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To rapidly rehabilitate mangrove forests, exotic mangrove species characterized by high growth rates have been introduced in China, which would undoubtedly affect the nutrient status, nutrient acquisition and utilization strategies of mangrove plants, but the mechanism remains unclear. Qi'ao Island (a suburb of Zhuhai City) has the largest continuous exotic mangrove forests in China, where a mass collection of mangrove soils, plant tissues and tidewater was conducted. Ecological stoichiometric ratios and isotopic compositions were then analyzed to evaluate the ecosystem-scale nutrient status and compare the nutrient acquisition and utilization strategies of native Kandelia obovata (KO) and exotic Sonneratia apetala (SA) species. Soil and foliar C:N:P stoichiometries indicated that there is high P availability but N limitations, while further isotopic evidence indicated that native KO and exotic SA responded differently to the N limitation status. First, native KO seemed to prefer NO3−, while exotic SA preferred NH4+, according to the Δ15Nleaf–root (leaf–root δ15N difference) as well as the relationships between foliar δ15N and soil-extracted NH4+ δ15N, and between N and heavy metal contents. This suggested possible inter-specific competition between native KO and exotic SA, leading to different N species' preferences to maximize resource utilization. Next, native KO likely adopted the "conservative" strategy to ensure survival with reduced investment in N-rich growth components but root systems leading to lower growth rates and higher N use efficiency (NUE) and intrinsic water use efficiency (iWUE), while exotic SA adopted the "aggressive" strategy to ensure fast growth with heavy investment in N-rich growth components, leading to rapid growth and lower NUE and iWUE, and showing signs of invasiveness. Further, native KO is more responsive to aggravated N limitation by enhancing NUE. This study will provide insights into the adaptation of different mangrove species to nutrient limitations and the risks associated with large-scale plantations of exotic mangrove species. [ABSTRACT FROM AUTHOR]

Abstract: This study examines the accumulation of major and trace elements in peat deposits in central Yunnan Province, southwestern China. The ashes of an approximately 2m long core spanning 32.7–11.4ka are analyzed to assess the elemental contributions of organic materials and to identify elemental paleoclimatic proxies in peats. Peat ash, which is mainly composed of silicate materials, makes up 20–80% of each of the samples. The analysis shows that organic materials are a significant source of many of the elements in the ashes. Among these elements, P and V are the most typical, with their concentrations in the ashes closely correlating to the total organic carbon (TOC) content of the peats. Al, Na, Sc, Cr, Co, Ni, Cu, Ge, Pb, and Th are also associated with biogenic materials, particularly in the lower section (below 122cm) of the core, where the organic material content is high. Ca, Sr, Mg, and Mn appear to have been part of carbonate deposits, such as authigenic FeCO3 and MnCO3 in the anoxic peats, whereas, K, Ti, Zn, Ga, Rb, Y, rare earth elements (REEs), Zr, Hf, Nb, Ta, Ba, and U are mainly associated with silicate materials. Local weathering products, rather than dust from northern China, are the main sources for the silicate materials in these peats. Some elemental ratios such as K/Rb and K2O/Na2O can reliably indicate changes in local chemical weathering intensity, and their variation patterns match the changes in the East Asian summer monsoon (EASM) very well. The less intensive chemical weathering indicated by lower K/Rb and K2O/Na2O ratios generally corresponds to weaker EASM strength during ∼30 to ∼10ka, which is consistent with the fact that weaker summer monsoons may arouse drier climates, and do not favor intense chemical weathering. This suggests that select elemental ratios in peats/organic rich sediments may be informative proxies for monsoon climate changes. [Copyright &y& Elsevier]

SUMMARY A composite Holocene sediment profile ∼5 m in length, constrained by both radiocarbon dating and magnetic susceptibility based correlation, was obtained from three Livingstone piston cores collected in ∼10-m water depth in the Huguangyan (HGY) maar lake, southern China. The homogeneous silty clay indicates stable and continuous deposition. The dominant magnetic carrier is magnetite in the pseudo-single-domain grain size range and thus is suitable for recording palaeomagnetic secular variations (PSV). Results show that the HGY PSV curves can be correlated faithfully to the counterparts at a regional scale. Therefore, the PSV data is a potential tool for stratigraphic correlation and for further refining the chronological framework of lake sediment sequences from Southern China. Further comparison of the HGY PSV records with the coeval European and North American counterparts confirms the existence of strong permanent magnetic flux lobes at the core-mantle boundary. The discrepancy in amplitude and out-phase pattern among the different regional records may be ascribed to the evolution of the magnetic flux lobes. [ABSTRACT FROM AUTHOR]

Summary: Oxygen and hydrogen stable isotopes (δ 18O and δD) in precipitation collected in every event from 2007 to 2009 in Guangzhou, South China, are presented in this paper. The total correlation between δ 18O and δD is obtained as δD =(8.46±0.13) δ 18O+(15.0±0.9). More negative δ 18O and δD generally occur during summer and autumn, while less negative or even positive δ 18O and δD occur during winter and spring. Significant negative correlations between precipitation δ 18O and temperature, and between precipitation δ 18O and precipitation amount are observed. Regression line changes from year to year are likely due to changes in moisture sources for the precipitation. The moisture contributed by adjacent seas or local evaporation account for the main precipitation during winter and early spring, while summer monsoon brings huge amounts of moisture from remote seas associated with higher temperature and larger precipitation amounts. Seasonal variations of the precipitation D-excess provide more details for changes in moisture sources. Higher D-excess values during winter and early spring are estimated to correspond to a lesser proportion of remote moisture, while lower D-excess values during summer and autumn correspond to larger remote moisture transported by summer monsoons. This generally agrees with the results of model analysis on single isobaric backward trajectories for air parcels during specific time periods. Results of this study imply that precipitation δ 18O and δD, as well as some related paleoclimate proxies such as δ 18O in speleothem and tree ring, and δD in plant-derived organic compounds and tree ring, currently cannot indicate changes in temperature or precipitation amount separately, but should be comprehensive proxies for monsoon climate. [ABSTRACT FROM AUTHOR]

Homologue distribution proxies of leaf wax n -alkanes (normal chain alkanes) have been widely used for chemotaxonomy and paleoclimate reconstruction, while modern calibrations of them reported contrasting conclusions in different climate settings, especially between the cold arid and other climate regions. To further explore n -alkane-abiotic factor correlation in cold arid regions, this study surveyed n -alkane patterns of soil and leaf wax of three plant species along confined temperature and precipitation gradients in the Junggar Basin of northwest China. Our results show that salinity has a possible strong constraint on the Average Chain Length (ACL) of soil n -alkanes in high salinity settings, while precipitation or water stress is the leading constraint on the Carbon Preference Index (CPI) of those in low salinity settings. Precipitation also shows strong control over CPI or ACL of leaf wax n -alkanes of different plant species. Our results confirmed that n -alkane patterns are sensitive to, and constrained by abiotic factors independently on levels of plant species and averaged biome. A compilation of soil CPI from transect studies across the hot-humid to cold-arid regions of China further revealed precipitation being the first-order constraint of soil CPI, and a CPI trend reversal pattern along the precipitation gradient, where CPI increases from arid to semiarid climate and then decreases toward humid climate. Further analysis of existing CPI records showed that this CPI trend reversal may help differentiate three climate states qualitatively, i.e. arid, semiarid-semihumid and humid climates, which could be a valuable complement to existing proxies for paleoclimate reconstruction. [ABSTRACT FROM AUTHOR]

Widely distributed wetlands in China play an important role in the global carbon cycle. However, the long-term response of wetland evolution and carbon storage in tropical southern China to climate change remains unclear. Here, we present a sediment core record from the Tiaoshu Wetland in the northern Leizhou Peninsula and multiple proxy indicators are investigated, with the aim of better understanding past vegetation and environmental changes. The following conclusions were drawn: (i) The organic matter deposited in the Tiaoshu Wetland was mainly derived from terrestrial C3 plants and aquatic plants growing in and/or around the catchment. The temporal variability in the relative proportions of organic matter contributed by various sources revealed paleoenvironmental changes in the study area, generally consistent with regional and global climate records. (ii) The peat formation pattern in the Tiaoshu Wetland is in contrast to some individual sites reported in subtropical China, suggesting that there may be different peat formation patterns in the tropical and subtropical regions of China, which may be closely related to specific hydrothermal conditions in different regions. In addition, by comparison with atmospheric CH 4 concentrations, our results suggest potential relationships between the evolution of wetlands in tropical China and global atmospheric CH 4 cycles. • Alternation between terrestrial and aquatic plants dominated the organic matter sources in the Tiaoshu Wetland. • Variations in organic matter sources reveal vegetation succession and a response to climate changes. • Peat formation patterns may differ between tropical and subtropical regions of China. [ABSTRACT FROM AUTHOR]

Mo isotopic composition in large rivers is very important for understanding global Mo cycle. At present, temporal variation signatures in the δ 98/95 Mo in large rivers have not been investigated, which hinder a comprehensive understanding on the mechanism for the variations of Mo isotopic compositions in river water. In this study, we report a one-year-long time series (March 2010 to March 2011) of the δ 98/95 Mo of both the water and suspended particulates collected at Guiping, from the middle reaches of the Xijiang River (XJR), and of the water δ 98/95 Mo from the lower reaches of the Huanghe River (HHR, or Yellow River) collected at Lijin, China. The results indicate that the temporal variations in the concentration and δ 98/95 Mo of dissolved Mo in the XJR range from 4.32 to 10.5 nmol/L (mean 7.31 nmol/L) and 1.04‰ to 1.31‰ (relative to NIST 3134) (mean 1.20‰), respectively, but that the particulates have a lower δ 98/95 Mo (− 0.18‰ to 0.58‰). Analysis of the suspended particulates and other chemical parameters of the river water suggests that the weathering of silicates and sulfides is the main contributor to the dissolved Mo content in the XJR. Subsequently, the highly efficient preferential trapping of lighter δ 98/95 Mo by weathering products such as clay minerals, Fe–Mn oxides, and organic materials in soils and saprolites, which are abundant in the tropical catchment, is the key to the heavy Mo isotope signatures in the XJR. Furthermore, it seems that neither Mo-scavenging by suspended particulates during riverine transportation, nor the weathering of sulfates, significantly influences the δ 98/95 Mo of the XJR water. Cross comparison among the δ 98/95 Mo in the waters of the three largest rivers in China (the Changjiang (CJR), HHR, and XJR) indicates that the HHR has the highest Mo concentrations, but the lightest δ 98/95 Mo, the XJR has the lowest Mo concentrations but the heaviest δ 98/95 Mo, and the values for the CJR are intermediate between those for the other two rivers. This supports the conclusion that the efficiency of the selective trapping of Mo by soils and saprolites is the main factor controlling δ 98/95 Mo in these large rivers. The tropical/subtropical XJR catchment experiences intense chemical weathering, the semi-arid temperate HHR catchment experiences very little, and the CJR catchment falls somewhere between the two. Such a relationship between water Mo concentrations and δ 98/95 Mo agrees with previous observations from many large rivers worldwide. It is therefore suggested that chemical weathering on continents is the key to variations in the isotopic composition of Mo in the waters of large rivers. [ABSTRACT FROM AUTHOR]

Lake Huguangyan (21°9′ N, 110°17′ E), a maar lake located near the South China Sea, can provide valuable sedimentary data regarding past changes of the East Asian monsoonal system. Here, we used the proxies of TOC, δ 13 C org , δ 15 N, and leaf wax n -alkane δ 13 C values (δ 13 C wax ) to reconstruct the lake conditions, which, in turn, revealed patterns in monsoonal changes during the Holocene. Two distinct patterns of proxy changes were identified in the sedimentary profile. A marked shift in the δ 13 C wax value at ∼9.2 ka (thousand years ago) suggests the abrupt disappearance of C 4 plants, signaling the enhancement of East Asian summer monsoon (EASM). Between 9.2 and 1.8 ka, a nearly pure C 3 terrestrial ecosystem was present, with the climax at ca 7–6 ka. After ca 3 ka, fewer tropical species and a reappearance of C 4 plants at 1.8 ka indicate a weakened EASM in the late Holocene. The TOC concentration and δ 15 N value proxies appear to be associated with lake aquatic production and upwelled nutrient supply and utilization, which are modulated by, and thus indicative of, the strength of the East Asian winter monsoon (EAWM). The two EAWM records suggest a weakening trend from the early to late Holocene, with the most significant transition at ∼6 ka; thus, the EAWM trend was broadly in-phase with that of the EASM. However, the marked EASM intensification at 9.2 ka occurred within the period of a strong EAWM between 10.5 and 6 ka and lagged the monsoonal enhancement as inferred from the Dongge Cave δ 18 O values. Our EASM records displays an overall arid-wet-arid pattern, which is in-phase with the hydrological variability in tropical Australia and anti-phase with that in the outer-tropical Andes. These phase relationships might be linked to changes in the thermal state of the tropical Pacific during the Holocene. [ABSTRACT FROM AUTHOR]

Soil microbial assembly in cold arid deserts is under dispute, while its possible constraints on n -alkane proxies have been posited without direct evidence. To further explore their underlying mechanisms, we analyzed the 16S rRNA data along two salinity and one precipitation gradient from the Junggar Basin of northwest China. The null-model phylogenetic composition analysis shows homogeneous selection of deterministic processes assembled prokaryotic (dominated by bacterial) communities, while stochastic processes dominated the archaeal community assembly. Multivariate linear regression analyses show precipitation-related variables and salinity are leading predictors of the prokaryotic beta diversity in the low- and high-salinity settings, respectively, but can only explain limited variance, while reliable predictors for alpha diversity are lacking along different gradients. We suggest instead of previously reported a primary one, multiple competing environmental variables assembled the prokaryotic communities. Further comparison with n -alkane proxies reveals multiple species could have potentially contributed to, but not controlled the previously reported negative n -alkane ACL (Average Chain Length)-salinity correlation in high-salinity soils, while the reported positive n -alkane CPI (Carbon Preference Index)-precipitation correlation is attributed to precipitation-regulated combined plant-biome input in low-salinity settings. This provided the first direct microbial evidence validating CPI's application in paleo-vegetation/precipitation reconstruction in low-salinity dry land settings. [ABSTRACT FROM AUTHOR]

Abstract: Seasonal changes in strontium (Sr) isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering, and help to better constrain the Sr isotopic budget of global oceans. However, such records are scarce. Here we present a year-long time-series of both radiogenic and stable Sr isotope measurements (87Sr/86Sr and δ88Sr) from river water at Guiping, in the middle reaches of the Xijiang River, South China. Temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both Sr isotopes and major ions in the river water. River water 87Sr/86Sr values range from 0.708487 to 0.710336, with most values being <0.7092, indicating a dominant contribution from the weathering of carbonate rocks. High 87Sr/86Sr values (>0.7092) are generally accompanied by high Rb/Sr ratios, and low pH and δ13C of dissolved inorganic carbo (DIC) and occur during periods of large river flux. This indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons. Seasonal variation in river water δ88Sr is large, from 0.147‰ to 0.661‰, with higher δ88Sr values generally corresponding to higher 87Sr/86Sr values. Again, low δ88Sr values (<0.3‰) suggest a dominant contribution from the weathering of carbonate rocks, whereas the high δ88Sr values may represent a contribution from intensive weathering of silicate rocks. Using the time-series data, we estimated the flux-weighted averages of Sr concentration, 87Sr/86Sr, and δ88Sr for the Xijiang River to be 1.00μmol/L, 0.70960, and 0.38‰, respectively. The Sr concentration and 87Sr/86Sr results are close to previous estimates, while the δ88Sr value is amongst the highest recorded for the large rivers of the world, and is close to that of seawater. Our results indicate that large rivers draining through tropical/sub-tropical regions could play an important role in regulating the stable Sr isotopic budget of global oceans. [Copyright &y& Elsevier]

The Ediacaran–Cambrian (E–C) transition witnessed profound biological and oceanic changes, among which the appearance of explosive radiation of skeletonized animals is considered as the most remarkable one. Although the prominent rise of oxygen concentration in atmosphere and ocean is considered to be the major trigger of the "Cambrian Explosion", the links between the oxygenated process of deep ocean and the diversification of Cambrian metazoans are still under debate. In this study, δ15N and δ13C org values, TOC and TN contents, as well as trace elements concentrations of fresh shale core samples were analyzed to explore the redox condition and nitrogen cycle of deep oceans and their relationships with biological evolution. The Mo concentrations, Mo–U covariations and Th/U ratios of our samples indicate suboxic/anoxic waters in the mid-depth ocean during the late Ediacaran to Cambrian Fortunian age, widespread anoxic/euxinic waters with temporary sulfidic waters during Cambrian Age 2 to early Age 3, and suboxic waters again during the middle to late Age 3. The positive δ15N values from late Ediacaran to Cambrian Age 2 indicate a large NO 3 − reservoir with a deep chemocline. In contrast, the low δ15N values (<0‰) in the deepwater slope regions suggest a dominant biological N 2 -fixation, and/or partial NH 4 +-assimilation in the photic zone during Cambrian Age 3. Integrated δ15N values of this study and early publications suggest a continuous redox stratified paleo-ocean with anoxic/suboxic deep waters from late Ediacaran to Cambrian Age 3. It is also worthy to note that although the deep ocean may not experience substantial oxygenation during the main phase of Cambrian diversification, the expanding oxic surface waters and supply of bioavailable fixed nitrogen may satisfy complex high O 2 -demanding animals, and thus at least have promoted the Cambrian biodiversity in shallow waters. • Positive δ15N values reflect bioavailable NO 3 − in surface oxic waters and a deepening chemocline. • The lower δ15N (<−2‰) may be related to partial NH 4 +-assimilation in the photic zone. • Nitrogen isotopes indicate a redox stratified ocean from late Ediacaran to Cambrian Age 3. • The expanding oxic surface waters and supply of bioavailable NO 3 − may promote the Cambrian biodiversity. [ABSTRACT FROM AUTHOR]

The supply and preservation of terrestrial organic matter (TOM) during early Carboniferous glacial-interglacial intervals in South China were investigated with respect to their roles in paleo-environmental variation and organic matter (OM) accumulation in black shales. The marine redox proxies such as V/Cr, C org /P ratios, and Mo–U covariation indicate a fully oxic water condition during the earliest Visean, while dominant oxic with occasional suboxic water conditions prevailed during the early to middle Visean. High sedimentary δ15N values (1.9–6.3‰) suggest the existence of enhanced water-column denitrification in the expanded oxygen minimum zones (OMZs) during the earliest Visean, whereas lower δ15N values (avg. 2.6‰) during the early to middle Visean indicate a decreasing water column denitrification in the reduced OMZs. Both the organic matter compositions and the relationship between C org /N ratios and δ13C org values indicate a significant contribution of terrestrial OM in the marine sediments, and the low abundance of marine OM is mainly attributed to the low paleoproductivity as evidenced by low P/Ti and Ba/Al ratios. One reason for such a high contribution of TOM is that a large amount of plant debris and wildfire-derived OM was preserved during Tournaisian glacier time and then released and buried rapidly in the marine sediments during the interglacial interval of Visean due to the temperature-driven glacial melting. The rapid transportation of large quantity of TOM from land to ocean may have resulted in remarkable drawdown of atmospheric pCO 2 and subsequent cool climate, as evidenced by the decoupled relationship between δ13C org and δ13C carb values. In summary, the sinking of TOM flux during the sea level lowstand and highstand may be the controlling factor for the paleo-environmental variation as well as OM accumulation in the Visean black shales. • Marine paleoproductivity is low during the Visean interglacial period. • Positive sedimentary δ15N values suggest the existence of water-column denitrification in the OMZs. • Enhanced 13C-enriched TOM input leads to the positive δ13C org excursion in the Visean black shales. • TOM flux may play a significant role in both the paleo-environmental variation and OM accumulation. [ABSTRACT FROM AUTHOR]

Modern acidification by the uptake of anthropogenic CO2 can profoundly affect the physiology of marine organisms and the structure of ocean ecosystems. Centennial-scale global and regional influences of anthropogenic CO2 remain largely unknown due to limited instrumental pH records. Here we present coral boron isotope-inferred pH records for two periods from the South China Sea: AD 1048-1079 and AD 1838-2001. There are no significant pH differences between the first period at the Medieval Warm Period and AD 1830-1870. However, we find anomalous and unprecedented acidification during the 20th century, pacing the observed increase in atmospheric CO2. Moreover, pH value also varies in phase with inter-decadal changes in Asian Winter Monsoon intensity. As the level of atmospheric CO2 keeps rising, the coupling global warming via weakening the winter monsoon intensity could exacerbate acidification of the South China Sea and threaten this expansive shallow water marine ecosystem.