The evolution of Holocene climate was investigated using grain size and magnetic susceptibility of the Holocene paleosols from Baicaoyuan(BCY),Xifeng(XF) and Linyou(LY) sections in the northwest,central and southern C...The evolution of Holocene climate was investigated using grain size and magnetic susceptibility of the Holocene paleosols from Baicaoyuan(BCY),Xifeng(XF) and Linyou(LY) sections in the northwest,central and southern Chinese Loess Plateau(CLP).The results show that the Holocene in the B CY,XF and LY paleosol sections could be divided into three phases:during the early Holocene(11.8-10.5 kyr B.P.),increased magnetic susceptibility(χ) and frequency-dependent magnetic susceptibility(χ) and decreased median grain size(Md) indicate that the East Asian Summer Monsoon(EASM) has become more intense and the climate has changed from cold to warm.During the middle Holocene(10.5-5.0 kyr B.P.),the values of χ,χand 2-5 μm grain-size fraction(GT2/5) are higher and Md and 30-63 μm grain-size fraction(GT3 0/6 3) are the lowest,which reflect a warm and humid regional climate.At~8.0 kyr B.P.,there was a transient dry-cold climatic spike corresponding to a Heinrich Event,the cold event was likely due to the collapse of the Laurentide ice sheet.During the late Holocene(5.0-0 kyr B.P.),χ and χvalues are the lowest,while Md and GT30/63 are high,as proxies of a weakened EASM,when the dry-cold climate prevailed in the region.Decreased irradiance since 5.0 kyr B.P.may have caused climatic cooling and drying.Spatially,the increased main peak values and skewness from BCY,XF to LY sections show that the grain size became fine,the East Asian Winter Monsoon(EAWM) reduced,and climate was warmer and wetter from northwest to southeast.In addition,Md can be used as alternative proxy for EAWM,while χis positive with the intensity of EASM under semiarid climate conditions in CLP.展开更多
The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systemati...The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.展开更多
纳米Al2O3/ZrO2复合陶瓷具有优良的力学性能,良好的高温稳定性和化学稳定性,并具有良好的抗辐照效应,是目前极具潜力的一种纳米陶瓷材料。采用正电子寿命谱分析同时配合着X射线衍射(X-ray Diffraction,XRD)和透射电子显微镜(Transmissio...纳米Al2O3/ZrO2复合陶瓷具有优良的力学性能,良好的高温稳定性和化学稳定性,并具有良好的抗辐照效应,是目前极具潜力的一种纳米陶瓷材料。采用正电子寿命谱分析同时配合着X射线衍射(X-ray Diffraction,XRD)和透射电子显微镜(Transmission Electron Microscope,TEM)对纳米Al2O3、ZrO2和Al2O3/ZrO2复合陶瓷在不同退火温度下(室温−1000℃)的微结构及缺陷进行了研究。XRD研究表明:Al2O3、ZrO2和Al2O3/ZrO2纳米复合陶瓷三种样品退火温度低于500℃时,晶粒尺寸保持不变;随着退火温度的增加,Al2O3晶粒尺寸变化不大,ZrO2和Al2O3/ZrO2有所增加,但由于Al2O3的抑制,Al2O3/ZrO2的晶粒生长更缓慢。正电子寿命分析表明:样品内主要缺陷是空位、空位团和微孔洞,缺陷主要集中在晶界处。对比ZrO2纳米陶瓷内缺陷,Al2O3和Al2O3/ZrO2纳米复合陶瓷内空位团或微孔洞缺陷尺寸更大,而相对数量更少。退火温度低于500℃时,三种样品内平均缺陷密度基本不变,高于500℃时由于晶粒生长,缺陷开始恢复,ZrO2变化更明显,而Al2O3/ZrO2由于相互抑制对方的晶粒生长,稳定性更高,这与XRD结果一致。纳米Al2O3的TEM图显示出晶粒大小基本不随退火温度变化发生改变,而纳米Al2O3/ZrO2只有在退火温度高于500℃时,晶粒开始慢慢长大,并且发生了团聚,非常直观地证实了XRD和正电子的实验结果。展开更多
基金Under the auspices of the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(No.2019QZKK0704)Natural Science Foundation of China(No.41772168,42103046)Natural Science Foundation of Gansu Province(No.20JR5RA272,20JR5RA226)。
文摘The evolution of Holocene climate was investigated using grain size and magnetic susceptibility of the Holocene paleosols from Baicaoyuan(BCY),Xifeng(XF) and Linyou(LY) sections in the northwest,central and southern Chinese Loess Plateau(CLP).The results show that the Holocene in the B CY,XF and LY paleosol sections could be divided into three phases:during the early Holocene(11.8-10.5 kyr B.P.),increased magnetic susceptibility(χ) and frequency-dependent magnetic susceptibility(χ) and decreased median grain size(Md) indicate that the East Asian Summer Monsoon(EASM) has become more intense and the climate has changed from cold to warm.During the middle Holocene(10.5-5.0 kyr B.P.),the values of χ,χand 2-5 μm grain-size fraction(GT2/5) are higher and Md and 30-63 μm grain-size fraction(GT3 0/6 3) are the lowest,which reflect a warm and humid regional climate.At~8.0 kyr B.P.,there was a transient dry-cold climatic spike corresponding to a Heinrich Event,the cold event was likely due to the collapse of the Laurentide ice sheet.During the late Holocene(5.0-0 kyr B.P.),χ and χvalues are the lowest,while Md and GT30/63 are high,as proxies of a weakened EASM,when the dry-cold climate prevailed in the region.Decreased irradiance since 5.0 kyr B.P.may have caused climatic cooling and drying.Spatially,the increased main peak values and skewness from BCY,XF to LY sections show that the grain size became fine,the East Asian Winter Monsoon(EAWM) reduced,and climate was warmer and wetter from northwest to southeast.In addition,Md can be used as alternative proxy for EAWM,while χis positive with the intensity of EASM under semiarid climate conditions in CLP.
基金supported by the National Natural Science Foundation of China (40830105,40772109,40721061)the China Scholarship Council
文摘The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.
文摘纳米Al2O3/ZrO2复合陶瓷具有优良的力学性能,良好的高温稳定性和化学稳定性,并具有良好的抗辐照效应,是目前极具潜力的一种纳米陶瓷材料。采用正电子寿命谱分析同时配合着X射线衍射(X-ray Diffraction,XRD)和透射电子显微镜(Transmission Electron Microscope,TEM)对纳米Al2O3、ZrO2和Al2O3/ZrO2复合陶瓷在不同退火温度下(室温−1000℃)的微结构及缺陷进行了研究。XRD研究表明:Al2O3、ZrO2和Al2O3/ZrO2纳米复合陶瓷三种样品退火温度低于500℃时,晶粒尺寸保持不变;随着退火温度的增加,Al2O3晶粒尺寸变化不大,ZrO2和Al2O3/ZrO2有所增加,但由于Al2O3的抑制,Al2O3/ZrO2的晶粒生长更缓慢。正电子寿命分析表明:样品内主要缺陷是空位、空位团和微孔洞,缺陷主要集中在晶界处。对比ZrO2纳米陶瓷内缺陷,Al2O3和Al2O3/ZrO2纳米复合陶瓷内空位团或微孔洞缺陷尺寸更大,而相对数量更少。退火温度低于500℃时,三种样品内平均缺陷密度基本不变,高于500℃时由于晶粒生长,缺陷开始恢复,ZrO2变化更明显,而Al2O3/ZrO2由于相互抑制对方的晶粒生长,稳定性更高,这与XRD结果一致。纳米Al2O3的TEM图显示出晶粒大小基本不随退火温度变化发生改变,而纳米Al2O3/ZrO2只有在退火温度高于500℃时,晶粒开始慢慢长大,并且发生了团聚,非常直观地证实了XRD和正电子的实验结果。
