No abstract

No abstract

Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining-one of the few palaeoclimate sites in the currently arid western Loess Plateau of China-illustrate the importance of making many types of rockmagnetic measurements other than susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentration and mineralogy of the magnetic fraction.The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. The resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. The data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites.In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records.

Abstract. The relative contributions of C3 and C4 plants to vegetation at a given locality may be estimated by means of δ13C of soil organic matter. This approach holds a great potential for paleoecological reconstruction using paleosols. However, two main uncertainties exist, which limits the accuracy of this application. One is δ13C-enrichment as the plant carbon becomes incorporated into soil organic matter. The other is due to environmental influences on δ13C of plants. Two types of data were collected and analyzed with an objective of narrowing the error of paleovegetation reconstruction. First, we investigated δ13C variations of 557 C3 and 136 C4 plants along a precipitation gradient in North China. A strong negative correlation is found between the δ13C value of C3 plants averaged for each site and the annual precipitation with a coefficient of −0.40‰/100mm, while no significant coefficients were found for C4 plants. Second, we measured δ13C of soil organic matters for 14 soil profiles at three sites. The isotopic difference between vegetation and soil organic matter are evaluated to be 1.8‰ for the surface soil and 2.8‰ for the soil at the bottom of soil profiles. We conducted a sample reconstruction of paleovegetation at the central Chinese Loess Plateau during the Holocene and the Last Glacial (LG), and conclude that, without corrections for δ13C-enrichment by decomposition, the C4 abundance would be overestimated. The importance and uncertainties of other corrections are also discussed.