Constraining the oceanic barium cycle with stable barium isotopes
Constraining the oceanic barium cycle with stable barium isotopes
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DOI：
10.1016/j.epsl.2015.11.017
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发表时间：
2016-01-15
影响因子：
5.3
通讯作者：
Frank, Martin
中科院分区：
文献类型：
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作者：
Cao, Zhimian;Siebert, Christopher;Frank, Martin
海水中Ba2+浓度的分布与营养盐的分布相似，Ba2+被广泛用作古生产力的代表。然而，控制类营养物行为的确切机制，以及海洋中巴化学的基本原理，还没有完全解决。本文介绍了一组从长江输入大量淡水的南中国海和东中国海的全水柱溶解的Ba137DBA(DBA)剖面。我们发现了显著和系统的水平和深度相关的增量巴137(DBA)梯度。除受河流影响外，上层水柱的BA-137(DBA)值(千分之+0.9)明显高于深水(千分之+0.5)。此外，在整个上部100米，溶解的硅同位素在硅藻生长过程中被分馏，导致地表水中最重的同位素组成，因此三角洲BA-137(DBA)特征在整个上部100米内基本上是恒定的。结合DBA浓度和DBA-137(DBA)与硝酸盐和磷酸盐浓度的解偶关系，这表明海水中Ba同位素的表观营养型分馏主要是由较轻的同位素在生物颗粒上的优先吸附引起的，而不是由生物利用引起的。次表层三角洲Ba137(DBA)分布以水团混合为主。因此，应谨慎考虑使用稳定的钡同位素作为养分循环的替代物，需要同时考虑生物和物理过程。然而，显然，巴同位素作为一种新的海陆相互作用和海洋混合过程的示踪剂显示出巨大的潜力。(C)2015爱思唯尔B.V.保留所有权利。
The distribution of barium (Ba) concentrations in seawater resembles that of nutrients and Ba has been widely used as a proxy of paleoproductivity. However, the exact mechanisms controlling the nutrient-like behavior, and thus the fundamentals of Ba chemistry in the ocean, have not been fully resolved. Here we present a set of full water column dissolved Ba (DBa) isotope (delta Ba-137(DBA)) profiles from the South China Sea and the East China Sea that receives large freshwater inputs from the Changjiang (Yangtze River). We find pronounced and systematic horizontal and depth dependent delta Ba-137(DBa) gradients. Beyond the river influence characterized by generally light signatures (0.0 to +0.3 parts per thousand), the delta Ba-137(DBa) values in the upper water column are significantly higher (+0.9 parts per thousand) than those in the deep waters (+0.5 parts per thousand). Moreover, delta Ba-137(DBa) signatures are essentially constant in the entire upper 100 m, in which dissolved silicon isotopes are fractionated during diatom growth resulting in the heaviest isotopic compositions in the very surface waters. Combined with the decoupling of DBa concentrations and delta Ba-137(DBa) from the concentrations of nitrate and phosphate this implies that the apparent nutrient-like fractionation of Ba isotopes in seawater is primarily induced by preferential adsorption of the lighter isotopes onto biogenic particles rather than by biological utilization. The subsurface delta Ba-137(DBa) distribution is dominated by water mass mixing. The application of stable Ba isotopes as a proxy for nutrient cycling should therefore be considered with caution and both biological and physical processes need to be considered. Clearly, however, Ba isotopes show great potential as a new tracer for land-sea interactions and ocean mixing processes. (C) 2015 Elsevier B.V. All rights reserved.