Dipolar mode of precipitation changes between north China and the Yangtze River Valley existed over the entire Holocene: Evidence from the sediment record of Nanyi Lake

Abstract

Instrumental data indicate the occurrence of a dipolar pattern of precipitation anomalies between north China and the Yangtze River Valley (YRV), which was termed “northern drought (flood)—southern flood (drought)” scenario. It has been shown that this pattern occurred during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). However, there are questions about whether this dipolar pattern also occurred during the entire Holocene, and the mechanism responsible. Addressing these questions is of fundamental importance for understanding the spatiotemporal evolution of precipitation in East Asian summer monsoon region. Numerous studies of north China have demonstrated that the mid‐Holocene was humid, and the early and late Holocene were dry. However, there are relatively few equivalent studies in the YRV. To this end, we conducted detailed geochemical analysis of an AMS 14C‐dated sediment core from Lake Nanyi in the YRV. Our results indicate humid periods at Lake Nanyi occurred during 11.5–8.0 ka and from 2.0 ka to the present, while dry conditions occurred during ~8.0–2.0 ka. These results, together with published records from Dajiuhu peatland and Heshang Cave, collectively indicate in the YRV, the mid‐Holocene (~8.0–3.0 ka) was dry, while the early and late Holocene were humid, which is the inverse of the pattern in north China. Thus, we conclude there was an asynchronous evolution of hydroclimatic changes between north China and the YRV during the Holocene. We interpret this dipolar pattern as the result of ENSO variations: in a La Niña‐like state, the Western Pacific Subtropical High retreated northeastward, which would enable the rainfall belt to move northward and result in increased (decreased) precipitation in north China (the YRV). Sea surface temperature records from the Pacific Ocean and model simulations support this mechanism: a La Niña‐like state in the mid‐Holocene resulted in more (less) precipitation in north China (the YRV).

Human activities have reduced plant diversity in eastern China over the last two millennia

“…Chen, Xu, et al, 2015;Cheng et al, 2016;Liu et al, 2014). Our analyses of the "south China" subgroup provide further evidence to support the idea that the improvement of analogue quality and reduction in pollen diversity is caused by human impacts because precipitation levels here in the late Holocene have been high and stable (e.g., Herzschuh et al, 2019;Liu et al, 2014;Liu, Shen, et al, 2020). In summary, we argue these simple and homogeneous pollen spectra may well reflect anthropogenic deforestation and land cultivation, with rice and wheat as the major crops (both of which are in the Poaceae family).…”

“…4 cal. ka BP for south China (Chen, Xu, et al, 2015; Cheng et al, 2016; Herzschuh et al, 2019; Liu et al, 2014, 2015; Liu, Shen, et al, 2020). These different spatial patterns of climate change fail to explain the same processes in diversity loss in north and south China (Appendix S3).…”

Quaternary environmental changes in central Chukotka (NE Russia) inferred from the Lake El'gygytgyn pollen records

“…Rarefaction‐based E ( T n ) has been used to reconstruct floristic diversity change over different time spans, such as the Holocene epoch (e.g. Birks and Line, 1992; Felde et al ., 2016; Liu et al ., 2021) and the glacial–interglacial cycles (e.g. Willis et al ., 2007; Whitney et al ., 2014).…”

Reconstructed precipitation in the Lohit River basin, southern Tibetan Plateau since 1720 CE and its weak linkages with monsoon‐season Brahmaputra discharge

“…Water resources are the foundation of civilized development and one of the basic needs of human life (Steffen et al ., 2015; Boltz et al ., 2019; Kılıç, 2020). In Asia, with rapid economic and population growth, the increasing water resource demand has led to some regional water shortage crisis (Huntington, 2006; Sivakumar, 2011; Wilson et al ., 2017; Liu et al ., 2021; Chen et al ., 2021; Wang et al ., 2021a). High Asia (26°–46°N and 62°–105°E) refers to a vast area with the Tibetan Plateau as the centre and extending to the surrounding areas (Pritchard, 2017).…”