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  • 1.
    Hirst, Catherine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Iron in the Lena River basin, NE Russia: Insights from microscopy, spectroscopy and isotope analysis2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Iron is an important mediator of biotic and abiotic processes on the Earth’s surface, being an electron acceptor in organic matter degradation, a surface for organic matter and trace element adsorption, and a required element for enzymatic processes during primary production. Yet, the role of iron as a mediator of carbon and trace element cycling in high latitude, permafrost-dominated regions remains poorly investigated. The aim of this study was to characterise the chemical reactivity (by size separation, microscopy and spectroscopy) and sources (by isotope composition) of Fe in the Lena River and major tributaries, spanning a wide range in lithology, topography and climate. The Fe transported in the Lena River and major tributaries carries an integrated signal of Fe weathering processes across the permafrost-dominated terrain.

    A spatial sample set was collected during the post-spring flood period (July 2012, June 2013), from the main channel and tributaries draining contrasting topography and permafrost extent. Across the basin, Fe is mainly transported as chemically reactive ferrihydrite that spans the particulate (> 0.22 µm) and colloidal (0.22 µm – 1 kDa) fractions. The remaining Fe transported as poorly reactive detrital Fe in clays and crystalline oxides. Fe is transported in larger size fractions than the dissolved OM showing that Fe is not a major carrier of DOM. Nano-sized ferrihydrite was attached to OM in the particulate fraction, evidence of a Fe – OM particle association in the Lena River basin.

    Ferrihydrite shows distinct isotope values in particulate and colloidal fractions, showing that there is a difference in isotopic composition between different size fractions of the same mineral. A conceptual model was developed to understand ferrihydrite formation in the riparian zone of the Lena River and tributaries.  Particulate ferrihydrite has isotope values lower than crustal values resulting from redox and organic-ligand promoted mineral dissolution and precipitation of Fe(II)aq to form coatings of ferrihydrite on particles in the riparian zone.  Ferrihydrite colloids span a wider range of isotope values, higher than Fe particles, resulting from variations in the size and isotope composition of the Fe(II)aq pool transported in soil groundwaters, and the isotope fractionation factor for Fe oxidation and organic complexation.

    A temporal sample set was collected in the main channel between September 2012 – March 2013 and every three days during May 2015. The colloidal Fe shows distinct seasonal Fe isotope signatures and Fe fluxes, with isotope values lower than crustal during winter baseflow, overlying crustal values during spring flood and higher than crustal values during summer, attributed to changing sources and thus conditions for isotope fractionation. The combined understanding of Fe reactivity and isotope composition allows us to isolate the dominant sources of Fe entering the Lena River.

  • 2.
    Hirst, Catherine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Iron isotopes and the sources of Fe-bearing particles and colloids in the Lena River basinManuskript (preprint) (Annet vitenskapelig)
  • 3.
    Hirst, Catherine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Source apportionment of iron using iron isotopes in the Lena River, Russia, during winter base flow, river ice break-up and spring floodManuskript (preprint) (Annet vitenskapelig)
  • 4.
    Hirst, Catherine
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Andersson, Per S.
    Kooijman, Ellen
    Schmitt, Melanie
    Kutscher, Liselott
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Maximov, Trofim
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Porcelli, Don
    Iron isotopes reveal the sources of Fe-bearing particles and colloids in the Lena River basin2020Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 269, s. 678-692Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Large Arctic rivers are important suppliers of iron to the Arctic Ocean. However, the sources of Fe-bearing particles in permafrost-dominated systems and the mechanisms driving this supply of Fe are poorly resolved. Here, Fe isotope ratios were used to determine the sources of Fe-bearing particles and colloids in the Lena River and tributaries. In samples collected after the spring floods, Fe-bearing particles (>0.22 mu m) carried similar to 70% of the Fe and have isotope ratios that are lower than, or similar to that of the continental crust. These particles are composed of a leachable Fe fraction of largely ferrihydrite, with isotope values of -1.40 parts per thousand to -0.12 parts per thousand, and a fraction of clays and Fe oxides with continental crust values. Co-existing Fe-bearing colloids (<0.22 mu m), composed mainly of ferrihydrite, have higher isotope values, of -0.22 parts per thousand to +1.83 parts per thousand. A model is proposed in which soil mineral weathering generates aqueous Fe with lower delta Fe-56 values. During transport, a small fraction of the dissolved Fe is precipitated as colloidal ferrihydrite with higher delta Fe-56 values. Most of the Fe is precipitated onto mineral grains in oxic riparian zones, with the delta Fe-56 values largely generated during weathering. Groundwater discharge and riparian erosion supply the colloids and coated particles to the rivers. The differences between delta Fe-56 values in leachates and detrital grains in Fe-bearing particles agree with values determined in mineral dissolution experiments and in Fe accumulation horizons in soils. The difference in delta Fe-56 values between leachates and colloids reflects isotope fractionation during incremental Fe(III)(aq) precipitation and Fe-OC complexation during transport towards the riparian zone. Overall, the Fe isotope values of riverine particles and colloids reflect processes that occur during mineral dissolution, transport, and secondary mineral formation in permafrost soils.

  • 5.
    Hirst, Catherine
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Andersson, Per S.
    Shaw, Samuel
    Burke, Ian T.
    Kutscher, Liselott
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Murphy, Melissa J.
    Maximov, Trofim
    Pokrovsky, Oleg S.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Porcelli, Don
    Characterisation of Fe-bearing particles and colloids in the Lena River basin, NE Russia2017Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 213, s. 553-573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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 mu m) and colloids (1 kDa-0.22 mm) 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) mu m) aggregates of smaller (20-30 nm) spherical colloids of chemically-reactive ferrihydrite. In contrast, there were also large (500 nm(-1) mu m) 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.

  • 6.
    Kutscher, Liselott
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Porcelli, Don
    Hirst, Catherine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Maximov, Trofim C.
    Petrov, Roman E.
    Andersson, Per Sune
    Spatial variation in concentration and sources of organic carbon in the Lena River, Siberia2017Inngår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, nr 8, s. 1999-2016Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Global warming in permafrost areas is expected to change fluxes of riverine organic carbon (OC) to the Arctic Ocean. Here OC concentrations, stable carbon isotope signatures (delta C-13), and carbon-nitrogen ratios (C/N) are presented from 22 sampling stations in the Lena River and 40 of its tributaries. Sampling was conducted during two expeditions: the first in July 2012 in the south and southeastern region and the second in June 2013 in the northern region of the Lena basin. The data showed significant spatial differences in concentrations and major sources of OC. Mean subcatchment slopes were correlated with OC concentrations, implying that mountainous areas in general had lower concentrations than lowland areas. delta C-13 and C/N data from tributaries originating in mountainous areas indicated that both dissolved and particulate OC (DOC and POC) were mainly derived from soil organic matter (SOM). In contrast, tributaries originating in lowland areas had larger contributions from fresh vegetation to DOC, while aquatically produced OC was the major source of POC. We suggest that these differences in dominant sources indicated differences in dominant flow pathways. Tributaries with larger influence of fresh vegetation probably had surficial flow pathways, while tributaries with more SOM influence had deeper water flow pathways. Thus, the future export of OC to the Arctic Ocean will likely be controlled by changes in spatial patterns in hydroclimatology and the depth of the active layers influencing the dominant water flow pathways in Arctic river basins.

  • 7.
    Sun, Xiaole
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Porcelli, Don
    Kutscher, Liselott
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Hirst, Catherine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Murphy, Melissa J.
    Maximov, Trofim
    Petrov, Roman E.
    Humborg, Christoph
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Schmitt, Melanie
    Andersson, Per S.
    Stable silicon isotopic compositions of the Lena River and its tributaries: Implications for silicon delivery to the Arctic Ocean2018Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 241, s. 120-133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silicon isotope values (delta Si-30(DSi)) of dissolved silicon (DSi) have been analyzed in the Lena River and its tributaries, one of the largest Arctic watersheds in the world. The geographical and temporal variations of delta Si-30(DSi) range from +0.39 to +1.86% with DSi concentrations from 34 to 121 mu M. No obvious patterns of DSi concentrations and delta Si-30(DSi) values were observed along over 200 km of the two major tributaries, the Viliui and Aldan Rivers. In summer, the variations of DSi concentrations and delta Si-30(DSi) values in the water are either caused by biological uptake by higher plants and phytoplankton or by mixing of water masses carrying different DSi concentrations and delta Si-30(DSi) values. DSi in tributaries from the Verkhoyansk Mountain Range seems to be associated with secondary clay formation that increased the delta Si-30(DSi) values, while terrestrial biological production is likely more prevalent in controlling delta Si-30(DSi) values in Central Siberian Plateau and Lena Amganski Inter-River Area. In winter, when soils were frozen, the delta Si-30(DSi) values in the river appeared to be controlled by weathering and clay formation in deep intrapermafrost groundwater. During the spring flood, dissolved silicate materials and phytoliths were flushed from the upper thawed soils into rivers, which reset delta Si-30(DSi) values to the values observed prior to the biological bloom in summer. The results indicate that the Si isotope values reflect the changing processes controlling Si outputs to the Lena River and to the Arctic Ocean between seasons. The annual average delta Si-30(DSi) value of the Lena Si flux is calculated to be +0.86 +/- 0.3 parts per thousand using measured delta Si-30(DSi) values from each season. Combined with the estimate of + 1.6 +/- 0.25 parts per thousand for the Yenisey River, an updated delta Si-30(DSi) value of the major river Si inputs to the Arctic Ocean is estimated to be + 1.3 +/- 0.3 parts per thousand. This value is expected to shift towards higher values in the future because of the impacts from a variety of biological and geochemical processes and sources under global warming.

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