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Control of a calcite inhibitor (phosphate) and temperature on ikaite precipitation in Ikka Fjord, southwest Greenland
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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Number of Authors: 82018 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 89, p. 11-22Article in journal (Refereed) Published
Abstract [en]

Ikaite (CaCO3 center dot 6H(2)O) 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 degrees 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 mu mol/ kg PO43-) in 0.1 M NaHCO3/0.1 M Na2CO3 solutions mixing with seawater at 5 degrees C and pH 9.6-10.6, and b) ikaite forms at temperatures up to 15 degrees 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 degrees C, increasing amounts of either nesquehonite (Mg(HCO3)(OH)center dot 2H(2)O) or an amorphous phase co-precipitate with ikaite. At 20 degrees C, only the amorphous phase is formed. In warming Arctic seawater, this suggests Mg carbonate precipitation could become dominant over ikaite in the future.

Place, publisher, year, edition, pages
2018. Vol. 89, p. 11-22
Keywords [en]
Ikaite, Ikka fjord, Seawater, Orthophosphate, Calcite inhibitors, Precipitation
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-153637DOI: 10.1016/j.apgeochem.2017.11.005ISI: 000424848200002OAI: oai:DiVA.org:su-153637DiVA, id: diva2:1189782
Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-03-12Bibliographically approved

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Stockmann, GabrielleTollefsen, ElinSkelton, AlasdairBrüchert, VolkerKarlsson, Andreas
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