The magnetic susceptibility of modern soils in China and its use for paleoclimate reconstruction

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.