Warming-induced northwestward migration of the East Asian monsoon rain belt from the Last Glacial Maximum to the mid-Holocene

Abstract

Glacial-interglacial changes in the distribution of C 3 /C 4 vegetation on the Chinese Loess Plateau have been related to East Asian summer monsoon intensity and position, and could provide insights into future changes caused by global warming. Here, we present δ 13 C records of bulk organic matter since the Last Glacial Maximum (LGM) from 21 loess sections across the Loess Plateau. The δ 13 C values (range: -25‰ to -16‰) increased gradually both from the LGM to the mid-Holocene in each section and from northwest to southeast in each time interval. During the LGM, C 4 biomass increased from <5% in the northwest to 10-20% in the southeast, while during the mid-Holocene C 4 vegetation increased throughout the Plateau, with estimated biomass increasing from 10% to 20% in the northwest to >40% in the southeast. The spatial pattern of C 4 biomass in both the LGM and the mid-Holocene closely resembles that of modern warm-season precipitation, and thus can serve as a robust analog for the contemporary East Asian summer monsoon rain belt. Using the 10-20% isolines for C 4 biomass in the cold LGM as a reference, we derived a minimum 300-km northwestward migration of the monsoon rain belt for the warm Holocene. Our results strongly support the prediction that Earth's thermal equator will move northward in a warmer world. The southward displacement of the monsoon rain belt and the drying trend observed during the last few decades in northern China will soon reverse as global warming continues.

Evolution of the relative abundance of C4 plants on the Chinese Loess Plateau since the Last Glacial Maximum and its implications

“…Comparison of our reconstruction of the percentages of C 4 plants during the LGM and mid‐Holocene with the results of other studies (Yao et al ., ; Yang et al ., ) reveals a general agreement that there was a significant NW–SE gradient in the representation of C 4 plants, as well as a significant increase in their representation throughout the CLP in the mid‐Holocene, compared to the LGM. However, there are some differences: our reconstructed C 4 plant abundances during the LGM are ∼5–10% higher than those of Yao et al .…”

“…Vidic and Montañez, ; Xie et al ., ; Liu et al ., ; Lu et al ., ), spatial changes have rarely been addressed. Moreover, while several studies have presented distribution patterns of C 4 plants for the LGM and mid‐Holocene intervals for the CLP and have shown that C 4 plant abundance was characterized by an increasing trend along a NW–SE transect (Yao et al ., ; Yang et al ., ), the evolution of the spatial pattern of C 4 plant representation since the LGM is unclear.…”

Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers

“…Therefore, the δ 13 C of soil CO 2 would be −23‰ for C3 plants and −9‰ for C4 plants (Clark & Fritz, ). Soil profiles from Jingbian, located approximately 150 km SE of the study area, shows that the δ 13 C of soil organic matter approximately ranges from −24‰ to −22‰ with the median value of −23‰ (Yang et al, ). Then, the δ 13 C of soil CO 2 can be expected to be −19‰, very similar to the value of −18‰ obtained in the Gobi Desert using carbon isotopic fractionation of recharging water (Gates, Edmunds, Darling et al, ).…”

Nanosized Authigenic Magnetite and Hematite Particles in Mature‐Paleosol Phyllosilicates: New Evidence for a Magnetic Enhancement Mechanism in Loess Sequences of China

“…The magnetic susceptibility of modern soils may provide a hint regarding the timing of pedogenic ferrimagnet formation. Magnetic susceptibility reaches mature‐paleosol values (>100 × 10 −8 kg −1 ) at a near‐surface layer (Kang et al, 2018; S. Yang et al, 2015) and have a linear relationship with proximal‐site modern precipitation (Balsam et al, 2011; Maher & Thompson, 1995). Thus, most pedogenic ferrimagnets form near the surface.…”