A three-year time series of mineral dust deposits on the West African margin: Sedimentological and geochemical signatures and implications for interpretation of marine paleo-dust records
A three-year time series of mineral dust deposits on the West African margin: Sedimentological and geochemical signatures and implications for interpretation of marine paleo-dust records
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DOI：
10.1016/j.epsl.2012.12.039
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发表时间：
2013-02
影响因子：
5.3
通讯作者：
C. Skonieczny;A. Bory;V. Bout‐Roumazeilles;W. Abouchami;S. Galer;X. Crosta;A. Diallo;T. Ndiaye
中科院分区：
文献类型：
--
作者：
C. Skonieczny;A. Bory;V. Bout‐Roumazeilles;W. Abouchami;S. Galer;X. Crosta;A. Diallo;T. Ndiaye
热带大西洋东北部的矿物粉尘沉积是重建西非古环境和古气候的重要贡献。然而，对NETao海洋沉积物中记录的尘埃沉积的沉积学和地球化学特征的变化的解释仍然不完整。为了增进我们对尘埃物质，特别是其矿物学和地球化学来源示踪剂的了解，在塞内加尔边缘的Mbour(达喀尔以南80公里处的∼)对今天的尘埃沉积进行了监测。在这里，我们报告了一个独特的连续三年的矿物粉尘沉积时间序列的多代理调查，该序列收集了2006年3月至2009年3月期间每周(或更好的)时间分辨率。质量沉积通量和平均模式粒度表现出明显的相反的季节特征，冬春季通量较大，夏季通量最小，反映了全年不同的输送模式。同样，粘土矿物学，特别是伊利石/高岭石比值，表现出季节性波动，表现出物源区的纬向位移，以响应ITCZ位置和相关风系的季节性迁移。我们的三年记录还显示，主要沉积事件的发生叠加在季节性模式上，通常发生在冬季/春季旱季，最常见的是在3月份。我们的研究表明，这些重大事件占年总沉积通量的很大一部分，都来自西撒哈拉-萨赫勒地区(该地区除博代尔凹陷之外的一个主要排放区，从毛里塔尼亚和西撒哈拉海岸一直延伸到霍加山脉)。结合气团三维反向轨迹和卫星图像，这些大型尘埃事件的矿物学和锶-钕同位素组成使我们能够识别这一广阔西部地区内几个在矿物学和地球化学性质上不同的物源部门。与背景尘埃沉积不同，主要干事件的87Sr/86Sr和ε非对位特征与晚全新世沉积物的特征非常接近，支持了这些事件是到达海底的风成陆源物质的主要来源的假说。尽管这一数据库需要扩大，但我们的结果已经为解释毛里塔尼亚/塞内加尔近海海洋沉积档案中的尘埃替代物在西非风向和干旱变化方面的变化提供了有用的约束。
Mineral dust deposits in the Northeastern Tropical Atlantic Ocean (NETAO) are an important contribution for reconstructing paleoenvironments and paleoclimates of West Africa. However, the interpretation of the changes in the sedimentological and geochemical characteristics of the dust deposits recorded in the marine sediments from the NETAO remains incomplete. In order to improve our understanding of dust proxies, in particular its mineralogical and geochemical provenance tracers, present-day dust deposition has been monitored at Mbour (∼80km south of Dakar) on the Senegalese margin. Here we report a multi-proxy investigation of a unique three-year continuous time series of mineral dust deposits collected at a weekly (or better) temporal resolution over the March 2006–March 2009 period. Mass deposition flux and mean modal grain size display marked but reverse seasonal features, with higher flux during the winter/spring seasons and coarser grain size mode in summer when flux is minimal, reflecting contrasting transport patterns throughout the year. Similarly, clay mineralogy, the illite/kaolinite ratio in particular, shows seasonal fluctuations, manifesting the latitudinal displacement of the contributing domains of provenance in response to the seasonal migration of the ITCZ position and the associated wind systems. Our three-year record also reveals the occurrence of major deposition events superimposed on the seasonal pattern, generally during the winter/spring dry seasons and most frequently during the month of March. Our study shows that these major events, which contribute a large fraction of the total annual deposition flux, all originate from the western Sahara–Sahel (a major area of emission in the region beside the Bodele Depression, stretching from the Mauritanian and Western Saharan coasts to the Hoggar Mountains). Combined with air mass tri-dimensional back-trajectories and satellite images, the mineralogical and Sr–Nd isotopic compositions of these large dust events enable us to identify several mineralogically and geochemically distinct provenance sectors within this vast western area. Unlike the background dust deposits, the87Sr/86Sr and the εNdisotopic signatures of the major dry events closely match that of the NETAO Late Holocene sediments, supporting the hypothesis that these events account for most of the aeolian terrigenous supply reaching the ocean floor. Although this database needs to be expanded, our results already provide useful constraints for the interpretation of the dust proxies' variations in marine sedimentary archives off Mauritania/Senegal in terms of changes in wind regimes and aridity over West Africa.