Paleorainfall Reconstructions from Pedogenic Magnetic Susceptibility Variations in the Chinese Loess and Paleosols

Abstract

The rock magnetic properties of the Chinese loess and paleosols constitute a unique and sensitive record of East Asian paleoclimate through the Quaternary Period. Systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal, which can be easily and rapidly measured at many sites across the Loess Plateau. Variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size, but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages, as well as glaciations and interglaciations. Past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations. The susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the Loess Plateau. Our rainfall reconstructions identify enhanced summer monsoonal activity in the Chinese Loess Plateau region in the early Holocene and the last interglaciation. In the presently semiarid western area of the plateau, annual precipitation in interglacial times was up to 80% higher than at present; in the more humid southern and eastern areas, values were up to 20% higher than today's levels. During the last glaciation, precipitation decreased across the entire plateau, typically by ∼25%. The relationship between pedogenic susceptibility, climate, and weathering age was examined over the Northern Hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate, rather than soil age, is the predominant factor that controls pedogenic susceptibility enhancement in loess soils.

Rainfall-dependent transformations of iron oxides in a tropical saprolite transect of Hainan Island, South China: Spectral and magnetic measurements

“…However, Fe d may increase more rapidly than Hm/(Hm+Gt) decreases in low-rainfall regions (Figures 6a and 6b), and the content of Hm (or Mgh) as their product can increase (Figure 6c). In this case, we can reconstruct the paleorainfall by the positive correlation between Fe d , MS, and rainfall as shown in previous studies in temperate regions with low and moderate rainfall [Kukla et al, 1988;Liu et al, 1995;Maher and Thomson, 1995;Maher, 1998]. However, with increasing rainfall, Fe d levels off compared to the decrease in Hm/(Hm+Gt) (Figures 6a and 6b), resulting in a decrease in the content of Hm or Mgh (Figure 6c).…”

“…MS has been suggested as a proxy to reconstruct paleorainfall in temperate monsoon zones, especially for the eolian sediments on the Chinese Loess Plateau (CLP) [Kukla et al, 1988;Heller et al, 1993;Liu et al, 1995;Maher and Thomson, 1995;Maher, 1998]. However, a growing body of evidence suggests a negative correlation between ferrimagnets and rainfall in extreme climates with excessive rainfall [Begét et al, 1990;Han et al, 1996;Singer et al, 1996;Chlachula et al, 1998;Liu et al, 2001Liu et al, , 2003Balsam et al, 2004].…”

Magnetic mineralogy of soils across the Russian Steppe: climatic dependence of pedogenic magnetite formation

“…The new steppe magnetic data can be incorpo- rated into Maher and Thompson's (1995) Northern Hemisphere temperate zone dataset. As can be seen from Fig.…”

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

“…Maher and Thompson (1995) reconstructed paleoprecipitation of CLP in the last glacial and interglacial by the susceptibility of topsoil. In the last interglacial (S1), the MAP is~25% higher than that of today and varied greatly by region.…”

“…Magnetic parameters, which are fast, inexpensive, non-destructive, and sensitive, have been commonly used as indicators of paleoprecipitation for decades, especially the mass-specific susceptibility (χ) (Balsam et al, 2004;Balsam et al, 2011;Liu et al, 2007;Liu et al, 2012;Maher, 1998;Maher et al, 2002;Maher and Possolo, 2013;Maher et al, 1994;Orgeira and Compagnucci, 2006). Maher and Thompson (1995) reported that pedogenic χ (defined as χ-χ C , where χ C represents the χ of the parent material) rises to a peak until MAP reaches about to reductive dissolution or alteration of the iron oxides. Han et al (1996) studied magnetic properties of 160 modern silt soil samples in China and found that the susceptibility of these soils is related not only with mean annual precipitation (MAP) but also with mean annual temperature (MAT).…”