A silicon depleted North Atlantic since the Palaeogene: Evidence from sponge and radiolarian silicon isotopes
A silicon depleted North Atlantic since the Palaeogene: Evidence from sponge and radiolarian silicon isotopes
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DOI：
10.1016/j.epsl.2016.08.006
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发表时间：
2016-11-01
影响因子：
5.3
通讯作者：
Conley, Daniel J.
中科院分区：
文献类型：
--
作者：
Fontorbe, Guillaume;Frings, Patrick J.;Conley, Daniel J.
尽管是地球的主要地球化学循环之一，硅循环的演变很少受到关注，海洋溶解硅（DSi）浓度的变化，通过地质时间仍然缺乏约束。海洋微体化石中的硅同位素比值（表示为δ Si-30）因其提供硅循环洞察力的能力而越来越受到认可。特别是，硅质海绵针状体的δ Si-30已被证明是过去DSi浓度的有用代表。我们分析了三角洲Si-30的放射虫测试和海绵骨针从布莱克鼻子古海洋断面（ODP腿171 B）跨越古新世-始新世（约。60 - 30 Ma）。对于放射虫和海绵记录，我们的δ Si-30结果范围分别为+0.32至+1.67份/千份和-0.48至+0.63份/千份。使用环境溶解硅（DSi）的浓度和硅质海绵的硅同位素分馏的幅度之间建立的关系，我们表明，西北大西洋DSi耗尽在古新世-始新世整个水柱，一个结论是强大的一系列假设和不确定性。这些数据可以构成对过去海洋环流重建的限制。以前的工作表明，海洋DSi浓度高于新生代之前的现代海洋浓度，并假设在古近纪早期由于硅藻的进化扩张而下降。我们的研究结果挑战了这种解释。我们认为，如果这样一个全球性的海洋DSi浓度下降发生，它必须早于60 Ma。(C)2016作者由爱思唯尔公司出版
Despite being one of Earth's major geochemical cycles, the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica (DSi) concentration through geologic time remain poorly constrained. Silicon isotope ratios (expressed as delta Si-30) in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling. In particular, the delta Si-30 of siliceous sponge spicules has been demonstrated to be a useful proxy for past DSi concentrations. We analysed delta Si-30 in radiolarian tests and sponge spicules from the Blake Nose Palaeoceanographic Transect (ODP Leg 171B) spanning the Palaeocene-Eocene (ca. 60-30 Ma). Our delta Si-30 results range from +0.32 to +1.67 parts per thousand and -0.48 to +0.63 parts per thousand for the radiolarian and sponge records, respectively. Using an established relationship between ambient dissolved Si (DSi) concentrations and the magnitude of silicon isotope fractionation in siliceous sponges, we demonstrate that the Western North Atlantic was DSi deplete during the Palaeocene-Eocene throughout the water column, a conclusion that is robust to a range of assumptions and uncertainties. These data can constitute constraints on reconstructions of past-ocean circulation. Previous work has suggested ocean DSi concentrations were higher than modern ocean concentrations prior to the Cenozoic and has posited a drawdown during the Early Palaeogene due to the evolutionary expansion of diatoms. Our results challenge such an interpretation. We suggest here that if such a global decrease in oceanic DSi concentrations occurred, it must predate 60 Ma. (C) 2016 The Authors. Published by Elsevier B.V.