The utilization of palynological data for plant diversity reconstructions offers notable advantages in addressing the discontinuity of plant fossils in the stratigraphic record. However, additional studies of modern p...The utilization of palynological data for plant diversity reconstructions offers notable advantages in addressing the discontinuity of plant fossils in the stratigraphic record. However, additional studies of modern processes are required to validate or refine the accuracy of diversity results obtained from palynological data. In this study, we used a modern pollen dataset of China to compare the accuracy of plant diversity reconstructions using five different palynological diversity indices(i.e., the pollen species number, Berger-Parker index, Simpson diversity index, Hill index, and Shannon-Wiener index) over a large spatial scale. We then identified climate factors that are most strongly correlated with these patterns of plant diversity. We found that the index that most accurately reflects plant diversity is the Shannon-Wiener index. Our analyses indicated that the most effective indices at reflecting plant diversity are the Shannon-Wiener index and Berger-Parker index. Numerical analysis revealed that palynological diversity(measured using the Shannon-Wiener index) was strongly correlated with climatic parameters, in particular average temperature in the coldest month and annual precipitation,suggesting these factors may be primary determinants of plant diversity distribution. We also found that a threshold value of the normalized Shannon-Wiener index(NH = 0.4) approximately aligns with the contour line specifying 400 mm annual precipitation, serving as a rudimentary indicator for assessing plant diversity in arid versus humid climates. This study suggests that pollen diversity indices have remarkable potential for quantitatively reconstructing paleoclimatic parameters.展开更多
As a crucial part of the Asian monsoon stretching from tropical India to temperate East Asia, the Indian monsoon(IM) contributes predominant precipitation over Asian continent. However, our understanding of IM’s onse...As a crucial part of the Asian monsoon stretching from tropical India to temperate East Asia, the Indian monsoon(IM) contributes predominant precipitation over Asian continent. However, our understanding of IM’s onset, development and the underlying driving mechanisms is limited. Increasing evidence indicates that the IM began in the Eocene or even the Paleocene and was unexceptionally linked to the early rise of the Tibetan Plateau(TP). These were challenged by the heterogeneous and diachronous uplift of the TP and all the reported records were confined to tropical zone under tropical monsoon driven by the Intertropical Convergence Zone(ITCZ) that is irrelevant to the TP. Therefore, reliable paleoclimatic records from the extra-tropical IM region is crucial to reveal how the tropical IM expanded to subtropical and temperate zones and what driving factors might be related to it. Here we present robust Eocene paleoenvironmental records from central Yunnan(~26°N) in subtropical East Asia. The multiproxy results of two sites demonstrate a consistent sudden switch from a dry environment in the early Eocene to a seasonally wet one at 41 Ma, suggesting a jump of the tropical IM to the southern subtropical zone at 41 Ma.The full collision of India with Asia, and the resulting changes in paleogeography at 41 Ma(closure of the Neotethys sea, retreat of the Paratethys seas, fast northward movement of the southern margin of the TP and rise of the central TP), aided by synchronous Antarctic cooling, might have worked together to drive the IM enhancement and northward expansion.展开更多
Digital holography was used for in situ monitoring of the dynamic stress corrosion processes occurring at the Alloy 625|0.5 M NaCl interface.The introduction of elastic deformation to Alloy 625 through constant extens...Digital holography was used for in situ monitoring of the dynamic stress corrosion processes occurring at the Alloy 625|0.5 M NaCl interface.The introduction of elastic deformation to Alloy 625 through constant extension rate tensile loading increased the anodic and corrosion currents.These increases were attributed to the increased stress caused by elastic deformation,which increased the number of defects in the oxide film on the surface of Alloy 625 and promoted stress corrosion;this was verified by the fact that the accept density(N_(A))was nearly ten times greater with elastic deformation than without elastic deformation.Intergranular corrosion(IGC)was induced without elastic deformation.IGC induction occurred because chloride ions were readily adsorbed at the grain boundaries and were more active than the grain bodies.However,the application of elastic deformation induced cracks on the alloy surface to enhance stress corrosion,and it inhibited the development of IGC because the cracks were more susceptible to corrosion than the grain boundaries.In-line digital holography revealed that the cracks were initiated in a certain area and progressively advanced to adjacent areas with applied elastic tensile stress.展开更多
基金co-supported by the National Key Research and Development Program of China(2022YFF0800800)the National Natural Science Foundation of China(41988101-01,42130205)the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0707)。
文摘The utilization of palynological data for plant diversity reconstructions offers notable advantages in addressing the discontinuity of plant fossils in the stratigraphic record. However, additional studies of modern processes are required to validate or refine the accuracy of diversity results obtained from palynological data. In this study, we used a modern pollen dataset of China to compare the accuracy of plant diversity reconstructions using five different palynological diversity indices(i.e., the pollen species number, Berger-Parker index, Simpson diversity index, Hill index, and Shannon-Wiener index) over a large spatial scale. We then identified climate factors that are most strongly correlated with these patterns of plant diversity. We found that the index that most accurately reflects plant diversity is the Shannon-Wiener index. Our analyses indicated that the most effective indices at reflecting plant diversity are the Shannon-Wiener index and Berger-Parker index. Numerical analysis revealed that palynological diversity(measured using the Shannon-Wiener index) was strongly correlated with climatic parameters, in particular average temperature in the coldest month and annual precipitation,suggesting these factors may be primary determinants of plant diversity distribution. We also found that a threshold value of the normalized Shannon-Wiener index(NH = 0.4) approximately aligns with the contour line specifying 400 mm annual precipitation, serving as a rudimentary indicator for assessing plant diversity in arid versus humid climates. This study suggests that pollen diversity indices have remarkable potential for quantitatively reconstructing paleoclimatic parameters.
基金co-supported by the Strategic Priority Research Program of Chinese Academy of Sciences(XDA20070201)the National Natural Science Foundation of China Basic Science Center for Tibetan Plateau Earth System(41988101-1)+1 种基金the National Natural Science Foundation of China(41620104002)the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0707).
文摘As a crucial part of the Asian monsoon stretching from tropical India to temperate East Asia, the Indian monsoon(IM) contributes predominant precipitation over Asian continent. However, our understanding of IM’s onset, development and the underlying driving mechanisms is limited. Increasing evidence indicates that the IM began in the Eocene or even the Paleocene and was unexceptionally linked to the early rise of the Tibetan Plateau(TP). These were challenged by the heterogeneous and diachronous uplift of the TP and all the reported records were confined to tropical zone under tropical monsoon driven by the Intertropical Convergence Zone(ITCZ) that is irrelevant to the TP. Therefore, reliable paleoclimatic records from the extra-tropical IM region is crucial to reveal how the tropical IM expanded to subtropical and temperate zones and what driving factors might be related to it. Here we present robust Eocene paleoenvironmental records from central Yunnan(~26°N) in subtropical East Asia. The multiproxy results of two sites demonstrate a consistent sudden switch from a dry environment in the early Eocene to a seasonally wet one at 41 Ma, suggesting a jump of the tropical IM to the southern subtropical zone at 41 Ma.The full collision of India with Asia, and the resulting changes in paleogeography at 41 Ma(closure of the Neotethys sea, retreat of the Paratethys seas, fast northward movement of the southern margin of the TP and rise of the central TP), aided by synchronous Antarctic cooling, might have worked together to drive the IM enhancement and northward expansion.
基金supported by the National Natural Science Foundation of China(No.21972059)the Priority Academic Programme Development of Jiangsu Higher Education Institutions(PAPD).
文摘Digital holography was used for in situ monitoring of the dynamic stress corrosion processes occurring at the Alloy 625|0.5 M NaCl interface.The introduction of elastic deformation to Alloy 625 through constant extension rate tensile loading increased the anodic and corrosion currents.These increases were attributed to the increased stress caused by elastic deformation,which increased the number of defects in the oxide film on the surface of Alloy 625 and promoted stress corrosion;this was verified by the fact that the accept density(N_(A))was nearly ten times greater with elastic deformation than without elastic deformation.Intergranular corrosion(IGC)was induced without elastic deformation.IGC induction occurred because chloride ions were readily adsorbed at the grain boundaries and were more active than the grain bodies.However,the application of elastic deformation induced cracks on the alloy surface to enhance stress corrosion,and it inhibited the development of IGC because the cracks were more susceptible to corrosion than the grain boundaries.In-line digital holography revealed that the cracks were initiated in a certain area and progressively advanced to adjacent areas with applied elastic tensile stress.
