CHANGES OF PROVENANCE INPUT AND SOURCE VEGETATION CHANGES AND THEIR IMPACT FACTORS SINCE LATE HOLOCENE BASED ON N-ALKANES RECORDS FROM CORE MD06-3039A IN THE MUDDY AREA OF THE EAST CHINA SEA
东海泥质区具有稳定的连续沉积,为开展气候环境演变提供了良好的研究载体,但前人主要侧重于沉积模式、季风、洋流及海洋环境研究,关于有机碎屑输入、源区植被变化及其影响因素等方面的研究还较缺乏。本研究通过晚全新世以来东海泥质沉积序列MD06-3039A的正构烷烃等有机地球化学指标分析,发现该区域4400 cal. a B.P.以来沉积有机质具有明显的陆源高等植物输入特征,其中在3200~1300 cal. a B.P.陆源输入相对减少,被认为与该区域夏季风减弱有关。nC_(31)/nC_(27)正构烷烃的变化表明,物源区植被呈现3个阶段的波动,早、晚阶段草本植物相对增多,中阶段3200~ 1300 cal.a B.P.木本植物相对较多;与此同时,植被变化呈现次一级的波动,如隋唐大暖期草本增多,明清小冰期早期木本增多。研究认为,这个区域的草/木本植物变化对气候冷暖变化的响应可能更明显。1300 cal.a B.P.以来气候总体上继续呈凉干状态,但草本植物大量增多,这与前阶段气候变冷呈现的木本植物相对增多不同,暗示人类活动土地利用方式的改变导致植被类型发生了变化。
英文摘要:
Continuous and relatively stable mud sediment depositions in the continental shelves of the East China Sea (ECS) provide high-quality archives for better understanding terrestrial climatic and environmental changes in the Holocene. However, few studies have focused on climatic and environmental reconstructions by the use of shelf sediments, in particular, to disentangle the complex interactions of the Asian monsoons, ocean currents, organic material inputs, and vegetation changes from the drainage areas of the Yangtze River into the ECS. In this study, organic geochemical indices of n-alkanes distribution patterns,and n-alkanes indices such as the ratio of long chain alkanes and medium-short chain alkanes (LCA/MSCA),Average Carbon Length (ACL),Odd-even predominance (OEP),and nC_(31)/nC_(27) from an ECS core MD06-3039A are presented. The core MD06-3039A (27°43.36'N, 121°46.88'E; water depth of 47 m) was located at the mud belt off the Zhejiang-Fujian coast on the inner shelf of ECS, and drilled by a giant gravity corer during the IMAGES MD155-Marco Polo cruise II by R/V Marion Dufresne in 2006. The total length of the core is 8.11 m,representing sediments deposited during the past 4400 years as indicated AMS14C dating. The averaged sedimentation rate of the core is 1.7 mm/a. The sediments are mainly composed of gray to gray yellowish silty silt with some small shellfish fragments and foraminifera shells visible in different depths. We have sampled 91 samples for this study and presented records here with an average resolution of approximately 50 years. Based on our analysis, the inputs of organic matter associated with terrestrial higher plants into the studied site have been decreased during a stage of 3200 ~ 1300 cal. a B.P., reflecting most likely the decreased summer precipitation in this region. In addition, the n-alkanes distributions indicate that the input of terrestrial organic matter is Yangtze River basin dominant. Furthermore,the indices of the n-alkanes suggest that the drainage area vegetation patterns have experienced fluctuations of three stages, with more herbaceous plants during the early and late stages and more woody plants during the middle stage of 3200 ~1300 cal. a B.P. Short-term fluctuations, such as the increases of herbaceous coincident with the Sui-Tang warm period and the increases of wood with the early Ming-Qing cold period are well-expressed in our records. Temperature change appears to be one of the most important effects in governing the change of grass/woody plants as inferred from our records. Our studies also suggest that since 1300 cal. a B.P., herbaceous plants have increased while the climate has been continuously cooler, implying anthropogenic changes in the land use patterns have been responsible for. During the past 300 years,the number of herbaceous plants has increased more rapidly,suggesting that the anthropogenic effects are accelerated.