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Late Holocene hydroclimatic changes inferred from a karst peat archive in the western Guizhou Plateau, SW China
No full textThe paleoenvironmental implications of Ca-related indices of peat from karst regions are poorly understood. In this study, we analyze a 450-cm peat core drilled from a sub-alpine karst mountain in the western Guizhou Plateau, SW China. This core is analyzed for carbonate contents and loss on ignition (LOI). High-resolution X-ray fluorescence (XRF) core scanning was also performed to see the variation of chemical compositions. Based on these measurements and 12 accelerator mass spectrometry (AMS)C-14 dates, we reconstructed the history of hydroclimatic shifts in SW China and explored the significance of Ca-related indices. The reconstructed hydro climatic conditions were consistent with the stalagmite, lacustrine sediment, and peat records from the regions controlled by the Indian monsoon. Abrupt decreases in precipitation and temperature were clearly shown during the 4.2 ka and Little Ice Age (LIA) cold events. High carbonate contents in the Yejiping peat during the Medieval Warm Period (MWP) were linked to a warm and humid climate. Additionally, wavelet analysis shows that variations in Ca content have 500, 125, 103, 80, 58, 43, 20, and 12-a quasi-periods, which correspond to the Gleissberg, Pacific Decadal Oscillation (PDO), and Schwabe cycles. Our results highlight the importance of Ca related indices in peat deposits from karst depressions and provide a detailed description of the MWP and the LIA
Holocene climate and soil water balance in Baoji Region of Southern Loess Plateau
No full textIn this paper, changes in the Holocene climate, soil water and soil resources in Southern Loess Plateau are studied based on field investigation, grain size and chemical analysis. The purpose is to reveal the impact of the Holocene environmental change on soil water and human activities. The study shows that the mid-Holocene paleosol S0 in Baoji Region had a CaCO3 content close to 0, was enriched with Fe2O3, Al2O3, was of homogenous dense silty microstructure containing red argillans and had moderate chemical weathering. This shows that the paleosol is luvisol. The mean annual precipitation was about 800 mm at that time. The late-Holocene loess had a high CaCO3 content, low Fe2O3 and Al2O3 content and of pore-developed crumb microstructure, indicating that the climate was cold and dry. The migration depth of CaCO3 and Sr in the mid-Holocene paleosol indicates that the distribution depth of gravity water in the soil at that time reached 1.8 m, and the water content in the soil above 1.8 m during the vegetation growing season was higher than 20%. This made it suitable for the development of forest vegetation. The migration depth of CaCO3 in the Holocene loess was small and the water content in the layers of loess during rainy season was generally lower than 12%; thus, it was not suitable for the development of forest vegetation. In the mid-Holocene soil, water intake was greater than water consumption and soil water was positive balance. Moreover, trace elements, organic matters, water holding capacity and water content in S0 were higher than those in the early-Holocene and late-Holocene loess, which facilitated agricultural production and human activities. In fact, it is also the primary reason that the mid-Holocene village sites are significantly larger in quantity and greater in scale than the early-Holocene and late-Holocene village sites
A comparison between exogenous carriers enhanced aerobic granulation under low organic loading in the aspect of sludge characteristics, extracellular polymeric substances and microbial communities
No full textIn this study, polymeric ferric sulfate (PFS), aluminum sulfate (AS) and diatomite were added to enhance the aerobic granulation under low organic loading rate (OLR) of 0.6 kg.COD/(m(3).d), and their effects of aerobic granule formation, extracellular polymeric substances (EPS) secretion and microbial community were investigated. The results showed that adding carriers could facilitated the growth of aerobic granules and improve the sludge settleability and biomass retention. Nutrient removal efficiencies were also enhanced. Compared with diatomite, adding PFS and AS resulted in more significant increase in EPS production, especially for the extracellular proteins. For microbial community, the dominated bacteria (Zoogloea, 18.47-23.95%) in the mature granular consortia were similar. Moreover, the introduction of PFS and diatomite contributed to the enrichment of Paracoccus, which was responsible for denitrification. Adding carriers potentially activated the functional genes related to metabolism and genetic information processing, and PFS had the most significant effects
Phylogeny, alkenone profiles and ecology of Isochrysidales subclades in saline lakes: Implications for paleosalinity and paleotemperature reconstructions
No full textLong-chain alkenones (LCAs) produced by phylogenetically classified Groups 1 and 3 Isochrysidales are increasingly used for paleotemperature and/or paleosalinity reconstructions in oligohaline lakes and marine environments. However, there are considerable difficulties in the paleoenvironmental interpretation of LCAs from Group 2 Isochrysidales thriving in saline lakes. The biggest challenge lies in our poor understanding of the complexity and ecological niches of individual Group 2 subclades in saline lakes. Here, we perform comprehensive analysis of haptophyte-specific 18S rRNA sequences and distributions of LCAs, and long-chain alkenoates (LCEs) in surface sediments and suspended particulate matter (SPM) from 37 saline lakes in northern China. These lakes span a large salinity gradient from 0.5 to 308%. Combined with published genomic data of Group 2 Isochrysidales, our phylogenetic analysis reveals three Group 2 subclades occupying distinct ecological niches: one ice-related bloomer Group 2i and two warm-season bloomers Groups 2w1 and 2w2. Group 2i, the earliest seasonal bloomer, frequently co-occurs with Group 2w1 in sediments from saline lakes with relatively low to intermediate salinity waters, whereas Group 2w2 blooms in hypersaline waters. Based on existing data, C-39:4 methyl alkenone is a chemotaxonomic biomarker for Group 2i. %C-3(7:)4 (relative abundance of C(3)(7:)(4 )to the total C-37 alkenones) values in the three Group subclades follow the order: Group 2i > Group 2w2 > Group 2w1. The %C(37:4 )in sediment cores of saline lakes does not directly record past salinity changes, but instead reflects variable contributions in production by these three subclades. This could indirectly and partially reflect overall salinity changes in some lakes dominated by Groups 2i and 2w1, but can be more complicated in lakes dominated by other assemblages. For our sites, we also demonstrate that direct use of C(37 )alkenone unsaturation indices (U-37(K), U-37(K'), and U-37(K '')) for paleotemperature reconstructions in saline lakes is generally not feasible, except for cases where alkenone-producing Isochrysidales are dominated by one single species/subclade and seasonal production effects can be circumvented. We propose two possible alternative proxies for paleotemperature reconstructions in saline lakes: 1) unsaturation ratios of C-41 and C-42 alkenones, as these compounds are predominantly produced by a limited number of Group 2 species, such as Isochrysis nuda (Liao et al., 2020) 2) C38Et/C36OEt ratio (ratio of C-38 ethyl alkenones and C-36 ethyl alkenoates), which appears to have similar temperature sensitivity for Groups 2w1 and 2w2, in lakes with no Group 2i inputs. Our study provides new insights into the phylogenetic classifications of Group 2 Isochrysidales and their ecological/environmental niches, which are fundamental for more quantitative and rigorous applications of LCAs and LCEs in saline lakes as paleosalinity and paleotemperature proxies. (C) 2021 Elsevier Ltd. All rights reserved
The sedimentary succession of the last 2.25 Myr in the Bohai Strait: Implications for the Quaternary paleoenvironmental evolution of the Bohai Sea
No full textThe Bohai Strait connects the Bohai Sea with the Yellow Sea, allowing material and energy exchange between the seas. The sedimentary record in this region is important for reconstructing the Quaternary sea-level changes and environmental evolution in the Bohai Sea area; however, long sedimentary sequences with a reliable chronological framework from this area are scarce. We assessed the sedimentary characteristics, grain size, microfossils, accelerator mass spectrometry 14C ages and optically stimulated luminescence ages of core BHS01 from the Bohai Strait. From these and previous paleomagnetic results, new insights into regional sea-level changes and environmental evolution in the Bohai Strait over the last 2.25 Myr are obtained. The sedimentology and environmental proxies (benthic foraminifera and marine ostracods) indicate that the sedimentary environment of the area around core BHS01 was mainly dominated by fluvial-lacustrine deposits from 2.25 to 0.89 Ma, and subsequently by alternating marine and fluvial deposits. Comparative analyses of the chronological and sedimentary results of core BHS01 with previous drilling records in the eastern marginal seas of China revealed that the Quaternary initial marine transgression of the Bohai Sea occurred no later than 0.89 Ma (latest early Pleistocene) since Quaternary. The initial transgression presumably resulted from the partial subsidence and disintegration of the Miaodao Islands Uplift with sea-level rise during this period or slightly earlier. This result is generally consistent with the timing of the Quaternary regional marine transgressive processes of the Yellow and Bohai seas; thus, we propose a conceptual model in which the first marine transgression of the Yellow Sea and the Bohai Sea during the Quaternary occurred no later than 1.66 Ma and 0.89 Ma, respectively. This study provides new evidence for understanding the Quaternary sea-level changes and regional environmental evolution in the Bohai Sea
Lithium isotopic composition of soil pore water: Responses to evapotranspiration
No full textLithium isotopes show great potential to trace Earth surface processes due to the large mass discrimination between Li-6 and Li-7 associated with clay uptake. However, factors controlling the Li isotopic composition (delta Li-7) of river water, especially those with a water-bedrock delta Li-7 difference higher than that of the equilibrium fractionation associated with clay formation (Delta(W-C)), have not yet been fully resolved. Traditional interpretation involves the Rayleigh distillation, but it unrealistically separates the stage of clay formation from that of silicate dissolution using fractionation factors that are much lower than laboratories can constrain. We propose an in situ mechanism that simulates high delta Li-7 by evapotranspiration. A model with coupled mineral dissolution and clay precipitation shows that evaporative enrichment of pore-water Li progressively increases the incorporation of Li into clays with light delta Li-7, resulting in higher delta Li-7 values in the residual water than Delta(W-C). We also provide evidence from the Chinese Loess Plateau, where an evaporative effect readily explains the observed delta Li-7. The influence of evapotranspiration on riverine delta Li-7 implies that changes in aridity may partly explain the variations of seawater delta Li-7. The same principle may also apply to other stable isotopic systems whereby incorporation into secondary precipitates controls the isotopic fractionation
Sea surface temperature seasonality in the northern South China Sea during the middle Holocene derived from high resolution Sr/Ca ratios of Tridacna shells
No full textSeasonal climate variability is an important component of Earth's climate system, and has a significant impact on ecosystems and social systems. However, the temporal resolution of most proxy-based paleoclimate records is limiting to fully understand the past seasonal changes. Here, we used high-precision monthly resolution Sr/Ca records of three Tridacna squamosa specimens from the northern South China Sea (SCS) to reconstruct the sea surface temperature (SST) seasonality during three time periods from the middle Holocene. The results suggested that SST seasonality in the northern SCS during the middle Holocene (3.21 +/- 0.98 degrees C) was smaller than that for recent decades (AD 1994-2004, 4.32 +/- 0.59 degrees C). Analysis of modern instrumental data showed that the SST seasonality in the northern SCS was dominated by the winter SST, which was deeply influenced by the intensity of East Asian winter monsoon (EAWM). A strong EAWM usually resulted in cooler winter SST and a larger SST seasonality in the northern SCS. The reconstructed Holocene EAWM records showed that the EAWM strengthened from the middle to late Holocene, which was seen in our reconstruction of less SST seasonality changes during the middle Holocene in the northern SCS. This study highlighted that the Sr/Ca ratios from Tridacna shells can be used as a potential high-resolution indicator of past seasonal climate changes
Topographic and Climatic Control on Chemical Weathering of Mountainous Riverine Sediments of Hainan Island, South China Sea
No full textHainan Island, the largest island in the northwestern South China Sea (SCS), is characterized by many tropical mountainous rivers that flow into the SCS. The geochemistry of these riverine sediments and the factors controlling the weathering intensity are still not well understood. In this study, sedimentary geochemistry has been investigated by using 45 riverine sediments collected from 18 major rivers on Hainan Island. The Hainan riverine sediments are only first-cycle rather than polycyclic sediments, and they faithfully reflect the present weathering intensity. The high and steady values of the Chemical Index of Alteration (CIA) indicate that the riverine sediments at different parts of the Hainan Island have overall undergone intensive chemical weathering. The low values of Weathering Index of Parker (WIP) and high alpha(Ca) , alpha(K), alpha(Sr), and alpha(Ba) values of north Hainan indicate the highest weathering degree, which is mainly influenced by the flat topography. The values of alpha(Na) , alpha(K), alpha(Sr), and alpha(Ba) of southwest Hainan which are higher than those of east Hainan suggest that the leaching of elements such as Na, K, Sr, and Ba is more extreme (i.e., more intensive weathering). These are mainly caused by the different physical denudation due to different summer precipitation. Overall, the Hainan Island is featured by intensive chemical weathering and is classified as a typical transport-limited weathering regime. Therefore, the geochemistry of the riverine sediments of the Hainan Island is different from that of sediments in tectonically active regions (e.g., Taiwan Island)
Innovative ochre processing and tool use in China 40,000 years ago
No full textHomo sapiens was present in northern Asia by around 40,000 years ago, having replaced archaic populations across Eurasia after episodes of earlier population expansions and interbreeding(1-4). Cultural adaptations of the last Neanderthals, the Denisovans and the incoming populations of H. sapiens into Asia remain unknown(1,5-7). Here we describe Xiamabei, a well-preserved, approximately 40,000-year-old archaeological site in northern China, which includes the earliest known ochre-processing feature in east Asia, a distinctive miniaturized lithic assemblage with bladelet-like tools bearing traces of hafting, and a bone tool. The cultural assembly of traits at Xiamabei is unique for Eastern Asia and does not correspond with those found at other archaeological site assemblages inhabited by archaic populations or those generally associated with the expansion of H. sapiens, such as the Initial Upper Palaeolithic(8-10). The record of northern Asia supports a process of technological innovations and cultural diversification emerging in a period of hominin hybridization and admixture(2,3,6,11)
Ancient DNA and deep population structure in sub-Saharan African foragers
No full textMultiple lines of genetic and archaeological evidence suggest that there were major demographic changes in the terminal Late Pleistocene epoch and early Holocene epoch of sub-Saharan Africa(1-4). Inferences about this period are challenging to make because demographic shifts in the past 5,000 years have obscured the structures of more ancient populations(3,5). Here we present genome-wide ancient DNA data for six individuals from eastern and south-central Africa spanning the past approximately 18,000 years (doubling the time depth of sub-Saharan African ancient DNA), increase the data quality for 15 previously published ancient individuals and analyse these alongside data from 13 other published ancient individuals. The ancestry of the individuals in our study area can be modelled as a geographically structured mixture of three highly divergent source populations, probably reflecting Pleistocene interactions around 80-20 thousand years ago, including deeply diverged eastern and southern African lineages, plus a previously unappreciated ubiquitous distribution of ancestry that occurs in highest proportion today in central African rainforest hunter-gatherers. Once established, this structure remained highly stable, with limited long-range gene flow. These results provide a new line of genetic evidence in support of hypotheses that have emerged from archaeological analyses but remain contested, suggesting increasing regionalization at the end of the Pleistocene epoch.
DNA analysis of 6 individuals from eastern and south-central Africa spanning the past approximately 18,000 years, and of 28 previously published ancient individuals, provides genetic evidence supporting hypotheses of increasing regionalization at the end of the Pleistocene