| Summary: | The input of iron to the Arctic Ocean plays a critical role in the productivity of aquatic ecosystems and is potentially impacted by climate change. We examine Fe isotope systematics of dissolved and colloidal Fe from several Arctic and sub-Arctic rivers in northern Eurasia and Alaska. We demonstrate that the Fe isotopic (delta Fe-56) composition of large rivers, such as the Ob' and Lena, has a restricted range of delta Fe-56 values ca. -0.11 +/- 0.13 parts per thousand, with minimal seasonal variability, in stark contrast to smaller organic-rich rivers with an overall delta Fe-56 range from -1.7 to + 1.6 parts per thousand. The preferential enrichment with heavy Fe isotopes observed in low molecular weight colloidal fraction and during the high-flow period is consistent with the role of organic complexation of Fe. The light Fe isotope signatures of smaller rivers and meltwater reflect active redox cycling. Data synthesis reveals that small organic-rich rivers and meltwater in Arctic environments may contribute disproportionately to the input of labile Fe in the Arctic Ocean, while bearing contrasting Fe isotope compositions compared to larger rivers. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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