Dynamic control on grain-size distribution of terrigenous sediments in the western South China Sea: Implication for East Asian monsoon evolution

Abstract

High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China Sea (SCS), was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density, fractional porosity and lithogenic content of the sediments, terrigenous mass accumulation rate (TMAR) was obtained, which is 4.9 6.0 g cm 2 ka 1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9 5.0 g cm 2 ka 1 , which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis of grain size distribution of all the samples, two main control factors (F1 and F2) were obtained, which are responsible for about 80% variance of granularity. The contents of grain size population 1.26 2.66 Pm% and 10.8 14.3 Pm% which are sensible to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15 N. They exhibit a distinct cyclicity with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24 7.42 Pm% and 30.1 43.7 Pm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations of surface current forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer monsoon has fluctuated with high frequency and been forced by changes in solar insolation in low latitude associated with precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing.South China Sea, late Quaternary, terrigenous sediments, grain size, East Asian monsoon As the significant component of the global climate, the finer details of East Asian monsoon are now coming to light through investigation of records from land and sea. The South China Sea, the largest marginal sea in the western Pacific, gives us the ideal materials to trace East Asian monsoon evolution, because it received abundant terrigenous products of chemical weathering and physical erosion in adjacent continents [1] . Through the research on the deep sea sediments, especially the sediment cores collected in ODP 184 cruise, abundant information about the tectonic history of the South China Sea and East Asian monsoon evolution during the Cenozoic has become known [1 4] . More and more paleo-oceanographic information such as changes of thermocline depth, sea water temperature and paleoproductivity, has been discovered mainly by studies on biogenic materials [5 9] .The South China Sea, a semi-closed basin with the

Strengthening of the East Asian winter monsoon during the mid-Holocene

“…Geological data indicated that, throughout the Quaternary, the EAWM was stronger overall during glacial periods but weaker during interglacial periods, which has been attributed to changes in global ice volume and/or orbital forcing (e.g. Chen et al, 2008; Ding et al, 1995; Hao et al, 2012; Sun et al, 2006; Xiao et al, 1995). However, due to the absence of high-resolution EAWM evidence, the accuracy of this interpretation remains unclear.…”

Paleoclimatic evolution and weathering in the Northern South China Sea during the last 61 kyr BP--Sedimentary records from the coastal zone

“…Previous studies have found that element ratios can effectively record the surface chemical weathering intensity 10,[33][34][35][36] 2015) believed that the correlation coe cient between geochemical parameters and particle size of KNG5 core was weak, and chemical alteration index, orthoclase alteration index, Rb/Sr, Al/Ti and K/Al could be used as reliable proxies for climate change 36 . Many studies suggest that the particle size of about 2-10 μm is weakly affected by sea level change or bottom current, and is a reliable source of aeolian dust and river input, so it can be used as a proxy index for the East Asian Summer monsoon [37][38][39] . Clay minerals are widely found in Marine terrigenous clastic sediments, which record the history of climatic changes in the source region in a time continuous period of cold and warm environment [40][41][42][43] , and play an important role in paleo-environmental reconstruction, paleo-monsoon transition, and ocean-land correlation studies [44][45][46][47][48] .…”

Paleoenvironmental changes in the coastal zone of the northwest South China Sea during the last 13 kyr

“…The sediments of the South China Sea record considerable paleoenvironmental information, which can be used to reconstruct the evolution of the East Asian monsoon history and to study paleo-oceanic evolution 11 – 13 , 35 , 42 , 43 . Previous studies have found that the ratios of Al/Si, Al/K, Rb/Sr, Al/Ti, and K/Ti can effectively record the intensity of surface chemical weathering 10 , 44 – 47 , which is a reliable proxy for climate change. Numerous studies suggest that the particle size fraction of 2–10 µm is a reliable record of wind dust and river sediment input and is thought to be weakly affected by sea level changes or undercurrents; it can thus be used as a proxy for the East Asian summer monsoon 48 – 50 .…”