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Locally rapid stratospheric air intrusions facilitate the transport of stratospheric material to the troposphere. Long-term continuous monitoring of such events by traditional techniques, such as sounding technology, is challenging. Beryllium-7 (7Be) and beryllium-10 (10Be) offer an alternative. These isotopes are formed by cosmic rays and are mainly produced in the lower stratosphere and upper troposphere. Due to their similar geochemical properties and substantial difference in half-lives favor relatively high 10Be / 7Be ratios in the stratosphere, as compared to the troposphere. Monitoring surface 10Be / 7Be ratios affords a potential means to identify stratospheric air intrusions. However, high temporal resolution 10Be / 7Be observational records must be taken and corrected for dust-borne 10Be to identify stratospheric air intrusions. In this study, we use Accelerator Mass Spectrometry to measure both 7Be and 10Be in rain and aerosol (down to ~ 200 cubic meters air) with an error of ~ 1.5 %. We correct for dust-borne 10Be using soil Al. This method provides precise measurements with daily resolution. We present annual beryllium isotopes (7Be, 10Be, and 10Be / 7Be ratio) record for the Chinese Loess Plateau that includes several regional sites. We show that for the city of Xi'an, the proportion of dust-borne (resuspended) 10Be was ~24 % in 2020/21. Our results confirm that stratospheric air intrusion events in the Loess Plateau are frequent and rapid throughout the year and are strongest in the spring (March–July), when 10Be / 7Be values were observed to increase about a factor of 3. Even in winter, weaker stratospheric air intrusion events can be detected. Calculated Δ(10Be / 7Be) values in winter suggest stratospheric ozone transport can lead to an ~25 % cumulative increase the surface ozone.

Wildfires play an important role in earth climate systems, with influences on the atmosphere, vegetation distributions, and human survival. Considerable debate persists with regard to the relationship between wildfire occurrence and climate. Some records indicate relatively fewer wildfires during glacial times as compared to the Holocene, while others support the opposite view. These contradictory views need to be resolved to fully understand the relationship and controlling mechanisms that relate biomass burning to climate. In this study, black carbon (BC), including both char and soot, is used to reconstruct wildfire history over the past 32 ka from Qinghai Lake. BC, especially as micrometer-size soot, is mainly transported via the atmosphere, and can carry evidence of wildfires over long distances. Qinghai Lake's position on the northeastern edge of the Tibet Plateau is especially well-suited to such long-distance transport, with a potentially global climatic impact. We observed a significantly positive relationship between char and soot fluxes that suggest that the Qinghai Lake BC record is dominated by material transported through the atmosphere in large-scale wildfires. We find that relatively more wildfires occurred during cold-dry late glacial time (32.8–11.7 ka), and fewer wildfires during the warm-humid Holocene. Our study demonstrates that drought is the key factor that determines wildfire occurrences on an orbital time-scale. These fundamental and persistent patterns can assist in our understanding of climate-wildfire interactions and in the assessment of feedbacks on the global climate system, for example, through the well-known relationship between soluble iron and atmospheric CO2.

The sources and fate of radiocarbon (14C) in the Dead Sea hypersaline solution are evaluated with 14C measurements in organic debris and primary aragonite collected from exposures of the Holocene Ze’elim Formation. The reservoir age (RA) is defined as the difference between the radiocarbon age of the aragonite at time of its precipitation (representing lakeʼs dissolved inorganic carbon [DIC]) and the age of contemporaneous organic debris (representing atmospheric radiocarbon). Evaluation of the data for the past 6000 yr from Dead Sea sediments reveal that the lakeʼs RA decreased from 2890 yr at 6 cal kyr BP to 2300 yr at present. The RA lies at ~2400 yr during the past 3000 yr, when the lake was characterized by continuous deposition of primary aragonite, which implies a continuous supply of freshwater-bicarbonate into the lake. This process reflects the overall stability of the hydrological-climate conditions in the lakeʼs watershed during the late Holocene where bicarbonate originated from dissolution of the surface cover in the watershed that was transported to the Dead Sea by the freshwater runoff. An excellent correlation (R2=0.98) exists between aragonite ages and contemporaneous organic debris, allowing the estimation of ages of various primary deposits where organic debris are not available.

Understanding climate change during the relatively warm Pliocene, as compared to the present, offers significant potential for understanding future global consequences of rising atmospheric CO2. Sensitivity differences among various climate proxies lead to divergent interpretations of the driving mechanisms of inland aridification. Minerals as a paleoclimatic indicator with high water-sensitivity can provide effective support for reconstructing climate evolution and clearly understanding driving mechanisms in extremely arid regions. Here we present results of mineral analyses from lacustrine–fluvial Neogene sediments in the eastern Tarim Basin. Evaporite minerals are composed principally of calcite, dolomite, and gypsum, with minor amounts of ankerite and celestite. Clay minerals are dominated by illite and chlorite. We find that evaporite minerals and illite reflect regional climate change through time, and specifically determine the following: (1) climate in the Tarim Basin during the late Miocene was relatively humid, with alternating dry and wet periods from 6.86~5.58 Ma; (2) immediately following that interval, aridification increased rapidly, with reduced regional precipitation that accelerated the shrinkage of the lake; (3) from 4.4 Ma to 3.62 Ma, regional precipitation increased slightly but afterwards, aridification resumed: the climate there has been extremely dry since about 2.7 Ma. Our results show that the climate in the Tarim Basin has followed a global cooling trend since the late Miocene, and suggest that the effect of uplift in the Tibetan Plateau is a secondary influence.

NSF [EAR1313588]; Taiwan, MOST [107-2116-M-002-001-MY3]; European Union; State of Hungary; European Regional Development Fund [GINOP-2.3.2-15-2016-00009]

We use the carbon content of charcoals from coastal sediments to evaluate the magnitude of alteration, and apply this as a screening criterion for radiocarbon dating. Charcoals with carbon yields

This study presents a proof-of-concept data reduction and analysis protocol that can be applied to the study of polluted sediments. Sediment cores from the Nankan River estuary are used as an example of how the protocol can be employed to quantify temporal heavy metal variability. The measurement protocol produces more detailed elemental profiles than conventional techniques using a combination of data transformation techniques and multivariate analysis. Conventional sediment analyses are used to confirm the robustness of the protocol by comparisons of heavy metal concentrations. X-ray fluorescence (XRF) core scanning provides rapid, high-resolution elemental profiles from sediment cores. The technique relies on a variety of calibration methods (ratio, additive and centred log-ratio) to transform the raw data and reduce bias caused by matrix and closed-sum effects. We further test all these calibration approaches since the transformation process is an essential step for the follow up multivariate analyses. The combination of principal component and cluster analysis objectively assesses the information implicit in the dataset. The settings in each procedure are optimized to account for the variance of the dataset. This optimization protocol explains the heavy metal trends using the sediment characteristics of the cores. Heavy metal pollution is characterized by three periods and classified by their oxidation states. We show that heavy metals have an affinity with fine-grained sediments and Mn. The interpretation is confirmed by grain size analysis and inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. This study provides an impartial, cost- and time-effective protocol suitable for the analysis of other heavy metal polluted sites and further studies using sediment cores as archives.

We report on an initial long-term study of dissolved inorganic and organic carbon (DIC) from Sabino Creek, located in Sabino Canyon, Pima County, Arizona. The purpose of this study was to monitor changes in dissolved radiocarbon (14C) with time and to understand the processes contributing to these variations. Our results span the period 2009–2016 and show a mixing trend between dissolved inorganic and organic carbon modern end-members with an older component. This study provides preliminary information for more detailed research on recycling of organic components in this stream system.

The Ming-Qing transition (MQT) was a watershed in Chinese history. Events in three critical regions—North China Plain (NCP), southern Inner Mongolia (IM), and the Liaodong Peninsula (LP)—paved the way for political change in the latter years of the Ming dynasty. These developments occured in part as a response to climate change. Climate in these regions is controlled by topography and monsoon intensity (summer and winter). Here, we compare historical records with multi-proxy temperature and moisture reconstructions to understand the linkage between climate, the rise of the Manchu, and the collapse of the Ming dynasty and Mongolian steppe. In the last decades of the Ming, both the Ming and Mongolian steppe suffered from the most severe drought and winter cold of the past 500 years. Under the stress of this event, the political and economic systems of the Ming dynasty collapsed, although drought and cooling in the LP were not so intense, due to a maritime effect on climate. This allowed for enhanced precipitation by typhoons, and sustained agricultural development. During this period, the Later Jin (then Qing) seized an opportunity and occupied the LP. Simultaneously, a Manchu-Mongolian alliance formed. They defeated Lindan Khan and conquered North Korea, which removed the military threat from the east. This alleviated the economic pressure imposed by war, and rapid population expansion ensued. Finally, a new dynasty was established in the Central Plains.

Increasing public awareness of anthropogenic CO2 emissions and consequent global change has stimulated the development of pragmatic approaches for the study of shallow-water CO2 vents and seeps as natural laboratories of CO2 perturbations. How CO2 propagates from the emission sites into surrounding environments (ocean and atmosphere), and its effects on seawater carbonate chemistry, have never been studied from a mechanistic perspective. Here, we combine experimental and modeling approaches to investigate the carbonate chemistry of a shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan. A simple Si-based mixing model is used to trace hydrothermal fluid mixing with seawater along convection pathways. The estimated vent fluid component in the near-vent region is generally dissolved inorganic carbon characteristics of the vertical plume as a synergistic interaction between CO 2 gas dissolution and fluid entrainment. The bubble-plume model provides a conservative estimate of the flushing time (tens of minutes) for water in the near-vent region. The acidic, dissolved inorganic carbon-rich water in the lateral buoyant plume readily releases CO2 , but mixing with seawater rapidly quenches its degassing potential, so that hydrothermal carbon is retained in the ocean. Ebullition, governed by initial bubble size distribution, is the key mechanism for vent CO 2 to exit the seawater carbonate system .

The catastrophic demise of the Aral Sea in the late twentieth century has stimulated significant international efforts to understand the geological, hydrological, and climatological controls on lake level at timescales ranging from years to millennia. Here we extend this time range to the Late Pleistocene with sedimentological, chronological and paleontological results from a core that dates from ca. 17.6 kyr cal BP. To our knowledge, this Aral Sea core (B-05-2009) is the oldest directly-dated sediment record with multiple late Pleistocene 14C dates currently available from the region. The core shows that the modern Aral Sea formed at least as early as the end of the Last Glacial Maximum. The main source of water was most likely glacial meltwater from the Tian Shan, Pamir, and other distant mountain systems in the modern day Aral Sea watershed, carried by the Syr Darya and Amu Darya rivers. The Late Pleistocene section of the core contains ostracods and foraminifera throughout, providing evidence that the lake supported life since its inception. Our chronology suggests a relatively high average sedimentation rate at the onset of lake development, and a significant sedimentation hiatus around the time of the Pleistocene/Holocene boundary.

Significance We reconstructed a unique record of soot variations from a classic Chinese loess section that reflects regional-to-continental scale high-intensity fires in central Asia over the entire Quaternary. This study shows cyclicity of wildfire over glacial–interglacial intervals. High-intensity wildfires were more common and dust loads were high during dry and cold glacial periods, implying a synchronous response to climate change. Our study suggests potential linkages among wildfire, mineral dust, marine biogeochemical cycles, atmospheric CO2, and glacial–interglacial climate change. Understanding these connections among earth systems provides insights into climate dynamics during the geological past and may improve predictions for the future., Wildfire can influence climate directly and indirectly, but little is known about the relationships between wildfire and climate during the Quaternary, especially how wildfire patterns varied over glacial–interglacial cycles. Here, we present a high-resolution soot record from the Chinese Loess Plateau; this is a record of large-scale, high-intensity fires over the past 2.6 My. We observed a unique and distinct glacial–interglacial cyclicity of soot over the entire Quaternary Period synchronous with marine δ18O and dust records, which suggests that ice-volume-modulated aridity controlled wildfire occurrences, soot production, and dust fluxes in central Asia. The high-intensity fires were also found to be anticorrelated with global atmospheric CO2 records over the past eight glacial–interglacial cycles, implying a possible connection between the fires, dust, and climate mediated through the iron cycle. The significance of this hypothetical connection remains to be determined, but the relationships revealed in this study hint at the potential importance of wildfire for the global climate system.

The Inner Mongolian Plateau lies along the northern limit reached by the East Asian summer monsoon. This geographic setting makes it especially sensitive to environmental change and an excellent site for understanding Quaternary East Asian monsoon variability. In this study we present new results of hydrogen isotopic compositions of fatty acids extracted from sediments, which were used to construct Holocene paleoprecipitation (or moisture) changes in Northern China. The hydrogen isotopic composition (D/H ratio) of n-acids in the sedimentary sequence of the Duoerji peat, Inner Mongolia, was determined with gas chromatography and mass spectrometry. Changes in the precipitation from middle Inner Mongolia are recorded by the D/H ratio of n-C20, n-C22, n-C24, n-C26, n-C28 acids (δD). From 10–9 ka, the relatively high δD values indicate reduced precipitation in the Early Holocene. Subsequently, increased precipitation is reflected by reduced δD values from 9–5.5 ka. After 5.5 ka, gradually increasing δD values record an overall decrease in precipitation. The precipitation trends established for the Duoerji sequence are consistent with other major paleoclimate proxies in the East Asian monsoon region, especially with a distinct Holocene optimum of increased monsoonal activity from 9–5.5 ka. The δD resulting paleo-precipitation record clearly shows that the Holocene climate in Northern China is basically controlled by the insolation changes.

International audience; This article presents the methods and results regarding the radiocarbon (AMS) dating of the site of Régismont-le-Haut. This site is one of the very few well-preserved Aurignacian open-air sites in southern France. It is also one of the only Aurignacian sites in France and Europe, more generally, to have conserved evident features, including many in situ fire-related structures. We selected charcoal and bone from all the major occupation sectors excavated so far, as well as from others which were important for understanding site formation. Considering difficulties faced when comparing the lithic industry of a site located in a poorly documented area with those belonging to the Aquitaine basin, where the "classical" definition of the Aurignacian was outlined, dating was conducted to accurately place the site within this technocomplex's internal chronology. In total, 19 charcoals (identified to Pinus sp. or gymnosperm) and 3 bones were submitted for AMS radiocarbon dating, each to one of three laboratories. We implemented a strict charcoal screening protocol for radiometric dating that required genus-identified individual charcoals that were well-associated with the fire-related structures. Despite this careful selection , most of the charcoals and all of the bones contained insufficient carbon for dating. Of the 19 charcoal dates attempted, 5 produced dates, from two loci. All fall in the span between the Middle Aurignacian and the Recent Aurignacian (between around 32,500 and 28,000 uncalibrated 14 C BP). An older subset of the dates (32.5-32 ka BP, ca. 37.5-35.5 ka cal BP) appears to be the most reliable. These results represent the first AMS dates ever performed on an Aurignacian open-air site in the Mediterranean area. The dates are compared to other recently dated southwestern France sites to establish which ones might be useful for future detailed archaeological comparisons. They are also instructive from a methodological point of view, in order to better appreciate the resolution of radiocarbon in this context. The focus of this article is on presenting the dating work, especially the protocol used in the selection of samples, the laboratory methods used for obtaining the dates and the challenges faced at this site. Among these, the divergence of dates between loci contrasted with geomorphological and archaeological evidence, with the latter two strongly pointing to one living floor, and either a single occupation or a few very close in time. This forced a reassessment of the chronological dating evidence. This article serves to show the importance of multi-prong approaches to archaeological dating, comparing and contrasting both contextual evidence and actual dates.

We present a history of late Quaternary coastal evolution based on the study of a 41.9-m-long sediment core from the Oujiang Delta. Multiple analytical methods are employed, including sedimentary facies analysis, radiocarbon dating, and the investigations of grain size, elemental, microfossil and pollen compositions. Two transgression-regression sequences, separated by a paleosol layer, are identified. Several lines of evidence indicate that the lower sequence was deposited during the mid-early MIS 3 stage, under a relatively warm and wet climate. An elevated MIS 3 highstand sea level (higher than − 24 m) is observed. The upper sequence was created after the paleosol was flooded during a marine transgression at ~ 9.5 cal kyr BP. Seven weak East Asian Summer Monsoon (EASM) events are identified with central years of ~ 8.4, 7.7, 6.3, 5.7, 4.7, 2.8 and 1.8 cal kyr BP. These coincide with those from the ECS sediment cores and the Dongge Cave δ18O record, indicating that EASM precipitation is a major controlling factor of sedimentation rates in the region. The Oujiang Delta is also subject to typhoon impacts and East Asian winter monsoon (EAWM)-induced coastal currents. Active typhoons and a relatively enhanced EAWM occurred during the weak EASM period between 4.9 and 6.4 cal kyr BP, producing high sedimentation rates in the middle Holocene. We emphasize the high sensitivity of small Asian river deltas as archives of the EASM, EAWM and typhoons. Such environments merit further as a means to understand past changes as well as future responses to projected climatic and sea-level change.

In this study, we used pore water dissolved inorganic carbon (DIC), SO 4 2− , Ca 2+ and Mg 2+ gradients at the sulfate-methane transition zone (SMTZ) to estimate biogeochemical fluxes for cored sediments collected offshore SW Taiwan. Net DIC flux changes (Δ DIC-Prod ) were applied to determine the proportion of sulfate consumption by organic matter oxidation (heterotrophic sulfate reduction) and anaerobic oxidation of methane (AOM), and to determine reliable CH 4 fluxes at the SMTZ. Our results show that SO 4 2− profiles are mainly controlled by AOM rather than heterotrophic sulfate reduction. Refinement of CH 4 flux estimates enhance our understanding of methane abundance from deep carbon reservoirs to the SMTZ. Concentrations of chloride (Cl − ), bromide (Br − ) and iodide (I − ) dissolved in pore water were used to identify potential sources that control fluid compositions and the behavior of dissolved ions. Constant Cl − concentrations throughout ∼30 m sediment suggest no influence of gas hydrates for the compositions within the core. Bromide (Br − ) and Iodine (I − ) concentrations increase with sediment depth. The I − /Br − ratio appears to reflect organic matter degradation. SO 4 2− concentrations decrease with sediment depth at a constant rate, and sediment depth profiles of Br − and I − concentrations suggests diffusion as the main transport mechanism. Therefore diffusive flux calculations are reasonable. Coring sites with high CH 4 fluxes are more common in the accretionary wedge, amongst thrust faults and fractures, than in the passive continental margin offshore southwestern Taiwan. AOM reactions are a major sink for CH 4 passing upward through the SMTZ and prevent high methane fluxes in the water column and to the atmosphere.

Chenier plain and mudflat development in the South Flank of the Yangtze Delta are examined by multi-disciplinary methods over different spatiotemporal scales and changing human-earth interactions. The study site contains a narrow belt of elongated ridge complexes that formed along the sediment-deficient open coast from 6500 to 4000 yr BP. Since then and until the past two decades, shoreline progradation has accelerated due to increasing sediment supply, fueling rapid deltaic expansion. Superimposed on this trend are a series of discrete sand-dominated ridges deposited during several stormy intervals. Tidal flat development is regulated by complex estuarine processes. Short-term morphodynamic variations at the site are caused by the alternations of tides and waves, while intermediate morphodynamic variations are controlled by the multi-decadal shifting of river stem channel and stormy climates. The ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level. Technological developments during the last ~ 2000 years are exemplified by seawall construction against sea flooding, marking a transition from passive to active. Dike construction has been used more frequently and intensively to reclaim land since the 1970s, in support of the booming socioeconomic development in the region. Lessons from complex morphodynamic change and human-earth interactions in the Southern Yangtze Delta admonish us to not reclaim coastal wetland by lower-flat enclosures (constructing new dikes near the low waterline), while an optimal alternative would be to implement upper-flat enclosures (constructing new dikes around the high waterline) on the continuously accretionary tidal flats, with auxiliary biological restoration engineering, to satisfy both socioeconomic development and sustainable wetland conservancy.

The authors present a time series of tree-ring cellulose stable oxygen isotope ratios (δ18O) constructed using a numerical mixing method, from five Pinus tabulaeformis from Yaoshan, eastern central China. The time series is synchronous with the observed April-to-September precipitation δ18O time series records from surrounding stations, implying that the tree-ring δ18O signals reflect Asian summer monsoon-related precipitation. Moreover, significant correlations were detected between the tree-ring δ18O records and central-eastern Pacific sea surface temperature (SSTs)/Asian summer monsoon indices. This suggests that the Yaoshan tree-ring δ18O time series offers a promising means to study past Asian summer monsoons and ENSO variability. The time series is significantly correlated with the mean relative humidity from April to September (RHAS) (r=-0.638, n=52, p

The transition between sedimentary environments is compressed along land-sea boundaries in space and time. At river mouths on high standing islands, sedimentary records with high temporal resolutions formed as a result of large sediment loads and pervasive post-glacial sea level rise. Here we report on sediment core records covering the late Quaternary from the mouth of a small mountainous river in Taiwan. Results show that the study site was initially terrestrial under fluvial control. Beginning at about 10,000 yr BP (before present) the site became inundated by the rising sea and the environmental facies transitioned from a floodplain/incised river valley to a succession of marine environments, from shoreface to offshore. As the rising sea level came to a pause at 6000 yr BP, fluvial processes became dominant and sediments began to aggrade at the river mouth. After 4500 yr BP, the accumulated sediment began to prograde seaward, taking on the form of a river delta, and subtidal sand ridges appeared in the nearshore. This also introduces the deltaic development, which was limited by topography of the receiving basin. The chronology expresses the duel between sea level and fluvial processes that determined the depositional environments along the land-sea boundary at the study site.

Radiocarbon (14C) has been widely used for quantification of fossil fuel CO2 (CO2ff) in the atmosphere and for ecosystem source partitioning studies. The strength of the technique lies in the intrinsic differences between the 14C signature of fossil fuels and other sources. In past studies, the 14C content of CO2 derived from plants has been equated with the 14C content of the atmosphere. Carbon isotopic fractionation mechanisms vary among plants however, and experimental study on fractionation associated with dark respiration is lacking. Here we present accelerator mass spectrometry (AMS) radiocarbon results of CO2 respired from 21 plants using a lab-incubation method and associated bulk organic matter. From the respired CO2 we determine Δ14Cres values, and from the bulk organic matter we determine Δ14Cbom values. A significant difference between Δ14Cres and Δ14Cbom (P

In this article, we present a study of seawater 129I/127I time-series data from several coastal sites in Taiwan, including Yehliu Geopark (north–northeast coast), Kaohsiung (southwest coast), and Zhuwei Fishing Village (northwest coast). The objective of this study was to document how 129I/127I responds to known seasonal variations in the surface ocean currents that carry 129I to each of these sites. The responses were shown to be quite distinct. The Zhuwei site, across Mainland China, had elevated spring and summer 129I/127I values, with abrupt peaks that reflected transient cross-strait currents that carry seawater with elevated 129I to the northwest coast of Taiwan. The Yehliu site, which receives all of its seawater from the Kuroshio Current, had relatively low and uniform 129I/127I values year-round. The Kaohsiung site showed a summertime minimum that likely stems from upwelling upstream induced by oceanic eddies associated with the Kuroshio intrusion. To our knowledge, these are the first continuous coastal 129I/127I time-series data published for Asian waters and the first to show large, abrupt, and regional 129I/127I changes in the surface seawater. We also documented 129I/127I values from multiple surface ocean sites in the South China Sea (SCS), including a vertical profile from the South East Asia Time-Series Station that extends to a depth of 3,700 m. The 129I from both coastal Taiwan and surface waters of the SCS is >98% anthropogenic, primarily released to the environment as a byproduct of nuclear fuel reprocessing.

Radiocarbon (C) is a useful tracer for surface ocean circulation and mixing, which reflects air-sea CO exchange. We present radiocarbon marine reservoir ages (R) and corrections (ΔR) in Holoc...

Radionuclides from the Fukushima Daiichi Nuclear Power Plant were released directly into the ocean as a result of the Great East Japan Earthquake on March 11, 2011. This material became entrained in surface ocean currents and subsequently transported for great distances. In June 2011, a few months after the disaster, we began a surface ocean

Organic and inorganic carbon reservoirs are investigated in surface and groundwater in the semi to hyper-arid Rio Loa Basin in Northern Chile. Part of the study area is within the Andean volcanic arc, and volcanism is responsible for large inputs of 14C-depleted CO2 which hampers groundwater residence time estimations using dissolved inorganic carbon (DIC). To better understand the area’s carbon system, we investigated 14C and δ13C in dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in groundwater and surface water. DOC concentrations are low in all water samples analyzed, 16–53 μM. Fluorescence and δ13C measurements on DOC indicate that dissolved organic matter (DOM) entering groundwater has characteristics of humic compounds derived from terrestrial plants in the recharge area. Fluorescence is lost in groundwater in the lower part of the system due to microbial or abiotic degradation. Changes in 14CDOC and δ13CDOC also indicate that microbial activity contributes to DOC, possibly from geogenic CO2. While the range of 14CDIC is very large, 1.6 to >50 pmC, that of 14CDOC is restricted between 53 and 72 pmC. We estimated C residence times in the volcanic arc, based on corrected 14CDOC, are

Lockdown measures to control the spread of the novel coronavirus disease (COVID-19) sharply limited energy consumption and carbon emissions. The lockdown effect on carbon emissions has been studied by many researchers using statistical approaches. However, the lockdown effect on atmospheric carbon dioxide (CO2) on an urban scale remains unclear. Here we present CO2 concentration and carbon isotopic (δ13C) measurements to assess the impact of COVID-19 control measures on atmospheric CO2 in Xi'an, China. We find that CO2 concentrations during the lockdown period were 7.5% lower than during the normal period (prior to the Spring Festival, Jan 25 to Feb 4, 2020). The observed CO2 excess (total CO2 minus background CO2) during the lockdown period was 52.3% lower than that during the normal period, and 35.7% lower than the estimated CO2 excess with the effect of weather removed. A Keeling plot shows that in contrast CO2 concentrations and δ13C were weakly correlated (R2 = 0.18) during the lockdown period, reflecting a change in CO2 sources imposed by the curtailment of traffic and industrial emissions. Our study also show that the sharp reduction in atmospheric CO2 during lockdown were short-lived, and returned to normal levels within months after lockdown measures were lifted.

Historical records for the Mu Us Desert margin during the Ming dynasty (1368–1644) and corresponding high-resolution climate proxy records have prompted studies on societal responses to climatic changes in this region. The Mu Us Desert margin is highly sensitive to changes in desertification and biological productivity controlled in part by Asian monsoon variations. Here the existing historical temperature and precipitation records are examined to understand spatiotemporal climate variations and to identify potential mechanisms that have driven desertification in the region over the past 500 years. The focus here is on three severe desertification events that occurred in 1529–46, the 1570s, and 1601–50. The relationships among temperature, precipitation, and desertification indicate that a cold/drought-prone climate drives the desertification process. During the Ming dynasty, this region was one of nine important military districts, where the frontier wall (the Great Wall) and other fortifications were constructed. To maintain the defense system, military officers made a valiant effort to decrease the influence of desertification. However, the human-waged war against nature was largely futile, and local rebellions in the stricken region were spawned by the inability of the government to cope with the severe environmental stresses associated with rapid desertification.

The long-lived radionuclide 129 I (half-life: 15.7 × 10 6 yr) is well-known as a useful environmental tracer. At present, the global 129 I in surface water is about 1–2 orders of magnitude higher than pre-1960 levels. Since the 1990s, anthropogenic 129 I produced from industrial nuclear fuels reprocessing plants has been the primary source of 129 I in marine surface waters of the Atlantic and around the globe. Here we present four coral 129 I time series records from: 1) Con Dao and 2) Xisha Islands, the South China Sea, 3) Rabaul, Papua New Guinea and 4) Guam. The Con Dao coral 129 I record features a sudden increase in 129 I in 1959. The Xisha coral shows similar peak values for 129 I as the Con Dao coral, punctuated by distinct low values, likely due to the upwelling in the central South China Sea. The Rabaul coral features much more gradual 129 I increases in the 1970s, similar to a published record from the Solomon Islands. The Guam coral 129 I record contains the largest measured values for any site, with two large peaks, in 1955 and 1959. Nuclear weapons testing was the primary 129 I source in the Western Pacific in the latter part of the 20th Century, notably from testing in the Marshall Islands. The Guam 1955 peak and Con Dao 1959 increases are likely from the 1954 Castle Bravo test, and the Operation Hardtack I test is the most likely source of the 1959 peak observed at Guam. Radiogenic iodine found in coral was carried primarily through surface ocean currents. The coral 129 I time series data provide a broad picture of the surface distribution and depth penetration of 129 I in the Pacific Ocean over the past 60 years.

We report here on a previously unpublished sediment core from Qinghai Lake, China, that preserves a continuous record of sedimentation for the past 40 ka. A striking feature of the record is a set of distinct meltwater events recorded at 35, 19 and 14 ka respectively. These events are manifest as distinct pulses of relatively old organic radiocarbon in the sediments. We interpret these as a signal of glacial melting in the Qinghai Lake watershed. The meltwater signals are closely correlated to temperature and precipitation records associated with deglaciation. The events at 19 ka and 14 ka correspond to well-established high latitude Melt Water Pulse (MWP) events during Marine Isotope Stage (MIS) 2, and the 35 ka event corresponds to a period of pervasive high lake levels in western China during late MIS 3. We interpret these anomalous dates as the result of relatively old carbon that was destabilized by the glaciers, and released into the lake as the glaciers melted. The data indicate that this process takes thousands of years. We expect that the approach employed here to identify these events is generally applicable to any lake system with a significant glacial meltwater component.

Radiocarbon has been widely used in determining the age of various geological materials and events. The validity of ages, particularly for sediments, has often been questioned due to the incorporation of carbon-bearing components with different abundances of 13 C and 14 C. This study examines carbon contained in clay minerals (kaolinite, illite and illite-smectite) extracted by temperature-stepped combustion experiments, ranging from 350 °C to 1100 °C. Distinct carbon components were identified in the samples using both their 13 C and 14 C contents. Two carbon end-members were observed for all of the clay minerals: a low temperature component ( 13 C and enriched in 14 C; and a high temperature component (>550 °C), relatively enriched in 13 C and depleted in 14 C. The high temperature carbon component is relatively old and not released until the clay is completely oxidized. This observation suggests that this carbon was incorporated into the clay mineral when it first formed by weathering. We applied the same procedure to sediments collected from terraces along the Kueichung River, in southwestern Taiwan, sieved to

The study presents a summary of the latest data on ostracod microfaunas from Middle–Upper Holocene lacustrine deposits of southern West Siberia collected from lakes Malye Chany, Bol’shaya Lozhka, Beloe, and paleolake Chicha. A total of 28 ostracod species were identified. The identified ostracod assemblages reveal local variations in the lake ecosystems as well as general trends, which can be correlated with both regional and global climate changes. A cooling episode during the second half of the Subboreal is marked by the transition from a warm-water mesohaline assemblage to cold-water candonid ostracods at ca. 3.4 cal ka BP. The widespread occurrence of mesopolythermophilic ostracod species at 1.9–0.6 cal ka BP indicates the end of cooling and lowering of lake-water level. From 0.6 cal ka BP to present, the ostracod assemblages area characterized by the high specific diversity, which is probably an indication of the increased variability of aquatic ecosystems due to fluctuations in salinity and water levels of the lakes. Climate changes identified by ostracod assemblages are consistent with the climatic trend constrained by early palynological studies.

Paleoclimate change research routinely takes advantage of a variety of climate proxies. Each proxy responds to climate in its own way and a combination of proxies offers the best means of understanding past climate at a given site. Here we present iodine variation patterns in one classical loess-paleosol sequence in the Chinese Loess Plateau to develop a new proxy that responds to climate-induced changes in the source availability, transport dynamics and depositional environment of iodine. Our iodine variation provides a continuous record for the past ∼260 kyr, and is highly correlated with traditional climate proxies, including magnetic susceptibility, mean grain size and organic matter content. We attributed the variations of the iodine record to past climate changes particularly in aspects of coupled air-sea circulation, transport dynamics, and depositional retention on the Chinese Loess Plateau. We propose that geochemistry of iodine variation provides a new tool for assessing paleoclimate changes in aspects of large-scale air-sea circulation mechanism, global iodine transport dynamics, and depositional environment as particular enrichment factors in the Chinese Loess Plateau.

This study used dissolved organic carbon (DOC) carbon-14 (14C) to determine groundwater ages that were then used to calculate groundwater travel times in southern Nevada aquifers that have low organic content. These travel times are compared with the more standard dissolved inorganic (DIC) 14C method for determining groundwater ages and travel times. Groundwater travel times for aquifers in southern Nevada using DOC 14C are thousands of years shorter than DIC 14C travel times for groundwater flow outside of recharge areas along four of the five flow paths evaluated for this study. The DOC 14C travel times range from 2,300 to 2,900 years (yrs) as compared to DIC 14C travel times that range from 8,200 to 22,000 yrs (uncorrected ages) and 4,700 to 19,000 yrs (corrected ages). The DOC 14C groundwater travel times in carbonate-rock and volcanic-rock aquifers of southern Nevada are similar to travel times determined from: (1) hydrogeologic data; (2) observations of rapid high-level tritium transport at the Nevada National Security Site; and (3) 550,000-yr δ18O and δ13C global climate records for calcite precipitated in Devils Hole, Nevada at the end of one of the flow paths. DOC 14C travel time calculations need to account for fewer processes than DIC 14C for aquifers that contain little organic matter and do not have redox reactions. DOC 14C travel-times can be calculated directly from the DOC 14C data in these aquifers without corrections if dissolution of organic carbon and sorption and matrix diffusion of DOC 14C onto or into the aquifer matrix is minimal. Laboratory experiments showed that little organic carbon was being leached from aquifer rocks, sorption of organic carbon ranged from 4.3% sorbed in carbonate rocks to 0.5% sorbed in volcanic rocks, and matrix diffusion coefficients were slower in lower porosity carbonate rocks (1.7 × 10−7 cm2/s) than in higher porosity volcanic rocks (2.9 × 10−7 cm2/s). The lack of dissolution of organic carbon in study area aquifers is also supported by the decrease in DOC along flow paths and the DOC composition of groundwater changing little as groundwater flows from recharge areas into the adjacent valleys. In contrast, DIC 14C groundwater travel-time calculations must be corrected for complex chemical reactions and physical processes, including mineral/gas dissolution, mineral/gas precipitation/exsolution, cation exchange, and carbon isotopic exchange that can significantly change the amount of DIC 14C in groundwater along flow paths by processes other than radioactive decay. DIC 14C can also be affected by sorption and matrix diffusion, but these processes may, or may not, be captured in geochemical modeling of precipitation/dissolution and carbon isotopic exchange reactions. Corrected DIC 14C ages, therefore, represent maximum ages.

China is an important fossil fuel CO2 (CO2ff) emitter and the international community is thus concerned with quantifying reductions in Chinese carbon emissions in the recent past. Compared to traditional statistical method, radiocarbon (14C) offers a different approach to quantify atmospheric CO2 derived from fossil fuel emissions. Here, we carry out a multi-year (2011–2016) CO2ff tracing by 14C in Xi'an, and a three-year (2014–2016) CO2ff tracing in 15 Chinese cities. The Xi'an results show that average CO2ff concentrations fell 35.9 ± 6.6% from 2014– 2016, compared to 2011–2013, and the timing of this decrease coincides with the implementation of nationwide carbon reduction measures in China, known as the Action Plan on Prevention and Control of Air Pollution. A WRF-Chem forward modeling simulation reveals that the CO2ff in Xi'an is mainly derived from local sources, and a source apportionment combined stable-carbon isotope showed that the CO2ff in this city is dominated by coal combustion (72.6 ± 10.4%). Strong CO2ff differences are found between January and July in most Chinese cities. High CO2ff concentrations often correspond to severe haze episodes and there are generally positive correlations between CO2ff and fine particulate (PM2.5) concentrations. Our study provides scientific data to understand the effects of CO2ff reduction strategies in China that can be applied to other countries as well.

In the absence of reliable charcoal, wood or plant macrofossils, organic matter in loess-paleosols is often used for 14C dating. However, organic matter can be contaminated by a variety of carbon sources within the sediments, and this may affect the radiocarbon dating results. Specific chemical pretreatments can be applied to minimize such effects, and comparisons with optically stimulated luminescence (OSL) dates from the same sediments allows us to assess potential open system effects on organic matter. Here we present comparisons of the two geochronometers from loess-paleosol deposits in the Chinese Loess Plateau. Our results show that loess -paleosol samples from the past 25 cal kyr BP generally yield reliable 14C dates, however, beyond this range, specifically ~25–59 cal kyr BP, we observe a steady increase in OSL ages with depth, but no consistent increase in corresponding AMS 14C ages. We suggest that relatively old samples from loess-paleosols should be studied using techniques such as compound-specific radiocarbon dating, ramped pyrolysis or stepped-temperature combustion.

Accelerator mass spectrometry (AMS) is the most sensitive method for measuring 129I in environmental samples available today, with a detection limit of about 10–15 for 129I/127I. A drawback of the technique is the time-consuming chemical separation required to prepare AMS targets from raw samples. This step significantly limits applications requiring rapid analyses and large numbers of samples, for example, in monitoring studies associated with nuclear accidents. This work introduces a direct method for 129I measurements by AMS that does not require chemical separation. In this approach, stable iodine (127I) is added to a matrix of niobium (Nb) powder and mixed with dried raw sample. This mixture is pressed directly into a sputter target for AMS analysis. Two types of environmental samples have been tested in this work, seaweed and sediment. No anomalous behavior was noted in the Cs+ sputtering behavior of the targets prepared from these materials. The 129I/127I ratios and 129I concentrations measured by this rapid method were found to be in agreement with reported values that used a conventional AMS method for the same material. Based on our findings, we expect that such rapid measurements can be applied to a wide variety of materials, in addition to seaweed and sediment, as long as the sputtering-induced adverse effects do not prevent the stable operation of the ion source. The method is especially useful for screening large numbers of samples before more precise analyses are made.

The formation, evolution, and potential as a climate archive of Tienchi Pond was evaluated using geomorphology, sedimentology, geochemistry, and AMS radiocarbon measurements of tree ring cores. Tienchi Pond is a small ephemeral lake situated on the subtropical Lanyu Island in the Western Pacific Ocean about 90 km east of southern Taiwan. The lake is situated on a mountain ridge and is today characterized by numerous dead trees and stumps. The position at the boundary between the two main components of the SE Asian monsoon system, the Asian landmass and the Western Pacific, makes this lake particularly interesting as a potential natural climate archive. Since previous studies have shown that the bedrock underlying the lake formed over 2 my ago, a volcanic crater origin was ruled out. Rather, element ratios of K/Ti and Ca/Fe together with 210 Pb dating suggest a recent origin for the lake, probably as the result of a natural damming event in the southern, narrower, part of the lake basin, or as a result of increased precipitation at the end of the Little Ice Age (or a combination of both). Radiocarbon measurements on a dead tree near the lake perimeter show 14 C levels of more than 1.7% modern radiocarbon near the bark, suggesting that the tree died in the early 1970s. In contrast, by correlating a large number of radiocarbon measurements to a northern hemisphere reference curve, it was shown that trees closer to the center of the lake died in the early 20th century. This agrees with a scenario where a small lake formed by initial damming, and gradually grew larger through erosion of the surrounding shore lines caused by rapid lake level oscillations.

The vast majority of known archaeological sites in arid Northeast Asia are surface assemblages containing few or no organic remains. The lack of stratified sites and a relative absence of organic remains in surface assemblages hinders our ability to date sites, create local chronologies, and contextualize technological and socio-economic change. Such problems are common in arid regions around the world. New radiocarbon and luminescence dates on collections from the Gobi Desert of Mongolia and China are used here to assess the potential for direct dating of commonly occurring artefacts like ostrich eggshell and pottery. Direct dating also allows for the identification and sorting of mixed-age assemblages. Here, we compare dates derived from Accelerator Mass Spectrometry (AMS) on ostrich eggshell, AMS on pottery, and luminescence on pottery. Our findings show that AMS and luminescence are highly complementary methods and produce results consistent with expected archaeological ages, while ostrich eggshell dates were older than the associated site assemblages.

Reconstructed coral skeletal Pb : Ca and Ba : Ca ratios from the Northern Coast of Lanyu Islet are shown to be sensitive indicators of land–use practices which took place on the islet during the past 30 years. Coral skeletal Pb : Ca and Ba : Ca both increased dramatically. Pb : Ca ratios are very sensitive to biomass burning on Lanyu Islet while Ba : Ca generally respond to rainfall variations except in case of instantaneous flooding. The method presented here provides a quantitative technique for identifying human effects that can be used for coastal land management and offers a way to study the environment during prehistoric times, where no written records are available.

This article discusses the magnitude and rate of change of radiocarbon reservoir ages from the surface ocean in the South Pacific during the Holocene. 14C reservoir ages are calculated from paired U/Th and 14C measurements. Seventeen pairs of coral dates were determined from samples collected on Rendova and Tetepare Islands, in the Solomon Islands, and from Espiritu Santo Island, Vanuatu. The samples are all Holocene in age, with 230Th ages ranging from about 400 to 9400 BP. Samples were collected as drill cores or surface outcrops. About half of the surface samples appear to have incorporated modern carbon through postdepositional recrystallization. Two of the core samples were also affected by carbon exchange. The Holocene 14C reservoir ages observed in this data set show stable values for the last 3000 yr, and substantial variability from 5000–6000 BP (~100 to ~950 14C yr). Persistent low values (14C yr) were observed for samples from 7000–8000 BP. We attribute these variations to temporal changes in lateral advection and vertical mixing, and possibly to local environmental conditions related to the interplay between sea-level rise and episodic uplift, characteristic of all the coral localities.

We propose an improved method for precise sulfur isotopic measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in conjunction with a membrane desolvation nebulization system. The problems of sulfur loss through the membrane desolvation apparatus are carefully quantified and resolved. The method overcomes low intrinsic sulfur transmission through the instrument, which was initially 1% when operating at a desolvation temperature of 160 °C. Sulfur loss through the membrane desolvation apparatus was resolved by doping with sodium. A Na/S ratio of 2 mol mol −1 produced sulfur transmissions with 98% recovery. Samples of 3 nmol (100 ng) sulfur achieved an external precision of ±0.18‰ (2 SD) for δ 34 S and ±0.10‰ (2 SD) for Δ 33 S (uppercase delta expresses the extent of mass-independent isotopic fractionation). Measurements made on certified reference materials and in-house standards demonstrate analytical accuracy and reproducibility. We applied the method to examine microbial-induced sulfur transformation in marine sediment pore waters from the sulfate-methane transition zone. The technique is quite versatile, and can be applied to a range of materials, including natural waters and minerals.

We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950–3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2.

The calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high-resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5–10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774–775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt ~ 15‰ 14C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible.