Mid-Holocene variability of the East Asian monsoon based on bulk organic δ¹³C and C/N records from the Pearl River estuary, southern China

Abstract

Understanding the mid-Holocene dynamics of the East Asian monsoon (EAM) is integral to improving models of the Holocene development of the global climate system. Here we reconstruct the mid-Holocene EAM history from the Pearl River estuary, southern China, using bulk organic carbon isotopes (δ13C), total carbon to total nitrogen (C/N) ratios and total organic carbon (TOC) concentration. Sedimentary δ13C, C/N and TOC are potentially good indicators of changes in monsoonal precipitation strength. Sediments buried during a period of high precipitation exhibit a high proportion of terrigenous material, and have low δ13C and high C/N, and vice versa during a period of low precipitation. Results suggest a general decreasing trend in monsoonal precipitation from 6650 to 2150 cal. yr BP because of the weakening Northern Hemisphere insolation most likely related to the current precession circle. Superimposed on this trend are apparent dry–wet oscillations at centennial to millennial timescales most likely in response to solar activity. Mismatches between our δ13C record and results from the Dongge Cave in southern China at millennial timescales may indicate that the δ13C from the Pearl River estuary reveals changes in precipitation over a broader area than the δ18O from Dongge Cave.

A new regional, mid-Holocene palaeoprecipitation signal of the Asian Summer Monsoon

“…Liu and Huang, 2005), cave speleothems (e.g. Dong et al, 2010;Wang et al, 2005;Zhang et al, 2004) and organic matter flux (Yu et al, 2012;Zong et al, 2006;Zong et al, 2010). Overall, these datasets indicate a general decline in precipitation across Asia from 6.5 ka to present.…”

“…Previous reconstructions of relative terrestrial sediment transport to the Pearl River Estuary using bulk organic carbon isotopes (Yu et al, 2012;Yu, 2009;Zong et al, 2006;Zong et al, 2010) have attempted to use this approach to provide a regional signal. These  13 C org records show a general increasing trend with time ( Fig.…”

“…2). These disparities have been attributed to a difference in basin size with the  13 C org reflecting a more regional climate signal relative to the more localised Dongge signal (Yu et al, 2012;Fig. 1).…”

Radiocarbon anomalies suggest late onset of agricultural intensification in the catchment of the southern part of the Yangtze Delta, China

“…High δ 13 C (less negative) values may thus represent marine inundation (e.g. Yu et al, 2011), with δ 13 C data thus providing an independent line of evidence to support marine signals identified through microfossil evidence. The difference between marine-influenced and non-marine-influenced δ 13 C values is primarily due to different photosynthesic pathways of both macro-and micro-plants in marine and terrestrial environments (Lamb et al, 2006).…”

“…For example, terrestrial/freshwater-sourced organic material from the Pearl River Delta of China has an average δ 13 C value of -25‰, whereas organic material of marine origin has a higher (less negative) value of -21‰ (Yu et al, 2011). Comparison between δ 13 C values of terrestrial and marine-sourced organic material are, however, likely to be complicated by -notably --changes in carbon isotope composition in the atmosphere on glacial-interglacial time scales and variations in contributions from C 4 plants (generally tropical and sub-tropical grasses and herbs).…”