Summer monsoon variations over the last 1.2 Ma from the weathering of loess‐soil sequences in China

Abstract

The loess‐soil sequence in northern China contains a near continuous record of Quaternary paleoclimate. Magnetic susceptibility and grain size have so far been the only proxies available to address the long‐term changes of the East‐Asian paleomonsoon extending back to more than one million years. In this study, the ratio of CBD (citrate‐bicarbonate‐dithionite)‐extractable free Fe2O3 (FeD), a measure of iron liberated by chemical weathering, versus the total Fe2O3 available (FeT) was measured on samples at 10 cm intervals taken from two loess sections deposited over the last 1.2 Ma. Variations of this index are highly consistent with other pedological indicators, but in addition provide a quantitative measurement of the degree of pedogenesis in the Loess Plateau. Since chemical weathering in the region mainly depends upon summer precipitation and temperature, weathering intensity primarily reflects changes in the East‐Asian summer monsoon. The new proxy has been used to document a series of summer monsoon changes of global significance, which are not necessarily recorded by magnetic susceptibility.

High Arabian Sea productivity conditions during MIS 13 – odd monsoon event or intensified overturning circulation at the end of the Mid-Pleistocene transition?

“…In contrast to the Antarctic methane record and model simulation, the exceptional high productivity conditions reached during MIS 13 coincided with an exceptional thick soil horizon S5 in some loess records of the central CLP (Guo et al, 2000;Sun et al, 2006b), and with an extreme event in a monsoon record from the Tibetan plateau (Chen et al, 1999). There are, however, noticeable regional differences in the expression of the S5 soil horizon (Sun et al, 2006a).…”

Variability of snail growing season at the Chinese Loess Plateau during the last 75 ka

“…It is one of the most classic loess sections where a large number of research has been previously carried out [5,6,10,[26][27][28][29][30][31][32][33]. Studies on fossil land snail assemblages since the last glacial are also well documented [32,33].…”

The global monsoon across timescales: coherent variability of regional monsoons

“…Table 1 shows a wide range of proxies indicative of humidity changes in marine and terrestrial records, including the Loess sequences. While the pioneering works on paleo-monsoons on the Loess Plateau of China mostly used wind-induced proxies, newer studies have emphasized the proxies resulting from pedogenesis (e.g., Guo et al, 2000).…”

“…Apparently, the most significant advances in the past two decades have been in understanding the GM during the Quaternary. Thanks to extensive works on loess-soil sequences (Guo et al 1996(Guo et al , 2000, stalagmites (Cheng et al, 2009a(Cheng et al, , 2012bYuan et al, 2004), lacustrine (e.g., , and marine records (e.g., Caley et al, 2011;Clemens et al, 1991;Clemens and Prell, 2003), Figure 12. Possible link between climate events and human culture (adapted from Cheng and Edwards, 2012).…”