East Asian Monsoon Climate Research Articles

Phylogeography and genetic diversity of Ulmus elongata (Ulmaceae), a Tertiary relict tree with extremely small populations (PSESP)

BackgroundAssessing the current status and identifying the mechanisms threatening endangered plants are significant challenges and fundamental to biodiversity conservation, particularly for protecting Tertiary relict trees and plant species with extremely small populations (PSESP). Ulmus elongata (Ulmus, Ulmaceae) with high values for the ornamental application, is a Tertiary relict tree species and one of the members from PSESP in China. Currently, the wild populations of U. elongata have been threatened by excessive deforestation and urbanization, but limited knowledges of its genetic diversity seriously hinder conservation efforts. Therefore, a further study on the genetic diversity and drivers of genetic pattern in U. elongata is crucial for preserving genetic resources and can serve as a reference for other Tertiary relict plants and PSESP under climate change.ResultsHere, a total of 12 populations from 70 individuals of U. elongata were collected covering its geographical distribution in China. Utilizing chloroplast genome datasets, we found that U. elongata exhibited remarkably low nucleotide diversity and gene flow (π = 0.00013, Nm = 0.03). Analysis of molecular variance (AMOVA) showed that genetic variation in U. elongata occurs mainly between eight clades (60.95%). The Mantel tests indicated a significant correlation between genetic differentiation and geographical distances (r = 0.3777, p < 0.05) in U. elongata populations. A notable phylogeographic structure was identified in U. elongata, comprising eight distinct haplogroups (NST = 0.917, GST = 0.876, p < 0.05), which was attributed to the global cooling in the East Asia and Quaternary climate oscillations.ConclusionsOverall, our study using Ulmus elongata as a representative supported the hypothesis that plants belonging to Tertiary relict species and PSESP simultaneously exhibits significantly lower genetic diversity compared to those are either Tertiary relict species or PSESP individually. Furthermore, the low genetic diversity and significant genetic differentiation in U. elongata populations can be primarily ascribed to a combination of factors, including habitat fragmentation resulting from human activities, populations contraction during LGM and small population sizes. This provides a crucial foundation for guiding conservation efforts and implementing management strategies for other Tertiary relict tree species and PSESP. Our findings also provide evidence for the important roles of East Asian monsoon system and climate oscillations in shaping the phylogeographic pattern in subtropical broad-leaved forests.

Temporal and vertical variations in carbon flux and export of zooplankton fecal pellets in the western South China Sea

The enhancement of particulate organic carbon transfer to the deep sea by zooplankton fecal pellets constitutes a crucial component of the marine biological carbon pump. Here, we investigated time-series variations in characteristic and flux of zooplankton fecal pellets at different water depths of two sediment-trap mooring stations from May 2021 to May 2022 in the western South China Sea. The results show that numerical fluxes of fecal pellets were 0.75 ± 0.60 × 104, 0.63 ± 0.63 × 104, and 0.38 ± 0.29 × 104 pellets m−2 d−1 at 500 m, 1170 m, and 1380 m water depth, respectively, corresponding to their carbon fluxes of 0.10 ± 0.06, 0.09 ± 0.04, and 0.10 ± 0.04 mg C m−2 d−1. Both numerical and carbon fluxes of fecal pellets exhibited clear seasonal variations, with two peaks occurred in August and early November at all water depths. The fecal pellets have distinct morphological types (spherical, cylindrical, and ellipsoidal) and their contributions to the numerical and carbon fluxes were different. At all water depths, ellipsoidal and spherical pellets accounted for 96.0% of the numerical flux and 72.1% of the carbon flux. Cylindrical pellets were rare in quantity, accounting for 4.0% of numerical flux, but their carbon contribution accounted for 27.9% of the total fecal pellet carbon flux. The proportional fractions of zooplankton fecal pellets contributed to the overall particulate organic carbon from 0.7% to 28.2% in the western South China Sea, and fell in a reasonable range around the world. Multiple mechanisms, including East Asian monsoon climate and zooplankton community structure may be responsible for the production and fate of fecal pellets as well as their contribution to the settling particulate organic carbon.

Long-term changes in vegetation and land use in mountainous areas with heavy snowfalls in northern Japan: an 80-year comparison of vegetation maps

Comparison of old and new vegetation maps is an effective way to detect vegetation dynamics. Recent developments in computer technology have made it possible to accurately compare old paper vegetation maps with current digitized vegetation maps to reveal long-term vegetation dynamics. Recently, a 1:50,000 scale vegetation map of the Hakkoda Mountains in northern Japan, located in the ecotone of cool temperate and subalpine forests in northern Japan under an East Asian monsoon climate, from 1930 was discovered. We compared the 1930s vegetation map with the most recent 2010 vegetation map to test the following hypotheses: 1) the occurrence of upward expansion of the upper limit of cool-temperate deciduous forests, and 2) whether designation as a national park in 1936 would have reduced forestry and land use, expanded beech forests, and cool-temperate deciduous forests. To compare vegetation changes, 67 types of vegetation legends for the 1930 and 2010 maps were unified to 21 based on plant species composition. Consequently, vegetation has changed substantially over the past 80 years. 1) In the subalpine zone above 1,000 m, the coniferous forest area decreased by half. In the cool temperate zone below 1,000 m, the area of beech forests increased 1.48 times, and some of them could be shifted upwards, replacing subalpine fir forests in the lower part of the subalpine zone. 2) In areas below 700 m, deciduous oak forests once used as thickets were almost halved. Instead, climax and beech forests expanded. However, we also found that even after the area was declared a national park, oak forests were cleared and converted to commercial forests such as cedar plantations, cattle ranches, and horse pastures in some areas. These results will be useful for future ecosystem and biodiversity research/conservation and will provide baseline information for climate change adaptation policies.

Comparison of transit time models for exploring seasonal variation of preferential flow in a Moso bamboo watershed

Understanding seasonal variations of the hydrological fluxes and preferential flow is crucial in exploring contaminant fate and transport processes in a watershed of interest. Here, performance of different StorAge Selection (SAS)-based rainfall-runoff models was compared for a Moso bamboo watershed under the East Asian monsoon climate. Most of these models are composed of a two-parallel-reservoir flow module and a companioned SAS module. The results show that the temporal variation in streamflow is well captured by a two-parallel-reservoir flow module. The tracer simulations from different models show that two-uniform-reservoir (SSU) model with no SAS function has the lowest NSE value (0.17), the model including an SAS in one of the two reservoir outflows (SSD(U) and SSD(L)) improves performance (NSE greater than 0.5). The performance in simulating streamflow δ18O is further improved when SAS functions are applied for outflows from both reservoirs (SSD (U, L), NSE = 0.76). Additional inclusion an SAS function for ET fluxes in the model (SSD (U, ET, L)) results in a minor improvement from SSD (U, L). The results of SSD (U, ET, L) have achieved the best transport performance (NSE = 0.77), with implication for preferential flow in the watershed. The preferential flow for deep drainage and lower reservoir outflow shows seasonal variation, with more young water in the East Asian summer monsoon period than that in the East Asian winter monsoon period. The upper reservoir storage and deep drainage rates are the main factors determining the temporal variation of preferential flow for deep drainage and lower reservoir outflow, respectively.

Long-Term Change and Analysis of the Sedimentary Environment of Dadae Beach Using Unmanned Aerial Vehicles

Dadae Beach, located at the Nakdong river estuary, has been continuously evolving over the years, and this is the result of complex interactions between natural and artificial factors. In particular, in the case of Dadae Beach, located at the estuary of the Nakdong river estuary, it is located at the boundary between the river and the ocean, and it is an environment in which various deposition mechanisms operate. It is a very difficult research task to analyze the beach evolution mechanism, and a long-term study using precise measurement methods is required. Therefore, in this study, precision unmanned aerial surveys were conducted three times (2015, 2019, and 2021) for 5 years to identify the sedimentary characteristics of Dadae Beach, and the sedimentary environment was analyzed through the analysis of surface sediment texture characteristics. Seasonal waves and winds caused by the East Asian monsoon climate are the main mechanisms for the sedimentation of Dadae Beach, and finegrained sediments are distributed throughout the beach. In addition, the formation of sandbar, which arose rapidly due to artificial influences such as the construction of estuary banks in the past, is a major factor in the evolution of large-scale beaches. This study is meaningful in identifying the mechanism of beach evolution and presenting quantitative analysis results through comparison of precision aerial survey data over a long period of time.

Seasonal variation of transit time distribution and associated hydrological processes in a Moso bamboo watershed under the East Asian monsoon climate

Understanding seasonal variation of the transit time distribution of stream discharge and evapotranspiration is crucial in exploring the flow pathways and the rainfall-storage-streamflow processes in a watershed of interest . Here, both time-variant and time-invariant StorAge Selection (SAS) functions were adopted to estimate the transit time distribution in a Moso bamboo watershed under the East Asian monsoon climate. Daily stable isotopic compositions (δ18O, δ2H) of precipitation and streamflow at the watershed outlet from 1 October 2017 to 31 December 2020 were measured to calibrate the model parameters. The time-variant SAS method considering watershed wetness performs slightly better than the time-invariant SAS method, implying adding a watershed wetness indicator in the time-variant model results in only a minor improvement. Young water fraction and median age as two streamflow age measures were derived from the time-variant SAS model. The median age decreases abruptly within several days at three periods (one is in January 2020, and the other two periods are in Meiyu season) with larger uncertainty, while the estimated young water fraction varies gradually with much smaller uncertainty. The young water fraction derived from the time-variant SAS method appears to be more reliable than that estimated by the tracer cycle damping method. For stream discharge, the storage preferentially releases younger water to discharge under wetter conditions in the East Asian summer monsoon (EASM; June-September) period, while this phenomenon does not occur in the East Asian winter monsoon (EAWM; October-May) period. The larger hourly rainfall intensity for the whole EASM period (mean intensity 2.08 mm/h) likely enhances direct contribution of event water to streamflow than that in the EAWM period (mean intensity 0.75 mm/h). The evapotranspiration is estimated to extract older water than stream discharge in both the EAWM period and the EASM period. That is likely related to the occurrence of ecohydrological separation, and root water uptake below the soil-bedrock interface.

Natural and human activities driving the spatiotemporal variability of water clarity in lakes across Eastern China

• The water clarity presents a pattern of “high in the south and low in the north”. • The month of highest Z sd is postponed from June in the south to August in the north. • Natural and human activities contributed equally to Z sd in Eastern lakes. Water clarity, indexed by Secchi disk depth ( Z sd ), comprehensively reflects water quality and can be monitored by satellite. Z sd may vary across lakes globally, driven by natural and human activities (climate, land use/land cover, lake morphological characteristics, etc.). Based on Sentinel-3 Ocean and Land Color Instrument (OLCI) imagery, we explored the driving factors of Z sd spatiotemporal patterns in lakes across Eastern China (including the Northeast Plain and Mountain Lake (NPML) Zone and the Eastern Plain Lake (EPL) Zone). Spatially, the responses of driving factors were assessed using feature importance and partial dependence in the random forest model. The results showed that the impacts of natural factors on the spatial variations of Z sd (accounting for 52.00 % of contributions) are comparable to that of human activities (accounting for 48.00 % of contributions). The dynamic sediment ratio (DSR = the square root of the surface area divided by the average depth) showed the highest impact (accounting for 19.64 % of contributions). Thus, small lakes have relatively small DSR indices, making them less susceptible to wind- and wave-induced sediment resuspension, leading to higher Z sd than large lakes. Seasonally, the variations could be linked with the East Asian monsoon climate, characterized by hot and rainy summers. Moreover, the month with the highest Z sd was postponed from June-July in EPL lakes (south) to August-September in NPML lakes (north), consistent with the movement of the rainfall belt of the East Asian monsoon. This study could facilitate the knowledge of water quality in Eastern China as well as other developed areas and provide support for the sustainable development and management of lakes.

Quantifying Concentrations and Emissions of Hexachlorobutadiene - A New Atmospheric Persistent Organic Pollutant in northern China

Hexachlorobutadiene (HCBD) was listed as a new persistent organic pollutant for global regulation under Stockholm Convention in 2015, and there has been scarce information on its atmospheric concentrations, distributions, and emission sources. HCBD air samples were collected and analyzed to characterize concentrations and distributions at high elevation and urban sites as well as emission source locations in Northern China. We found ambient concentrations of HCBD in Northern China averaged at 34 ± 16 and 36 ± 28 pptv at urban sites in Jinan and Tai'an, respectively, and 31 ± 21 pptv at a high-elevation site Mount Tai. HCBD concentrations at the high elevation and urban sites were found to be affected by long-range transport under the influence of the East Asian monsoon climate. Over potential sources areas, we found concentrations of 76 ± 33 pptv in a mixed factory park, 59 ± 21 pptv in a rubber plant and 74 ± 8 pptv in a municipal solid waste (MSW) landfill area, which were all several times higher than in urban sites. The large concentration gradient across the various environments revealed strong emission sources of HCBD, especially over MSW landfill and Cl-compound production and application areas. An emission rate of 9.2 × 104 kg/yr and an oxidation rate of 32.9 kg/yr for HCBD were estimated for the mixed factory park. OH and Cl are much more active in reaction with HCBD than other oxidants in the atmosphere. Dry deposition and oxidation removed about 5.3% and 0.04%, respectively, of the emitted, suggesting that ∼95% of the emitted HCBD remaining in the atmosphere and could be transported for redistribution. Our findings revealed significant emission sources of HCBD in northern China, which was in turn affected by major sources in East-central China. The regional influence of HCBD pollution warrants serious concerns and points to the need to develop mitigation strategies.

Drivers of Coral Reconstructed Salinity in the South China Sea and Maritime Continent: The Influence of the 1976 Indo‐Pacific Climate Shift

AbstractThe flow of Pacific water into the Indian Ocean via the South China Sea (SCS) and Maritime Continent (MC) plays an important role in the ocean thermohaline circulation providing the only low‐latitude pathway for the inter‐ocean exchange of heat and salt. The transport of the SCS and Indonesian throughflows is modulated by the East Asian monsoon and major climate modes associated with the Pacific and Indian Oceans. As an indicator of surface layer buoyancy, sea surface salinity (SSS) is critical to rates of exchange but instrumental records of SSS are short and sparse. Using empirical orthogonal functions, a synthesis of proxy‐based reconstructions of SSS from coral δ18O is used to study the role of climate variability on long‐term SSS behavior in the region. The leading mode of SSS variability in the boreal winter and summer responds to the influence of the 1976 Indo‐Pacific climate shift. At multi‐decadal timescales, only the East Asian monsoon and the Indian Ocean Dipole (IOD) retain their signal in winter and summer SSS after 1976. At higher frequencies, winter SSS shifts from having a strong East Asian monsoon signal to a more dominant impact of the IOD and the El Niño Southern Oscillation (ENSO) following the shift. In the summer, only a change in ENSO's influence on SSS variability is observed after 1976. The recent intensification and dominance of the IOD and ENSO in driving SSS variability in the SCS and MC may influence circulation in the regional throughflows and perhaps global thermohaline circulation.

Regional climate modeling to understand Tibetan heating remote impacts on East China precipitation

The Tibetan Plateau, as a major elevated heat source, plays a critical role in the Asian monsoon and global climate. Observational data revealed significant correlations between spring surface air temperature in the Tibetan Plateau and downstream summer precipitation interannual variations. Sensitivity experiments using the regional Climate-Weather Research and Forecasting model (CWRF) were conducted to understand the physical processes and mechanisms underlying such delayed teleconnections. A positive temperature forcing was imposed over the plateau on the surface and subsurface soil layers only at the initial conditions around May 1st, 2003. This regional forcing quickly induces positive perturbations in local air temperature and, more importantly, maintains its signal in local soil, especially deep layers, for several months. Consequently, the soil temperature serves as a charged capacitor to modulate the planetary atmospheric circulation and through Rossby wave chains to cause significant summer precipitation anomalies over broad regions. This relayed teleconnection pattern is consistent with that identified from observational data records and CWRF climate simulations during 1980–2015. Diagnostic analyses of observations and simulations suggest that the Tibetan Plateau heating significantly impacts summer East Asian monsoon climate through influencing the South Asian High and shifting the East Asian jet.

Macro-evolutionary patterns of East Asian opsariichthyin-xenocyprinin-cultrin fishes related to the formation of river and river-lake environments under monsoon climate

Although the East Asian monsoon is believed to be an important driver for the origin and evolution of the biotas in this region, the association has rarely been rigorously tested. Here, using phylogenetic comparative methods and analyses of key innovations of adaptive traits, we investigated evolutionary patterns of the East Asian cyprinid opsariichthyin-xenocyprinin-cultrin clade; the dominant species in lakes and rivers, which are the typical productions of monsoon climate. Our molecular phylogenetic analyses revealed the relationships as (Opsariichthys-tribe + (((Oxygaster-tribe ​+ ​Aphyocypris-tribe) ​+ ​Metzia-tribe) ​+ ​(Paralaubuca-tribe + (Squaliobarbus-tribe + (Hypophthalmichthys-tribe + (xenocyprinins ​+ ​cultrins)))))). Based on Bayesian relaxed-clock methods, we found that origins of the Squaliobarbus- and Hypophthalmichthys-tribes bearing the key adaptation of riverine spawning with drifting eggs occurred 22.5 and 21.1 Mya, respectively. These times are consistent with the Early Miocene origin of major rivers (e.g., Yangtze River) and the appearance of the East Asian monsoon climate. Diversification of the cultrins, characterized by spawning of adhesive eggs as well as swimming and feeding in lentic waters, were estimated to have evolved 16.6 to 0.2 Mya. This period covers three phases of enhancement of the East Asian monsoon from the Middle Miocene to the Pliocene (around 15–13, 10–7, and 3.5 Mya). The habitats of these cultrins and their evolution also suggest the appearance and development of a lake-river environment during those periods. Therefore, our results suggest close relationships between the evolution of these fishes and geological events in East Asia. Further, they provide knowledge that may help facilitate future conservation strategies such as the maintenance of high river flows during dam construction and operation.

Seasonal flooding regime effects on the survival, growth, and reproduction of Bolboschoenus planiculmis under East Asian monsoon

Seasonal flooding regimes are key hydrodynamic features in estuarine ecosystems, and are mainly influenced by climatic conditions. Today, the original seasonal flooding regimes can be altered due to artificial infrastructure or following sea-level rise. Although the altered flooding regimes determine flooding duration and depth, which further influence growth and development of marsh plants, little is known about the effects of seasonal flooding regimes on marsh plants under the East Asian monsoon climate zone. Therefore, we investigated the effects of different seasonal flooding regimes on survival, growth, and reproduction of the marsh plant Bolboschoenus planiculmis. A greenhouse experiment was conducted to compare the responses of B. planiculmis under combinations of four flooding durations (0-month, 2-month, 3.5-month, and 5-month) and flooding depths (0-cm, 20-cm, and 40-cm). Flooding duration affected the survival and growth of B. planiculmis: Extended flooding (5-month) decreased the survival rate and initial shoot density, while shoot length and biomass increased under extended (5-month) and natural (3.5-month) seasonal flooding after shoots reached the water surface. The flooding depth affected sexual reproduction: Medium flooding depth (20-cm) resulted in the highest flowering rate. According to the results, the natural seasonal flooding duration in the East Asian monsoon climate did not negatively influence survival, growth, and reproduction of B. planiculmis. However, if the seasonal flooding duration was extended, B. planiculmis responded negatively to survival and growth during the young stage. The shortened seasonal flooding duration resulted in the repressed shoot length and biomass of B. planiculmis. For the sustainable conservation of B. planiculmis under East Asian monsoon, it is important to maintain the original seasonal flooding regimes and minimize the effects of embankment on the seasonal flooding regimes.

Modelling the effect of local and regional emissions on PM2.5 concentrations in Wuhan, China during the COVID-19 lockdown

PM2.5 concentrations in Wuhan, China decreased by 36.0% between the period prior to the COVID-19 pandemic (1–23 January, 2020) and the COVID-lockdown period (24 January to 29 February, 2020). However, decreases in PM2.5 concentration due to regional PM2.5 transport driven by meteorological changes, and the relationship between the PM2.5 source and receptor, are poorly understood. Therefore, this study assessed how changes in meteorology, local emissions, and regional transport from external source emissions contributed to the decrease in Wuhan's PM2.5 concentration, using FLEXPART-WRF and WRF-Chem modelling experiments. The results showed that meteorological changes in central China explain up to 22.2% of the total decrease in PM2.5 concentrations in Wuhan, while the remaining 77.8% was due to air pollutant emissions reduction. Reduction in air pollutant emissions depended on both local and external sources, which contributed alomst equally to the reduction in PM2.5 concentrations (38.7% and 39.1% of the total reduction, respectively). The key emissions source areas affecting PM2.5 in Wuhan during the COVID-lockdown were identified by the FLEXPART-WRF modeling, revealing that regional-joint control measures in key areas accounted for 89.3% of the decrease in PM2.5 concentrations in Wuhan. The results show that regional-joint control can be enhanced by identifying key areas of emissions reduction from the source–receptor relationship of regional PM2.5 transport driven by meteorology under the background of East Asian monsoon climate change.

Changes in rainfall of different intensities due to urbanization-induced land-use changes in Shenzhen, China

Shenzhen city, located in southern China and governed by the East Asian monsoon climate system, has experienced rapid urbanization since the beginning of the 1980s, and had become an international metropolis by the 2010s. Urban-induced changes in rainfall of various intensity grades over Shenzhen are investigated using nested numerical integrations at 3.3 km spatial resolution, within which urban surface distributions and expansions are well represented by satellite-based data. The urban-induced impact on subregion average of daily rainfall (DRAIN) and cumulative volumetric rainfall (VRAIN) intensity and variability, as well as rain areas and number of rain days, are evaluated. For total rainfall amounts, significant changes are only detected in VRAIN and DRAIN variability on seasonal scales. However, for different intensity grades of rainfall, urban-induced changes in VRAIN and DRAIN intensity and variability of both annual and seasonal results are more pronounced. Significant changes are detected only for heavy storm rain on annual scales, whereas marked subregional characteristics are found for various grades of rainfall on seasonal scales. The increased DRAIN/VRAIN intensity and variability for heavy storm rain due to urban surface expansion from the 1980s to the 2010s can be linked to intensified vertical circulation and changes in moisture flux. A reduced local evaporation-related moisture flux and a weakened southeasterly water vapor transport result in a decreased relative humidity in the near-surface layers. However, an intensified southwesterly moisture flux induces an increased relative humidity in the low-middle troposphere.

Temperature reconstruction based on 361 year old dendrochronology of Platycladus orientalis (L.) franco in the Wula Mountains, China

The northern edge of the East Asian monsoon region is also a transition zone of temperate continental and monsoon climate, which is a sensitive zone of global climate and ecological environment change. It is an urgent problem to find out the long-term climate change rules of this region. Using 101 tree core samples obtained from 54 trees, a 343-year tree-ring width chronology of the Platycladus orientalis (L.) Franco (1673–2016) in the Wula Mountains, Inner Mongolia, China was established. The analysis shows that the radial growth of P. orientalis is closely related to hydrothermal conditions, the average minimum temperature and relative humidity are the main factors that determine the growth of P. orientalis. Based on the strong correlation between the tree-ring indices and the annual average minimum temperature (r = −0.870, p < 0.001), we reconstructed an average annual minimum temperature series from 1673 to 2016 using a linear regression equation, and the reconstructed equation can explain 75.724% of the variance, respectively. According to the data from the past 343 years, the changes in the annual average minimum temperature series had the cycles of 58.6-, 7.7-, 3.4-, 3.1-, 2.2-, and 2.1-years; the series showed three warm periods (1824–1830, 1909–1922, and 1986–2011) and 4 cold periods (1703–1712, 1731–1738, 1754–1763, and 1937–1951). The low temperature periods recorded in the reconstructed series for the 17th and 18th centuries are consistent with the Little Ice Age that occurred in the northern hemisphere, and the heating rate significantly increased at the end of the 20th century. In addition, the cold and warm periods recorded by the reconstruction result is basically consistent with the extreme climate events recorded in the historical documents of the region and the reconstruction results in other regions. In this paper, the world's first chronology of P. orientalis tree ring width was established. A historical sequence of annual average minimum temperature of 343 years was reconstructed in a typical region of the East Asian monsoon climate. It fills in the blank of reconstruction sequence and variation characteristics of mean minimum temperature in the northern edge of East Asian monsoon and transition zone of temperate continental and monsoon climate in recent four centuries.

Century-scale climatic oscillations during the Last Glacial Maximum revealed by stalagmite isotopic records from Longfugong Cave, China

The isotopic records of two 230Th-dated stalagmites from Longfugong Cave, Mt. Shennongjia, central China, reveal a highly resolved Asian summer monsoon (ASM) history from 29.5 to 14.5 ka BP. The two δ18O records are consistent with other Chinese cave δ18O records, suggesting that our new records are of regional significance. Due to the reservoir mixing of seepage water in the epikarst system, the stalagmite δ18O signals in this cave are more severely muted than those in other caves. Here, we observed that the amplitude of the δ13C variability is approximately twice that of the δ18O signal and can be used as a sensitive proxy of East Asian monsoon climates. First, the two stalagmite δ13C records are consistent with each other on decadal to centennial timescales. Second, there are high correlation coefficients between the δ13C and δ18O signals over shorter timescales. Third, from 25.2 to 19.6 ka BP, six peaks in the δ13C records were identified and are coincident with corresponding warming events in the Greenland ice-core δ18O records, suggesting that strong coupling occurred between the high- and low-latitude northern climates on centennial timescales. Therefore, we propose that atmospheric transmission mechanisms probably played an important role in linking the ASM and Greenland climates on short timescales. A shift in westerly winds associated with variability in the extent of temperature in the North Atlantic likely influenced changes in hydrological and thermal conditions at the cave site, leading to changes in vegetation cover and soil CO2 concentrations above the cave. Therefore, the calcite δ13C records probably had faster and more sensitive responses to rapid climate shifts compared with their related δ18O records.

Phylogenomics of the aquatic plant genus Ottelia (Hydrocharitaceae): Implications for historical biogeography

Ottelia Pers. is the second largest genus of the family Hydrocharitaceae, including approximately 23 extant species. The genus exhibits a diversity of both bisexual and unisexual flowers, and complex reproductive system comprising cross-pollinated to cleistogamous flowers. Ottelia has been regarded as a pivotal group to study the evolution of Hydrocharitaceae, but the phylogenic relationships and evolutionary history of the genus remain unresolved. Here, we reconstructed a robust phylogenetic framework for Ottelia using 40 newly assembled complete plastomes. Our results resolved Ottelia as a monophyletic genus consisting of two major clades, which correspond to the main two centers of diversity in Asia and Africa. According to the divergence time estimation analysis, the crown group Ottelia began to diversify around 13.09 Ma during the middle Miocene. The biogeographical analysis indicated the existence of the most recent common ancestor somewhere in Africa/Australasia/Asia. Basing on further insights from the morphological evolution of Ottelia, we hypothesized that the ancestral center of origin was in Africa, from where the range expanded by transoceanic dispersal to South America and Australasia, and further from Australasia to Asia. We suggested that the climatic change and global cooling since the mid-Miocene, such as the development of East Asian monsoon climate and tectonic movement of the Yunnan-Guizhou Plateau (YGP), might have played a crucial role in the evolution of Ottelia in China.

Sedimentary history of the coastal plain of the south Yellow Sea since 5.1 Ma constrained by high-resolution magnetostratigraphy of onshore borehole core GZK01

The thick sedimentary sequences of the East Asian continental shelves are archives of information on tectonics, sea-level fluctuations, flood plain evolution, and changes in the East Asian monsoon climate. However, long sedimentary sequences with a reliable chronological framework from this setting are scarce. Here, we present an integration of lithostratigraphic, rock magnetic, and magnetostratigraphic results for the sedimentary sequence of a 285.0 m core (GZK01) recovered from the northern Jiangsu coastal plain of the onshore South Yellow Sea, eastern China. Alluvial, fluvial, lacustrine, and marine deposits were identified according to lithofacies analysis, and detrital magnetite and hematite are the main magnetic carriers. The magnetostratigraphic results show that core GZK01 records the Brunhes, Matuyama, Gauss, and Gilbert chrons, and has an extrapolated basal age of ∼5.1 Ma. This record is the oldest sedimentary sequence yet reported from the continental shelf of the South Yellow Sea. Integrating the geochronological framework with changes in lithofacies, a conceptual model of the environmental evolution of the northern Jiangsu coastal plain is proposed. For a long interval during the Pliocene, the drilling area was a lacustrine environment. From the Late Pliocene to the Early Pleistocene, the disappearance of the paleolake and a transition to a fluvial and marine environment suggests the peneplanation of the northern Jiangsu coastal plain. Cumulative land-sea interactions since 0.8 Ma subsequently shaped the modern geomorphology. The observed process of sedimentary evolution was possibly controlled by regional tectonics and long-term climate changes.

Diversity, pattern and ecological drivers of freshwater fish in China and adjacent areas

China is one of the megadiverse freshwater regions in the world, but the detailed diversity inventory, distribution pattern and ecological drivers are incompletely known, which hinders large-scale freshwater diversity conservation and pattern analysis at the global scale. Aiming to fill this knowledge gap, we compiled a comprehensive richness and distribution database of freshwater fishes in China and adject areas based on our long-term survey and exhaustive data collection from 165 hydrologic units at tributary and sub-basin grain. Then, we elucidated a biogeographical pattern using a β dissimilarity matrix with species presence/absence data and taxonomic relationships. Finally, we evaluated the explanatory power of three hypotheses, i.e., ‘area’, ‘energy’, and ‘history’, in explaining the diversity patterns. A total of 2,063 species utilizing freshwater habitats were identified in the study area. Among them, 1,651 freshwater species were recorded in China, of which 1034 species are endemic to China. Four major freshwater zoogeographic regions, the Palearctic, High Central Asia, East Asia, and South Asia, were identified from a dendrogram, and each region was characterized by different taxonomic categories (i.e., from species to order). ‘Historical’ factors play the most important role (43.64–62.96% of the total variation), or at least a comparable role to that of contemporary climate, in explaining the freshwater fish diversity patterns (species richness and species endemicity). In conclusion, the uplift of the Qinghai-Tibetan Plateau, nearby orogeny, and the following formation of the East Asian monsoon climate had profound impacts on the diversification and distribution of ichthyofauna in China and adjacent areas.

Carbon and nitrogen exports from forested headwater catchment in southwestern Japan

Accurate estimation of carbon and nitrogen exports from forest ecosystems via streams is important because of the critical role these losses play in the carbon and nitrogen budgets in forest ecosystems. However, little is known about the export of carbon and nitrogen from small hilly catchment under an East Asian monsoon climate In this study, carbon and nitrogen exports in both particulate and dissolved forms were measured under baseflow and stormflow conditions of a forested catchment in southwestern Japan. Coarse particulate matter (CPM) was collected continuously by using mesh frames deployed across a channel. Exports of fine particulate matter (FPM) and dissolved organic and inorganic matter were calculated by using load–discharge relationships. Total estimated yields for carbon and nitrogen were 369.6 kg ha−1 year−1 and 18.3 kg ha−1 year−1, respectively. FPM accounted for more than 60% of the total stream yield of both carbon and nitrogen, and was on the upper end of the range found in worldwide reviews. The contribution of CPM to the total yield was limited to 2% and 1% for carbon and nitrogen, respectively. Most of the carbon (81%) and nitrogen (93%) was exported by stormflows which occurred only 8% of the time. Large rainstorms occurred during the bai-u season and typhoons, which is a typical rainfall pattern in the monsoon climate. Therefore, to estimate the total yield of carbon and nitrogen from hilly catchments experiencing large frequent storms, adequate sampling and computation particularly of FPM export by stormflows is critical.