伶仃洋ZK19孔全新统有机物δ13C和C/N值特征及东亚季风演变记录

Characteristics of δ13C and C/N in the Holocene organic material of borehole ZK19 in Lingdingyang bay and the records of east Asian Monsoon variation

为了深入探讨珠江河口区全新世东亚季风演变历史,对珠江口伶仃洋海区ZK19孔全新统开展年代学、有机碳同位素等地球化学多指标的研究。年代测试结果分析显示:钻孔早、晚全新世沉积完整,缺失高海平面期的中全新世沉积,研究认为该地层缺失是因水下侵蚀导致。钻孔δ^13C和C/N值分析结果表明,早全新世沉积物中偏负的δ^13C值和逐渐增大的C/N值,指示早全新世东亚强夏季风不断增强,不断增强的降水使钻孔区含较多的陆源有机质;而晚全新世逐渐偏正的δ^13C值和变小的C/N值表明,东亚夏季风不断减弱,降水量逐渐减小,陆源有机质输入逐渐减少,但这些指标在1.5calkaBP开始受人类活动影响,近500年来影响较显著。早、晚全新世东亚夏季风变化趋势主要与岁差相关的北半球日照量相关,而在东亚夏季风整体变化趋势下,还存在千年-百年尺度的气候波动周期,与太阳活动强度和周期的相对应。

In order to explore the history of dynamics of the East Asian monsoon (EAM) in the early and late Holocene in the Pearl River Estuary, the research of chronology and organic geochemistry was carried out on the borehole ZK19 from the Lingdingyang Bay.The borehole reveals the early and late Holocene deposits, lacking middle Holocene sediments due to underwater erosion during the high sea level period. According to the carbon isotope(δ^13 C) of bulk organic, and total carbon and nitrogen ratio(C/N) variations, the early Holocene sediments deposited during a period of high precipitation with a high proportion of terrigenous organic material, and have low δ^13 C and high C/N, and the late Holocene sediments were deposited during a period of low precipitation. The results suggest that the East Asian summer monsoon increased gradually during the early Holocene, but gradually decreased during the late Holocene. The human activities started to affect these indicators at 1.5 cal ka BP, and during the last 500 years, the effect became obvious. The general trend in monsoon precipitation in the early and late Holocene may be related to the variation of Northern Hemisphere Insolation, most likely related to the current precession circle. The dry-wet oscillations at centennial to millennial timescales superimposed on this trend are most likely in response to solar activity.