Assessment of Seawater Nd Isotope Signatures Extracted From Foraminiferal Shells and Authigenic Phases From Volcanogenic Sediments of the Adriatic Sea

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Guohui Gao, Christophe Colin, Giuseppe Siani, Sophie Sepulcre, Rosella Pinna-Jamme, Frederic Haurine, Arnaud Dapoigny
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Abstract

The neodymium isotope signatures (εNd) of the authigenic fraction have been extensively used to reconstruct past seawater εNd and hydrological circulation. Among the various methods, sequential extraction of hydrogenic ferromanganese oxyhydroxides from bulk sediments represents a rapid and straightforward approach that may potentially induce artifacts due to the potential release of non-seawater-derived Nd during the extraction procedure. Here we investigated different methods for extracting past seawater Nd isotope compositions from a core collected in the Adriatic Sea whose tephra layers have been previously well documented. We analyzed εNd in planktonic foraminifera samples and in non-decarbonated sediment leachates obtained with three solutions commonly used in the context of the Mediterranean Sea: (a) 0.02 M hydroxylamine hydrochloride (HH) solution, (b) 1N HCl, and (b) a 25% (v/v) acetic acid (AA). Our results show that (a) the foraminiferal εNd remains unaffected by the diagenesis of tephra content; (b) all three methods indicate significantly more radiogenic εNd values in tephra levels (up to 1.5 εNd unit), which is attributed to tephra dissolution accounting for 2.7% of extracted Nd; (c) of the three leaching methods applied to samples with low tephra content, hydroxylamine hydrochloride (HH) yields εNd values that are more consistent with those obtained on planktonic foraminifera; (d) the εNd values of planktonic foraminifera in core MD90-917 remained constant indicating that the Adriatic deep water primarily reflects the local Nd isotope composition over the last 20 kyr.

Abstract Image

从亚得里亚海火山沉积物的有孔虫贝壳和自生相中提取的海水钕同位素特征评估
自生部分的钕同位素特征(εNd)已被广泛用于重建过去的海水εNd和水文循环。在各种方法中,从大块沉积物中连续提取氢锰铁氧氢氧化物是一种快速、直接的方法,但由于在提取过程中可能释放出非海水来源的钕,因此可能会产生假象。在此,我们研究了从亚得里亚海采集的岩芯中提取过去海水钕同位素组成的不同方法,该岩芯的凝灰岩层之前已有详细记录。我们分析了浮游有孔虫样品和非脱碳沉积物浸出液中的εNd,这些样品是用地中海地区常用的三种溶液提取的:(a)0.02 M 盐酸羟胺(HH)溶液;(b)1N HCl;(b)25%(v/v)乙酸(AA)。结果表明:(a) 有孔虫εNd 的含量不受有孔虫成因的影响;(b) 三种方法都表明有孔虫εNd 的放射性含量在有孔虫含量中明显增加(高达 1.5 εNd 单位),这是由于有孔虫的溶解占萃取 Nd 的 2.7% 的萃取钕;(c) 在三种用于低壁屑含量样品的萃取方法中,盐酸羟胺(HH)法得到的εNd 值与浮游有孔虫的εNd 值更为一致;(d) MD90-917 岩芯中浮游有孔虫的εNd 值保持不变,表明亚得里亚海深层水主要反映了过去 20 千年中当地的钕同位素组成。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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