Records of late-Holocene East Asian winter monsoon in the East China Sea: Key grain-size component of quartz versus bulk sediments

Abstract

Quartz isolated from bulk sediments taken from a core obtained from the distal mud area in the outer shelf of the East China Sea was used as a proxy in order to determine the strength of the East Asian Winter Monsoon (EAWM). This data was compared with the grain-size of bulk sediment from the same core. It was found that the content of the key quartz-based indicator fraction (15.2–65.6 μm) correlated well with the EAWM strength. With reference to current conditions, high content of quartz in the selected fraction reflected strong EAWM and vice-versa. The core record spanned 2100 years, and three periods of change in EAWM strength were identified. A period of increased EAWM strength prior to 1520 cal. BP was followed by a period of weakened EAWM strength from 1520 to 720 cal. BP, which is consistent with the Sui-Tang Warm Period and the Medieval Warm Period. This is followed by a period of slightly increased EAWM between 720 and 220 cal. BP, which corresponds to what is called the Little Ice Age. The history of EAWM revealed by the quartz-based proxy is in striking agreement with results from a previous study on bulk sediment-based proxy. However, the quartz-based proxy showed much higher sensitivity and resolution to the EAWM strength, and displayed much more distinct and sharper boundaries of transition across the three intervals of EAWM change compared to the bulk sediment records. Eleven short EAWM strengthening periods were found, compared with four by the bulk sediment-based proxy. Therefore, this suggests that the quartz grain-size proxy is a superior indicator of the winter monsoon strength in the study area.