Constraints on the source of reactive phases in sediment from a major Arctic river using neodymium isotopes ...

• Main Authors: Larkin, Christina, Piotrowski, Alex, Hindshaw, Ruth, Bayon, Germain, Hilton, Robert, Baronas, Jotautas, Dellinger, Mathieu, Wang, Ruixue, Tipper, Edward
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2021
• Subjects: iron oxides; bioavailable; neodymium isotopes; Arctic; Arctic Ocean; Mackenzie River; Mackenzie river
• Online Access: https://dx.doi.org/10.17863/cam.72226; https://www.repository.cam.ac.uk/handle/1810/324773

Riverine suspended particulate matter (SPM) is essential for the delivery of micronutrients such as iron (Fe) to the oceans. SPM is known to consist of multiple phases with differing reactivity, but their role in the delivery of elements to the oceans is poorly constrained. Here we provide new constraints on the source and composition of reactive phases in SPM from the Mackenzie River, the largest sediment source to the Arctic Ocean. Sequential leaching of SPM shows that river sediments contain labile Fe phases. We estimate the labile Fe flux is substantial (0.21(+0.06,-0.05) Tg/yr) by quantifying Fe concentrations in weak leaches of the SPM. The labile Fe phase hosts a considerable amount of rare earth elements (REE), including neodymium (Nd). We demonstrate that the labile Fe phase and dissolved load have radiogenic Nd isotope ratios that are identical within uncertainty, but up to 8 epsilon units distinct from the silicate phase. We interpret this as evidence for dynamic cycling between Fe-oxide phases in ...