Ocean circulation and freshwater pathways in the Arctic Mediterranean based on a combined Nd isotope, REE and oxygen isotope section across Fram Strait
Ocean circulation and freshwater pathways in the Arctic Mediterranean based on a combined Nd isotope, REE and oxygen isotope section across Fram Strait
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基于横跨弗拉姆海峡的 Nd 同位素、稀土元素和氧同位素组合剖面的北冰洋地中海海洋环流和淡水路径
DOI：
10.1016/j.gca.2016.12.028
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发表时间：
2017
影响因子：
5
通讯作者：
Kassens
中科院分区：
文献类型：
--
作者：
Laukert;Hathorne;von Appen;Wegner;Zieringer;Kassens
通过弗拉姆海峡的水团主要负责北欧海和北冰洋（北极地中海，AM）之间的热量和淡水交换。然而，要弄清它们的确切来源、分布和混合是很复杂的。这项工作基于详细的地球化学示踪剂清单，包括沿海峡全水深剖面的溶解Nd同位素（εNd）、稀土元素（REE）和稳定氧同位素（δ18O）数据，提供了新的见解。发现开放AM中Nd同位素和REE分布主要反映水团的横向平流及其混合。海水-粒子的相互作用仅在大陆架区域上方发挥重要的控制作用，正如在格陵兰岛东北大陆架上方所观察到的那样。在海峡东中部~ 500 m的上游，ε nd7和Nd浓度[Nd]为16 pmol/kg，清楚地反映了大西洋暖流向北流动的平流。在经过中压的过程中，暖流的变冷和变冷伴随着向更放射性ε n特征的持续变化（例如−10.4的北大西洋浓水）。这主要反映了与中间水的混合，也反映了稠密的喀拉海水和太平洋源水的混合。中深水（- 9.5）的辐射成因ε n主要在北欧海西南部与冰岛和格陵兰岛东部玄武岩地层交换获得。没有观测到来自斯瓦尔巴群岛的Nd输入，而斯瓦尔巴大陆架上的地表水和Nd来自巴伦支海。浅水南下的北极源水（<200 m）在格陵兰坡上形成了东格陵兰流的核心，其相对放射成因εNd（达到- 8.8）和[Nd]升高（21-29 pmol/kg）可追溯到东格陵兰流。这些性质与δ18O和标准水文示踪剂一起用于确定太平洋衍生水（基于Nd同位素< ~ 30%）和大西洋衍生水以及河流水（< ~ 8%）的比例。东北格陵兰陆架的浅水（<150 m）具有北极源水的一些特征，但在上~ 100 m表现出较小的辐射成因ε nd值（达到- 12.4）和较高的[Nd]（高达38 pmol/kg）。这表明格陵兰岛的本地淡水添加量高达6%。此外，研究还表明，上游水柱中显著的ε - n特征和REE特征梯度为评价AM内浅层水文变化提供了可靠的依据。
The water masses passing the Fram Strait are mainly responsible for the exchange of heat and freshwater between the Nordic Seas and the Arctic Ocean (the Arctic Mediterranean, AM). Disentangling their exact sources, distribution and mixing, however, is complex. This work provides new insights based on a detailed geochemical tracer inventory including dissolved Nd isotope (εNd), rare earth element (REE) and stable oxygen isotope (δ18O) data along a full water depth section across Fram Strait.We find that Nd isotope and REE distributions in the open AM primarily reflect lateral advection of water masses and their mixing. Seawater-particle interactions exert important control only above the shelf regions, as observed above the NE Greenland Shelf. Advection of northward flowing warm Atlantic Water (AW) is clearly reflected by anεNdsignature of −11.7 and a Nd concentration ([Nd]) of 16 pmol/kg in the upper ∼500 m of the eastern and central Fram Strait. Freshening and cooling of the AW on its way trough the AM are accompanied by a continuous change towards more radiogenicεNdsignatures (e.g. −10.4 of dense Arctic Atlantic Water). This mainly reflects mixing with intermediate waters but also admixture of dense Kara Sea waters and Pacific-derived waters. The more radiogenicεNdsignatures of the intermediate and deep waters (reaching −9.5) are mainly acquired in the SW Nordic Seas through exchange with basaltic formations of Iceland and CE Greenland. Inputs of Nd from Svalbard are not observed and surface waters and Nd on the Svalbard shelf originate from the Barents Sea. Shallow southward flowing Arctic-derived waters (<200 m) form the core of the East Greenland Current above the Greenland slope and can be traced by their relatively radiogenicεNd(reaching −8.8) and elevated [Nd] (21–29 pmol/kg). These properties are used together with δ18O and standard hydrographic tracers to define the proportions of Pacific-derived (<∼30% based on Nd isotopes) and Atlantic-derived waters, as well as of river waters (<∼8%). Shallow waters (<150 m) on the NE Greenland Shelf share some characteristics of Arctic-derived waters, but exhibit less radiogenicεNdvalues (reaching −12.4) and higher [Nd] (up to 38 pmol/kg) in the upper ∼100 m. This suggests local addition of Greenland freshwater of up to ∼6%. In addition to these observations, this study shows that the pronounced gradients inεNdsignatures and REE characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the AM.
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