Abstract
The inner shelf sediments of the East China Sea (ECS) preserve valuable information regarding climatic changes on land through detrital material discharged from large rivers, particularly the Yangtze River. In this paper, we examine the provenance changes of fine-grained detrital quartz preserved in the sediment of the MD06-3040 core retrieved from the mud belt on the inner shelf of the ECS during the last 6 kyrs. The provenance of the fine silt fraction (4–16 μm) of the sediments, which is considered to represent the suspended particulate matter (SPM) from the Yangtze River, is estimated based on the electron spin resonance (ESR) signal intensity and crystallinity index (CI) of quartz. By comparing the ESR signal intensity and CI of quartz in the fine silt fraction of sediments to those from different parts of tributaries in the modern Yangtze River drainage, we can discriminate the SPM sourced from the northwestern and southeastern tributaries of the Yangtze River. Shifts in the East Asian summer monsoon (EASM) front are monitored by changes in the main precipitation areas which are manifested as changes in source rock ages and types implied from the ESR signal intensity and CI of quartz in the fine silt fraction of the studied sediments discharged from the Yangtze River. Temporal changes in provenance of the fine silt fraction through time suggest that shifts in the main location of EASM precipitation (most likely representing the EASM front) occurred at a multi-centennial-to-millennial scale with the deepest northwestward penetration of the EASM precipitation front (an enhanced EASM) occurring during the period 3.5–2.0 kyr BP and a southeastward retreat (a weak EASM) occurring during the periods 6.0–4.1 and 2.0–0 kyr BP.
Highlights
The East Asian summer monsoon (EASM) is a distinctive component of the Asian climatic system due to unique orographic forcing and huge thermal contrast between the world’s largest continent, Eurasia, and the largest ocean, the Pacific (Zhou et al 2009)
Saito et al (2017) suggested that if migration of the main precipitation area occurred within the Yangtze River drainage, it would have been manifested as changes in the provenance of suspended particulate matter (SPM) discharged from the Yangtze River
Because the MD06-3040 core, in which fine silt is the relatively dominant faction derived from the Yangtze River with lesser impacts from local rivers and Taiwan island, is the longest continuous piston core collected from the central mud belt representing extensive sediment succession far, we examined the provenance changes in the fine silt fraction of the MD06-3040 core sediments to reconstruct spatiotemporal variability in the EASM precipitation area (EASM front) within the Yangtze River drainage
Summary
The East Asian summer monsoon (EASM) is a distinctive component of the Asian climatic system due to unique orographic forcing and huge thermal contrast between the world’s largest continent, Eurasia, and the largest ocean, the Pacific (Zhou et al 2009). Shifts in δ18Oc largely reflect changes in the oxygen isotope ratio of precipitation (δ18Op) at the site, which in turn reflect changes in the amount of precipitation (the so-called amount effect) and characterize the EASM precipitation intensity (Wang et al 2005). One needs to carefully consider regional, geographical, and seasonal effects and in particular consider the amount-weighted δ18O (Maher 2008; Maher and Thompson 2012)
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