Riverine fluxes of high field strength elements Zr, Hf, Nb, Ta into the oceans and their impact on the Hf isotopic composition of seawater

虽然现有的资料很少，但人们通常认为河流是向海洋输送粒子活性元素Zr、Hf、Nb和Ta的主要来源。然而，对这些元素从大陆到海洋的运输进行系统的调查，以及对不同地质和环境条件对它们的地球化学行为的影响的适当认识是缺乏的。沿着从陆地到海洋的路径的大黑盒子是河口，在那里淡水和海水的混合物深刻地影响了颗粒活性元素进入海洋的河流通量。本文研究了格陵兰北部和温带河流以及冰川融水河流中Zr、Hf、Nb和Ta的分布以及Hf同位素组成，并考虑了这些元素与淡水中不同物理微量元素池的关联，即颗粒（>0.2µm）、纳米颗粒/胶体（0.2µm ~ 1 KDa）和真正溶解（<1KD）池。这些元素进入海水的净河流通量及其对海洋Hf同位素组成的影响将通过淡水和海水端元之间的混合实验进行研究。复杂的方法工作包括过滤和超滤步骤以及随后的预富集步骤。本研究的结果将大大提高我们对不同地质和环境条件下淡水中Zr、Hf、Nb和Ta的运输和命运及其从大陆进入海洋的途径的认识。Hf同位素的研究结果将有助于更好地解决大陆风化和径流条件对海水Hf同位素组成的控制作用。

Although there are only little data available, rivers are commonly assumed to be the major source of the particle-reactive elements Zr, Hf, Nb, and Ta to the oceans. However, a systematic investigation of the transport of these elements from the continents to the oceans and a proper understanding of the impact of different geological and environmental conditions on their geochemical behavior are lacking. The large black box along the pathway from land to sea are the estuaries where the mixture of freshwater with seawater profoundly affects the riverine flux of particle-reactive elements into the ocean. This study addresses the distribution of Zr, Hf, Nb and Ta, and the Hf isotopic composition in boreal and temperate river water and in glacial melt water rivers in Greenland, taking into account the association of such elements with the different physical trace element pools in freshwater, i.e. the particulate (>0.2µm), the nanoparticle/colloid (0.2µm to 1 KDa), and the truly dissolved (<1KD) pools. The net riverine flux of these elements to seawater and its impact on the Hf isotopic composition of the oceans will be investigated by mixing experiments between the freshwater and seawater endmembers. The complex method work includes filtration and ultrafiltration steps and subsequent preconcentration steps. The outcome of this study will significantly enhance our understanding on the transport and fate of Zr, Hf, Nb, and Ta in freshwater and their pathways from the continents into the ocean at different geological and environmental conditions. The results for the Hf isotopes will help to better address the role of continental weathering and runoff conditions in controlling the Hf isotopic composition of seawater.