正构烷烃组成的古环境指示:以中全新世以来珠江口沉积物研究为例

Paleoenvironmental indication of n-alkanes composition:A case study of sediments from the Pearl River Estuary since the mid-Holocene

该文分析了珠江口沉积物柱状样HKUV16中正构烷烃的长链奇碳烷烃含量(∑oddC_(25~33))、碳优势指数(CPI)、平均链长(ACL)、C_(31)C_(27)和海洋水生植物比重(P mar-aq),探讨了中全新世以来正构烷烃来源变化及对珠江流域环境变迁的指示。HKUV16的长链正构烷烃特征指示其主要来自陆源高等植物。在8.0~7.0 ka BP期间,∑oddC_(25~33)、CPI值和P mar-aq值增加,ACL和C_(31)C_(27)为低值,指示该时期陆源有机质输入增加,木本植物占比大,珠江流域气候湿润。在7.0~3.2 ka BP期间,∑oddC_(25~33)降低,表明陆源有机质输入减少,而ACL和C_(31)C_(27)呈增—减—增的变化趋势,指示珠江流域可能经历了干旱—湿润—干旱的气候变化。3.2~2.2 ka BP,ACL、C_(31)C_(27)的高值显示此时草本植物占比明显增大,可能意味着该时期的气候较为干旱。多指标综合显示2.2 ka BP之前珠江口沉积物的正构烷烃变化主要受夏季风的影响,而2.2 ka BP以来不断增强的人类活动可能成为影响珠江流域生态环境的主导因素。

The multiple indices of n-alkanes including∑oddC_(25-33),CPI,ACL,C_(31)C_(27)and P mar-aq from a sediment core HKUV16 retrieved in the Pearl River Estuary were analyzed to explore their sources and environmental changes since the mid-Holocene.The distribution features of n-alkanes of core HKUV16 indicated that they were mainly from terrestrial higher vegetation.From 8.0 to 7.0 ka BP,∑oddC_(25-33),CPI,and P mar-aq increased,while ACL and C_(31)C_(27)were low,which showed that terrestrial organic matter input increased and woody vegetation increased.The decrease of∑oddC_(25-33)during 7.0~3.2 ka BP indicated that the input of terrestrial organic matter decreased,while the ACL and C_(31)C_(27)showed an increase-decrease-increase trend,suggesting that the Pearl River Basin might have experienced dry-wet-dry climate change.From 3.2 to 2.2 ka BP,high ACL and C_(31)C_(27)indicated that herbaceous plants expanded and the climate was relatively arid.The multi-indices showed that the input of n-alkanes to the Pearl River Estuary before 2.2 ka BP was mainly affected by East Asian summer monsoon.However,increasing human activities since 2.2 ka BP might have become the dominant factor for the ecological environment of the Pearl River Basin.