Ikaite nucleation at 35 °C challenges the use of glendonite as a paleotemperature indicator

• Published in: Scientific reports Vol. 10; no. 1; p. 8141
• Main Authors: Tollefsen, Elin, Balic-Zunic, Tonci, Mörth, Carl-Magnus, Brüchert, Volker, Lee, Cheng Choo, Skelton, Alasdair
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.05.2020; Nature Publishing Group
• Subjects: 704/106/413; 704/2151/209; 704/2151/330; Calcite; Calcium carbonate; Cooling; Experiments; geologi; Geology; High temperature; Humanities and Social Sciences; Laboratories; Minerals; multidisciplinary; Nucleation; pH effects; Science; Science (multidisciplinary); Seawater; Sediments; Sodium carbonate
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-64751-5

Glendonites have been found worldwide in marine sediments from the Neoproterozoic Era to the Quaternary Period. The precursor of glendonite, ikaite (CaCO 3 · 6H 2 O), is metastable and has only been observed in nature at temperatures <7 °C. Therefore, glendonites in the sedimentary record are commonly used as paleotemperature indicators. However, several laboratory experiments have shown that the mineral can nucleate at temperatures>7 °C. Here we investigate the nucleation range for ikaite as a function of temperature and pH. We found that ikaite precipitated at temperatures of at least 35 °C at pH 9.3 −10.3 from a mixture of natural seawater and sodium carbonate rich solution. At pH 9.3, we observed pseudomorphic replacement of ikaite by porous calcite during the duration of the experiment (c. 5 hours). These results imply that ikaite can form at relatively high temperatures but will then be rapidly replaced by a calcite pseudomorph. This finding challenges the use of glendonites as paleotemperature indicators.