Variation in δ^(15)N of a lacustrine sedimentary sequence in the Nanling Mountains and its potential implication for climatic conditions over the past ~16000 years  

作　　者：钟巍 曹家元 薛积彬 欧阳军 

机构地区：[1]School of Geographic Sciences, South China Normal University

出　　处：《Chinese Journal of Oceanology and Limnology》2013年第5期1098-1106,共9页中国海洋湖沼学报（英文版）

基　　金：Supported by the National Natural Science Foundation of China(Nos.41071137,40671189);the Research Program of Higher Education Institution in Guangdong Province for High-level Talents,and the Natural Science Foundation of Guangdong Province(Nos.S2011010003413,8151063101000044)

摘　　要：Although extensive studies have been performed on nitrogen isotopes in lake sediments, understanding the complexity of the δ15N variation related to past environmental and climatic conditions still remains unclear. Supported by multi-proxy records including litho-units, organic carbon isotopes, ration of total organic carbon and total nitrogen, organic matter content, bulk dry density, the accumulation rate of organic matter, median grain size, magnetic susceptibility, and Rb/Sr and Ca/Mg ratios obtained from a sedimentary sequence in a small lake （i.e., Dahu Swamp） in the eastern Nanling Mountains in South China, we deduce that variation in the δ15N values results primarily from the sources of organic matter, which are significantly influenced by climatic conditions over the past -16 000 years. A low （or high） lake level resulting from dry （or wet） conditions would lead to more （or fewer） vascular plant remains in the sediments and stronger （or weaker） denitrification associated with hypolimnetic anoxia, resulting in lower （or higher） 615N values. In addition, dry （or wet） conditions would favor weakened （or strengthened） biogeochemical activity in the catchment, which could result in less （or more） external input of δ15N-enriched OM, thus leading to decreased （or increased） δ15N values. Our results indicate that the lake sediment δ15N record in the Nanling Mountains has the potential to provide valuable insight into past East Asian monsoon climate- driven environmental changes.Although extensive studies have been performed on nitrogen isotopes in lake sediments,understanding the complexity of the δ~15N variation related to past environmental and climatic conditions still remains unclear.Supported by multi-proxy records including litho-units,organic carbon isotopes,ration of total organic carbon and total nitrogen,organic matter content,bulk dry density,the accumulation rate of organic matter,median grain size,magnetic susceptibility,and Rb/Sr and Ca/Mg ratios obtained from a sedimentary sequence in a small lake(i.e.,Dahu Swamp) in the eastern Nanling Mountains in South China,we deduce that variation in the δ15N values results primarily from the sources of organic matter,which are significantly influenced by climatic conditions over the past ~16 000 years.A low(or high) lake level resulting from dry(or wet) conditions would lead to more(or fewer) vascular plant remains in the sediments and stronger(or weaker) denitrification associated with hypolimnetic anoxia,resulting in lower(or higher) δ15N values.In addition,dry(or wet) conditions would favor weakened(or strengthened) biogeochemical activity in the catchment,which could result in less(or more) external input of15N-enriched OM,thus leading to decreased(or increased) δ15N values.Our results indicate that the lake sediment δ15N record in the Nanling Mountains has the potential to provide valuable insight into past East Asian monsoon climatedriven environmental changes.

关 键 词：nitrogen isotopes lacustrine sediments climate changes Nanling Mountains 

分 类 号：P343.3[天文地球—水文科学]