Using lithium isotopes to quantitatively decode continental weathering signal:A case study in the Changjiang(Yangtze River)Estuary  

作　　者：Fang CAO Shouye YANG Chengfan YANG Yulong GUO Lei BI Yuze LI 

机构地区：[1]State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China [2]Polar Research Institute of China,Shanghai 200136,China [3]School of Mathematical Sciences,Fudan University,Shanghai 200433,China

出　　处：《Science China Earth Sciences》2021年第10期1698-1708,共11页中国科学（地球科学英文版）

基　　金：funded by the National Natural Science Foundation of China(Grant Nos.41991324,41730531,40830107);The sampling cruise(No.YEC2017)was supported by the State Key Laboratory of Marine Geology,Tongji University.

摘　　要：As the key link connecting the earth’s spheres,continental weathering plays an important role in regulating the global biogeochemical cycle and long-term climate change.Siliciclastic sediments derived from large river basins can record continental weathering and erosion signals,and are thus widely used to investigate weathering processes.However,sediment grain size,hydrodynamic sorting and sedimentary recycling complicate the interpretation of sediment weathering proxies.This study presents elemental and lithium isotope compositions of estuarine surface sediments(SS)and suspended particulate matters(SPM)collected from the Changjiang(Yangtze River)Estuary.Based on a simple mass balance model,the proportions of different end-members(i.e.,igneous rocks,modern weathering products and inherited weathering products)in sediments were quantitatively calculated and thus the silicate weathering process can be estimated.Overall,the sediments in the Changjiang Estuary are mainly eroded from un-weathered rock fragments(>60%),while modern weathering products account for less than 40%.The fine-grained SPM contain more shale components(52–66%),and the modern weathering products account for 21–40%.Comparatively,the coarse-grained surface sediments contain more un-weathered igneous rock fragments(63–84%)and less modern weathering products(only 4–18%).The comparison ofδ^(7)Li values with the weathering proxy(Chemical Index of Alteration,CIA)suggests that sediment weathering intensity declines with increasing proportion of un-weathered igneous rock fragments.Additionally,the occurrence of inherited weathering products(i.e.,shale)in modern sediments makes it a challenge to simply use CIA andδ^(7)Li as indicators of weathering intensity.This study confirms that fine-grained particles are more suitable for tracing contemporary weathering process,albeit with the influence of sedimentary recycling.Lithium isotopes combining with the mass balance model can quantitatively constrain the continental weathering processes in large

关 键 词：Lithium isotopes Changjiang Estuary Chemical weathering Sedimentary recycling 

分 类 号：P512.2[天文地球—地质学] P597