Characterisation of Fe-bearing particles and colloids in the Lena River basin, NE Russia

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Hirst, Catherine, Andersson, Per, Shaw, Samuel, Burke, Ian, Kutscher, Liselott, Murphy, Melissa, Maximov, Trofim, Pokrovsky, Oleg, Mörth, Carl-Magnus, Porcelli, Don
• Format: Article in Journal/Newspaper
• Language: English
• Published: Naturhistoriska riksmuseet, Enheten för geovetenskap 2017
• Subjects: Lena River; Iron particles; colloids; TEM imaging; STMX imaging; Geochemistry; Geokemi; Arctic Ocean; Climate change; lena river; permafrost
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-2470; https://doi.org/10.1016/j.gca.2017.07.012

Rivers are significant contributors of Fe to theocean. However, the characteristics of chemically reactive Fe remain poorly constrained, especially in large Arctic rivers, which drain landscapes highly susceptible to climate change and carbon cycle alteration. The aim of this study was a detailed characterisation (size, mineralogy, and speciation) of riverine Fe-bearing particles (> 0.22 µm) and colloids (1 kDa – 0.22 µm) and their association with organic carbon (OC), in the Lena River and tributaries, which drain a catchment almost entirely underlain by permafrost. Samples fromthe main channel and tributaries representing watersheds that span a wide rangein topography and lithology were taken after the spring flood in June 2013 and summer baseflow in July 2012. Fe-bearing particles were identified, usingTransmission Electron Microscopy, as large (200 nm – 1 µm) aggregates of smaller (20 nm - 30 nm) spherical colloids of chemically-reactive ferrihydrite.In contrast, there were also large (500 nm – 1 µm) aggregates of clay (illite) particles and smaller (100 - 200 nm) iron oxide particles (dominantly hematite) that contain poorly reactive Fe. TEM imaging and Scanning Transmission X-raymicroscopy (STXM) indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon (POC) and attached to the surface of primary produced organic matter and clay particles.Together, these larger particles act as the main carriers of nanoscale ferrihydrite in the Lena River basin. The chemically reactive ferrihydrite accounts for on average 70 ± 15 % of the total suspended Fe in the Lena River and tributaries. These observations place important constraints on Fe and OC cycling in the Lena River catchment area and Fe-bearing particle transport to the Arctic Ocean. The Lena River Study