Abstract Seawater rare earth element (REE) concentrations and Nd isotopic composition (eNd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and eNd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the eNd values here. On the other side, distributions of dissolved heavy REE (HREE) and eNd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and eNd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW takes on major importance when considering HREE in the model, EMDW fractions are preferentially detected with eNd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before.

中文翻译：

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稀土元素和 Nd 同位素作为地中海中部现代海洋环流的示踪剂

摘要 海水稀土元素 (REE) 浓度和 Nd 同位素组成 (eNd) 越来越多地用作海洋学过程的宝贵示踪剂，例如水团混合和海水岩性输入。然而，他们的测量在地中海水柱中基本上是缺乏的。本研究分析了地中海中部周围的 9 个海水站，以阐明外部来源、垂直（生物地球化学）过程和横向水团输送在控制 REE 和 eEnd 分布方面的相对重要性。REE 的浓度没有显示出与深度相似的营养成分，这可能表明再矿化 REE 积累有限的相对年轻的水域。轻稀土 (LREE) 表现出非保守行为，主要在地表水达到峰值，并随深度迅速下降。地表轻稀土富集与离岸距离的负相关突出了从意大利西部海岸到第勒尼安地表水的大陆输入的影响。与报告边界交换的其他区域相比，此过程不会修改此处的 eNd 值。另一方面，溶解的重稀土 (HREE) 和 eNd 的分布表现出保守的行为，这可以通过西部（MAW 和 WMDW）和东部（LIW 和 EMDW）起源水的混合来解释。我们使用包括 HREE 和 eNd 参数的最优多参数分析 (OMPA) 来检验这一假设。尽管数据集有限，但对于四种主要水团获得了一致的水质量分数结果，尽管有一些特殊性。虽然 LIW 在模型中考虑 HREE 时非常重要，EMDW 部分优先用 eNd 检测。后一个发现意味着一个明显的深水通量穿过西西里海峡进入西地中海，这在以前没有得到明确证明。