Indian monsoon variability on millennial-orbital timescales

The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ18O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ18O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales

East Asian hydroclimate modulated by the position of the westerlies during Termination I.

Speleothem oxygen isotope records have revolutionized our understanding of the paleo East Asian monsoon, yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes. We report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle Yangtze region, which indicates a wetter central eastern China during North Atlantic cooling episodes, despite the oxygen isotopic record suggesting a weaker monsoon. We show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the Meiyu rains and shortened post-Meiyu stage, in accordance with a recent hypothesis. Model simulations support this interpretation and further reveal the role of the westerlies in communicating the North Atlantic influence to the East Asian climate

Macrophages depletion alleviates lung injury by modulating AKT3/GXP4 following ventilator associated pneumonia

BackgroundAKT3 appears to play a role in lung cancer. However, its role in ventilator-associated pneumonia is still unclear. Therefore, this study aimed to investigate the role of AKT3 in macrophages during ventilator-associated pneumonia.MethodsThe mRNA level of AKT3, Data from The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), The data is analyzed using the Xiantao academic analysis tool. Additionally, the roles of AKT3 in ventilator-associated pneumonia (VAP) were investigated through in vivo experiments.ResultsAKT3 was differentially expressed in various normal and tumor tissues. Functional enrichment analysis indicated the immunomodulatory function and inflammatory response of AKT3 in lung cancer. Depletion of macrophages protected against lung epithelial cells and significantly decreased MMP9, MMP19, FTH, and FTL expression levels and increased GPX4 expression levels, while partially reversing the changes in macrophage. Mechanistically, macrophage depletion attenuates ferroptosis of lung epithelial cells by modulating AKT3 following VAP.ConclusionCollectively, this study suggests the need for further validation of the immunoregulatory function of AKT3 in lung cancer. Additionally, macrophage depletion mitigates lung injury by modulating the AKT3/GPX4 pathway in the context of VAP

Climatic controls on travertine deposition in southern Tibet during the late Quaternary

Large volumes of travertine deposits are preserved at hydrothermal spring sites on the Tibetan Plateau (TP). Yet, most of these deposits are under-researched with respect to their diagenetic and depositional history and there is still very limited understanding of the tectonic and climatic influences on travertine precipitation in the arid high-altitude setting of Tibet. In this study, a detailed uranium-series dating campaign was carried out for the Qiusang travertine (similar to 4270 m above sea level), southern Tibet that has been previously dated back to 486 thousand years ago (ka). Based on 42 new Th-230/U ages, combined with geomorphological and sedimentological investigations, several travertine zones were identified and distinct travertine depositional phases constrained: 11.7-6.8 ka and similar to 13.4 ka (zone 1), 128-122 ka (zone 2),-193 ka (zone 3),similar to 292 ka and 324 ka (zone 4), > 317 ka (zone 5), ca. 415 to 470 ka (zone 6) and ca. 419 to 445 ka (zone 7). Comparison of these depositional phases with local and regional proxy records suggests that travertine accumulation at Qiusang occurred during main interglacials when monsoon precipitation peaked on the TP. This coincidence, together with a sensitive response of Tibetan hydrothermal spring activity to meteoric recharge, implies that climate controls the precipitation of large travertine volumes on orbital timescales on the plateau. We propose that (i) tectonic activity is of subor-dinate importance and influences travertine precipitation on the TP only episodically and on significantly shorter (i.e. centennial to millennial) timescales related to the recurrence rates of large earthquakes and that (ii) intensive monsoonal-driven groundwater recharge is required on top of tectonic activity for generating volu-metrically significant travertine accumulations. Because of the high precipitation rates typical for hydrothermal spring carbonates, we conclude that travertine deposits on the TP could be utilized as valuable high-resolution proxy records of peak monsoon conditions in the currently arid to semi-arid landscape.& nbsp;Furthermore, the Qiusang travertine zone 7 is terraced and the travertine layers adjusted to a paleo-riverbed elevation similar to 30 m above the current river, allowing us to constrain fluvial incision to-0.07 m/ka for the south -central sector of the TP since the Mid-Pleistocene. The abundant travertine occurrences in Tibet in combination with uranium-series dating can thus also provide detailed insights into earth surface dynamics and landscape evolution on the world highest plateau

Did An Extensive Forest Ever Develop on the Chinese Loess Plateau During the Past 130 Ka?: A Test Using Soil Carbon Isotopic Signatures

Pleistocene vegetation history on the Chinese Loess Plateau has been traditionally investigated using palynological methods, and questions remain regarding whether an extensive broadleaf deciduous forest ever developed on the loess table under favorable climatic conditions. The authors have employed a C isotope approach to address this question by comparing δ13C values in soil organic matter from different loess ecological domains with known source vegetation to the C isotope values obtained from a paleosol section that can be dated back to 130 ka. The C isotopic compositions of modern soils from the loess table and the loess–desert transition gave δ13C values of −24.5‰ to −18.2‰ and −25.7‰ to −20.7‰, respectively. These C isotopic ratios are consistent with the standing modern vegetation that is dominated by a mixture of C3 and C4 plants and can be distinguished from that in the patchy forest areas where exclusive C3 trees yield a narrow δ13C value range from −26.9‰ to −25‰ (average −26.1‰). Obtained δ13C compositions from paleosols and loess sediments in the Lantian and the Luochuan profiles vary from −24‰ to −16.9‰, indicating a grass dominated steppe with shifting C3 and C4 contributions controlled mainly by paleoclimatic changes during the late Pleistocene. The present results suggest no extensive forest coverage on the loess table during the past 130 ka even under the most suitable conditions for forest development. This conclusion supports the explanation of natural causes for the development of only patchy forests on the modern loess table and provides critical historical information toward the vegetation restoration project that is currently underway on the Chinese Loess Plateau

Distribution Characteristics and Influencing Factors of Uranium Isotopes in Saline Lake Waters in the Northeast of Qaidam Basin

Four saline lakes in the northeast of Qaidam Basin were selected to explore the distribution characteristics and influencing factors of uranium isotopes in lake waters with high evaporation background. The U-238 concentration and the activity ratios of U-234/U-238 ([U-234/U-238](AR)) showed that there was no significant change in the same lake, but there was a certain degree of difference in the distribution between different lakes. We found that aqueous U-238 concentration within a certain range increased with an increase in TDS (total dissolved solid) and salinity, as was also the case with pH. As in natural waters, the pH affects the speciation of U-238, but TDS and salinity affect the adsorption process of aqueous U-238. Further, the replenishment of water will also affect the uranium isotope concentration for lakes, but it is not the main influencing factor for saline lakes. Therefore, we suggest that pH is the dominant factor affecting changes in aqueous U-238 concentration of the sampled saline lakes. The [U-234/U-238](AR) in these saline lakes are closely related to the input water and the associated water-rock interactions involving sediments, atmosphere dust, and organic material, etc. during the evolution stage, metamorphous degree, and hydrochemistry of the saline lakes. Lake water samples collected in the maximum and minimum discharge water period, were used to evaluate the seasonal distribution characteristics of aqueous U-238, and we found that U-238 concentration did not show an evident change with the seasons in these saline lakes. If the U-238 concentration and [U-234/U-238](AR) can remain consistent during a period of time, then the sediment ages and/or sedimentation rates could be determined by lake sediment and/or biogenic carbonate in future, thus allowing for the accurate reconstruction of the paleoclimate and paleoenvironment

Preparation of high-precision CO2 with known triple oxygen isotope for oxygen isotope analysis

The objective of this work is to propose a more effective way to prepare an in-house CO2 with known triple oxygen isotope compositions. The major experimental steps include: (1) the O-2 is combusted to CO2 on a graphite rod at 750 degrees C with Pt-catalyst for 3-4 min; and (2) converted CO2 is subsequently purified by two cryogenic traps. The results show high reproducibility of delta C-13 and delta O-18 values of the converted CO2 within 0.010-0.020 parts per thousand and 0.006-0.010 parts per thousand (1 sigma, SD), and the identical delta O-18 value within error with that of the original O-2. Additionally, we have measured the triple oxygen isotope compositions of converted CO2 using an O-2-CO2 Pt-catalyzed oxygen-isotope equilibration method. The measured delta O-17 values of CO2 show high reproducibility within 0.006 parts per thousand (1 sigma, SD), and are identical within error with the original O-2 as well. Notably, our experiments also found that the O-2 with heavier oxygen isotope ratios (delta O-18 > 40 parts per thousand, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O-2 to CO and CO to CO2, may explain the observed lower O-17/O-16 and O-18/O-16 ratios of the converted CO2 relative to the original O-2

Geochemical and isotopic (U, Th) variations in lake waters in the Qinghai Lake Basin, Northeast Qinghai-Tibet Plateau, China: origin and paleoenvironmental implications

A uranium (U) geochemical study of lake water samples from Qinghai Lake, Northeast Qinghai-Tibet Plateau, China, was undertaken to assess the primary controls on lake water chemistry. The U-234/U-238 activity ratios of lake water exhibited limited spatial and vertical variations and were relatively high compared to the values measured in rivers worldwide ((U-234/U-238)=1.171), lower than in the four river discharge inside the Lake Qinghai catchment. The U concentrations also varied minimally within three vertical sampling profiles and exhibited spatial patterns in surface waters that correlated with the distribution of total dissolved solid (TDS) values and salinity concentrations. These data suggest that the variability in U, TDS, and salinity are partially controlled by evaporation or a different secondary concentration pathway. Moreover, the U concentration and U-234/U-238 activity ratio indicates that the length of this procedure, which is controlled by the duration of water-rock interaction, is probably an important factor to consider when accounting for the variable salinities of lakes located in similar geographical areas. The Th-230(XS) content is primarily derived from the decay of dissolved U-234. The various (230)Thxs concentrations observed in the water column are interpreted to reflect various scavenging residence times in Qinghai Lake, ranging from 0.7 to 4years. The lower water mass age, such as at site 123, suggests a more rapid scavenging rate. Dissolved Th-232 is placed into the lake via the incomplete dissolution of lithogenic substances, such as dust aerosol, or other lithogenic sources (e.g., lake bed sediment or suspended riverine sediment). Water column Th-232 concentration data suggest that the Th concentrations of the lake water are controlled by three processes: (1) the dissolution of aerosol dust, (2) the dissolution of riverine and lake bed sediment, and (3) the scavenging of Th from the water

Mapping and U Th dating of the world's deepest blue hole (South China Sea): Implications for its timing, possible volcanogenic origin, and Pleistocene eolianites in the Xisha Islands

International audienceThe Sansha Yongle Blue Hole (SYBH) is the deepest (301.19 m) blue hole known in the world and is a water-filled karst opening in the intertidal reef flats of the eastern Yongle Atoll, Xisha Islands, South China Sea. It is differentiated from the surrounding environment by its deep blue colour as observed when viewed from above. The SYBH exhibits extremely rare karst networks and speleothems and differs from the blue holes of the Bahamas and Bermuda, indicating a different development process. Here, we present the morphology and Usingle bondTh ages of the SYBH, which document the evolution of the coastal cave over time. Morphology and lithostratigraphy indicate that the hole resulted from dissolution via ascending acidic water/gas followed by subsequent collapse. The adjacent volcanoes surrounding the eastern Yongle Atoll are the most likely source of these ascending fluids. Usingle bondTh ages of the cemented carbonate sand underlying the entrance constrain an upper limit of the opening time of the SYBH to be up to 111.7 ± 9.5 kyr BP. Deeply submerged speleothems at −116 m determine the lower collapse time of the SYBH to be 29.16 ± 0.17 kyr BP. The SYBH probably formed due to the upward release of volcanogenic acid water/gas through low-lying unconsolidated carbonate sediments, followed by buoyant collapses due to a 40-m fall in the sea level during 31–29 kyr BP. As the sea level rose to −15 m in the early Holocene, corals grew in the cave opening since 8.58 kyr BP and surrounded the entrance for the SYBH