ESR signal intensity of quartz in the fine-silt fraction of riverbed sediments from the Yangtze River: a provenance tracer for suspended particulate matter

Abstract

The Asian summer monsoon exerts a strong influence on the hydrologic cycle in East Asia. Moreover, the distribution of heavy precipitation in the Yangtze River basin, which covers a large area of South China, is sensitive to changes in monsoon intensity. Thus, the paleo-distribution of heavy precipitation in the Yangtze basin is key in reconstructing the paleo-monsoon intensity. In this study, we established proxies for distinguishing sediments from the northwestern and southeastern parts of the Yangtze River basin, with the goal of using them to reconstruct the paleo-distribution of heavy precipitation in the basin based on changes in the provenance of detrital sediments, as determined using sediment records at the river mouth. The proxies included the electron spin resonance (ESR) signal intensity and the crystallinity index (CI) of quartz in modern riverbed sediments along the mainstream and tributaries of the Yangtze River. The data revealed that the fine-silt fraction of the sediments (which represents suspended particulate matter, SPM) from each major tributary can be distinguished on the basis of ESR signal intensity and CI values. The values for each tributary reflect the age and type of bedrock in the tributary basin and show distinct regional variations according to the distribution of geological blocks within the Yangtze basin. In addition, the analyzed ESR signal intensity and CI values of the fine-silt fraction of riverbed sediments below mainstream-tributary junctions agree well with values calculated according to a simple mixing model of SPM discharged from the tributaries and the mainstream.

Provenance changes in fine detrital quartz in the inner shelf sediments of the East China Sea associated with shifts in the East Asian summer monsoon front during the last 6 kyrs

“…According to our previous study, the fine silt fraction (4-16 μm) of the detrital sediment is considered as mainly representing SPM (Saito et al 2017) whereas the coarse silt fraction (16-63 μm) represents suspension particles under high water discharge and/or saltation particles transported by bottom currents (Wang et al 2011). The grain size distribution of the MD06-3040 core sediments showed a modal size of the major grain size population at 4-8 μm and modal sizes of minor grain size populations at 0.8-4 μm and 16-22 μm (Fig.…”

“…The provenance of sediment as well as paleoenvironmental changes on the inner shelf of the ECS have been well studied (Zheng et al 2010;Wang et al 2014;Liu et al 2014;Yang et al 2015;Bi et al 2017;Fang et al 2018;Liu et al 2018). In this study, we conducted provenance discrimination using the electron spin resonance (ESR) signal intensity and crystallinity index (CI) of quartz, which has been successfully applied to modern surface samples to trace eolian dusts from various deserts in western China (Sun et al 2007(Sun et al , 2013, to core sediment recovered from the Japan Sea to trace dust provenance changes in association with the southward-northward shifts of the Westerly Jet (WJ) (Nagashima et al 2007(Nagashima et al , 2011(Nagashima et al , 2012(Nagashima et al , 2013 and to characterize suspended particulate matter (SPM) collected from various segments of the Yangtze River drainage (Saito et al 2017). Saito et al (2017) established a new method to evaluate relative contribution of sediment discharge from different parts of the Yangtze drainage basin based on the provenance of quartz in the fine silt fraction (4-16 μm) of riverbed sediments collected from all the major tributaries of the Yangtze River using ESR signal intensity and CI of quartz as a provenance tracer.…”

“…Saito et al (2017) established a new method to evaluate relative contribution of sediment discharge from different parts of the Yangtze drainage basin based on the provenance of quartz in the fine silt fraction (4-16 μm) of riverbed sediments collected from all the major tributaries of the Yangtze River using ESR signal intensity and CI of quartz as a provenance tracer. They concluded that the changes in provenance of the fine silt fraction of detrital material are caused by changes in the high-precipitation area between the upper reaches and the middle-lower reaches (Saito et al 2017). The Yangtze River drainage basin occupies the major part of South China in the middle of the present EASM region.…”

“…Consequently discharge of SPM from the Yangtze River could reflect precipitation amounts in the drainage. Based on these observations, changes in the SPM provenance reflect changes in the distribution of highprecipitation areas (Saito et al 2017). The SPM discharged from the Yangtze River, whose grain size is dominantly a fine silt size, is distributed on the inner shelf of the ECS extending southwestward from the Yangtze River estuary along the southeastern coast of South China, forming mud belts (Qin 1979;Qin et al 1987;Liu et al 2007).…”

“…The SPM discharged from the Yangtze River, whose grain size is dominantly a fine silt size, is distributed on the inner shelf of the ECS extending southwestward from the Yangtze River estuary along the southeastern coast of South China, forming mud belts (Qin 1979;Qin et al 1987;Liu et al 2007). Based on this reasoning, we applied the provenance discrimination method of Saito et al (2017) to the MD06-3040 core retrieved from the mud belt on the inner shelf of the ECS to reconstruct spatiotemporal variations in the EASM precipitation area within the Yangtze River drainage during the middle and late Holocene by examining provenance changes of fine detrital quartz (4-16 μm) derived from the Yangtze River.…”