We have studied iron (Fe)-isotope signals in particles (> 0.22 µm) and the dissolved phase (< 0.22 µm) in two subarctic, boreal rivers, their estuaries and the adjacent sea in northern Sweden. Both rivers, the Råne and the Kalix, are enriched in Fe and organic carbon (up to 29 µmol/L and up to 730 µmol/L, respectively). Observed changes in the particulate and dissolved phase during spring flood in May suggest different sources of Fe to the rivers during different seasons. While particles show a positive Fe-isotope signal during winter, during spring flood, the values are negative. Increased discharge due to snowmelt in the boreal region is most times accompanied by flushing of the organic-rich sub-surface layers. These upper podzol soil layers have been shown to be a source for Fe-organic carbon aggregates with a negative Fe-isotope signal. During winter, the rivers are mostly fed by deep groundwater, where Fe occurs as Fe(oxy)hydroxides, with a positive Fe-isotope signal. Flocculation during initial estuarine mixing does not change the Fe-isotope compositions of the two phases. Data indicate that the two groups of Fe aggregates flocculate diversely in the estuaries due to differences in their surface structure. Within the open sea, the particulate phase showed heavier δ⁵⁶Fe values than in the estuaries. Our data indicate the flocculation of the negative Fe-isotope signal in a low salinity environment, due to changes in the ionic strength and further the increase of pH.

中文翻译：

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北极河口低盐度混合过程中铁同位素特征的稳定性

我们已经研究了两个北极，北方河道，河口和瑞典北部邻近海域中颗粒中的铁（Fe）-同位素信号（> 0.22 µm）和溶解相（<0.22 µm）。罗纳河和卡利克斯河这两个河流都富含铁和有机碳（分别高达29 µmol / L和730 µmol / L）。在五月份的春季洪水期间观察到的颗粒相和溶解相的变化表明，在不同季节，河流中铁的来源不同。尽管颗粒在冬季显示出正的铁同位素信号，但在春季洪水期间却显示为负值。北方地区由于融雪而增加的排放量通常伴随着富含有机物的次表层的冲洗。这些上Podzol土壤层已被证明是具有负铁同位素信号的铁有机碳聚集体的来源。在冬季，河流主要由深层地下水供水，其中的Fe以氢氧化正铁的形式存在，并具有正的铁同位素信号。初始河口混合过程中的絮凝不会改变两相的铁同位素组成。数据表明，两组Fe聚集体由于其表面结构的不同而在河口中不同程度地絮凝。在公海内，颗粒相显示出较大的δ铁含量比河口高⁵⁶。我们的数据表明，在低盐度环境中，由于离子强度的变化以及pH值的增加，负铁同位素信号的絮凝。