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Records of iodine isotopes (I-129, I-127) in the Barkol peat bog from northwest China and their sources, transport and preservation
No full textThe research on geochemical behaviors of iodine is significant for deep understanding of the source and distribution of iodine on the earth. However, as one of the most important sources, the ocean emissions and relative transport pathways of iodine, as well as the preservation after deposition are still not well known, especially in the arid areas of central Asia. A peat sediment core collected nearby Barkol Lake from northwest China was analyzed for iodine isotopes (I-127 and I-129). The observed high I-127 concentration in the top 2 cm indicated a significant accumulation of iodine in the surface oxic conditions due to the continuous sources of incompletely decomposed organic matter. Dissociation of iodine into pore waters occurred once the anoxic conditions established beneath the surface by a serial reduction reaction during the degradation of organic matter. The temporal variation of anthropogenic I-129 in the peat sediment recorded its sources and transport pathways. Besides the global fallout I-129 during late 1950s and early 1960s, the significantly increased air releases from the European nuclear fuel reprocessing plants during 1975-1997 and the increased marine discharges since 1990s contributed the major portion of I-129 in the peat core. The major transport pathway of I-129 from the Europe was through Westerlies following the re-emission of the marine discharged I-129 to the atmosphere, indicating a clearly ocean emitted iodine in the concerned central Asia. (C) 2021 Elsevier Ltd. All rights reserved
Unify the exposure and the burial age calculating methods by in situ produced cosmogenic nuclides
No full textThe exposure and burial ages were calculated using in situ produced cosmogenic nuclides by different methods. In fact, both exposure and burial processes involve production and reduction of cosmogenic nuclides, thus the nuclide concentration calculating methods have similarities in principle. As far as the depth from earth surface of a sample in its exposure or burial history is considered, erosion decreases the depth of the sample, while burial increases the depth, which is just an opposite process. The produce rates of in situ produced cosmogenic nuclides are correlated with the depth from the earth surface in the form of exponential function. According to the calculating principle of the relationship among in situ produced cosmogenic nuclide concentration, exposure time and erosion rate, it is deduced that the constant burial rate (beta) can be regarded as negative constant erosion rate (-epsilon) in calculating the sample concentration variation with time in the process of burial, taking the current produce rate of the sample as the standard. Thus, the equation for calculating exposure age and burial age is unified. In the case of non -uniform burial rate, the burial rate can still be regarded as the negative erosion rate by derivative calculation. On the basis that burial rate and erosion rate are denoted by the same parameter, and the burial rate can be regarded as the negative erosion rate, the calculation equation of nuclide concentration of sample under different burial (erosion) modes is deduced. The burial (exposure) age of samples with complex evolution processes can be calculated according to different burial (erosion) modes theoretically
Process optimization of plasma-catalytic formaldehyde removal using MnOx-Fe2O3 catalysts by response surface methodology
No full textTo remove the toxic formaldehyde efficiently, a non-thermal plasma (NTP) system incorporated with MnOx-Fe2O3 catalyst has been developed herein. A response surface methodology (RSM) was utilized to explore the effects of a variety of experimental parameters (gas flow rate, molar ratio of Fe/Mn, and discharge power) on formaldehyde degradation systematically. The results demonstrated that the discharge power has the greatest impact on the formaldehyde degradation process, while the molar ratio of Fe/Mn has the least influence. Moreover, the amount of adsorbed oxygen species, reducibility, and average specific surface area of the tested catalyst are estimated as the dominant factors influencing the catalytic performance. Importantly, the optimal formaldehyde removal efficiency (95.01%) and CO2 selectivity (86.20%) were acquired at 5 W discharge power, 0.5 L min(-1) gas flow rate, and 0.71 Fe/Mn molar ratio. This study can thus provide an efficient strategy for formaldehyde removal
A 120-year seasonally resolved speleothem record of precipitation seasonality from southeastern China
No full textSpeleothem oxygen isotope (delta O-18(s)) record as a climatic proxy in southeastern China is still in debate due to multifaceted influencing factors, a modern delta O-18(s) record, which can be calibrated or compared with observational data, is critical to explore the interpretation of delta O-18(s) proxy. Here we present a seasonally resolved delta O-18(s) record spanning the interval of 1898-2018 CE from Niubi Cave, Guangdong Province, southeastern China. A comparison between the Niubi delta O-18(s) and instrumental data reveals that the Niubi delta O-18(s) variability is primarily controlled by changes in precipitation seasonality modulated by El Nino-Southern Oscillation on interannual to interdecadal timescales. Higher (lower) delta O-18(s) values correspond to lower (higher) ratios of the East Asian summer monsoon/non-summer monsoon precipitation during the El Nino (La Nina) events associated with concomitant changes in the outgoing longwave radiation, wind field and Western Pacific Subtropical High. While similar to 73% historical drought events correlate to positive anomalies in Niubi delta O-18(s) values over the last 120 years, the rest of drought events associate with the negative delta O-18(s) anomalies. This observation suggests two different mechanisms for the drought events with more and less diminution of rainfall amount in the East Asian summer monsoon relative to the non-summer monsoon precipitation, respectively. Additionally, our Niubi delta O-18(s) record from southeastern China, together with other high-resolution speleothem and tree ring records, demonstrate a "tripole pattern" of summer precipitation during the last similar to 100 years in eastern China. (C) 2021 Elsevier Ltd. All rights reserved
GDGTs-based quantitative reconstruction of water level changes and precipitation at Daye Lake, Qinling Mountains (central-east China), over the past 2000 years
No full textAlpine lakes are natural rain gauges, and reconstructing changes in their water level is a key to understanding the regional hydrological environment, climate change and vegetation evolution. Precipitation in the northern and the southern parts of the eastern monsoon region of China exhibits a centennial scale inverse relationship over the past 2000 years; however, there is substantial uncertainty regarding the temporal range of this dipolar pattern. In order to better understand this north-south pattern of precipitation variation and its driving mechanism, we analyzed isoGDGTs biomarker compounds in a sediment core from alpine Daye Lake, in the Qinling Mountains, in the north-south climatic transition zone of eastern China. Measurements of %Cren were used to reconstruct changes in lake level over the past 2000 years. The results show that, from 240 to 1300 CE, prior to the Little Ice Age, the lake level changes were consistent with the precipitation record for the northern part of eastern China, with the lake reaching its highest level of 25 +/- 7.17 mat 555 CE; subsequently, the lake fell to its lowest level of 12 +/- 7.17 m at 1030 CE. During the Little Ice Age, the water level maintained an increasing trend, especially during the last three centuries, when it remained above 20 +/- 7.17 m, which is consistent with the precipitation record from southern China. The results indicate that the climatically transitional Qinling region has a complex history of climate change. During the early part of the record (240-130 0 CE), the level of Daye Lake and the East Asian summer monsoon precipitation were in phase, controlled mainly by the strength of the East Asian summer monsoon. In contrast, since the Little Ice Age (1300 CE to the present), under the influence of ENSO, the westward extension and southward retreat of the West Pacific Subtropical High caused the rain belt to shift southward, decreasing the water vapor supply to the Qinling Mountains. The ascent of moisture-bearing air over the Qinling Mountains resulted in orographic rainfall, while the weakening of evaporation during the Little Ice Age reduced the evaporation of water vapor and also contributed to the continued rise of the level of Daye Lake. The abundant precipitation in the Qinling region during the Little Ice Age provided water resources to sustain human activities in the downstream Weihe Plain, but was also a major cause of flooding. (C) 2021 Elsevier Ltd. All rights reserved
Determination of ultra-trace level plutonium isotopes in soil samples by triple-quadrupole inductively coupled plasma-mass spectrometry with mass-shift mode combined with UTEVA chromatographic separation
No full textAlthough triple-quadrupole inductively coupled plasma-mass spectrometry (ICP-MS/MS) has become an attractive technique for the measurement of long-lived radionuclides, the abundance sensitivity, isobaric and polyatomic ions interferences seriously restrict the application. The spectral peak tailing and uranium hydrides (UH+, UH2+) from U-238 have a serious influence on the accurate measurement of Pu-239 and Pu-240, especially for the ultra-trace level plutonium isotopes in the higher uranium sample. A new method was developed using ICPMS/MS measurement in mass-shift mode with collision-reaction gas combined with a chemical separation procedure. As O-2 readily converted Pu+ ion to PuO2+, while disassociated the interfering diatomic ions of interfering elements (U, Pb, Hg, Tl, etc.), the interferences from these elements were completely eliminated if plutonium was detected as PuO2+ at the m/z more than 270. By the mass filter in MS/MS mode combined with O-2 as reaction gas the lower peak tailing of U-238(+) (<5 x 10(-12)) was significantly suppressed. By this way, the (UO2H+)-U-238/(UO2+)-U-238 atomic ratio was reduced to 4.82 x 10(9), which is significantly lower than that of other collision-reaction gas modes. Interferences from Pb, Hg and Tl polyatomic ions were also completely eliminated. Thus, accurate measurement of ultra-trace level 239Pu in high uranium sample solutions with the Pu-239/U-238 concentration ratio of 10(-10) was achieved by the mass-shift mode with 0.15 mL/min O-2/He + 12.0 mL/min He as collision-reaction gas, and high elimination efficiency of uranium interferences up to 10(14) can be obtained by combination with the chemical separation using a single UTEVA resin column. The developed method can be applied to accurately determine the fg level Pu-239 in high uranium samples, such as large-size deep seawater, deep soil and sediment, uranium debris of nuclear fuel
"Tiny Wiggles" in the Late Miocene Red Clay Deposits in the North-East of the Tibetan Plateau
No full textSmall amplitude or short period geomagnetic anomalies known as "tiny wiggles" (TWs) are often hard to identify because of magnetic signal smoothing in the marine record of geomagnetic reversals. We report here the late Miocene record of geomagnetic reversals in the aeolian red clay sediments of Linxia Basin in China that enables us to identify two TWs. We performed magnetostratigraphy dating and used spectral analysis to distinguish orbital cycles in the records of magnetic susceptibility (MS) and sedimentary grain size (GS) and develop an orbitally tuned age model. The presence of two TWs in the study section, that correspond to C5n.2n-3 and C5r.2r-1, is confirmed by orbital calibration of our age model through recognition of eccentricity, obliquity and precession in MS and GS records
The "Hockey Stick" Imprint in Northwest African Speleothems
No full textWe present absolutely dated speleothem delta O-18 records spanning the past similar to 1.5 kyr, which provide new evidence of the transmission of an anthropogenic signal to natural climatic archives in NW Africa. Combined with three other speleothem delta O-18 records from SW Morocco, the results indicate unprecedentedly dry conditions during the 20th century, which developed more rapidly than those during the Medieval Climate Anomaly (900-1350 CE), likely due to rising atmospheric CO2 levels. The 20th century drying evident in the speleothem records is consistent with the "Hockey Stick" pattern of increasing temperatures due to global warming. We demonstrate that this rapid drying is linked to warmer sea surface temperatures (SSTs) over the Azores High region, and cooler local SSTs off the coast of NW Africa. These changes intensified the Canary Current Upwelling, which promoted increased biological productivity in the surface water and enhanced the coastal fishing industry in Morocco
Re-utilization of Chinese medicinal herbal residues improved soil fertility and maintained maize yield under chemical fertilizer reduction
No full textExcessive utilization of chemical fertilizers (CF) is not a sustainable agricultural development strategy due to adverse effects on soil health. In contrast, a combination of organic and mineral fertilizers has a positive effect on both soil health and productivity. Chinese medicinal herbal residues (CMHR) is the plant material wastes remaining after drug extraction but has not been extensively used as fertilizer. We evaluated application of CMHR to maize fields over 3 consecutive growing seasons in the presence and absence of standard CF to assess improvements in soil fertility, maize yields and sustainable development. CMHR fertilization increased soil organic matter and total N and K when mixed with chemical fertilizer at 50 and 75% the standard application rate. Soil organic matter increased by 27.0-51.4% and available -N, -P and -K levels and grain yields as well as N and P use efficiency in the presence of CMHR mixes were similar to levels obtained with chemical fertilizer only. These increases in production were due to increased leaf areas, photosynthetic rates, grain number and 1000-grain weights. The addition of CMHR to fields posed a slightly risk of toxic-metal pollution. Overall, we found that (1) CMHR can be used as an effective organic fertilizer and replace up to 50% of the amount of chemical fertilizer normally applied to fields without hampering maize grain yields and (2) CMHR application to agricultural fields is an effective recycling strategy and nutrient management practice to improve soil fertility under CF usage reduction
Permafrost thaw induced abrupt changes in hydrology and carbon cycling in Lake Wudalianchi, northeastern China
No full textLakes in the permafrost zone have been proposed to serve as key outlets for methane and carbon dioxide emissions. However, there has been no geological record of the hydrological and biogeochemical responses of lakes throughout the thawing of surrounding permafrost. We use multiple biomarker and isotopic proxies to reconstruct hydrological and biogeochemical changes in Lake Wudalianchi in northeastern China during regional thawing of the permafrost. We show permafrost thawing, as indicated by lignin degradation, initiated rapid lake water freshening as a result of the opening of groundwater conduits, and negative organic delta 13C excursion due to increased inorganic and organic carbon fluxes. These hydrological changes were followed, with an similar to 5-7 yr delay, by abrupt and persistent increases in microbial lake methanotrophy and methanogenesis, indicating enhanced anaerobic organic decomposition and methane emissions from lakes as permafrost thaws. Our data provide a detailed assessment of the processes involved during permafrost thaw, and highlight the importance of lakes in ventilating greenhouse gases to the atmosphere