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Rixiang Zhu - One of the best experts on this subject based on the ideXlab platform.
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mineral Magnetic Variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling
Earth and Planetary Science Letters, 2006Co-Authors: Chenglong Deng, Qingsong Liu, John Shaw, Yongxin Pan, Rixiang ZhuAbstract:A high-resolution mineral Magnetic investigation has been carried out on the Jingbian loess/paleosol sequence at the northern extremity of the Chinese Loess Plateau. Results show that the Magnetic assemblage is dominated by large pseudo-single domain and multidomain-like magnetite with associated maghemite and hematite. Variations in the ratios of SIRM100mT/SIRM, SIRM100mT/SIRM30mT and SIRM100mT/SIRM60mT (SIRM is the saturation isothermal remanent magnetization; SIRMnmT represents the residual SIRM after an n mT alternating field demagnetization) have been used to document regional paleoclimate change in the Asian interior by correlating the mineral Magnetic record with the composite δ18O record in deep-sea sediments. The long-term up-section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long-term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema, respectively, which reveals a long-term decreasing trend in chemical weathering intensity in both glacial-stage source region (the Gobi and deserts in northwestern China) and interglacial-stage depositional area (the Loess Plateau region). We further relate this long-timescale Variation to long-term increasing aridification and cooling, during both glacial extrema in the dust source region and interglacial extrema in the depositional area, over the Quaternary period. Changes in those ratios are most likely due to Quaternary aridification and cooling driven by ongoing global cooling, expansion of the Arctic ice-sheet, and progressive uplift of the Himalayan–Tibetan complex during this period.
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mineral Magnetic Variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability
Journal of Geophysical Research, 2005Co-Authors: Chenglong Deng, Natasa J Vidic, Kenneth L Verosub, Michael J Singer, Qingsong Liu, John Shaw, Rixiang ZhuAbstract:[1] To retrieve reliable long-term paleoclimatic signals from the Chinese loess/paleosol sequences deposited over the past 2.6 Myr, multiparameter mineral Magnetic investigations have been conducted on the Jiaodao section on the Chinese central Loess Plateau. First, the lithogenic Magnetic components and the pedogenic overprinting were chemically separated by the citrate-bicarbonate-dithionite (CBD) method. The Magnetic properties of the least pedogenically altered loess units and post-CBD loess/paleosols are dominated by coarse-grained lithogenic magnetite. Increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite/maghemite. Long-term changes of the pre-CBD Magnetic properties suggest a long-term decrease in summer monsoon intensity and a long-term increase in winter monsoon intensity from the late Pliocene to the late Pleistocene. Long-term Variations of the post-CBD Magnetic properties suggest an increase in both concentration and grain size of coarse-grained lithogenic PSD/MD magnetite grains, and hence indicate a long-term increase in winter monsoon intensity over that period. The coercivity decrease of the lithogenic component for the loess unit L15 may be related to the accelerated uplift of the Tibetan Plateau and its adjacent regions during the period of L15 deposition. From paleosol S5 to loess L1, higher values of coercivity of the lithogenic component occur in typical loess and paleosols, and lower values are found at the loess/paleosol transition. These coercivity Variations are thought to be related to significant changes in the source region as well as dust deposition in the Loess Plateau caused by changes in ice/snow or vegetational cover. These new results lead to a better understanding of the relationships between the effects of tectonic, paleoclimatic, and paleoenvironmental processes in northwestern China.
Chenglong Deng - One of the best experts on this subject based on the ideXlab platform.
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mineral Magnetic Variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling
Earth and Planetary Science Letters, 2006Co-Authors: Chenglong Deng, Qingsong Liu, John Shaw, Yongxin Pan, Rixiang ZhuAbstract:A high-resolution mineral Magnetic investigation has been carried out on the Jingbian loess/paleosol sequence at the northern extremity of the Chinese Loess Plateau. Results show that the Magnetic assemblage is dominated by large pseudo-single domain and multidomain-like magnetite with associated maghemite and hematite. Variations in the ratios of SIRM100mT/SIRM, SIRM100mT/SIRM30mT and SIRM100mT/SIRM60mT (SIRM is the saturation isothermal remanent magnetization; SIRMnmT represents the residual SIRM after an n mT alternating field demagnetization) have been used to document regional paleoclimate change in the Asian interior by correlating the mineral Magnetic record with the composite δ18O record in deep-sea sediments. The long-term up-section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long-term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema, respectively, which reveals a long-term decreasing trend in chemical weathering intensity in both glacial-stage source region (the Gobi and deserts in northwestern China) and interglacial-stage depositional area (the Loess Plateau region). We further relate this long-timescale Variation to long-term increasing aridification and cooling, during both glacial extrema in the dust source region and interglacial extrema in the depositional area, over the Quaternary period. Changes in those ratios are most likely due to Quaternary aridification and cooling driven by ongoing global cooling, expansion of the Arctic ice-sheet, and progressive uplift of the Himalayan–Tibetan complex during this period.
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mineral Magnetic Variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability
Journal of Geophysical Research, 2005Co-Authors: Chenglong Deng, Natasa J Vidic, Kenneth L Verosub, Michael J Singer, Qingsong Liu, John Shaw, Rixiang ZhuAbstract:[1] To retrieve reliable long-term paleoclimatic signals from the Chinese loess/paleosol sequences deposited over the past 2.6 Myr, multiparameter mineral Magnetic investigations have been conducted on the Jiaodao section on the Chinese central Loess Plateau. First, the lithogenic Magnetic components and the pedogenic overprinting were chemically separated by the citrate-bicarbonate-dithionite (CBD) method. The Magnetic properties of the least pedogenically altered loess units and post-CBD loess/paleosols are dominated by coarse-grained lithogenic magnetite. Increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite/maghemite. Long-term changes of the pre-CBD Magnetic properties suggest a long-term decrease in summer monsoon intensity and a long-term increase in winter monsoon intensity from the late Pliocene to the late Pleistocene. Long-term Variations of the post-CBD Magnetic properties suggest an increase in both concentration and grain size of coarse-grained lithogenic PSD/MD magnetite grains, and hence indicate a long-term increase in winter monsoon intensity over that period. The coercivity decrease of the lithogenic component for the loess unit L15 may be related to the accelerated uplift of the Tibetan Plateau and its adjacent regions during the period of L15 deposition. From paleosol S5 to loess L1, higher values of coercivity of the lithogenic component occur in typical loess and paleosols, and lower values are found at the loess/paleosol transition. These coercivity Variations are thought to be related to significant changes in the source region as well as dust deposition in the Loess Plateau caused by changes in ice/snow or vegetational cover. These new results lead to a better understanding of the relationships between the effects of tectonic, paleoclimatic, and paleoenvironmental processes in northwestern China.
Qingsong Liu - One of the best experts on this subject based on the ideXlab platform.
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mineral Magnetic Variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling
Earth and Planetary Science Letters, 2006Co-Authors: Chenglong Deng, Qingsong Liu, John Shaw, Yongxin Pan, Rixiang ZhuAbstract:A high-resolution mineral Magnetic investigation has been carried out on the Jingbian loess/paleosol sequence at the northern extremity of the Chinese Loess Plateau. Results show that the Magnetic assemblage is dominated by large pseudo-single domain and multidomain-like magnetite with associated maghemite and hematite. Variations in the ratios of SIRM100mT/SIRM, SIRM100mT/SIRM30mT and SIRM100mT/SIRM60mT (SIRM is the saturation isothermal remanent magnetization; SIRMnmT represents the residual SIRM after an n mT alternating field demagnetization) have been used to document regional paleoclimate change in the Asian interior by correlating the mineral Magnetic record with the composite δ18O record in deep-sea sediments. The long-term up-section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long-term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema, respectively, which reveals a long-term decreasing trend in chemical weathering intensity in both glacial-stage source region (the Gobi and deserts in northwestern China) and interglacial-stage depositional area (the Loess Plateau region). We further relate this long-timescale Variation to long-term increasing aridification and cooling, during both glacial extrema in the dust source region and interglacial extrema in the depositional area, over the Quaternary period. Changes in those ratios are most likely due to Quaternary aridification and cooling driven by ongoing global cooling, expansion of the Arctic ice-sheet, and progressive uplift of the Himalayan–Tibetan complex during this period.
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mineral Magnetic Variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability
Journal of Geophysical Research, 2005Co-Authors: Chenglong Deng, Natasa J Vidic, Kenneth L Verosub, Michael J Singer, Qingsong Liu, John Shaw, Rixiang ZhuAbstract:[1] To retrieve reliable long-term paleoclimatic signals from the Chinese loess/paleosol sequences deposited over the past 2.6 Myr, multiparameter mineral Magnetic investigations have been conducted on the Jiaodao section on the Chinese central Loess Plateau. First, the lithogenic Magnetic components and the pedogenic overprinting were chemically separated by the citrate-bicarbonate-dithionite (CBD) method. The Magnetic properties of the least pedogenically altered loess units and post-CBD loess/paleosols are dominated by coarse-grained lithogenic magnetite. Increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite/maghemite. Long-term changes of the pre-CBD Magnetic properties suggest a long-term decrease in summer monsoon intensity and a long-term increase in winter monsoon intensity from the late Pliocene to the late Pleistocene. Long-term Variations of the post-CBD Magnetic properties suggest an increase in both concentration and grain size of coarse-grained lithogenic PSD/MD magnetite grains, and hence indicate a long-term increase in winter monsoon intensity over that period. The coercivity decrease of the lithogenic component for the loess unit L15 may be related to the accelerated uplift of the Tibetan Plateau and its adjacent regions during the period of L15 deposition. From paleosol S5 to loess L1, higher values of coercivity of the lithogenic component occur in typical loess and paleosols, and lower values are found at the loess/paleosol transition. These coercivity Variations are thought to be related to significant changes in the source region as well as dust deposition in the Loess Plateau caused by changes in ice/snow or vegetational cover. These new results lead to a better understanding of the relationships between the effects of tectonic, paleoclimatic, and paleoenvironmental processes in northwestern China.
M. Menvielle - One of the best experts on this subject based on the ideXlab platform.
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Solar flare effects at Ebre: Regular and reversed solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents
Journal of Geophysical Research, 1994Co-Authors: Joan-josep Curto, Christine Amory-mazaudier, J.m. Torta, M. MenvielleAbstract:This paperp resentsth e resultso f the analysiso f geoMagnetice ffectso f solarf lares (sfe) recordeda t Ebre observatory(4 0.8ø l atitudeN , 0.5ø l ongitudeE ) during3 3 years( 1953- 1985). At Ebre, locatedn eart he focusl atitude,t wo typeso f sfe can be observedr:e gulara nd reverseds fe.R egulars fea ret hosew hichh avep hased ifferencelse sst han9 0ø w ith the regular diurnal Magnetic Variation of the day, Sn. Reversed sfe are those which have phase differences greatert han 90ø with Sn.F rom these3 3 years,1 40 sfe eventsw ere selecteda nd a statistical studyw as performed.W e founda local time dependencoef the phased ifferencesb etweent he sfe and S n vectors. Morning hours have slightly positive values and afternoon hours have slightly negative ones. Reversed sfe, with a phase difference exceeding 90 ø, concentrate between1 0 and 12 hours.R everseds fe showa dominante quinoctiacl haracterA. lso, a weaker correlationw as foundb etweens olara ctivityw ith reverseds fe (r=-0.47)t han with regulars fe (r=-0.68).U sing data from 67 observatoriesw, e performeda globals tudyo f a sfe case,s een at Ebre as reverseds fe. In this case,i n the northernh emispheret,h e sfe systemw as about 1 hour of local time eastward of the S n system and formed 4 ø higher in latitude. Finally, we presenta model of two elliptical ionospherice quivalentc urrent systemsw ith focus offset about1 hour in local time to explaint he phased ifferenceb etweent he sfe and Sq Magnetic vectorso bserveda t Ebre. The parameterso f this model have been fitted from the resultso f a previouss tatisticaal nalysisf rom Ebre data. Spatiala nd temporald istributiono f the sfe and $q vector phasesa re calculatedw ith this model, and conditionsf or reverseds fe occurrence are predicted.
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Solar Flare effects at Ebre : regular and reversed solar flare effects, stastitical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents
Journal of Geophysical Research Space Physics, 1994Co-Authors: Joan-josep Curto, Christine Amory-mazaudier, J.m. Torta, M. MenvielleAbstract:This paper presents teh results of the analysis of geoMagnetic effects of solar flares (sfe) recorded at Ebre observatory (40.8° latitude N, 0.5° longitude E) during 33 years (1953-1985). At Ebre, located near the focus latitudes, two types of Sfe can be observed : regular an reversed Sfe. regular Sfa ar those which have phase differences less than 90° with the regular diurnal Magnetic Variation of the day, Sr. Reversed sfe are those which have phase differences greater than 90° with Sr. Frome these 33 years, 140 sfe events were selected and a ststistical study was performed. We found a local time dependenc of the phase differences between the Sfe and Sr vectors. Morning hours have slightly positive values and afternoon hours have slightly negative ones. Reversed Sfe, with a phase differenec exceeding 90°, concentrate between 10 and 12 hours. Reversed Sfe show a dominant equinoctial character. Also a weaker cirrelation was found between solar activity with reversed sfe (r=0.47) than with regular sfe (r=0.68).Using data from 67observatories, we performed a global study of a sfe case, seen at Ebre as reversed sfe. In this case in the northern hemispher, the sfe system was about 1 hour in local time eastward of the Sr system and formed a 4° higher in latitude. Finally we present a model of two elliptical ionospheric equivalent current systems with focus offset about 1 hour in local time to explain the phase difference between the sfe and sq Magnetic vectors observed at Ebre. The parameters of this model have been fitted from the result of a previoys statistical analysis from Ebre data. Spatial and temporal distribution of the Sfe and Sq vector phases are calculated with this model, and conditions for reversed Sfe occurence are predicted
D.w. Livelybrooks - One of the best experts on this subject based on the ideXlab platform.
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The simulation of Magnetic Variation anomalies using single-station data
Physics of the Earth and Planetary Interiors, 1993Co-Authors: R.j. Banks, A.a.k. Irving, D.w. LivelybrooksAbstract:Abstract Hypothetical event maps of the vertical field derived from single-station Magnetic Variation transfer functions are biased by the anomalous horizontal fields. An iterative scheme, proposed earlier, is used to estimate and correct for the anomalous fields. The scheme here is applied to single-station transfer functions from 90 sites in southern Scotland and northern England. It converges to a stable solution in four iterations, and the results compare favourably with those predicted in the southern part of the area using measured inter-station transfer functions. The resultant hypothetical event maps of the anomalous horizontal fields show that the Northumberland Trough and Southern Uplands conductivity anomalies are both strikingly linear features which correlate more closely than previously supposed with other geological and geophysical observations.