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  • 1. Salifu, Musah
    et al.
    Aiglsperger, T.
    Hällström, Lina
    Martinsson, Olof
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Ingri, Johan
    Dold, B.
    Alakangas, Lena
    Strontium (87Sr/86Sr) isotopes: A tracer for geochemical processes in mineralogically-complex mine wastes2018In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 99, p. 42-54Article in journal (Refereed)
  • 2. Sallstedt, E.
    et al.
    Karhu, J.A.
    Pitkänen, P.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Biogenic processes in crystalline bedrock fractures indicated by carbon isotope signatures of secondary calcite.2016In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 67, p. 30-41Article in journal (Refereed)
    Abstract [en]

    Variation in 13C/12C-isotope ratios of fracture filling calcite was analyzed in situ to investigate carbon sources and cycling in fractured bedrock. The study was conducted by separating sections of fracture fillings, and analyzing the 13C/12C-ratios with secondary ion mass spectrometry (SIMS). Specifically, the study was aimed at fillings where previously published sulfur isotope data indicated the occurrence of bacterial sulfate reduction. The results showed that the δ13C values of calcite were highly variable, ranging from −53.8‰ to +31.6‰ (VPDB). The analysis also showed high variations within single fillings of up to 39‰. The analyzed calcite fillings were mostly associated with two calcite groups, of which Group 3 represents possible Paleozoic fluid circulation, based on comparison with similar dated coatings within the Baltic Shield and the succeeding Group 1–2 fillings represent late-stage, low temperature mineralization and are possibly late Paleozoic to Quaternary in age. Both generations were associated with pyrite with δ34S values indicative of bacterial sulfate reduction. The δ13C values of calcite, however, were indicative of geochemical environments which were distinct for these generations. The δ13C values of Group 3 calcite varied from −22.1‰ to +11‰, with a distinct peak at −16‰ to −12‰. Furthermore, there were no observable depth dependent trends in the δ13C values of Group 3 calcite. The δ13C values of Group 3 calcite were indicative of organic matter degradation and methanogenesis. In contrast to the Group 3 fillings, the δ13C values of Group 1–2 calcite were highly variable, ranging from −53.8‰ to +31.6‰ and they showed systematic variation with depth. The near surface environment of <30 m (bsl) was characterized by δ13C values indicative of degradation of surface derived organic matter, with δ13C values ranging from −30.3‰ to −5.5‰. The intermediate depth of 34–54 m showed evidence of localized methanotrophic activity seen as anomalously 13C depleted calcite, having δ13C values as low as −53.8‰. At depths of ∼60–400 m, positive δ13C values of up to +31.6‰ in late-stage calcite of Group 1–2 indicated methanogenesis. In comparison, high CH4 concentrations in present day groundwaters are found at depths of >300 m. One sample at a depth of 111 m showed a transition from methanogenetic conditions (calcite bearing methanogenetic signature) to sulfate reducing (precipitation of pyrite on calcite surface), however, the timing of this transition is so far unclear. The results from this study gives indications of the complex nature of sulfur and carbon cycling in fractured crystalline environments and highlights the usefulness of in situ stable isotope analysis.

  • 3.
    Stockmann, Gabrielle
    Department of Geological Sciences, Stockholm University, Sweden.
    Skelton, Alasdair (Contributor)
    Department of Geological Sciences, Stockholm University, Sweden.
    Brüchert, Volker (Contributor)
    Department of Geological Sciences, Stockholm University, Sweden.
    Balic-Zunic, Tonci (Contributor)
    Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark.
    Langhof, Jörgen (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Karlsson, Andreas (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Control of a calcite inhibitor (phosphate) and temperature on ikaite precipitation in Ikka Fjord, southwest Greenland2018In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 89, p. 11-22Article in journal (Refereed)
    Abstract [en]

    Ikaite (CaCO3·6H2O) forms submarine tufa columns in Ikka Fjord, SW Greenland. This unique occurrence is thought to relate to aqueous phosphate concentration and low water temperatures (<6 °C). Phosphate ions are well-known inhibitors of calcite precipitation and Ikka Fjord has a naturally high-phosphate groundwater system that when mixing with seawater leads to the precipitation of ikaite. In the study presented here, experiments simulating conditions of Ikka Fjord show that a) the formation of ikaite is unrelated to the aqueous phosphate concentration (0–263 μmol/kg PO43−) in 0.1 M NaHCO3/0.1 M Na2CO3 solutions mixing with seawater at 5 °C and pH 9.6–10.6, and b) ikaite forms at temperatures up to 15 °C without phosphate and in open beakers exposed to air. Instead, supersaturation of ikaite and the seawater composition are the likely factors causing ikaite to precipitate in Ikka Fjord. This study shows that adding Mg2+ to a NaHCO3/Na2CO3 – CaCl2 mixed solution leads to the formation of ikaite along with hydrated Mg carbonates, which points to the high Mg2+ concentration of seawater, another known inhibitor of calcite, as a key factor promoting ikaite formation. In experiments at 10 and 15 °C, increasing amounts of either nesquehonite (Mg(HCO3)(OH)·2H2O) or an amorphous phase co-precipitate with ikaite. At 20 °C, only the amorphous phase is formed. In warming Arctic seawater, this suggests Mg carbonate precipitation could become dominant over ikaite in the future.

  • 4.
    Stockmann, Gabrielle
    Department of Geological Sciences, Stockholm University, Sweden.
    Brüchert, Volker (Contributor)
    Department of Geological Sciences, Stockholm University, Sweden.
    Skelton, Alasdair (Contributor)
    Department of Geological Sciences, Stockholm University, Sweden.
    Balic-Zunic, Tonci (Contributor)
    Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark.
    Langhof, Jörgen (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Karlsson, Andreas (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Control of a calcite inhibitor (phosphate) and temperature on ikaite precipitation in Ikka Fjord, southwest Greenland2018In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 89, p. 11-22Article in journal (Refereed)
    Abstract [en]

    Ikaite (CaCO3·6H2O) forms submarine tufa columns in Ikka Fjord, SW Greenland. This unique occurrence is thought to relate to aqueous phosphate concentration and low water temperatures (<6 °C). Phosphate ions are well-known inhibitors of calcite precipitation and Ikka Fjord has a naturally high-phosphate groundwater system that when mixing with seawater leads to the precipitation of ikaite. In the study presented here, experiments simulating conditions of Ikka Fjord show that a) the formation of ikaite is unrelated to the aqueous phosphate concentration (0–263 μmol/kg PO43−) in 0.1 M NaHCO3/0.1 M Na2CO3 solutions mixing with seawater at 5 °C and pH 9.6–10.6, and b) ikaite forms at temperatures up to 15 °C without phosphate and in open beakers exposed to air. Instead, supersaturation of ikaite and the seawater composition are the likely factors causing ikaite to precipitate in Ikka Fjord. This study shows that adding Mg2+ to a NaHCO3/Na2CO3 – CaCl2 mixed solution leads to the formation of ikaite along with hydrated Mg carbonates, which points to the high Mg2+ concentration of seawater, another known inhibitor of calcite, as a key factor promoting ikaite formation. In experiments at 10 and 15 °C, increasing amounts of either nesquehonite (Mg(HCO3)(OH)·2H2O) or an amorphous phase co-precipitate with ikaite. At 20 °C, only the amorphous phase is formed. In warming Arctic seawater, this suggests Mg carbonate precipitation could become dominant over ikaite in the future.

  • 5.
    Stockmann, Gabrielle
    et al.
    Department of Geological Sceinces, Stockholm University.
    Tollefsen, Elin
    Department of Geological Sceinces, Stockholm University.
    Skelton, Alasdair
    Department of Geological Sceinces, Stockholm University.
    Brüchert, Volker
    Department of Geological Sceinces, Stockholm University.
    Balic-Zunic, Tonci
    Department of Geosceinces and Natural Resource Management, University of Copenhagen.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Karlsson, Andreas
    Swedish Museum of Natural History, Department of Geology.
    Control of calcite inhibitor (phosphate) and temperature on ikaite precipitation in Ikka Fjord, southwest Greenland2018In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 89, p. 11-22Article in journal (Refereed)
  • 6.
    Wortberg, Katharina
    et al.
    Luleå Technical University.
    Conrad, Sarah
    Luleå Technical University.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Ingri, Johan
    Luleå Technical University.
    Strontium Isotopes - A Tracer for River Suspended Iron Aggregates2017In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 95, p. 85-90Article in journal (Refereed)
    Abstract [en]

    The Kalix River shows distinct temporal variations in the Sr-isotope ratio in filtered water (0.726 to 0.732). During base flow in winter the 87Sr/86Sr ratio is on average 0.730. When discharge increases and peaks during spring flood the 87Sr/86Sr ratio shows the most radiogenic (0.732) values. The temporal variations in the 87Sr/86Sr ratio in the Kalix River can be explained by mixing of water from the woodlands and the mountain areas.

    During high water discharge in May the 87Sr/86Sr ratios are more radiogenic in the suspended phase (1 kDa - 70 µm) compared to the truly dissolved phase (<1 kDa). The difference in 87Sr/86Sr ratio between the two phases (Δ 87Sr/86Sr) is linearly correlated with the suspended iron concentration. During spring flood Sr and Fe derived from an additional source, reach the river. Deep groundwater has a more radiogenic 87Sr/86Sr isotope ratio than the Kalix River during spring flood and thus, represents a possible source for the suspended Fe and the associated Sr. Strontium can be coprecipitated with and adsorbed to different types of Fe aggregates. We propose that the Sr-isotope ratio in the suspended phase reflects the isotopic composition of the water at the interface between anoxic groundwater and oxic stream water in the riparian zone, where the Fe aggregates are formed. These particles dominate the suspended phase in the river and the mixing with mountain waters, poor in Fe, produces the difference in the isotopic signature. The different signatures in suspended and truly dissolved fraction indicate that these aggregates are relatively stable during stream-river transport. As such the 87Sr/86Sr can be used to trace the origin of the non-detrital suspended phase.

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