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  • 1.
    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.

  • 2.
    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.

  • 3.
    Kutscher, Liselott
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Export and sources of organic carbon in the Lena River basin, Northeastern Siberia2016Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Permafrost areas are considered to be one of the largest terrestrial storages of carbon. In a warming climate these areas are expected to experience changes in carbon transport to rivers and the oceans due to permafrost thawing, which could enhance erosion, change water flow pathways and increase greenhouse gas emissions. Large amounts of the carbon transported from the terrestrial environment to rivers are in the form of natural organic matter (NOM). The Lena River basin in northeastern Siberia, which is mainly underlain by continuous permafrost, is the largest contributor of NOM to the Arctic Ocean. In this study we present a spatial data set of NOM, including concentrations and stable carbon isotope values (δ13C) of dissolved (DOC) and particulate organic carbon (POC) as well as carbon and nitrogen ratios (C/N) from 77 sample stations in the Lena River and its tributaries. The samples were collected during two field seasons in July 2012 and June 2013.

    The results from this study showed large spatial variations in concentrations, annual export and fluxes of organic carbon. These variations were primarily due to variations in discharge and topography. The δ13C and C/N indicated that terrestrial sources such as plants and soil organic matter (SOM), were the main sources of the dissolved organic matter (DOM), while particulate organic matter (POM) was mainly derived from aquatic produced material or SOM. There were clear differences in δ13C and C/N of DOM between sampling years, indicating more surficial flow pathways in samples collected earlier in the summer compared to samples collected later in the summer. The δ13C of POM was correlated with water temperatures and topography, showing that tributaries with origin in mountainous areas in general had soil derived POM and lower water temperatures, while tributaries from lowland areas had higher water temperatures and more influence of aquatic sources. We suggest that this pattern is probably due to differences in water flow pathways. Shifts in export of NOM from drainage areas underlain by permafrost will likely be dependent of spatial changes in hydroclimate and the depth of the active layer in a warming climate.

  • 4.
    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.

  • 5. Murphy, Melissa J.
    et al.
    Porcelli, Don
    von Strandmann, Philip A. E. Pogge
    Hirst, Catherine A.
    Kutscher, Liselott
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Swedish Museum of Natural History, Sweden.
    Katchinoff, Joachim A.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Maximov, Trofim
    Andersson, Per S.
    Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes2019Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 245, s. 154-171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increasing global temperatures are causing widespread changes in the Arctic, including permafrost thawing and altered freshwater inputs and trace metal and carbon fluxes into the ocean and atmosphere. Changes in the permafrost active layer thickness can affect subsurface water flow-paths and water-rock interaction times, and hence weathering processes. Riverine lithium isotope ratios (reported as delta Li-7) are tracers of silicate weathering that are unaffected by biological uptake, redox, carbonate weathering and primary lithology. Here we use Li isotopes to examine silicate weathering processes in one of the largest Russian Arctic rivers: the Lena River in eastern Siberia. The Lena River watershed is a large multi-lithological catchment, underlain by continuous permafrost. An extensive dataset of dissolved Li isotopic compositions of waters from the Lena River main channel, two main tributaries (the Aldan and Viliui Rivers) and a range of smaller sub-tributaries are presented from the post-spring flood/early-summer period at the onset of active layer development and enhanced water-rock interactions. The Lena River main channel (average delta Li-7(diss) similar to 19 parts per thousand) has a slightly lower isotopic composition than the mean global average of 23 parts per thousand (Huh et al., 1998a). The greatest range of [Li] and delta Li-7(diss) are observed in catchments draining the south-facing slopes of the Verkhoyansk Mountain Range. South-facing slopes in high-latitude, permafrost-dominated regions are typically characterised by increased summer insolation and higher daytime temperatures relative to other slope aspects. The increased solar radiation on south-facing catchments promotes repeated freeze-thaw cycles, and contributes to more rapid melting of snow cover, warmer soils, and increased active layer thaw depths. The greater variability in delta Li-7 and [Li] in the south-facing rivers likely reflect the greater infiltration of melt water and enhanced water-rock interactions within the active layer. A similar magnitude of isotopic fractionation is observed between the low-lying regions of the Central Siberian Plateau (and catchments draining into the Viliui River), and catchments draining the Verkhoyansk Mountain Range into the Aldan River. This is in contrast to global rivers in non-permafrost terrains that drain high elevations or areas of rapid uplift, where high degrees of physical erosion promote dissolution of freshly exposed primary rock typically yielding low delta Li-7(diss), and low-lying regions exhibit high riverine delta Li-7 values resulting from greater water-rock interaction and formation of secondary mineral that fractionates Li isotopes. Overall, the range of Li concentrations and delta 7Lidiss observed within the Lena River catchment are comparable to global rivers located in temperate and tropical regions. This suggests that cryogenic weathering features specific to permafrost regions (such as the continual exposure of fresh primary minerals due to seasonal freeze-thaw cycles, frost shattering and salt weathering), and climate (temperature and runoff), are not a dominant control on delta Li-7 variations. Despite vastly different climatic and weathering regimes, the same range of riverine delta Li-7 values globally suggests that the same processes govern Li geochemistry - that is, the balance between primary silicate mineral dissolution and the formation (or exchange with) secondary minerals. This has implications for the use of delta Li-7 as a palaeo-weathering tracer for interpreting changes in past weathering regimes.

  • 6.
    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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