New High‐Temperature Dependence of Magnetic Susceptibility‐Based Climofunction for Quantifying Paleoprecipitation From Chinese Loess

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 20; no. 8; pp. 4273 - 4291
• Main Authors: Gao, Xinbo, Hao, Qingzhen, Oldfield, Frank, Bloemendal, Jan, Deng, Chenglong, Wang, Luo, Song, Yang, Ge, Junyi, Wu, Haibin, Xu, Bing, Li, Fengjiang, Han, Long, Fu, Yu, Guo, Zhengtang
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.08.2019
• Subjects: Annual precipitation; Chinese Loess Plateau; Fractionation; Haematite; Heating; Loess; maghemite; Magnetic susceptibility; magneto‐climofunction; Mean annual precipitation; Mineralogy; modern soil; Paleoprecipitation; Paleosols; Soil; Soil properties; Temperature
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2019GC008401

The ferrimagnetic properties of soils are used to quantitatively reconstruct paleomonsoon precipitation from Chinese loess. Numerous magneto‐climofunctions have been established based on the magnetic proxies that are selectively sensitive to neoformation of fine‐grained superparamagnetic (SP) or single‐domain (SD) ferrimagnetic particles. Accumulating evidence has indicated that maghemite is the final product of the ferrimagnetic phases during pedogenesis in loessic soils. Quantitative estimates of abundance of maghemite of both SP and SD grains are therefore still required in developing magneto‐climofunctions. Here, we present detailed measurements on a suite of modern soil samples from the Chinese Loess Plateau to determine pedogenic ferrimagnetic mineralogy and to develop a new magneto‐climofunction based on a new parameter derived from the high‐temperature‐dependent magnetic susceptibility. Particle size fractionation processes combined with magnetic measurements indicate that fine‐grained SP and SD maghemite is the dominant pedogenic ferrimagnetic phases. High‐temperature‐dependent susceptibility measurements show that the thermally induced susceptibility drops between ~230 and ~400 °C during heating mainly result from the conversion of maghemite to hematite. We proposed a new parameter quantifying changes in the temperature dependence of magnetic susceptibility between 230 and 400 °C, χtd, that captures the concentration of pedogenically formed maghemite. Results show that χtd has a strong correlation with known quantities of maghemite in synthetic standard samples and that χtd of modern soils correlates with modern mean annual precipitation quite well (R2 = 0.82, n = 24). The established χtd‐mean annual precipitation climofunction provides a new approach to reconstructing paleorainfall during past warm interglacials from paleosols in Chinese loess. Key Points Maghemite is confirmed as the dominant pedogenic ferrimagnetic mineral present in soils over the Chinese Loess Plateau A new parameter derived from the temperature‐dependent magnetic susceptibility is used to quantify the abundance of the pedogenic maghemite From this, a new magnetic‐parameter‐based climofunction is developed to quantitatively reconstruct paleoprecipitation from Chinese loess