Assessing bulk carbonates as archives for seawater Li isotope ratios
Assessing bulk carbonates as archives for seawater Li isotope ratios
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评估散装碳酸盐作为海水锂同位素比的档案
DOI：
10.1016/j.chemgeo.2019.119338
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发表时间：
2019
期刊：
影响因子：
3.9
通讯作者：
Pogge Von Strandmann P
中科院分区：
文献类型：
--
作者：
Pogge Von Strandmann P
硅酸盐风化是碳循环的主要控制因素，因此也是长期气候的主要控制因素。几十年来，在地质记录中追踪硅酸盐风化一直是一个挑战，提出了一些替代方案，并确定了它们的限度。最近，海洋碳酸盐中的锂同位素已成为一种潜在的示踪剂。散装碳酸盐越来越多地被用作锂同位素档案，尽管到目前为止，这种方法在现代海洋中的稳健性测试有限。由于海洋远洋碳酸盐的散装成分随着时间和地理的变化而发生变化，因此评估散装碳酸盐作为代理运输船的保真度是基本的。为了研究块状碳酸盐的组成变化对Li同位素的影响，我们研究了27个巴哈马文石块状碳酸盐和16个大西洋主要钙化的核顶沉积物样品。两个岩心顶部只有微量(<；10%)碳酸盐，并进行了分析，以测试这些部分的碳酸盐是否仍然是可行的档案。我们从岩心顶部样品中选择性地提取可交换组分和碳酸盐组分。可交换部分的∼占总锂的2%，与海水的偏移量相当恒定，为16.5%±100.8‰。在浸出含硅酸盐的碳酸盐时，与稀盐酸相比，用醋酸钠缓冲的醋酸似乎是一种更可靠的单独攻击碳酸盐的方法，这也可能释放出一些硅酸盐结合的锂。不含文石的样品碳酸盐的海水同位素分馏为Δ7‰-方解石=66.1±91.3 Sd，不受纬度或样品沉积水深的影响。巴哈马纯文石块状碳酸盐的分馏为Δ7-水-文石=99.6±100.6‰。加利西亚海岸的一个沉积物样品，主要由石英组成，与海水的偏移量为∼20‰，也具有相对较高的Li/Ca比值。这些高的值不是由于硅酸盐材料的直接浸出(铝/钙比很低)。我们解释这种加成是通过重结晶过程中锂离子与硅酸盐的阳离子交换来实现的。总体来说，来自公海的散装碳酸盐是海水δ7Li的可靠档案，但必须小心处理碳酸盐矿物学和低碳酸盐样品。因此，总体而言，对古海水δ7Li记录的任何检查都必须在不同的全球环境下(例如，多个全球岩心)复制，才能被认为是可靠的。
Silicate weathering is a primary control on the carbon cycle and therefore long-term climate. Tracing silicate weathering in the geological record has been a challenge for decades, with a number of proxies proposed and their limits determined. Recently lithium isotopes in marine carbonates have emerged as a potential tracer. Bulk carbonates are increasingly being used as a Li isotope archive, though with limited tests thus far of the robustness of this approach in the modern ocean. As the bulk composition of marine pelagic carbonates has changed through time and geographically, assessing the fidelity of bulk carbonate as proxy carrier is fundamental. To address the impact of compositional variability in bulk carbonate on Li isotopes, we examine 27 Bahamian aragonitic bulk carbonates and 16 Atlantic largely calcitic core-top sediment samples. Two core-tops only have trace (<10 %) carbonate, and are analysed to test whether carbonates in such sections are still a viable archive. We selectively extract the exchangeable and carbonate fractions from the core-top samples. The exchangeable fraction contains ∼2 % of the total Li and has a fairly constant offset from seawater of 16.5 ± 0.8‰. When leaching silicate-containing carbonates, acetic acid buffered with sodium acetate appears a more robust method of solely attacking carbonates compared to dilute HCl, which may also liberate some silicate-bound Li. Carbonates from samples that do not contain aragonite have the isotopic fractionation of seawater of Δ7Liseawater-calcite= 6.1 ± 1.3‰ (2sd), which is not affected by latitude or the water depth the sample was deposited at. The pure aragonite bulk carbonates from the Bahamas have a fractionation of Δ7Liseawater-aragonite= 9.6 ± 0.6‰. A sediment sample from the Galician coast that mostly consists of quartz is highly offset from seawater by ∼20‰ and also has relatively high Li/Ca ratios. These high values are not due to leaching of silicate material directly (Al/Ca ratios are low). We interpret this addition via cation exchange of Li from silicate during recrystallisation. Overall bulk carbonates from the open ocean are a reliable archive of seawaterδ7Li, but care must be taken with carbonate mineralogy and low-carbonate samples. Overall, therefore, any examination of the palaeo-seawaterδ7Li record must be reproduced in different global settings (e.g. multiple global cores) before it can be considered robust.
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影响因子：
5
作者：
R. Hindshaw;Rebecca Tosca;Thomas L. Goût;I. Farnan;N. Tosca;E. Tipper
通讯作者：
R. Hindshaw;Rebecca Tosca;Thomas L. Goût;I. Farnan;N. Tosca;E. Tipper
巴哈马微生物岩基质的多样性
影响因子：
5.3
作者：
R. Ginsburg;N. Planavsky
通讯作者：
N. Planavsky
影响因子：
5.8
作者：
P. V. Strandmann;G. Henderson
通讯作者：
P. V. Strandmann;G. Henderson
DOI：
10.7185/geochemlet.1726
发表时间：
2017-06
期刊：
--
影响因子：
--
作者：
P. V. Strandmann;A. Desrochers;M. Murphy;A. Finlay;D. Selby;T. Lenton
通讯作者：
P. V. Strandmann;A. Desrochers;M. Murphy;A. Finlay;D. Selby;T. Lenton
展示的碳酸盐水泥织物：横穿埃克苏马群岛李斯托金岛附近的巴哈马平台边缘
影响因子：
2.9
作者：
G. Whittle;C. Kendall;R. Dill;Linda S. Rouch
通讯作者：
Linda S. Rouch