TAG Plume: Revisiting the Hydrothermal Neodymium Contribution to Seawater
TAG Plume: Revisiting the Hydrothermal Neodymium Contribution to Seawater
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TAG Plume：重新审视热液钕对海水的贡献
DOI：
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发表时间：
2018
影响因子：
3.7
通讯作者：
H. Scher
中科院分区：
文献类型：
--
作者：
T. Stichel;K. Pahnke;B. Duggan;S. Goldstein;A. E. Hartman;Ronja Paffrath;H. Scher
本文介绍了2011年10月GEOTRACES GA03巡航收集的TAG热液喷口场及其邻近位置的eNd和[Nd]分布结果。结果表明，羽流正下方和上方的Nd同位素与平均NADW （eNd = -12.3±0.2）没有显著偏差。然而，在羽流内部，同位素值略微向更具有放射性的值偏移，直至eNd = -11.4。有趣的是，与此同时，随着稀土元素（REE）的分异，[Nd]也显著减少，这表明尽管Nd同位素发生了变化，但羽流内部的清除作用增强了。Nd元素浓度从19.6 pmol/kg下降到18.5 pmol/kg，与地幔衍生氦（xs3He）从0.203增加到0.675 fmol/kg的最大值一致，导致[Nd]相对于预期的随深度线性增加平均下降1.8 pmol/kg。如果假设[Nd]随深度持续增加，羽流中Nd的存量损失总计为614 nmol /m2，即6%。与BATS和西部相邻站点USGT11-14相比，当地库存损失甚至更高，为10%。xs3He增加和[Nd]减少的紧密关系使我们能够估计TAG的清除率，表明在TAG羽流中清除了40 mol/yr。根据沿洋脊的功率输出，全球估计每年的Nd去除量为3.44 × 106 mol/年，约占河流和尘埃通量总和的71%，或估计全球进入海洋的Nd通量的6%至8%。Nd同位素组成的变化高达0.7以上的放射性成因eNd值表明，水热衍生颗粒与海水之间存在交换过程，在去除过程中，估计有1.1 mol/yr的热液Nd被贡献到TAG位置的海水中。这一估计仅占海洋边缘边界交换过程向海洋添加的全球Nd信号的0.1%，限制了在全球范围内改变Nd同位素组成的能力，而相比之下，热液羽流中元素Nd的估计更为重要
We present results on the distribution of eNd and [Nd] from the TAG hydrothermal vent field and adjacent locations collected during the GEOTRACES GA03 cruise in October 2011. Our results show that Nd isotopes directly below and above the plume do not significantly deviate from average NADW (eNd = -12.3±0.2). Within the plume, however, isotope values are shifted slightly towards more radiogenic values up to eNd = -11.4. Interestingly at the same time a significant decrease in [Nd] along with rare earth element (REE) fractionation is observed, indicating enhanced scavenging within the plume despite the change in Nd isotopes. Elemental concentrations of Nd are reduced by 19.6 to 18.5 pmol/kg, coinciding with the maximum increase of mantle derived helium (xs3He) from 0.203 to 0.675 fmol/kg, resulting in an average 1.8 pmol/kg decrease in [Nd] relative to an expected linear increase with depth. The inventory loss of Nd within the plume sums up to 614 nmoles/m2, or 6 %, if a continuous increase of [Nd] with depth is assumed. Compared to BATS and the western adjacent station USGT11-14, the local inventory loss is even higher at 10 %. The tight relationship of xs3He increase and [Nd] decrease allows us to estimate scavenging rates at TAG suggesting 40 mol/yr are removed within the TAG plume. A global estimate using power output along ocean ridges yields an annual Nd removal of 3.44x106 mol/yr, which is about 71% of riverine and dust flux combined or 6 to 8% of the estimated global flux of Nd into the ocean. The change in Nd isotopic composition of up to 0.7 more radiogenic eNd values suggests an exchange process between hydrothermally derived particles and seawater in which during the removal process an estimated 1.1 mol/yr of hydrothermal Nd is contributed to the seawater at the TAG site. This estimate is only 0.1 % of the global Nd signal added to the ocean by boundary exchange processes at ocean margins, limiting the ability of changing the Nd isotopic composition on a global scale in contrast to the more significant estimated sink of elemental Nd in hydrothermal plumes from
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