To understand the origin of the ultrafine pedogenic components responsible for the magnetic susceptibility (MS) enhancement remains a major challenging problem in linking magnetic signal with paleoclimate. Here we examine the effect of the natural fires on the MS signal of both plants and modern soils and in particular the MS difference between C3 and C4 plant ashes and their influence on magnetic susceptibility. We also proved the influence of the different floral root systems on the MS signal of modern soils. We find that the C3 and C4 plants are different in their ability to enhance MS signal of modern soils. Increased MS signal of modern soils by C4 plants was much greater than that by C3 plants. 相似文献
Summary Magnetic susceptibility of more than 160 modern silty soil samples in China was measured to assess the relationship between
the magnetic susceptibility and modern climatic parameters. Correlation between magnetic susceptibility and mean annual temperature
(MAT) or mean annual precipitation (MAP), shows a complex picture and no single function can be found to fit all the data
on the national scale. In East China, where East Asian monsoon plays an important role for the climate conditions, magnetic
susceptibility increases with the increase of MAT or MAP in temperate semi-arid regions of the Loess Plateau and surrounding
areas. This can be attributed to increasing intensity of pedogenesis which would favor the formation of strongly magnetic
minerals and/or reduce depositional rate of eolian dust. Magnetic susceptibility tends to decrease with the increase of temperature
and precipitation in the tropical and subtropical warm and humid regions of the vast areas south of the Yangtze River. This
may be explained by pedogenic transformation of iron-bearing minerals to weakly magnetic minerals. Between these two different
correlation patterns, 15°C of MAT and/or 1200 mm of MAP seem to be the thresholds. In West China, the correlation becomes
quite complex in the great mountains and vast sedimentary basins in the north-west. This may be due to the prevailing continental
climate in this region and topographic contrast within short distance. The correlation for the Qinghai-Xizang (Tibetan) Plateau
is not clear because very few samples were collected. Fluctuations of paleo-temperature and paleo-precipitation at Luochuan
for the last 130 ka were estimated using the climofunction obtained from this study. 相似文献
A new pollen record from the lake of Co Ngoin in the central Tibetan Plateau provides information on the vegetation and climate changes during the last 2.8 Ma. Seven major significant changes in pollen associations indicate the processes of vegetation change and possible tectonic uplifts. The seven changes in vegetation succession include a temperate montane conifer and broad-leaved mixed forest, cold temperate montane dark conifer forest, alpine shrub-meadow and alpine desert, montane dark coniferous forest and alpine shrub meadow, montane dark coniferous forest and alpine shrub meadow, montane dark coniferous forest and alpine meadow, and alpine desert and meadow. The pollen record provides the evidence of at least five times tectonic uplifts occurring at about 2.58 Ma, 1.87 Ma, 1.17 Ma, 0.83 Ma, and 0.3 Ma ago, respectively. Before 0.8 Ma, this region maintained the altitude below 4000 m a.s.l. Larger amplitude of uplift occurring at about 0.8 Ma ago enforced the plateau rising into cryosphere, shaping the basic topographic pattern of modern plateau. The major successions in vegetation of this area were largely controlled by stepwise uplift of the Tibetan Plateau.