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Variation of summer precipitation delta O-18 on the Chinese Loess Plateau since the last interglacial
No full textOrbital-scale East Asian Summer Monsoon (EASM) variations inferred from loess deposits in northern China and speleothems from southern China display different dominant periods, complicating our understanding of monsoon response to insolation and ice-volume forcings. Here we integrate a new microcodium delta O-18 record from a high-resolution last interglacial loess profile with previously published data and provide a composite microcodium delta O-18 record on the Chinese Loess Plateau (CLP) since the last interglacial. The composite microcodium delta O-18 record displays distinct precessional cycles, consistent with speleothem delta O-18 records, but with different amplitude contrast (particularly during the peak interglacials). We propose that both loess and speleothem delta O-18 records exhibit covariations at precessional timescale oscillations. The discrepancy between loess and speleothem from southern China can be attributed to the influences of other processes besides summer precipitation on the proxies. A slight difference in amplitude between microcodium and speleothem delta O-18 records implies that the EASM is also influenced by inland surface boundary conditions, which has important impacts on the occurrence of EASM precipitation. Therefore, microcodium delta O-18 from the Chinese loess-paleosol sequences can be regarded as a representative proxy of EASM precipitation in northern China and then a reliable proxy reflecting the variation of EASM intensity
Speleothem-based chronology and environmental context of deposits from the Mishin Kamik Cave, NW Bulgaria - A contribution to the archaeological study of the Late Pleistocene human occupation in the Balkans
No full textThe Balkan Peninsula represents one of the most important human pathways into and out of Europe during the Pleistocene. Mishin Kamik cave, located in the karst region of Western Stara Planina, has a rich faunal content and shows promising features indicating a human occupation site with the discovery of potential bone artefacts and an intriguing accumulation of bear skulls and bones. Petrographic study and U-series dating of a stalagmite and other calcite deposits in the cave provide an absolute chronological frame for the detrital infillings and their archaeological content and inform the environmental and climatic context of the cave evolution. Most detrital deposits in the cave were probably deposited before Marine Isotope Stage (MIS) 5 and the cave morphology and sedimentary deposits display current morphologies since similar to 135 ka. Consequently, the palaeontological and archaeological findings are older than similar to 135 ka. Calcite dated on and under the accumulation of bear skulls and bones suggests deposition during MIS 7. A first depositional contextualization of the bone accumulation does not allow us to discriminate between a natural or anthropogenic origin. The study emphasizes the added value of speleothem studies in archaeological sites and particularly in bringing a well-constrained chronological and environmental framework. Copyright (c) 2021 John Wiley & Sons, Ltd
Effects of glaciation on karst hydrology and sedimentology during the Last Glacial Cycle: The case of Granito cave, Central Pyrenees (Spain)
No full textIn Alpine regions, speleothem development on karst systems largely occurs during warm interglacial or interstadial phases due to their limited growth during cold stages. Still, recent attention has been given to the role of clastic sediments in caves, less dependent on temperature conditions. Yet, only a small number of caves worldwide preserve both speleothems and detrital deposits. Here we present an outstanding record of fine-grain laminated sediments and carbonate speleothems from the Granito cave (South Central Pyrenees, Spain) associated with seasonal to annual hydroclimatic pulses through the Last Glacial Cycle (LGC). Analysis of cave clastic facies together with new absolute dates on glacial deposits along the valley has provided new insights into the karst-glacial interactions in relation with long-term landscape evolution, with support of geomorphological, sedimentological, mineralogical, palynological, geochemical and geochronological data (U/Th series, OSL and IRSL).
The Granito cave was formed before 153.6 +/- 1.2 ky (Marine Isotopic Stage, MIS 6), as indicated by the oldest stalagmites dated in the cave, although speleothem formation occurred preferentially during MIS 5 and the Holocene interglacial stages. A 60 m thick clastic deposit was IRSL dated from 71.8 +/- 5.6 ky to after 26.5 +/- 2.5 ky corresponding with the maximum ice extent (MIE) during the LGC and subsequent glacial stabilization at 30.3 +/- 1.7 - 36.2 +/- 2.2 ky. The sediment infill was produced by water ponded in the cave coeval with the presence of glacial ice blocking the cave entrance. The cave clastic sequence includes channel, slackwater and backswamp facies, interpreted to result from pulses of sediment-laden water flow under vadose and phreatic flow regimes. The cave sediment's mineralogical composition points to an exogenous source associated with glacial till sediments overlying the hillslope above the cave and along the Ara River valley. The palynological results obtained from the cave sediments show the dominance of an open landscape composed of steppe vegetation indicating cold glacial climatic conditions. The opening of the cave occurred before 14.9 +/- 1.5 ky, the stabilization age of the innermost Ara glacier moraine, giving rise to scouring and cut-and-fill sequences within the detrital infill. Speleothem growth during the Holocene indicates the return to warm climatic conditions with the development of a soil and vegetation cover above the cave. This study shows how a combined interpretation of clastic and speleothem lithofacies is critical for elucidating landscape evolution and surface-groundwater palaeohydrological changes in northern Iberia during the LGC
Soil quality assessment in different dammed-valley farmlands in the hilly-gully mountain areas of the northern Loess Plateau, China
No full textThere are numerous valley farmlands on the Chinese Loess Plateau (CLP), where suffers from low soil quality and high risk of soil salinization due to the shallow groundwater table and poor drainage system. Currently, research on the evolution processes and mechanisms of soil quality and salinization in these dammed-valley farmlands on the CLP is still inadequately understood. In this study, three kinds of dammed-valley farmlands in the hilly-gully areas of the northern CLP were selected, and the status of soil quality and the impact factors of soil salinization were examined. The dammed-valley farmlands include the new farmland created by the project of Gully Land Consolidation, the 60-a farmland created by sedimentation from check dam, and the 400-a farmland created by sedimentation from an ancient landslide-dammed lake. Results showed that (1) the newly created farmland had the lowest soil quality in terms of soil bulk density, porosity, soil organic carbon and total nitrogen among the three kinds of dammed-valley farmlands; (2) soil salinization occurred in the middle and upper reaches of the new and 60-a valley farmlands, whereas no soil salinization was found in the 400-a valley farmland; and (3) soil salinization and low soil nutrient were determined to be the two important factors that impacted the soil quality of the valley farmlands in the hilly-gully mountain areas of the CLP. We conclude that the dammed-valley farmlands on the CLP have a high risk of soil salinization due to the shallow groundwater table, alkalinity of the loessial soil and local landform feature, thus resulting in the low soil quality of the valley farmlands. Therefore, strengthening drainage and decreasing groundwater table are extremely important to improve the soil quality of the valley farmlands and guarantee the sustainable development of the valley agriculture on the CLP
Asian Winter Monsoon Imprint on the Water Column Structure at the Northern South China Sea Coast
No full textCoastal regions of the northern South China Sea (SCS) strongly interact with the Asian monsoon circulation (AMC). Thus, variations of sea surface temperature (SST) here are newly suggested to document AMC changes in an effective manner, but additional physical parameters of oceanic conditions, probably also in relation to the AMC system, remain poorly understood. In this study, we analyzed glycerol dialkyl glycerol tetraethers (GDGTs) from a well-dated sediment core YJ, retrieved at the northern SCS coast, to further scrutinize the intrinsic response of water column to winter AMC strength. It shows that within the time frame of past similar to 1,000 years, the tetraether index of lipids with 86 carbon atoms (TEX86 ) and published alkenone ( U-37(K)') temperature records together confirm a reduced thermal gradient during the Little Ice Age (LIA), in comparison to that during the Medieval Climate Anomaly (MCA). Considering concurrent variations of the branched and isoprenoid tetraether (BIT) and the ratio of archaeol to caldarchaeol (ACE), for example, with decreased values (<similar to 0.3) for the former and relatively high values for the latter at the LIA, indicative of stratification and salinity changes, respectively, these multiple lines of evidence thereby call for well mixing of onsite water at site YJ correspondingly. Our results suggest that winter AMC strength is a critical factor for mixing subsurface waters and modifying thermal/saline conditions at the northern SCS coasts through the last millennium and also, perhaps, on longer timescales.</p
Synergistically boosting highly selective CO2-to-CO photoreduction over BiOCl nanosheets via in-situ formation of surface defects and non-precious metal nanoparticles
No full textHollow hierarchical BiOCl (BOC) assembled by nanosheets with highly exposed (001) facet is synthesized via a gas-bubble-template strategy. The as-synthesized BOC is further modified by thermal treatment in N2 to in-situ introduce oxygen vacancies (OVs) and metallic bismuth (Bi0) nanoparticles from the BOC lattice (Bi0/OVs-BOC). Thermal treatment in N2 enables an intimate contact between OVs-BOC and Bi0 nanoparticles, which is conducive to the transfer of photogenerated charge carriers. In CO2 photoreduction test, the Bi0/OVs-BOCs exhibit almost 100 % selectivity towards CO, and some of the samples also have a significant increase in yield. For instance, BOC-250 shows about 24.82 mu mol center dot g-1 h-1 CO2-to- CO photoreduction efficiency which is nearly four times higher than that of the BOC with high stability. It is found that suitable energy band structure and desirable intrinsic carrier mobility account for the substantial enhancement of CO2-to- CO photoreduction activity due to the in-situ introduction of OVs and Bi0 nanoparticles. Density functional theory (DFT) calculations unveil that the decreased reaction energy, the weakened adsorption energy for CO, and suitable adsorption energy for H and OH of Bi0/OVs-BOC lead to high selectivity. This work sheds light on the synergistic effect of insitu formed OVs and metal nanoparticles on enhancing the photocatalytic activity and selectivity of solar energy materials
Application of XRF Scanning to Different Geological Archives
No full textHigh-resolution XRF scanning is widely used on marine and lake sediment cores as a means of rapidly acquiring elemental concentrations from closely spaced intervals with no damage to the samples. Therefore, guidance on how to obtain reliable datasets and select suitable step sizes for different geological media are of great importance. Here we apply this efficient analytical method to loess, stalagmite, and tridacna samples. The results show that 11 elements (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr, and Ba), eight elements (Ca, Si, K, Fe, Cu, Ni, Sc, and Sr) and seven elements (Ca, Sr, Cu, Fe, Sc, Ni, and Si) can be robustly detected by this method for loess, stalagmite and tridacna archives respectively, demonstrating the capacity to reconstruct high-resolution paleoclimate changes. For loess cores, efficiency emission decay of the X-ray tube, water content, matrix, and grain size effects are the main factors influencing elemental intensities. The efficiency emission decay of the X-ray tube, scanning path, scanning interval, and radiation area have a significant effect on element intensities of stalagmite and tridacna samples. Based on our investigations, we suggest optimal resolutions for scanning these three archives for millennial to seasonal-scale paleoclimatic reconstructions. We compare our analyses with existing results from traditional (discrete) analyses, demonstrating similar scales of variability. Our results suggest that geochemical proxies measured by XRF scanning, such as Rb/Sr, Zr/Rb, and Ca/Ti ratios of loess and the Sr/Ca ratio of speleothem and tridacna, can be effectively used to reconstruct high-resolution paleoclimate changes
Application of XRF Scanning to Different Geological Archives
No full textHigh-resolution XRF scanning is widely used on marine and lake sediment cores as a means of rapidly acquiring elemental concentrations from closely spaced intervals with no damage to the samples. Therefore, guidance on how to obtain reliable datasets and select suitable step sizes for different geological media are of great importance. Here we apply this efficient analytical method to loess, stalagmite, and tridacna samples. The results show that 11 elements (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr, and Ba), eight elements (Ca, Si, K, Fe, Cu, Ni, Sc, and Sr) and seven elements (Ca, Sr, Cu, Fe, Sc, Ni, and Si) can be robustly detected by this method for loess, stalagmite and tridacna archives respectively, demonstrating the capacity to reconstruct high-resolution paleoclimate changes. For loess cores, efficiency emission decay of the X-ray tube, water content, matrix, and grain size effects are the main factors influencing elemental intensities. The efficiency emission decay of the X-ray tube, scanning path, scanning interval, and radiation area have a significant effect on element intensities of stalagmite and tridacna samples. Based on our investigations, we suggest optimal resolutions for scanning these three archives for millennial to seasonal-scale paleoclimatic reconstructions. We compare our analyses with existing results from traditional (discrete) analyses, demonstrating similar scales of variability. Our results suggest that geochemical proxies measured by XRF scanning, such as Rb/Sr, Zr/Rb, and Ca/Ti ratios of loess and the Sr/Ca ratio of speleothem and tridacna, can be effectively used to reconstruct high-resolution paleoclimate changes
Abrupt Indian summer monsoon shifts aligned with Heinrich events and D-O cycles since MIS 3
No full textThe tropics experienced a unique monsoon climate that drove important changes in socio-economic conditions and shaped different phases of human history during the late Quaternary across the Indian subcontinent. This study presents a new high-resolution speleothem-record of Indian summer monsoon (ISM) variability ranging from similar to 45,000 to 34,000 yr BP combined with a published record up to 5500 yr BP from the Mawmluh cave, northeastern India. We document significant changes in solar insolation and precession harmonics, implicating solar activity as one of the major forcing factors for rapid monsoonal shifts. Our new delta O-18 time series shows high-amplitude shifts in the ISM during the marine isotope stage 3 (MIS 3), similar to Dansgaard-Oeschger (D-O) oscillations recorded at high northern latitudes, which mimic the Greenland ice sheet record. The sun driven Northern Hemisphere high latitude climate anomalies played an active role in driving ISM variability and changes in the regional hydrological cycle on centennial to millennial time scales across the Indian subcontinent
Exploring diurnal thermal variations in urban local climate zones with ECOSTRESS land surface temperature data
No full textExcessive heat in urban areas affects the overall livability of cities and harms the health of urban dwellers. Understanding the spatiotemporal variations of land surface temperature (LST) and the thermal impacts of heterogeneous urban forms is crucial for informing mitigation strategies to improve the urban thermal environment. However, the diurnal thermal dynamics over urban areas has been rarely studied due to the polarorbiting nature of conventional satellite platforms (e.g., Landsat Series, Terra, Aqua). The National Aeronautics and Space Administration's (NASA) latest Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) provides LST observations at a 70 m resolution for different times of day and night, and thereby offers unprecedented opportunities for exploring the LST diurnal dynamics. We used ECOSTRESS data to explore the diurnal cycling of LST and variations among local climate zones (LCZs) in Xi'an, a megacity in Northwest China. The urban area was segmented into 2733 community units that were classified into seven LCZs. We examined the intra-LCZ variation of LST at different times of day and night to investigate the thermal impact of urban landscapes. Distinct thermal patterns across LCZs were observed during the day: urban landscapes of compact buildings tended to heat up faster than open buildings, and low-rise zones generally had higher LST than high-rise LCZs in both compact and open urban forms. At night, compact buildings had higher LST than the open buildings, but the LST difference was insignificant. Meanwhile, building heights had little effects on LST at night. We also found that vegetation cover, percentage of impervious surface, and population size were related to LST, while the strength of the relationship varied for different times of day and night. Our study demonstrates the great potential of the new ECOSTRESS LST observations in studying the diurnal variations of urban thermal environments with fine spatial resolution. Our findings can provide insight into the impacts of urban form on local climate and can inform municipalities on the development of targeted heat mitigation strategies