11 research outputs found
Carbon isotopic composition and its implications on paleoclimate of the underground ancient forest ecosystem in Sihui, Guangdong
No full textWe present the carbon isotopic composition of the total organic carbon (TOC) and fine roots in the sedimentary profile from the underground ancient forest in Sihui to study the climatic and environmental changes from 4.5 ka BP to 0.6 ka BP. Results show that C(3) plant was the main vegetation from 4.5 ka BP to 0.6 ka BP in this region. The ancient forest began to develop in the wetland at around 4 ka BP and disappeared together with the wetland at about 3.0 ka BP, implying that the climate had changed greatly at around 3.0 ka BP. As indicated by the simulation results, the content of atmospheric CO(2) increased slightly during 3.5 ka BP to 3.0 ka BP, implying climate warming during that period. The interval of radiocarbon age between 3.0 ka BP to 1.2 ka BP was possibly caused by the strong erosion when the block was lifted in the neotectonic movement. From 1.2 ka BP to 0.6 ka BP, the region remained in terrestrial sedimentary environment, and the surface plant biomass declined gradually. Drought caused by the climate change was the likely cause for the disappearance of the ancient forest. South transition of Intertropical Convergence Zone (ITCZ) was probably the main mechanism for the climate change.Geosciences, MultidisciplinarySCI(E)EI3ARTICLE5638-6465
AMS measurements of Be-10 and C-14 in loess profile at Donglingshan, Beijing
No full textA loess profile in Donglingshan site (40 degrees 02'N, 115 degrees 27'E) near Beijing was chosen to study the loess formation process and paleo-climate variation. Thirty eight samples were collected and analyzed for C-14, Be-10 as well as MS. TOC and delta C-13. Based on C-14 measurements, we established a time scale for this loess profile during Holocene. The averaged Be-10 deposition flux was found to be 4.87 x 10(6) atoms/cm(2) year. This is similar to the flux of 4.2 x 10(6) atoms/cm(2) year estimated for Chinese Loess Plateau in central China. High Be-10 concentrations of 3.85-5.66 x 10(8) atoms/g for the samples in layer 23-39 cm from 2965 to 528 years BP suggest a warm and humid weather during this period. MS values have similar variation with Be-10 and reflect the similar paleo-climate information. TOC and delta C-13 suggest that the vegetation around Donlingshan area was C-3 type plants during entire Holocene. (C) 2009 Elsevier B.V. All rights reserved.Instruments & InstrumentationNuclear Science & TechnologyPhysics, Atomic, Molecular & ChemicalPhysics, NuclearSCI(E)EICPCI-S(ISTP)
Carbon isotopic composition, turnover and origins of soil CO2 in a monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir, South China
No full textCarbon isotopic compositions of soil CO2 in rainy season (July) from two natural soil profiles (DHLS & DHS) in the monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir (DBR), South China, are presented. Turnover and origins of soil CO2 are preliminarily discussed in this paper. Results show that the content of soil CO2 varies between 6120 and 18718 ppmv, and increases with increasing depth until 75 cm, and then it declines. In DHLS, soil CO2 delta C-13 ranges from -24.71aEuro degrees to -24.03aEuro degrees, showing a significant inverse correlation (R (2)=0.91) with the soil CO2 content in the same layer. According to a model related to soil CO2 delta C-13, the soil CO2 is mainly derived from the root respiration (> 80%) in DHLS. While in DHS, where soil CO2 delta C-13 ranges from -25.19aEuro degrees to -22.82aEuro degrees, soil CO2 is primarily originated from the decomposition of organic matter (51%-94%), excluding the surface layer (20 cm, 90%). Radiocarbon data suggest that the carbon in soil CO2 is modern carbon in both DHLS and DHS. Differences in C-14 ages between the "oldest" and "youngest" soil CO2 in DHLS and DHS are 8 months and 14 months, respectively, indicating that soil CO2 in DHLS has a faster turnover rate than that in DHS. The Delta C-14 values of soil CO2, which range between 100.0aEuro degrees and 107.2aEuro degrees and between 102.5aEuro degrees and 112.1aEuro degrees in DHLS and DHS, respectively, are obviously higher than those of current atmospheric CO2 and SOC in the same layer, suggesting that soil CO2 is likely an important reservoir for Bomb-C-14 in the atmosphere.Multidisciplinary SciencesSCI(E)1ARTICLE232548-25565
SEASONAL C-14 AND SR/CA RECORDS OF A MODERN CORAL AROUND DAYA BAY NUCLEAR POWER PLANTS
No full textDue to an increasing number of nuclear reactors in operation, the radiocarbon (C-14) released from nuclear power plants (NPPs) has become an important anthropogenic source of C-14. The examination of seasonal. 14C and monthly Sr/Ca, Mg/Ca variations in a coral in Daya Bay (China) shows that NPPs located there have an impact on the Delta C-14 level and sea surface temperature (SST). The Mg/Ca variation was in good correlation with the Pacific Decadal Oscillation (PDO) before the operation of Ling'ao NPP in 2002, but this correlation became weak due to an abnormally higher SST after 2002. As illustrated by the Delta C-14 variation in the coral, there were two relative increases of Delta C-14 values in 1994 and 2002 when Daya Bay NPP and Ling'ao NPP began operations, respectively. The C-14 released from NPPs, instead of oceanic circulation, is probably the primary factor on the Delta C-14 variation in Daya Bay during the NPPs' operation. The relative increase in Delta C-14 value was similar to 80%, which equals to similar to 18Bq/kgC in specific activity. The seasonal variability in Delta C-14 value usually peaked in summer, the real reason of which was unknown. This study sheds light on how the NPPs influence the C-14 content and SST in surrounding marine environment.National Natural Science Foundation of China [41403011]SCI(E)ARTICLE31035-10465
Regional Δ14C patterns and fossil fuel derived CO2 distribution in the Beijing area using annual plants
No full text
Carbon isotopic composition, turnover and origins of soil CO2 in a monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir, South China
No full textA high resolution method for C-14 analysis of a coral from South China Sea: Implication for "AD 775" C-14 event
No full textA pre-heating method that improves the background and precision of C-14 dating significantly was applied for fossil coral dating with high resolution in our lab in Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS). The reaction tube is heated under 300 degrees C in a vacuum line before it is used for graphitization. The method can reduce the contamination absorbed in TiH2, Zn and Fe power placed in the graphitization tube. With the pre-heating and average drilling method, bi-weekly resolution C-14 dating in a fossil coral is carried out to investigate the "AD 775 C-14 spike event". Different from the tree ring C-14 archives with the C-14 spike of similar to 15 parts per thousand (Delta C-14), the C-14 spike in the coral shows an abrupt peak of 45 parts per thousand and two smaller spikes of Delta C-14 > 20 parts per thousand in half a year in AD 776. And then, the C-14 content in coral decreases gradually in AD 777. The peak time of the C-14 spike event likely occurs in the summer of AD 776 according to the delta O-18 variation in coral. High-resolution dating of C-14 in coral provides not only a more detail process of the event than that from tree rings, but also the first report of the event from sea ecosystem. Both of them suggest an extraterrestrial origin of the event cause. (C) 2015 Elsevier B.V. All rights reserved.Chinese Academy of Sciences Equipment Function Development and Technological Innovation [YZ2011046]; State Key Laboratory of Isotope Geochemistry [SKLIG-KF-12-01, SKLIG-KF-12-02, SKLIG-JY-12-01]SCI(E)[email protected]
Ocean circulation and climate variability in the northern South China Sea during the Greek Minimum derived from coral Delta 14C and Sr/Ca records
No full textOcean circulation transports heat, salt and nutrients, and has profound impacts on the marine environment and climate change. However, the seasonal to centennial variations of the paleocirculation of the South China Sea (SCS) and their driving forces are still unclear due to limited records. Here we reconstructed a high-resolution Delta 14C record of a coral from Sanya to investigate the seasonal variations of the SCS ocean circulation around 2300 cal yr BP during a grand solar minimum (GSM) period. The seasonal Delta 14C variability shows the influence of coastal upwelling caused by the East Asian Summer Monsoon (EASM) in summer and the effect of water intrusion from the western Pacific Ocean driven by the Kuroshio Intrusion (KI) in winter. We compiled the marine radiocarbon reservoir correction (Delta R) records since 2500 cal yr BP, which indicate a gradual decrease of up -welling significantly correlated with the EASM. Comparisons with other climate records suggest that both the EASM and KI may regulate the ocean circulation variability on centennial time scales. As a good index of the sea surface temperature (SST), our Sr/Ca record and spectral analysis results show a low temperature and a low frequency of El Nin similar to o-Southern Oscillation (ENSO) events around 2300 cal yr BP. Moreover, the composite coral Sr/Ca-SST and ENSO index records since 2500 cal yr BP show relatively low SST and weak ENSO during GSMs, supporting the modulation of tropical SST and ENSO by solar activity. Our study has provided high-resolution proxy data and revealed the driving forces of ocean circulation and climate change in the SCS at multiple time scales, which should be considered in further modeling work
Low-Velocity Impact Behaviour of Titanium-Based Carbon-Fibre/Epoxy Laminate
No full textThis study investigated the low-velocity impact response of titanium-based carbon-fibre/epoxy laminate (TI-CF FML). A comprehensive experimental study was carried out with impact energies ranging from 16.9 J to 91.9 J. Finite element analysis, performed using ABAQUS, was employed to elucidate the failure mechanisms of the laminate. Three distinct damage modes were identified based on the impact energy levels. The energy absorption characteristics of the TI-CF FML were analysed, revealing that maximum energy absorption is achieved and remains constant after penetration occurs. The relationship between impact force and displacement was also explored, showing that the laminate can withstand a peak force of 13.1 kN. The research on the impact resistance, damage mechanisms and energy absorption capacity of TI-CF FML provides an in-depth understanding of the impact behaviour of the laminate and its suitability for various industrial applications
