[1] Quaternary glacial/interglacial cycles have been imprinted on the Chinese loess/ paleosol sequences through pedogenesis. In order to accurately decode the paleoclimatic signals carried by these pedogenic particles it is essential to quantify the pedogenically produced magnetic particles in terms of mineralogy as well as grain size distribution (GSD). To date, the GSD has not been accurately determined because of the dearth of available means for analyzing extremely fine grained (nanometer-scale) pedogenic magnetic particles. Using low-temperature techniques, we systematically investigated the temperature dependency of c fd (defined as c 1Hz À c 10Hz , where c 1Hz and c 10Hz are AC magnetic susceptibility measured at 1 and 10 Hz, respectively) from two characteristic loess profiles, one located at the western Chinese Loess Plateau and the other in the central plateau. On the basis of Néel theory for a shape anisotropy dominant grain and experimental analysis at low temperatures, a quantitative GSD for pedogenic particles in Chinese loess/paleosols was constructed. We found that the dominant magnetic grain size lies just above the superparamagnetic/single-domain threshold ($20-25 nm) and that the GSD is almost independent of the degree of pedogenesis. This observation agrees well with other constraints from previous studies. This new GSD model improves our understanding of the pedogenic processes in Chinese loess, enabling further explicit linkage of environmental magnetism to paleoclimate changes.

[1] Chinese loess/paleosol sequences have been regarded as excellent continental archives for encoding continuous paleoclimatic variations over the past 2.5 Myr. However, the mechanism for magnetic enhancements (especially the low-field mass-specific magnetic susceptibility, c) of Chinese paleosols is still not completely resolved. This study quantifies contributions of aeolian and pedogenic magnetic particles to the bulk magnetic properties of the Chinese loess/paleosols by using a magnetic extraction technique. Magnetic properties of magnetic separates (extractable) and the corresponding residues (nonextractable) for five characteristic samples covering both loesses and paleosols were comprehensively investigated by hysteresis loops, frequency and low-temperature dependence of magnetic susceptibility, and interparametric ratios. Results show that (1) with moderate degrees of pedogenesis (c < 10 Â 10 À7 m 3 kg À1 ), c is enhanced more by increased concentration of stable single domain (SD) magnetic particles than by viscous superparamagnetic (SP) particles. For more mature paleosols with c > (10-12) Â 10 À7 m 3 kg À1 , contributions of pedogenically related fine-grained pseudosingle-domain (PSD, $100 nm to several microns) particles become significant; (2) pedogenic particles have a narrow grain size distribution concentrated above the SP/SD threshold; and (3) anhysteretic remanent magnetization (ARM) is carried dominantly by SD grains. Moreover, we propose that only the nonextractable fraction of c, saturation magnetization (M s ) and remanent magnetization (M rs ) show a strong relationship with the degree of pedogenesis. This new interpretation of magnetic enhancements helps us to retrieve more accurate and quantitative paleoclimatic signals recorded by the Chinese loess/paleosol sequences.