Quantifying paleoprecipitation of the Luochuan and Sanmenxia Loess on the Chinese Loess Plateau

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Paleoprecipitation is one of the most important paleoclimatic factors for monsoon studies. Magnetic properties of the Chinese loess/paleosol sequences have been demonstrated to be controlled strongly by the mean annual precipitation (MAP). In this study, temporal variations of MAPs were systematically investigated for the Luochuan (LC) and Sanmenxia (SMX) sequences from the loess unit L1 (~10ka) to the paleosol unit S5 (~620kyr) by applying the new climofunction MAP=8.06×χFD/HIRM+254 (where χFD and HIRM are frequency-dependent magnetic susceptibility and “hard” isothermal remanent magnetization, respectively). For both the LC and SMX sequences, our climofunction indicates paleosols have higher MAPs than loess units and the maximum MAP value occurs in S5, indicating that the East Asian summer monsoon was the strongest during the formation of S5. In agreement with previous studies, overall, MAPs of SMX are higher than those of LC, as SMX is in the southeast of LC and receives more precipitation. The positive correlation between the reconstructed MAPs and χFD and ARM suggests that precipitation is a key factor controlling degree of pedogenesis. MAPs of paleosols from SMX display a negative correlation with synchronous insolation maxima and a positive correlation with corresponding insolation minima. However at LC, MAPs have a less significant relationship with insolation. This may be because the summer monsoon signals are relatively weak in LC and covered by local climate and environmental alterations. In interglacials, the summer monsoon, associated with precipitation, is controlled by the corresponding insolation maxima and minima. In addition, the MAP gradient between LC and SMX is also modulated by the insolation amplitude.