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Water mass mixing versus local weathering inputs along the Bay of Biscay: Evidence from dissolved hafnium and neodymium isotopes
Marine Chemistry ( IF 3 ) Pub Date : 2020-06-11 , DOI: 10.1016/j.marchem.2020.103844
V. Dausmann , M. Frank , M. Zieringer

We present dissolved neodymium and hafnium concentrations and isotope compositions of surface and deep-water masses from the Bay of Biscay. Neodymium isotope signatures in surface waters of the Bay of Biscay are mostly dominated by local weathering inputs from the surrounding continental margin. Subsurface Eastern North Atlantic Central Water (ENACW) shows a distinct Nd isotope signature (εNd ≅ −12) at the southwestern-most station and is significantly diluted by mixing with more radiogenic waters or shifted by inputs of relatively radiogenic particulate Nd on its way north along the European margin. Furthermore, the Nd isotope data clearly show a declining fraction of Mediterranean Sea Water (MSW) at intermediate depths on its way north indicating that only 40% to 60% of MSW still present in the mixture at the Galician margin arrive at the stations further north in the Bay of Biscay. An interannual variability of the flow path of MSW is identified when comparing the results of the Nd isotope compositions and salinity data of this study with those of earlier studies from the area.

In agreement with Nd isotope and concentration analyses the Hf isotope composition of MSW is set by large-scale inputs of terrigenous material into the Mediterranean as can be deduced from elevated Hf concentrations still observable at the Galician margin. Hf isotope signatures of all water masses of the Bay of Biscay, moreover, are overprinted by local weathering inputs and do not reflect water mass mixing. However, combined dissolved Nd and Hf isotopes serve as indicators of local weathering influences on signatures expected from long distance water mass mixing.



中文翻译:

比斯开湾水质混合与当地风化输入的关系:来自溶解ha和钕同位素的证据

我们介绍了比斯开湾的溶解钕和ha浓度以及地表和深水团的同位素组成。比斯开湾地表水的钕同位素特征主要来自周围大陆边缘的局部风化输入。地下东北大西洋中央净水(ENACW)显示了独特的Nd同位素组成(ε ≅-12)在最西南的台站,并通过与更多放射源水混合而显着稀释,或在沿欧洲边缘向北行进时被相对放射源Nd的输入所移动。此外,Nd同位素数据清楚地表明,在向北的中间深度处,地中海水(MSW)的比例下降了,这表明加利西亚边缘的混合气中仍有40%至60%的MSW到达更北的站在比斯开湾。在比较本研究的Nd同位素组成和盐度数据与该地区较早的研究结果时,可以确定MSW流动路径的年际变化。

与Nd同位素和浓度分析相吻合,城市固体废物的Hf同位素组成是由向地中海中大量输入陆源物质确定的,这可以从仍在加利西亚边缘观测到的升高的Hf浓度推算得出。此外,比斯开湾所有水团的Hf同位素特征均被当地的风化输入所套印,不能反映水团的混合情况。但是,结合的溶解的Nd和Hf同位素可作为当地风化作用对长距离水团混合所预期特征的影响的指标。

更新日期:2020-06-11
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