Constraining the marine strontium budget with natural strontium isotope fractionations (87Sr/86Sr*, δ88/86Sr) of carbonates, hydrothermal solutions and river waters
Constraining the marine strontium budget with natural strontium isotope fractionations (87Sr/86Sr*, δ88/86Sr) of carbonates, hydrothermal solutions and river waters
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DOI：
10.1016/j.gca.2010.04.009
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发表时间：
2010-07-15
影响因子：
5
通讯作者：
Wallmann, K.
中科院分区：
文献类型：
--
作者：
Krabbenhoeft, A.;Eisenhauer, A.;Wallmann, K.
与传统的Sr-87/Sr-86数据不同，我们提出的锶（Sr）同位素比值未归一化为8.375209的固定Sr-88/Sr-86比值（定义为相对于NIST SRM 987的δ Sr-88/86 = 0）。相反，我们在质谱分析期间用Sr-87-Sr-84双加标校正同位素分馏。该技术产生Sr-87/Sr-86和Sr-88/Sr-86的两个独立比率，分别报告为（Sr-87/Sr-86*）和（δ Sr-88/86）。传统的放射成因（Sr-87/Sr-86标准化为Sr-88/Sr-86 = 8.375209）和新的Sr-87/Sr-86* 值之间的差异反映了自然质量依赖的同位素分馏。为了限制冰期/间冰期海洋锶收支的变化，我们比较了现代海水的同位素组成，（（Sr-87/Sr-86*，δ Sr-88/86）（海水））和现代海洋生物碳酸盐岩（（Sr-87/Sr-86*，δ（88）/Sr-86）（碳酸盐））与河流沃茨的相应值（（Sr-87/Sr-86*，delta Sr-88/86）（River））和热液（（Sr-87/Sr-86*，delta（88）/Sr-86）（HydEnd））。测得的（Sr-87/Sr-86*，δ（88）/Sr-86）（河流）。所选河流的锶排放量约占全球锶排放量的18%，其锶通量加权平均值为（0.7114（8），0.315（8）ppm）。大西洋热液的平均（（Sr-87/Sr-86*，delta Sr-88/86）（HydEnd）值分别为（0.7045（5），0.27（3）ppm）。相反，代表海洋Sr输出的（Sr-87/Sr-86*，δ Sr-88/86）（碳酸盐）值为（0.70926（2），0.21（2）ppm）。我们估计这些源区的现代Sr同位素组成为（0.7106（8），0.310（8）ppm）。估算的（Sr-87/Sr-86*，δ Sr-88/86）和（Sr-87/Sr-86*，δ（88）/Sr-86）（输出）值之间的差异反映了Sr输入和输出的同位素不平衡。与现代海洋相反，在末次盛冰期（距今10-30 ka）的输入和输出之间的同位素平衡可以通过调用一个独特的“冰川”来源的三倍高的Sr输入来解释：暴露在低海平面的陆架碳酸盐的风化。我们的数据也是一致的“风化峰”的假设，调用增强Sr输入导致丰富的细粒物质的冰后期暴露的风化。(C)2010爱思唯尔有限公司版权所有。
We present strontium (Sr) isotope ratios that, unlike traditional Sr-87/Sr-86 data, are not normalized to a fixed Sr-88/Sr-86 ratio of 8.375209 (defined as delta Sr-88/86 = 0 relative to NIST SRM 987). Instead, we correct for isotope fractionation during mass spectrometry with a Sr-87-Sr-84 double spike. This technique yields two independent ratios for Sr-87/Sr-86 and Sr-88/Sr-86 that are reported as (Sr-87/Sr-86*) and (delta Sr-88/86), respectively. The difference between the traditional radiogenic (Sr-87/Sr-86 normalized to Sr-88/Sr-86 = 8.375209) and the new Sr-87/Sr-86* values reflect natural mass-dependent isotope fractionation. In order to constrain glacial/interglacial changes in the marine Sr budget we compare the isotope composition of modern seawater ((Sr-87/Sr-86*, delta Sr-88/86)(Seawater)) and modern marine biogenic carbonates ((Sr-87/Sr-86*, delta(88)/Sr-86)(Carbonates)) with the corresponding values of river waters ((Sr-87/Sr-86*, delta Sr-88/86)(River)) and hydrothermal solutions ((Sr-87/Sr-86*, delta(88)/Sr-86)(HydEnd)) in a triple isotope plot. The measured (Sr-87/Sr-86*, delta(88)/Sr-86)(River)). values of selected rivers that together account for similar to 18% of the global Sr discharge yield a Sr flux-weighted mean of (0.7114(8), 0.315(8)parts per thousand). The average ((Sr-87/Sr-86*, delta Sr-88/86)(HydEnd) values for hydrothermal solutions from the Atlantic Ocean are (0.7045(5), 0.27(3)parts per thousand). In contrast, the (Sr-87/Sr-86*, delta Sr-88/86)(Carbonates) values representing the marine Sr output are (0.70926(2), 0.21(2)parts per thousand). We estimate the modern Sr isotope composition of the sources at (0.7106(8), 0.310(8)parts per thousand). The difference between the estimated (Sr-87/Sr-86*, delta Sr-88/86) and (Sr-87/Sr-86*, delta(88)/Sr-86)(output) values reflects isotope disequilibrium with respect to Sr inputs and outputs. In contrast to the modern ocean, isotope equilibrium between inputs and outputs during the last glacial maximum (10-30 ka before present) can be explained by invoking three times higher Sr inputs from a uniquely "glacial" source: weathering of shelf carbonates exposed at low sea levels. Our data are also consistent with the "weathering peak" hypothesis that invokes enhanced Sr inputs resulting from weathering of postglacial exposure of abundant fine-grained material. (C) 2010 Elsevier Ltd. All rights reserved.