM2.5 (or PM10) indicated the high challenge of synergic control of aerosol and ozone pollution in China.

Vulnerability of each stock in the catches from trawl fisheries in the Gulf of Thailand was assessed by productivity susceptibility analysis. Separate assessments were made based on type of trawler (otter-board, pair and beam) and vessel size (SS, S, M, L and XL, according to gross tonnage). Catches were distinctly different among trawler types and were dominated by demersal fishes, pelagic fishes and shrimps in the otter-board, pair and beam trawlers, respectively. The stocks of over 200 taxa were included in the study; high-vulnerability taxa were found for all trawl types and sizes, except the beam trawler size S. Only seven (7) taxa were classified as high vulnerability, including four (4) teleost taxa, namely Saurida elongata, Plotosus spp., Gymnothorax spp. and Sphyraena spp., and three (3) elasmobranch taxa, namely Carcharhinus spp., Brevitrygon heterura and Neotrygon kuhlii. Meanwhile, as many as 26 high-medium vulnerability taxa were found in catches by otter-board trawler size L, which included not only fishes but also cephalopods. Trends and variation in fish landings of 20 high and high-medium vulnerability taxa were analyzed. Eighteen (18) taxa showed monotonic trends, both continuous and discontinuous, in their time series of annual landings, but not Muraenesox spp. nor Uroteuthis spp. The long-term variations in fish landings ranged mostly between 40% and 50%. The short-term variations showed positive absolute and relative skewness, i.e., mostly between 10% and 20%. Results of this study highlight the taxa that require a precautionary approach for fishery management and warrant comprehensive fish stock assessment. Such data will allow more accurate determination of their status compared to the reference points and facilitate better management of trawl fisheries in the Gulf of Thailand.

Long-term variation of nitrate in the East Sea was monitored in order to investigate impact of Three Gorges Dam (TGD) in the Changjiang River's upstream, China and Nakdong River's estuary dam, Korea. Tracing source of nitrate was another objective in this study. For this study, nutrient data were collected for 20 years from 1999 to 2018 in the East Sea, and divided into 4 sections, and evaluated whether a significant difference exists among the averages of nitrate concentrations. The concentrations of nitrate were affected by the major rivers (the Nakdong and the Taehwa Rivers) and Tsushima Warm Current (TWC) which diverged from the Kuroshio Current passing through East China Sea (ECS). Our results also indicated that long-term nitrate concentrations decreased and its reasons. First, the construction of TGD in the upstream of the Changjiang River may have resulted in the decrease of the nitrate supply in the river and ECS which is carried by TWC, toward the East Sea. Second, decrease in the nitrate flux of the Nakdong River's estuary due to the construction of the estuary dam and sewer treatment plant could also be a factor for the nitrate decrease in the East Sea. Therefore, anthropogenic activities from the Nakdong River and Changjiang River had a long-term effect on the East Sea's nitrate concentrations. The amount of nitrate runoff reduced by the anthropogenic activities influenced the nitrate levels over a long period by the flow of currents in the East Sea. [ABSTRACT FROM AUTHOR]

Ecological restoration projects, such as the Grain‐to‐Green Program (GTGP) and the Natural Forest Conservation Program (NFCP), have been implemented to improve vegetation cover since 1998. However, rapid urbanization has caused severe land use/cover (LUC) changes in the Dong River upstream basin. Therefore, it is urgent to study the long‐term (1999–2017) spatial–temporal variation of LUC and soil erosion since the implementation of GTGP and NFCP began in this area. Soil erosion and carbon sequestration were calculated using the revised universal soil loss equation (RUSLE) and C‐fix model. During 1999–2017, forest decreased by 28,857.81 ha and built‐up area increased by 17,193.01 ha. This area experienced severe LUC change, but vegetation cover has been effectively improved. When the observation period was measured in years, vegetation cover had a greater impact on decreasing soil erosion (554.11 × 104 t yr−1) than rainfall, while in months, the impact of rainfall is greater (causing a dramatically rebound of soil erosion in 2014). Furthermore, high‐intensity human activities made soil erosion increased by 37.70% in Yuancheng District, whereas soil organic carbon, total nitrogen, and total phosphorus loss decreased by 49.96, 33.03, and 44.44%, respectively. Moreover, GTGP and NFCP also bring collateral benefits, carbon sequestered by vegetation increased from 99.11 × 106 to 124.38 × 106 t CO2, during 1999–2014. And vegetation was the major factor of increased carbon sequestration, rather than temperature or solar radiation. These results elaborate on the impact of LUC changes on spatial–temporal variation of soil erosion. And it can provide a reference for the formulation of soil and water conservation measures in the future. [ABSTRACT FROM AUTHOR]

Using NCEP/NCAR reanalysis data, we investigate the statistical characteristics and the long-term variations of major sudden stratospheric warming (SSW) events in the Northern Hemisphere. We find that the strength and duration of major SSW events have increased from 1958 to 2019 because of the strengthening of winter planetary wave activity. The frequency of the SSW events related to displacement or split of the polar vortex differs between early, middle, and late winter. Early (middle) winter is dominated by displacement (split) SSW events, while late winter sees almost equal frequency of these two types of events. This is due to the differences in the relative strength of wavenumber-1 and wavenumber-2 planetary wave activity among the three winter periods. As a result of the increase in upward planetary wave activity and the decrease in westerly winds around the polar vortex in middle winter, more SSW events tend to occur in middle winter. In addition, we reveal the influence of the downward propagation of different types of SSW events on the surface temperature anomaly. Compared with early displacement SSW events, middle split SSW events are followed by more surface cold centers in Russia, northern China, and North America. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is a potent and long-lived greenhouse gas that contributes to global warming with a global warming potential (GWP) 298 times that of carbon dioxide (CO2). In this paper, we analyzed the trend of N2O concentration in vertical layers of the stratosphere from 2005 to 2020 using the N2O observed from the Microwave Limb Sounder (MLS) that is on board the Aura satellite. We found that the local N2O concentration showed a downward trend in the lower stratosphere but rose or fluctuated in the upper stratosphere. The reduction reached −5 ppb/yr at pressure levels of 31.62 hPa and 68.13 hPa, with a confidence level of over 90%. The growth was around 1–2 ppb/yr in the upper stratosphere. In addition, a concentration anomaly was observed in the tropical stratosphere in 2013. After the appearance of this anomaly, the N2O concentration in the middle and lower layers of the tropical stratosphere was lower than before 2013. We speculated that the enhancement of the Brewer–Dobson circulation (BDC) upwelling before and after stratospheric sudden warming (SSW) is the main reason for the abnormal concentration distribution in 2013. Stratospheric N2O has changed significantly in the past 16 years with the mutual coupling effect of BDC and SSW and such changes can have further impact on the chemical equilibrium and radiation balance in the stratosphere, as well as on the persistent climate-warming trend.

Long-term trend of crop yields has been widely studied in global scales to find which crops and which geographic regions offer the best hope of meeting food demands, and which regions needed the most improvements. In this study, a mathematical method was applied to analyze spatial patterns in long-term temporal trends of three major crops’ yields in Japan archipelago. The changes in annual yields of rice, wheat, and soybean over a period of about 60 years in all 47 prefectures of Japan was analyzed by using the data of agricultural records. For all the three crops, the nationwide yields previously improved, but currently were stagnating in Japan. The result suggests that the annual yields were not improving in 53, 85, and 89% of those prefectures in Japan for rice, wheat, and soybean, respectively. The spatial patterns in temporal trends show that the percentage of number of yield-not-improving prefecture was higher in low latitude regions than high latitude regions. These results highlight the increasingly difficult challenge of meeting the growing demands and stagnating supplies in daily staple foods not only for agricultural scientists but also for Japanese society.

To examine how compositional changes in a community vary depending on time scales, we estimated temporal β-diversity of zooplankton in Lake Hataya Ohnuma, a small lake in Yamagata, Japan. The zooplankton community was monitored for 9 years with monthly samplings. We estimated the inter-annual, inter-seasonal, intra-seasonal, and inter-month β-diversity with the magnitude of sampling errors, and examined relative contributions of these time scales on changes in the zooplankton community structure. The temporal β-diversity was high at the inter-seasonal scale than at the intra-seasonal and inter-annual time scales, suggesting that taxonomic turnover in the zooplankton community was regulated by seasonally changing parameters such as water temperature. Indeed, the temporal β-diversity is related significantly to water temperature, although no significant relationship was detected between the temporal β-diversity and chlorophyll-a concentrations. In addition, the large inter-month β-diversity with significant inter-annual β-diversity indicated that the phenology of the zooplankton community changed depending on years, especially before and after 2012. These results indicate that temporal β-diversity is a useful gauge for detecting phenological changes and for quantifying the temporal stability of plankton communities at various time scales. [ABSTRACT FROM AUTHOR]

We obtained historical and observational data on phytoplankton communities from 1959 to 2023 to explore the responses of the phytoplankton community structure to long-term environmental changes in the southern Yellow Sea (SYS), China. The results revealed a decrease in the proportions of diatom cell abundance within the phytoplankton community by 8 %, accompanied by a corresponding increase in that of dinoflagellates. Dominant phytoplankton species were mainly chain-forming diatoms before 2000, and large dinoflagellate species from the genera Tripos and Noctiluca increased their dominance after 2000. Warm-water phytoplankton species have increased in dominance over the study period. Correlation analysis revealed that the ocean warming and alterations in nutrient structure (N/P and Si/N ratios) were mostly responsible for the long-term evolution trend, and these changes may result in an increase in dinoflagellate harmful algal blooms, reduced efficiency of the biological carbon pump, and heightened hypoxia in the future, which should draw our attention. • Long-term phytoplankton dynamics were studied in the SYS. • Diatom proportions declined, whereas dinoflagellate proportions rose. • Warm-water phytoplankton species increased. • Ocean warming and nutrient shifts drove these changes. [ABSTRACT FROM AUTHOR]

A tidal shear front (TSF) can be defined as an obvious horizontal gradient of flow velocity formed by opposing tidal currents (reversed TSF) or same-direction tidal currents (homogenous TSF) on both sides of the front with limited impact by river runoff. Observational and modeling studies have been conducted to investigate the impact of a reversed TSF on the transport of freshwater and sediment in the Yellow River Mouth (YRM). The reversed TSF existence period is only about 40% of a tidal cycle (around slack of flood and ebb); however, when this front disappears (around maximum flood and ebb), sediment transport across the frontal zone is still rare. This suggests that the dynamic mechanism of cross-frontal sediment transport in a tidal cycle remains unclear. In this study, synchronous observations of sea current and suspended sediment concentrations along the river mouth profiles at the YRM in 1995, 2003, and 2019 were used to investigate the long-term variation characteristics, mechanisms, and impacts of the TSF on cross-frontal sediment transport. The results indicate that in addition to the reversed TSF, there are also homogenous TSF during flood and ebb tides, with the ebb homogenous TSF being more significant due to tidal asymmetry in the YRM. The ebb homogenous TSF is located between shallow shoals and the slopes of the subaqueous delta front and lasts for about 3 h around the maximum ebb. Its maximum shear strength is similar to that of the reversed TSF, and the formation mechanism is also similar. The presence of the ebb homogenous TSF reduces the efficiency of cross-frontal sediment transport during the ebb. The reversed and homogenous TSFs alternately block sediment moving towards the sea. Thus, terrigenous sediment is difficult to cross the frontal zone to the central Bohai Sea by tidal currents solely. Over the past two decades of low discharge, with the Yellow River implementing artificial water and sediment regulation, the homogenous TSF during the ebb tide has become more and more important and cannot be neglected for cross-frontal sediment transport under normal conditions. Furthermore, from a long-term perspective, the shear strength of the TSF is positively correlated with the distance of river mouth siltation into the sea. Additionally, salinity and turbidity gradients are also positively correlated with the shear strength in the estuary. This indicates that the blocking of cross-frontal sediment transport by the TSF is a key process in river-sea interaction in the YRM. • The tidal shear fronts (TSFs) evolution and their impact on cross-frontal sediment transport are revisited. • The homogenous TSFs are found as one of the key sedimentary dynamic factors too. • Fluvial sediment seaward transport is hindered not only by reverse TSFs, but also ebb homogeneous TSFs. • Interaction between topography, TSFs, and sediment transport is a key process in long-term river-estuary-sea interaction. [ABSTRACT FROM AUTHOR]

When investigating the long-term variation of wave characteristics as associated with storm surges in the Bohai Sea, the Simulating Waves Nearshore (SWAN) model and ADvanced CIRCulation (ADCIRC) model were coupled to simulate 32 storm surges between 1985 and 2014. This simulation was validated by reproducing three actual wave processes, showing that the simulated significant wave height (SWH) and mean wave period agreed well with the actual measurements. In addition, the long-term variations in SWH, patterns in SWH extremes along the Bohai Sea coast, the 100-year return period SWH extreme distribution, and waves conditional probability distribution were calculated and analyzed. We find that the trend of SWH extremes in most of the coastal stations was negative, among which the largest trend was −0.03 m/a in the western part of Liaodong Bay. From the 100-year return period of the SWH distribution calculated in the Gumbel method, we find that the SWH extremes associated with storm surges decreased gradually from the center of the Bohai Sea to the coast. In addition, the joint probability of wave and surge for the entire Bohai Sea in 100-year return period was determined by the Gumbel logistic method. We therefore, assuming a minimum surge of one meter across the entire Bohai Sea, obtained the spatial SWH distribution. The conclusions of this study are significant for offshore and coastal engineering design. [ABSTRACT FROM AUTHOR]

Abstract The temporal and spatial distributions of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi), and their long-term changes were investigated in Bohai Bay (BHB) in spring, summer, and autumn (2013–2014). The high DIN values were consistently distributed in the western inshore waters, mainly determined by terrestrial factors, e.g., riverine input, while DIP and DSi were mostly distributed in the southern coastal waters, the central BHB, or near the sea port Caofeidian in northern BHB, largely related to non-terrestrial factors, e.g., sediment release. Based on the nutrient distribution, BHB could be partitioned into western and eastern parts, with −15 m depth as the separation. The long-term variations of nutrients since 2000 showed an increase in DIN and decreases in DIP and DSi. Relatively slow changes in DIN and DIP and a rapid decrease in DSi were exhibited in summer, which was associated with precipitation and sediment release. Highlights • BHB is partitioned into two parts based on nutrient sources and impact factors. • In western BHB, terrestrial inputs lead to the consistent high values of DIN. • In eastern BHB, non-terrestrial factors impact DIP and DSi distributions. • Since 2000, DIN increased together with DIP and DSi decreased. • Summer showed slow changes in DIN and DIP, and a rapid change in DSi. [ABSTRACT FROM AUTHOR]

Plenty of dust aerosols are emitted into the atmosphere in East Asian regions and significantly impact the regional environment and climate. In the past decade, the frequency of dust storm outbreaks has largely declined in the sources of Asian dust. However, it is still rarely reported how the dust properties after long-range transport in the downstream regions respond to this downtrend. Here we report on the long-term characteristics of dust aerosols over central China with the observations of a polarization lidar at Wuhan (30.5°N, 114.4°E) during 2010–2020. The dust optical depths (DOD) exhibit a decrease trend with a rate of −0.011 yr−1, accounting for 22% of the decrease rate for total aerosol optical depths (AOD) in Wuhan. The mass concentration and columnar mass density of dust also decline with a rate of −2.03 μg·m−3·yr−1 and -1.97 mg·m−2·yr−1, respectively. Spring and winter are the most active seasons for dust intrusion, with seasonal mean DOD of 0.21 and 0.15, respectively. Compared with spring, dust aerosols in winter generally concentrate at lower levels below 1.0 km with a slightly smaller particle depolarization ratio of 0.11 (0.14 in spring), attributing to the weakened nonspherical shape of dust particles under wintertime high-level moisture/polluted conditions. Both the surface PM 10 concentration and lidar-derived dust mass concentration at 0.3 km present a downtrend with a rate of −8.0 μg·m−3·yr−1 and -20.1 μg·m−3·yr−1, respectively. This study provides a comprehensive long-term and seasonal analysis of dust properties in central China, which can supplement our understanding of the feedback in the downstream regions to the reduction of dust emissions in the deserts of East Asia. • Dust aerosols are observed in central China during 2010–2020 with ground-based polarization lidar. • Dust optical depths (DOD) exhibit a decrease of −0.011 yr−1, accounting for 22% decrease rate for total AOD. • Dust frequently intrudes into Wuhan in spring and winter, with DOD of 0.21 and 0.15. • Dust in winter concentrates at lower levels (<1.0 km) with a smaller PDR (0.11) than in spring (0.14). [ABSTRACT FROM AUTHOR]

The East Asian winter monsoon (EAWM) exhibits long-term variations in intensity and spatial pattern, though the latter one is less understood. To investigate the long-term spatial variations of the EAWM and their possible causes, we propose a new position index of the EAWM by quantifying the low-level East Asian stream (EAS) of cold airmass in the Lagrangian sense. Based on the new-defined index, we find that the EAS undergoes an evident zonal shift between two channels over the land and coast. At interdecadal timescale, the peak location of the EAS is displaced eastward, with an increasing southward cold airmass flux at the coast since the mid-1960s. The interannual shift of the EAS presents not only the zonal oscillation of peak location between two channels but also the width changes of coastal channel over the northwestern Pacific. These shifts in the EAS are related to the strength changes of two source cold airmass streams from Siberia or Bering Sea, which are associated with the phase changes in the upper-tropospheric atmospheric teleconnections. At interdecadal timescale, the phase change in the North Atlantic Oscillation modulates the zonal shift in the EAS via the East Atlantic-West Russia teleconnection. At interannual timescale, the Pacific/North American teleconnection becomes the dominant factor altering the zonal shift and width change of the EAS.

Using high-resolution satellite-derived sea surface temperature (SST) data from September 1981 to December 2015, the present study develops a new index to detect the long-term variation in mesoscale eddy activity over the Kuroshio Extension (KE) region. This eddy activity index (EAI) highlights the strength of eddy-induced poleward heat transport and has obvious advantages over the other existing KE indices in depicting the low-frequency changes in KE eddy activity. An analysis of the EAI shows that over the long term, the KE eddy activity variability presents a significant spectral peak of about 8 years and is not directly modulated by wind-driven oceanic Rossby waves generated in the central North Pacific. When the EAI is positive, the strengthened KE eddy activity significantly enhances the heat release from ocean to atmosphere over the Kuroshio–Oyashio confluence region (KOCR). This induces an anomalous dipole pattern of near-surface baroclinicity over this region that can persist for up to 6 months, favoring a weakened and northward-moving East Asian jet, and vice versa. It is believed that the new EAI will facilitate future studies focusing on the climatic effects of the KE eddy activity variation.

The Tibetan Plateau (TP) has been experiencing warming and wetting since the 1980s. Under such circumstances, we estimated the summer latent heat flux (LE) using the maximum entropy production model driven by the net radiation, surface temperature, and soil moisture of three reanalysis datasets (ERA5, JRA-55, and MERRA-2) at the Ali site over the western TP during 1980-2018. Compared with the observed LE of the Third Tibetan Plateau Atmospheric Scientific Experiment, the coefficient of determination, root-mean-square error, and mean bias error of the estimated summer LE are 0.57, 9.3 W m−2, and −2.25 W m−2 during 2014-2016, respectively, which are better than those of LE of the reanalysis datasets. The estimated long-term summer LE presents a decreasing (an increasing) trend of −7.4 (1.8) W m−2 decade−1 during 1980-1991 (1992-2018). The LE variation is closely associated with the local soil moisture influenced by precipitation, glacier, and near-surface water conditions at the Ali site. The summer soil moisture also presents a decreasing (an increasing) trend of −0.082 (0.022) decade−1 during 1980-1991 (1992-2018). The normalized difference vegetation index generally shows the consistent trend with LE at the Ali site.

An article contains the data on the investigations of season and long-term variations of radiation safety indexes of the water of some underground sources and centralized water-supply system of Tver city.

Abstract Concentrations of atmospheric pollutants over East China have varied considerably during the past decades. These variations are partly due to variations of human activities, e.g., increasing energy consumption and implementation of government emission control policies, and partly to natural fluctuations. This study aims to separate the effects of natural processes and anthropogenic activities on the increase/decrease of the concentrations of some of the most important pollutants (SO 2 , NO 2 , CO and aerosols) over East China in the last decade. This was achieved by the comparison of the temporal variations in long-term time series of satellite-retrieved aerosol optical depth (AOD) and vertical column densities (VCDs) of SO 2 , NO 2 , and CO, with those in model-simulated time series of the natural variations only. The latter were created by the use of the same anthropogenic emissions throughout the whole simulation, while using re-analysis data (MERRA) to describe meteorological processes and natural emissions. Thus, the comparison between observed and simulated temporal variations reveals the effects due to anthropogenic emissions only, assuming that the atmospheric processes affect natural and anthropogenic species in the same way. In the analysis, a Kolmogorov–Zurbenko (KZ) filter is used to extract long-term components from both the observed and simulated data and normalization to the situation at a certain reference point is used to eliminate bias between observations and simulations. By this new method, natural and anthropogenic contributions to long-term variations of trace gases and AOD are quantitatively estimated. The results show that NO 2 VCDs increased from 2004 to 2011 by 76% and of the overall increase in this period only 1% ± 1% was attributed to natural factors, 99% ± 1% attributed to anthropogenic factors. AOD increased by 24% between 2001 and 2011 and of the overall increase 24% ± 32% was due to natural factors and 76% ± 32% was due to anthropogenic factors. SO 2 VCDs decreased by 15% from 2007 to 2013, natural and anthropogenic factors contributed respectively 16% ± 14% and 84% ± 14% to the overall decrease in this period. CO decreased since 2003 with 13% and of the overall decrease 6% ± 6% was due to natural factors and 94% ± 6% was due to anthropogenic factors. Highlights • A new method to separate natural and anthropogenic contributions to long-term variations of SO 2 , NO 2 , CO, and AOD. • Quantified natural and anthropogenic contributions. • Variations of trace gases and AOD are mostly attributed to anthropogenic activities. [ABSTRACT FROM AUTHOR]

The Eastern Baltic Stone Age is characterized by several major shifts in tool technology. Our picture of cultural change is currently based on typological variation in well-preserved bone tools, ceramics, stone tools, and on diversity in lithic raw-material use. These variations have partly been interpreted as the result of external influences, and partly as internal development. However, the understanding of relations with neighbouring regions is still limited. Recent decades have seen a growing interest in the chaîne opératoire approach and technological analysis, and their relevance for studying intra-site activity and development of skill, and for describing ancient technologies has been demonstrated. Technological and cultural relationships in the North European Stone Age have also been discussed within this frame. In this article, we take a new approach, employing variation in lithic technological craft traditions as proxy for investigating long-term development and variability in lines of communication. This study addresses three chronological contexts of the Latvian Stone Age, based on technological analysis of 26 sites. In describing the overall development in stone technology during the period c 10 500--2900 calBC, the article demonstrates not only technological variations but also af- firms fluctuation/change in directions of social contacts throughout the Stone Age, demonstrating variation in knowledge transmission and communication routes across large geographical areas. [ABSTRACT FROM AUTHOR]

As China's only continental sea, the Bohai Sea is a relatively closed environment and is vulnerable to natural changes and human activities. In this paper, the long‐term variations in nutrients in the Bohai Sea and the potential influencing factors were analyzed based on historical summer and winter data from 1978 to 2016. The results showed that the concentrations of dissolved inorganic nitrogen (DIN) in the Bohai Sea continuously increased from 1990 and rapidly increased after 2002, the phosphate (PO4‐P) concentration exhibited a decreasing trend, and the silicate (SiO3‐Si) concentration decreased from 1978 to 1987 and increased from 1987 to 2008. The nutrient concentrations were lower in summer than in winter, and the bottom concentrations were higher than the surface concentrations in summer, whereas the vertical differences were insignificant in winter. The dominant factor determining the long‐term variations in DIN were atmospheric deposition and nonpoint sources due to various human activities; the primary factors affecting PO4‐P were riverine inputs and nonpoint sources related to natural changes and human activities; the primary factors afftecting SiO3‐Si were riverine inputs. The N/P ratio followed the DIN variation, the Si/P ratio followed the SiO3‐Si variation, and the Si/N ratio decreased. The nutrient ratios were lower at the bottom than at the surface and were lower in winter than in summer. The nutrient limitation changed from nitrogen limitation to phosphorus and silicon limitations. The long‐term nutrient variations in the Bohai Sea have potential ecological impacts on the local red tide features. Plain Language Summary: Nutrients are important to primary productivity and thus important to marine ecosystems. Nutrient variations in coastal oceans may potentially impact the occurrence of ecological disasters. As the only continental sea in China, the Bohai Sea is a relatively closed environment and is vulnerable to natural and anthropogenic impacts. We found that the concentration of dissolved inorganic nitrogen in the Bohai Sea increased from 1990 to 2006; the phosphate concentration decreased from 1978 to 2016, and the silicate concentration decreased before 1987 and increased after 1987. We also found that N/P increased and Si/N decreased. The nutrient concentrations were higher, whereas the nutrient ratios were lower in winter than in summer. In summer, the bottom nutrient concentrations were higher than the surface concentrations, whereas the bottom ratios were lower than the surface ratios; in winter, the vertical differences were insignificant. The primary factors driving the silicate variations were riverine inputs related to natural changes and human activities; the primary factors in the phosphate variations could be riverine inputs and nonpoint sources related to natural changes and human activities; the dominant factor in the dissolved inorganic nitrogen variations could be atmospheric deposition and nonpoint sources due to various human activities. The red tide features in the Bohai Sea seemed to be potentially related to the long‐term nutrient variations. Key Points: DIN increased; PO4‐P decreased; SiO3‐Si decreased before 1987 and increased after 1987 in the Bohai Sea; winter concentrations are higherN/P increased, Si/N decreased, and Si/P slightly increased in the Bohai Sea; ratios are higher in winter than in summerVariations in Si/N ratios may have ecological impacts on the red tide features in the Bohai Sea [ABSTRACT FROM AUTHOR]

Abstract This study investigated the long-term variations and compositions of nutrients and the associated controlling factors in the western North Yellow Sea on the basis of historical data. The NO 3 -N and DIN concentrations and N/P showed continuous increases over the past two decades, which were dominantly affected by riverine inputs, such as inputs from the Yellow River, Yalujiang River and Jia River and atmospheric deposition. However, due to human activities, such as dam construction in rivers and climate change, the SiO 3 -Si concentrations and Si/P ratios decreased before the early 1990s and then gradually increased. The vertical distributions of nutrients displayed higher concentrations at the bottom than those at the surface in summer, which was attributed to the combined influence of the thermocline, the Yellow Sea Cold Water Mass, the Yellow Sea Warm Current and biological activities. Highlights • The NO 3 -N and DIN and N/P showed continuous increases over the past two decades. • The SiO 3 -Si and Si/P decreased before the early 1990s and then gradually increased. • Variations in N and N/P were affected by riverine inputs and atmospheric deposition. • Variations in SiO 3 -Si and Si/P were caused by human activities and climate change. [ABSTRACT FROM AUTHOR]

Long-term trend of crop yields has been widely studied in global scales to find which crops and which geographic regions offer the best hope of meeting food demands, and which regions needed the most improvements. In this study, a mathematical method was applied to analyze spatial patterns in long-term temporal trends of three major crops' yields in Japan archipelago. The changes in annual yields of rice, wheat, and soybean over a period of about 60 years in all 47 prefectures of Japan was analyzed by using the data of agricultural records. For all the three crops, the nationwide yields previously improved, but currently were stagnating in Japan. The result suggests that the annual yields were not improving in 53, 85, and 89% of those prefectures in Japan for rice, wheat, and soybean, respectively. The spatial patterns in temporal trends show that the percentage of number of yield-not-improving prefecture was higher in low latitude regions than high latitude regions. These results highlight the increasingly difficult challenge of meeting the growing demands and stagnating supplies in daily staple foods not only for agricultural scientists but also for Japanese society. [ABSTRACT FROM AUTHOR]

The Mesozoic Dipole Low (MDL), when the mean geomagnetic field intensity did not exceed one-third of the mean value in the Late Cenozoic, was suggested from the end of the Early Jurassic to the Late Cretaceous (180–120 Ma) in the 1990s. Subsequent studies evidenced that the MDL could have lasted from 260 to 50 Ma. We report new high-quality absolute paleointensity data based on a multispecimen approach from basaltic lava flows associated with the 132–135 Ma Paraná Magmatic Province. Our results suggest that the geomagnetic field in the middle Cretaceous was higher compared to the present-day value, and the MDL extent was likely shorter than usually considered. [ABSTRACT FROM AUTHOR]

We present observations of CH4 concentrations from the lower to upper troposphere (LT and UT) over Japan during 1988–2010 based on aircraft measurements from the Tohoku University (TU). The analysis is aided by simulation results using an atmospheric chemistry transport model (i.e. ACTM). Tropospheric CH4 over Japan shows interannual and seasonal variations that are dependent on altitudes, primarily reflecting differences in air mass origins at different altitudes. The long-term trend and interannual variation of CH4 in the LT are consistent with previous reports of measurements at surface baseline stations in the northern hemisphere. However, those in the UT show slightly different features from those in the LT. In the UT, CH4 concentrations show a seasonal maximum in August due to efficient transport of air masses influenced by continental CH4 sources, while LT CH4 reaches its seasonal minimum during summer due to enhanced chemical loss. Vertical profiles of the CH4 concentrations also vary with season, reflecting the seasonal cycles at the respective altitudes. In summer, transport of CH4-rich air from Asian regions elevates UT CH4 levels, forming a uniform vertical profile above the mid-troposphere. On the other hand, CH4 decreases nearly monotonically with altitude in winter–spring. The ACTM simulations with different emission scenarios reproduce general features of the tropospheric CH4 variations over Japan. Tagged tracer simulations using the ACTM indicate substantial contributions of CH4 sources in South Asia and East Asia to the summertime high CH4 values observed in the UT. This suggests that our observations over Japan are highly sensitive to CH4 emission signals particularly from Asia.