The potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past
The potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past
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DOI：
10.1002/2016gc006782
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发表时间：
2017-04-01
影响因子：
3.5
通讯作者：
Frank, Martin
中科院分区：
文献类型：
--
作者：
Osborne, Anne H.;Hathorne, Ed C.;Frank, Martin
溶解稀土元素（REE）浓度数据从中间和深层海水形成一个阵列，其特征在于较高的中稀土富集（MREE/MREE*）在北大西洋和逐步增加的重轻稀土比（HREE/LREE）的水团年龄。有孔虫中稀土元素相对于海水而言，表现为高MREE/MREE* 和低HREE/LREE的分馏特征。基于清除模型的计算表明，在未清洗的核心顶部有孔虫的稀土模式类似于吸附到方解石，颗粒有机物，和水合氧化铁，但有孔虫中测得的稀土分馏的全部程度没有再现的模型。然而，在海洋盆地之间的HREE/LREE和MREE/MREE* 比值的差异和铈异常被保存，并与海水稀土分布一致。在富氧条件下，沉积物/海水界面未净化有孔虫的HREE/LREE和MREE/MREE* 组成在埋藏过程中得以保留，但铈异常对埋藏深度敏感。在亚氧沉积环境中，所有未清洗有孔虫稀土元素浓度升高相对于核心的顶部值，表明从孔隙沃茨的稀土元素。重稀土/轻稀土比值最高时，沉积速率最大，当高的Fe/Ca比值在未清洗的有孔虫表明，铁是移动的。在埋藏过程中没有经历过亚氧条件的沉积物中，未清洗的有孔虫保存了沉积物/海水界面处吸收的海水信号，因此建议将过去底部沃茨的REE信号变化作为合适的存档。
Dissolved rare earth element (REE) concentration data from intermediate and deep seawater form an array characterized by higher middle-REE enrichments (MREE/MREE*) in the North Atlantic and a progressive increase in heavy-to-light REE ratios (HREE/LREE) as water masses age. The REEs in foraminifera are fractionated toward higher MREE/MREE* and lower HREE/LREE relative to seawater. Calculations based on a scavenging model show that the REE patterns in uncleaned core-top foraminifera resemble those adsorbed onto calcite, particulate organic material, and hydrous ferric oxides but the full extent of the REE fractionation measured in foraminifera was not reproduced by the model. However, differences in the HREE/LREE and MREE/MREE* ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater REE distribution. Under oxic conditions, the HREE/LREE and MREE/MREE* compositions of uncleaned foraminifera at the sediment/seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth. In suboxic sedimentary environments, all uncleaned foraminiferal REE concentrations are elevated relative to core-top values indicating addition of REEs from pore waters. The HREE/LREE ratio is highest when sedimentation rates were greatest and when high Fe/Ca ratios in the uncleaned foraminifera indicate that Fe was mobile. In sediments that have not experienced suboxic conditions during burial, uncleaned foraminifera preserve the seawater signal taken up at the sediment/seawater interface and are therefore suggested to be a suitable archive of changes in the REE signal of past bottom waters.