Institute of Earth Environment
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Increasing atmospheric oxidizing capacity weakens emission mitigation effort in Beijing during autumn haze events
No full textAlthough strict mitigation measures have been implemented since 2013 in Beijing-Tianjin-Hebei (BTH), China, air pollution still frequently occurs. Observations reveal that during pollution episodes in autumn, fine particulate matter (PM2.5) concentrations have not decreased, and particularly, ozone (O-3) concentrations have increased remarkably from 2013 to 2015 in Beijing. Additionally, a concurrence of O-3 and particulate pollution with high secondary aerosol contributions has been observed frequently, indicating high atmospheric oxidizing capacity (AOC) during particulate pollution. The WRF-Chem model simulations show elevated O-3 concentrations and high fractions of oxygenated secondary aerosols (OSA) in PM2.5 (0.53-0.73) during the severe pollution period. During daytime there exhibits an AOC-sufficient regime with the persistently high OSA fraction and an AOC-deficient regime with varied OSA fractions, separated by the O-3 level of 80 mu g m(-3). Our results suggest that increasing AOC can considerably weaken the emission mitigation effort by enhancing the secondary aerosol formatio
Comparison and Calibration of Elemental Measurements in Sediments Using X-Ray Fluorescence Core Scanning with ICP Methods: A Case Study of the South China Sea Deep Basin
No full textThe X-ray fluorescence (XRF) core scanning method is widely applied in studies of sedimentary paleoenvironments due to its convenient pretreatment, nondestructive characteristics, fast execution, continuous scanning, and high resolution. XRF core scanning for sediments is commonly used in the studies on the South China Sea. This study compares XRF-scanned intensities and measured inductively coupled plasma (ICP) elemental contents of core CS11 in the northeast South China Sea deep basin. The results show that the analyzed elements can be separated into three classes. Class I includes elements with high correlation coefficients, such as Ca, Sr, and Zr; Class II contains elements with average correlation coefficients, such as Fe, Mn, Ti, and Cu; and Class III comprises elements with low correlation coefficients, such as K, Ni, Zn, Rb, and Al. In the South China Sea deep basin, pore water, compaction, and grain size have weak effects on the elemental intensities and contents of short core sediments. Hence, for elements with high correlation coefficients, a linear relationship model can be established by the least-squares method, in which the converted XRF intensities are approximately equal to the measured ICP contents. Based on the established log-ratio calibration model, the resulting ln(K/Ca), ln(Ti/Ca), ln(Fe/Ca), and ln(Zr/Ca) values generally display the same variation trends as the measured curves. The elemental contents and ratios produced by the linear model via the least-squares method and the log-ratio calibration model are expected to provide high-resolution data support for future paleoenvironmental research on the South China Sea deep basin
High-frequency East Asia monsoon variability during 115000-93000 a BP in Northern China
No full textThe FGS5c-d segment of the Fanjiagouwan section is located in the Salawusu River Valley on the southeast margin of the Mu Us Desert in China. It contains 17 sedimentary cycles consisting of aeolian dune sands and lacustrine facies during 115000 - 93000 a BP. Analyses of grain size and trace geochemical elements in the FGS5c-d segment revealed that the element contents were higher in lacustrine facies than in dune sands, displaying 17 element cycles that were similar to the sedimentary cycles in the FGS5c-d. The correlation between element contents and Mz(Phi)r was > 0.59. Grain size and trace geochemical elements during MIS5c-d indicate that 17 warm-humid and cold-arid climate cycles occurred in the FGS5c-d segment. This suggests that millennium-scale climate changes occurred in the alternations of the East Asian winter and summer monsoons during 115000 - 93000 a BP in the deserts of China and that these changes are the regional response to the global climate changes during that period
Immediate temperature response in northern Iberia to last deglacial changes in the North Atlantic
No full textMajor disruptions in the North Atlantic circulation during the last deglaciation triggered a series of climate feedbacks that influenced the course of Termination I, suggesting an almost synchronous response in the ocean-atmosphere system. We present a replicated 818O stalagmite record from Ostolo cave in the northern Iberian Peninsula with a robust chronological framework that continuously covers the last deglaciation (18.5-10.5 kyr B.P.). The Ostolo 818O record, unlike other speleothem records in the region that were related to humidity changes, closely tracks the well-known high-latitude temperature evolution, offering important insights into the structure of the last deglaciation in the Northern Hemisphere. In addition, this new record is accompanied by a clear signal of the expected cooling events associated with the deglacial disruptions in North Atlantic deep convection during Heinrich event 1
Concentrations, optical properties and sources of humic-like substances (HULIS) in fine particulate matter in Xi'an, Northwest China
No full textHumic-like substances ( HULLS) are ubiquitous in the atmospheric environment, which affects both human health and climate. We present here the mass concentration and optical characteristics of HULIS isolated from aerosol samples collected in Xi'an, China. Both mass concentration and absorption coefficient (Abs (385)) of HULIS show clear seasonal differences, with the highest average in winter (3.91 mu gC m(-3) and 4.78 M m(-1), respectively) and the lowest in summer (0.65 mu gC m(-3) and 0.55 M m(-1), respectively). The sources of HULIS _C and light absorption of HUUS were analyzed by positive matrix factorization (PMF) and four major sources were resolved, including secondary formation, biomass burning, coal burning, and vehicle emission. Our results show that secondary formation (i.e., gas-to-particle conversion from e.g., photochemical oxidation) was the major contributor to both HULIS _C (50%) and light absorption (55%) of HULIS in summer, biomass burning and coal burning were major sources of HULIS_C (similar to 70%) and light absorption (similar to 80%) of HULIS in winter. It is worth noting that biomass burning and coal burning had higher contribution to HUUS light absorption (47% in spring, 37% in summer, 73% in fall, and 77% in winter) than their corresponding contribution to HUUS_C concentration (41% in spring, 37% in summer, 54% in fall, and 69% in winter). However, vehicle emission had lower contribution to HUUS light absorption (26% in spring, 8% in summer, 18% in fall, and 11% in winter) than to HUUS_C concentration (24% in spring, 13% in summer, 28% in fall, and 18% in winter). These results suggest that HULIS from biomass burning and coal burning have higher light absorption ability than from vehide emission. (C) 2021 Elsevier B.V. All rights reserved
East Asian monsoon during the past 10,000 years recorded by grain size of Yangtze River delta
No full textPaleoenvironmental research is critical for understanding delta evolution processes and managing delta sustainability, particularly for delta experiencing significant recent fluvial sediment discharge. Based on other previously reported optically stimulated luminescence (OSL) data, Holocene environmental changes of the Yangtze River delta in response to climate fluctuations and human activities were reviewed on the basis of grain-size analyses of core YZ07. The results of grain-size and end-member analysis (EMA) provide a detailed history of East Asian monsoon variability and environmental changes since similar to 10,000 cal year B.P. The lower median values (Md) and sand content reflect relatively cool and dry climate conditions between 10,000 and 9,570 cal year B.P. During the early Holocene (9,570-7,630 cal year B.P.), the highest Md values and sand contents and the lowest end member 2 (EM2) contents suggest the Holocene transgression. The increased Md values and sand contents indicate that the climate conditions were warm and wet during the mid-Holocene thermal optimum. From 4,690 to 4,150 cal year B.P., the climate was cool and dry, corresponding to the cool event, as indicated by the finer grain size. Subsequently, between 4,150 and 2,850 cal year B.P., the grain size derived from the Md value and sand content increased, which reflect a wet and warm episode. The climate, which shifted from warm and wet to cool and dry between 2,850 and 1,020 cal year B.P., may have caused a reduction in the sand contents and Md values. After 1,020 cal year B.P., the lowest values of Md and Standard deviation (Sd) and the highest contents of EM2 and clay suggest that the Yangtze River delta has been severely affected by anthropogenic activity. The variability of the East Asian monsoon intensity in the Yangtze River delta strongly correlates with other East Asian monsoon paleoclimate records in China. These results are important for investigations into the interactions between regional systems and global change in monsoonal climatic regions and can provide an example of the evolution of a large scale geomorphic feature resulting from river-sea interaction
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
Seasonal/Interannual Variation and Controlling Factors for Oxygen and Carbon Isotopes of Ostracod Shells Collected From a Time-Series Sediment Trap in Lake Qinghai
No full textBecause the shell substance of an ostracod is derived entirely from the water body where it lives, its chemical compositions are sensitive to aquatic environment and thus have been used to reconstruct past climatic and environmental changes. However, there is controversy about the controlling factors for the different compositions of ostracod shells from various water bodies. In this study, seasonal and interannual variations in daily flux and stable oxygen-carbon isotopic compositions (delta O-18, delta C-13) for two species of ostracod shells (Limnocythere inopinata and Eucypris mareotica) and their controlling factors are discussed, based on ostracod shell samples collected from a time-series sediment trap from July 2010 through September 2012 and from surface sediments in Lake Qinghai, which were correlated with the state-of-the-art sensing data of the lake water. The results show that the daily flux of L. inopinata shells is an order of magnitude higher than that of E. mareotica. The delta O-18 and delta C-13 of both L. inopinata and E. mareotica shells have distinctly interannual and seasonal variations, with species differences. Interannual differences of delta O-18 for the two species of ostracod shells directly reflect the systematic differences of the summer water temperature between 2010 and 2012. We propose that seasonal variations of both delta O-18 and delta C-13 for the two species are affected by the precipitation of authigenic carbonates in microenvironment induced by high water temperature in summers, highlighting their environmental implications in Lake Qinghai
Association between the Biophysical Environment in Coastal South China Sea and Large-Scale Synoptic Circulation Patterns: The Role of the Northwest Pacific Subtropical High and Typhoons
No full textSynoptic weather conditions can modulate short-term variations in the marine biophysical environment. However, the impact of large-scale synoptic circulation patterns (LSCPs) on variations in chlorophyll-a (chl-a) and sea surface temperature (SST) in the South China Sea (SCS) remains unclear. Using a T-mode principal component analysis method, four types of LSCP related to the Northwest Pacific subtropical high are objectively identified over the SCS for the summers of 2015-2018. Type 1 exhibits a lower chl-a concentration of 0.3 mg m(-3)) along the coast of Guangdong exhibits the widest areas of coverage. The offshore chl-a bloom jet (>0.3 mg m(-3)) formed in southern Vietnam is the most obvious under Type 3. Under Type 4, the high chl-a concentration zone along the coast of Guangdong is the narrowest, while the chl-a concentration in the middle of the SCS is the lowest (<0.1 mg m(-3)). These type differences are mostly caused by the various monsoon circulations, local ocean mesoscale processes and resultant differences in localized precipitation, wind vectors, photosynthetically active radiation and SST. In particular, precipitation over land helps to transport nutrients from the land to the shore, which is conducive to the increase of chl-a. However, precipitation over ocean will dilute the upper seawater and reduce chl-a. Typhoons pump the deeper seawater with nutrients to the surface, and therefore make a positive contribution to chl-a in most offshore areas; however, they also disturb shallower water and hinder the growth of phytoplankton, making a negative contribution near the coast of Guangdong. In general, our findings will provide a better understanding of wind pump impact: the responses of marine biophysical environments to LSCPs
Variability in Indonesian Throughflow Upper Hydrology in Response to Precession-Induced Tropical Climate Processes Over the Past 120 kyr
No full textThe Indonesian Throughflow (ITF), as the sole low-latitude conduit connecting the Pacific and Indian Oceans, regulates the thermohaline balance between these oceans. Thus, investigating the variability in the ITF and its relationship with the precessional forcing is crucial for understanding the drivers of tropical climate change. Here, we reconstruct the history of the ITF over the past similar to 120 kyr based on high-resolution (similar to 400 years) delta O-18 and Mg/Ca records of Globigerinoides ruber and Pulleniatina obliquiloculata from core SO217-18540 retrieved from the Flores Sea upwelling region within the main pathway of the ITF. A comparison of these new records with published paleo-oceanographic and climatological data from the western tropical Pacific Ocean suggests that annual mean conditions in the Flores Sea were controlled by ITF variability rather than by monsoonal upwelling. Our results further indicate that precessional insolation was a major forcing for the hydrological evolution of the ITF during the past 120 kyr. We suggest that the precessional insolation forcing paced ITF variability by modulating the mean state of El Nino-Southern Oscillation-like conditions and latitudinal shifts and/or expansion/contraction of the Intertropical Convergence Zone.
Plain Language Summary The Indonesian Throughflow (ITF) is the only low-latitude current transporting warmer, fresher water masses from the Pacific to the Indian Ocean, regulating the interocean heat and fresh water budgets. The ITF is strongly influenced by shifts in winds and temperatures across the tropical Pacific Ocean (El Nino-Southern Oscillation; ENSO) and by variations in the latitudinal position and intensity of the hottest part of the tropical climate belt (Intertropical Convergence Zone; ITCZ). Hence, understanding past ITF variability is highly relevant to constrain projections of future tropical climate change. Here, we present new upper ocean temperature and salinity records spanning the last 120 kyr from core SO217-18540 retrieved within the main ITF pathway. These records are based on delta O-18 and Mg/Ca analyses of surface and deeper dwelling microscopic zooplankton shells (foraminifera). We found that variations in the ITF intensity and vertical structure were controlled by the similar to 20 kyr wobble of the Earth's axis, which affects the distribution of incoming solar radiation. We ascribe this pattern of variability to shifts in the intensity and/or position of the ITCZ and to changes in winds and temperatures over the tropical Pacific Ocean, similar to the modern ENSO but acting on longer timescales in Earth's history