Abstract
Characterizing the spatiotemporal variability of the East Asian summer monsoon (EASM) advances our understanding of its rhythm, dynamics, and future impacts. EASM variations during the Holocene have been reconstructed from a variety of geological archives and proxies. However, the spatiotemporal heterogeneity of EASM rainfall during the Holocene remains controversial. Taiwan is geographically suitable for studying the EASM history through its geological archives. Herein, we synthesize the reported lake and peat sedimentary records of the entire Holocene, in addition to the records of mass-wasting and on-land deposition from cores collected from Taiwan to illustrate the EASM induced hydroclimate changes in Taiwan throughout the Holocene. Records from Taiwan indicate that the EASM rainfall maximum occurred during the early Holocene, concurring with other EASM records from monsoon region of southern China. We suggest that the early Holocene EASM rainfall maximum in southern China was mainly forced by the higher Northern Hemisphere summer insolation and sea surface temperatures in the Western Pacific Warm Pool (WPWP). A synthesis of EASM rainfall records from across China shows that the timing of Holocene EASM rainfall maximum occurred progressively later from southern to northern China. This time-transgressive EASM rainfall maximum may be due to the latitudinal shift of the westerlies and Western Pacific subtropical high (WPSH) that induced by changes of interhemispheric temperature gradients (ΔTN‐S) and northern high latitude ice volume. Moreover, records from Taiwan suggest a significant collapse of the EASM in Taiwan at ~4–2 ka BP. Based on the records from Taiwan, coastal East Asian and Tropical Pacific, we propose that the sea surface temperatures (SSTs) of the WPWP and/or El Niño -Southern Oscillation (ENSO) activity may have exerted a strong influence on the EASM rainfall changes during the late Holocene. Moreover, increased EASM rainfall in southern China during the last 2 ka was likely caused by a southward shift of WPSH which was associated with gradual decreases in ΔTN‐S during the late Holocene.
Highlights
As an important component of the global atmospheric circulation system, the East Asian summer monsoon (EASM) plays a significant role in global hydrologic and energy cycles and is the primary driver of hydroclimatic changes in East Asia (Ding and Chan, 2005; An et al, 2015)
We propose that the “2-ka shift” might or at least partly, be induced by a southward shift of the Western Pacific subtropical high (WPSH), associated with a gradual decrease in TN−S during the late Holocene (Figure 4)
We suggest that the early Holocene EASM rainfall maximum in southern China was mainly forced by a higher Northern hemisphere solar insolation (NHSI) and elevated sea surface temperatures (SSTs) in the Western Pacific Warm Pool (WPWP)
Summary
As an important component of the global atmospheric circulation system, the East Asian summer monsoon (EASM) plays a significant role in global hydrologic and energy cycles and is the primary driver of hydroclimatic changes in East Asia (Ding and Chan, 2005; An et al, 2015). The summer monsoon rainfall in southern China was high during the early and late Holocene, but low during the middle Holocene (Xu et al, 2020) Such a pattern is evident in subtropical East Asia (20–27◦N, 110–125◦E) precipitation in the TraCE−21ka simulations (Xu et al, 2020). With a steep gradient and abundant rainfall, Lanyang River has one of highest sediment yields in the world, with a present-day annual sediment load of approximately 8–17 Mt/year (Jeng and Kao, 2002; Dadson et al, 2003; Milliman and Kao, 2005) In this synthesis, we compiled data from three individual lake and peat cores that span most of the Holocene period. Northern Taiwan, 24◦29 N, 121◦26 E Central Taiwan, 23◦49 N; 120◦53 E Southern Taiwan, 23◦49 N; 120◦53 E Northern Taiwan
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