The hafnium and neodymium isotope composition of seawater in the Atlantic sector of the Southern Ocean
The hafnium and neodymium isotope composition of seawater in the Atlantic sector of the Southern Ocean
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DOI：
10.1016/j.epsl.2011.11.025
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发表时间：
2012-02
影响因子：
5.3
通讯作者：
T. Stichel;M. Frank;J. Rickli;B. Haley
中科院分区：
文献类型：
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作者：
T. Stichel;M. Frank;J. Rickli;B. Haley
我们提出了第一个合并溶解铪（Hf）和钕（Nd）的浓度和同位素组成的深水质量从大西洋部门的南大洋。八个完整的深度配置文件进行了分析，铪和12钕。哈夫里翁浓度一般在上层几百米处耗尽，在0.2至0.4皮摩尔/千克之间，在较深的水柱中增加到相对恒定的0.6皮摩尔/千克左右。在极锋（PF）以北的站点，Nd浓度从~ 200 m深度的约10 pmol/kg线性增加到接近底部的31 pmol/kg，表明颗粒清除和释放。然而，在威德尔环流（WG），Nd浓度基本上是恒定的25 pmol/kg的深度大于1000米。这两种元素的分布与溶解硅呈正相关，这意味着与硅藻地球化学密切相关。铪的同位素组成基本不变，平均εHf=+4.6，而钕的同位素则显示了水团之间的明显差异，例如修正的北大西洋深水（NADW，εNd=−11至−10）和南极底层水（AABW，εNd=−8.6至−9.6），但也可以通过它们的非放射性Nd同位素组成来识别通过厄古拉斯海流平流的沃茨。混合计算表明，一小部分的Nd被去除的颗粒清除过程中混合的水团北部的PF。然而，Nd同位素组成显然没有显着影响的Nd从颗粒的吸收和释放，所示的混合计算。一个近似的北太平洋和北大西洋端员的混合包络线表明，钕同位素和浓度模式在较低的绕极深水（LCDW）可以完全解释的约30：70的百分比贡献，这些各自的端员。
We present the first combined dissolved hafnium (Hf) and neodymium (Nd) concentrations and isotope compositions of deep water masses from the Atlantic sector of the Southern Ocean. Eight full depth profiles were analyzed for Hf and twelve for Nd. Hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0.2pmol/kg and 0.4pmol/kg and increase to relatively constant values of around 0.6pmol/kg in the deeper water column. At the stations north of the Polar Front (PF), Nd concentrations increase linearly from about 10pmol/kg at depths of ~200m to up to 31pmol/kg close to the bottom indicating particle scavenging and release. Within the Weddell Gyre (WG), however, Nd concentrations are essentially constant at 25pmol/kg at depths greater than ~1000m. The distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry. Hafnium essentially shows invariant isotope compositions with values averaging at εHf=+4.6, whereas Nd isotopes mark distinct differences between water masses, such as modified North Atlantic Deep Water (NADW, εNd=−11 to −10) and Antarctic Bottom Water (AABW, εNd=−8.6 to −9.6), but also waters locally advected via the Agulhas Current can be identified by their unradiogenic Nd isotope compositions. Mixing calculations suggest that a small fraction of Nd is removed by particle scavenging during mixing of water masses north of the PF. Nevertheless, the Nd isotope composition has apparently not been significantly affected by uptake and release of Nd from particles, as indicated by mixing calculations. A mixing envelope of an approximated North Pacific and a North Atlantic end-member shows that Nd isotope and concentration patterns in the Lower Circumpolar Deep Water (LCDW) can be fully explained by ~30:70 percentage contributions of these respective end-members.