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

Abstract

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.

Enviromagnetic study of Late Quaternary environmental evolution in Lower Volga loess sequences, Russia

“…5.5–8.5 m) no magnetic grain size and thermomagnetic data is available but in situ formed maghemite was detected in pilot samples from MIS 3 pedogenic layers developed in the loess of RG and LN, also indicating mineral alteration induced by weak pedogenesis during a phase of less arid climate. Increased abundance of pedogenic maghemite with increased rainfall has also been shown by Gao et al (2019) for the monsoon-affected CLP.…”

Mineral magnetic properties of loess–paleosol couplets of northern Serbia over the last 1.0 Ma

“…3) clearly demonstrate the neoformation of magnetite. Therefore, the Curie point of 585°C cannot be used to determine whether or not magnetite is present in the original samples, which has been widely reported previously (e.g., Gao et al, 2019).…”

“…The decrease in susceptibility between ~330°C and 420°C, or a higher temperature, which is more significant in paleosol than in loess samples, is generally attributed to the thermally induced conversion of metastable maghemite to weakly magnetic hematite (Oches and Banerjee, 1996; Deng et al, 2000; Gao et al, 2019). Therefore, the significant susceptibility decrease during this interval for the paleosol samples suggests a higher maghemite concentration in paleosols, while the relatively small amplitude of the decrease for loess samples is indicative of a minor maghemite concentration.…”

“…3). In the Chinese Loess Plateau, this susceptibility decrease has been used to quantitatively estimate the abundance of pedogenic maghemite (Gao et al, 2019). The ferrimagnetic minerals of pedogenic origin are mainly SP and SD, as indicated by the FORC diagrams (Fig.…”

Suscetibilidade magnética na caracterização da variabilidade espacial de atributos do solo em solos subtropicais

“…Nesse sentido, Camargo et al (2018) observaram que técnicas que não utilizam reagentes químicos para obtenção de dados, associado a leitura das amostras com maior facilidade e rapidez, são abordagens sustentáveis que estão ganhando cada vez mais espaço. A análise da suscetibilidade magnética (SM) tem mostrado resultados promissores na identificação e descrição de ambientes pedogenéticos de diferentes locais como, na China (PINGGUO et al, 2016;GAO et al, 2019), no Oriente Médio (AYOUBI et al, 2018), Europa (BAUTISTA et al, 2018;HIRSCH et al, 2019) e nas diferentes regiões do Brasil: Nordeste (SANTOS et al, 2013), Norte (OLIVEIRA et al, 2015), Sudeste (MATIAS et al, 2015;SIQUEIRA et al, 2015;BARBOSA et al, 2019) e Sul (SILVA et al, 2010;RAMOS et al, 2017). Esses estudos têm abordado o uso da SM como ferramenta auxiliar na caracterização quantitativa de atributos do solo e da variabilidade espacial das mesmas.…”