Mass accumulation rate changes in Chinese loess during MIS 2, and asynchrony with records from Greenland ice cores and North Pacific Ocean sediments during the Last Glacial Maximum

Sensitivity-corrected quartz optically stimulated luminescence (OSL) dating methods have been widely accepted as a promising tool for the construction of late Pleistocene chronology and mass or dust accumulation rates (MARs or DARs) on the Chinese Loess Plateau (CLP). Many quartz OSL ages covering marine isotope stage (MIS) 2 (equal to L1-1 in Chinese loess) have been determined for individual sites within the CLP in the past decade. However, there is still a lack of detailed MAR or DAR reconstruction during MIS 2 across the whole of the CLP. Here, we present detailed MARs determined for eight sites with closely-spaced quartz OSL ages covering MIS 2, and relative MARs suggested by a probability density analysis of 159 quartz OSL ages ranging from 30 to 10 ka ago, from 15 sites on the CLP. The results show enhanced dust accumulation during the Last Glacial Maximum (LGM), with particularly rapid dust accumulation from 23 to 19 ka ago (the late LGM). In contrast, MARs determined for the last deglaciation (from 19 to 12 ka ago) are low. The MAR changes during MIS 2 in Chinese loess are mainly controlled by the East Asian winter monsoon (EAWM) intensity, which is forced by Northern Hemisphere ice volume. The MAR changes also indicate that dust accumulation during MIS 2 is generally continuous at millennial time scales on the CLP. Comparison of Asian-sourced aeolian dust MARs in Chinese loess with those preserved in Greenland ice cores and North Pacific Ocean sediments indicates that rapid dust accumulation occurred from 26 to 23 ka ago (the early LGM) in Greenland ice cores and North Pacific Ocean sediments, suggesting a several kilo-year difference in timing when compared with the rapid dust accumulation during the late LGM in Chinese loess. This asynchronous timing in enhanced dust accumulation is probably related to both changes in the EAWM intensity and changes in the mean position of zone axis of the Westerly jet, both of which are greatly influenced by Northern Hemisphere ice volume. This study highlights the possible influence of changes in the mean position of zone axis of the Westerly jet on long-range transport of Asian-sourced dust.</p

Radiometric dating of late Quaternary loess in the northern piedmont of South Tianshan Mountains: Implications for reliable dating

Reliable chronologies are prerequisites when interpreting proxy records in terrestrial archives of Quaternary climate and environmental change. Optically stimulated luminescence (OSL) dating and accelerator mass spectrometry radiocarbon dating (AMS C-14) are commonly used to date late Quaternary loess deposits in the Chinese Loess Plateau, but the range and reliability of the two methods in Central Asia are still debated. In this study, we investigate both fine-grained quartz OSL and AMS C-14 dating of a late Quaternary loess section located at the northern piedmont of the South Tianshan Mountains in Central Asia and discuss the reliability of the two radiometric dating methods. The results show that the OSL and AMS C-14 ages are generally consistent with the stratigraphic sequence when the ages are younger than 25cal ka BP, which means that both can be used to establish a reliable chronology in the Ili Basin. But beyond this age, the OSL dating method seems to be a more reliable approach. The results also supported previous dates based on medium-grained quartz OSL dating of the Ili loess in the southern piedmont of the North Tianshan Mountains. Radiocarbon ages older than 25cal ka BP should be treated with caution, and attention must be paid to the influence of pedoturbation on OSL signals in the Central Asian loess. Multiple dating approaches for mutual authentication and exploring new dating materials are suggested in further loess chronological research. These findings will be helpful in establishing a reliable timescale and in reconstructing high-resolution environmental change in Central Asia

Late Holocene anti-phase change in the East Asian summer and winter monsoons

Changes in East Asian summer and winter monsoon intensity have played a pivotal role in the prosperity and decline of society in the past, and will be important for future climate scenarios. However, the phasing of changes in the intensity of East Asian summer and winter monsoons on millennial and centennial timescales during the Holocene is unclear, limiting our ability to understand the factors driving past and future changes in the monsoon system. Here, we present a high resolution (up to multidecadal) loess record for the last 3.3 ka from the southern Chinese Loess Plateau that clearly demonstrates the relationship between changes in the intensity of the East Asian summer and winter monsoons, particularly at multicentennial scales. At multimillennial scales, the East Asian summer monsoon shows a steady weakening, while the East Asian winter monsoon intensifies continuously. At multicentennial scales, a prominent similar to 700-800 yr cycle in the East Asian summer and winter monsoon intensity is observed, and here too the two monsoons are anti-phase. We conclude that multimillennial changes are driven by Northern Hemisphere summer insolation, while multicentennial changes can be correlated with solar activity and changing strength of the Atlantic meridional overturning circulation. (C) 2018 Elsevier Ltd. All rights reserved

Multi-agent based beam search for intelligent production planning and scheduling

abstractpublished_or_final_versionIndustrial and Manufacturing Systems EngineeringDoctoralDoctor of Philosoph

Quartz OSL chronology and dust accumulation rate changes since the Last Glacial at Weinan on the southeastern Chinese Loess Plateau

The fine-grained (4-11m) quartz Optically Stimulated Luminescence (OSL) dating technique was applied to the Weinan section on the southeastern Chinese Loess Plateau (CLP) with a high luminescence sampling resolution (10- and 20-cm intervals). Fifty-eight OSL ages, spanning c. 1-74ka, were obtained for the 10-m loess-palaeosol sequences. The reliability of the OSL dating and the constructed chronology was confirmed by comparing the OSL ages with independent dates from other studies and by correlation with palaeoclimatic time series. The closely spaced OSL ages at Weinan indicate that the mean dust accumulation rate (DAR) of L1-1 (MIS 2, 7.0 +/- 0.9cmka(-1)) is lower than those of L1-3 (MIS 4, 19.1 +/- 6.1cmka(-1)) and L1-2 (MIS 3, 16.0 +/- 0.7cmka(-1)) and that the mean DARc. 30-20ka ago (11.4 +/- 2.4cmka(-1)) is higher than that c. 20-10ka ago (3.0 +/- 0.1cmka(-1)) in L1-1. The subsequent calculation of the mass accumulation rate (MAR) indicates that the MAR of L1-1 (107gm(-2)a(-1)) is much lower than those of L1-2 (247gm(-2)a(-1)) and L1-3 (307gm(-2)a(-1)). By comparing the mean DAR results during the Last Glacial at Weinan with those at a further six sites from other studies, we observed that the mean DAR of L1-2 is higher (lower) than that of L1-1 on the eastern (western) CLP, and that the mean DAR during MIS 2 has an evident transition from high to low at c. 20ka on the entire CLP. Possible mechanisms for the above mean DAR changes at orbital and sub-orbital time scales are presented.</p

Closely-spaced recuperated OSL dating of the last interglacial paleosol in the southeastern margin of the Chinese Loess Plateau

The objective of this study is to construct a numerically dated chronology of the last interglacial paleosol (Si) in Chinese loess using luminescence dating. The recuperated optically stimulated luminescence (ReOSL) dating approach was applied to 18 closely-spaced (20 cm intervals) samples, with 15 of these collected from the S(1) unit at the Weinan site, which is located at the southeastern margin of the Chinese Loess Plateau (CLP). By using the multiple-aliquot regenerative-dose (MAR) approach, 18 fine-grained quartz ReOSL equivalent dose (D(E)) values, spanning about 249-466 Gy, were obtained. The validity of ReOSL MAR protocol was checked by dose recovery measurements and recycling ratio tests. By comparison of the dose-response curves of all the samples, we found that it is feasible to construct a standardized growth curve (SGC) for the ReOSL signal at the Weinan site. Considering the effects of pedogenesis of the S(1) unit during formation, the dose rate during the last interglacial was corrected, which should be beneficial for constructing a more reliable chronology. Finally, a detailed chronology of the S(1) unit was established. The results show that S(1) was deposited between approximately 76-127 ka, which confirms the early suggestion that the S(1) unit in Chinese loess corresponds to the whole marine oxygen-isotope stage (MIS) 5. The detailed ReOSL chronology of S(1) indicates the consistency of the substrata of S(1) with MIS 5a-e, but cannot determine whether they are exactly coeval. According to the present ReOSL age results, it is suggested that dust deposition is continuous at timescales larger than 14.1 +/- 11.8 ky during the last interglacial and there is no hiatus longer than 4.4 +/- 13.0 ky at the L(2)/S(1) transition. Further work, e.g. minimizing the errors on ages and reducing the luminescence sampling intervals, is needed to understand the more detailed dust deposition conditions during the last interglacial in Chinese loess. (C) 2011 Elsevier B.V. All rights reserved.</p

Temporal-spatial variations in aeolian flux on the Chinese Loess Plateau during the last 150 ka

Aeolian dust deposits from continent and ocean have been extensively investigated to reflect past changes in source aridity and atmospheric circulations. Aeolian flux (AF) as a quantitative dust proxy has been widely used in both palaeoenvironmental reconstruction and numerical simulation. However, available AF data on the Chinese Loess Plateau (CLP) is too limited to assess the temporal-spatial variations at glacial-interglacial timescales, and therefore cannot be used as robust input parameters in palaeoclimate models. Here we investigate eight loess profiles along two N-S-aligned transects on the CLP to quantitatively estimate the AF variations over the last glacial-interglacial cycle. We first establish a refined chronological framework based on optically stimulated luminescence chronology and pedostratigraphic correlation. AF was then estimated by multiplying the sedimentation rate and bulk density. The results show that the AF increases from 2-18 g cm(-2) ka(-1) in the southeastern CLP to 14-105 g cm(-2) ka(-1) in the northwestern CLP. At glacial-interglacial scales, the AF varies from 2-20 g cm(-2) ka(-1) during the last interglacial to 8-105 g cm(-2) ka(-1) in the last glaciation. Due to more spatial coverage and better age constraints, our AF data can be used to refine other AF datasets and to improve the proxy-model comparison

Study on the Pseudo-Slope Length Effect of Buried Pipe Extraction in Fully Mechanized Caving Area on Gas Migration Law in Goaf

To study the law of gas transportation in mining areas, Fluent numerical simulation software was applied to examine the influence of different pseudo-slope lengths (PSL) on gas concentration in a U-ventilated working area under no-extraction conditions. Based on this, numerical simulation experiments were conducted on the buried pipe extraction arrangement parameters. The simulation found that when there was no extraction, the PSL had an impact on the airflow in the extraction area, which caused the airflow in the extraction area to be disordered, causing gas to accumulate locally at the working area. When the buried pipe depths (BPDs) and PSLs of the working area worked together, the gas concentration of the working area was lower when the inlet air influence zone and the extraction influence zone were through; otherwise, gas concentration accumulation occurred at the working area. The research results showed that when the PSL was at 25 m and BPD was at 20 m, the gas concentration at the working area was not abnormal, and the gas concentration in the upper corner was lower. By adjusting the PSL and BPD of the test working area, the maximum gas concentration in the upper corner was reduced to 0.46% and the maximum gas concentration in the return air outlet was reduced to 0.41%. The experimental and practical results provide important reference values for coal and gas co-mining

Early Holocene weakening and mid- to late Holocene strengthening of the East Asian winter monsoon

Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) and its mechanisms during the Holocene are controversial, partly due to the lack of high-quality records from Chinese loess. Here, we present high-resolution reconstruction of Holocene EAWM intensity based on optically stimulated luminescence dating and grain-size analysis from three loess sections taken from the Chinese Loess Plateau. The EAWM showed a persistent weakening trend during the early Holocene (ca. 11.7-6.5 kyr B.P.) and a strengthening trend during the mid- to late Holocene (since ca. 6.5 kyr B.P.). We propose that this was caused by changes in high-latitude Northern Hemisphere ice volume and middle- to high-latitude Northern Hemisphere atmospheric temperatures, respectively. We also observed an anti-correlation between EAWM and East Asian summer monsoon. Our findings provide a robust solution to the debate regarding Holocene EAWM changes and contribute to the understanding of potential future variations in EAWM intensity