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

DOI: 10.1016/j.gca.2017.07.012 DOI Help

Authors: Catherine Hirst (Stockholm University; Swedish Museum of Natural History) , Per S. Andersson (Swedish Museum of Natural History) , Samuel Shaw (The University of Manchester) , Ian T. Burke (University of Leeds) , Liselott Kutscher (Stockholm University; Swedish Museum of Natural History) , Melissa J. Murphy (University of Oxford) , Trofim Maximov (Institute for Biological Problems of the Cryolithozone, Siberian Branch of the Russian Academy of Sciences) , Oleg S. Pokrovsky (University of Toulouse; Tomsk State University) , Carl-Magnus Mörth (Stockholm University) , Don Porcelli (Oxford University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Geochimica Et Cosmochimica Acta

State: Published (Approved)
Published: July 2017
Diamond Proposal Number(s): 11282

Abstract: Rivers are significant contributors of Fe to the ocean. 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 from the main channel and tributaries representing watersheds that span a wide range in topography and lithology were taken after the spring flood in June 2013 and summer baseflow in July 2012. Fe-bearing particles were identified, using Transmission 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-ray microscopy (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.

Subject Areas: Environment, Earth Science, Chemistry

Instruments: I08-Scanning X-ray Microscopy beamline (SXM)

Added On: 15/07/2017 13:54

Discipline Tags:

Earth Sciences & Environment Mineralogy Geology Geochemistry

Technical Tags:

Microscopy X-ray Microscopy Scanning X-ray Microscopy