Ikaite: CaCO3.6H2O

Introduction

Glendonite (Oxford University Museum of Natural History)Ikaite is a calcium carbonate hexahydrate considered to be stable only at low temperatures. Ikaite converts to calcite and water at temperature above 4°C. The decomposition products can maintain the original crystal shape and such calcite pseudomorph (glendonite) has been considered to be an indicator of cold sedimentary environments.


Geochemistry of ikaite in marine sediments

Stellate ikaite crystal clusterOur preliminary data suggest that the ikaite formation in marine sediments is closely associated with methanogenesis and anaerobic methane oxidation (AOM). It requires rapid build-up of dissolved inorganic carbon (DIC) in shallow depths and is restricted by low Ca concentration in deep sediments. The crystals probably formed rapidly in the ikaite formation zone and were buried to deeper depths. The high phosphate concentrations in ikaite sites, especially within the IFZs, might have inhibited calcite precipitation and stabilized the crystals.

Potential record of ice volume in the past


Ikaite waterGlacial-interglacial variations of d18O recorded in marine foraminifera were affected both by temperature and the d18O of the seawater which is controlled by ice volume. One of the “million dollar questions” in paleoceanography is that how much of these variations were really related to temperature. Ikaite has potentials for reconstruction of ice volume in the past. Lab synthesis experiments suggest that the hydration water in ikaite crystals records the oxygen isotope composition of the medium water where the crystals formed. Natural crystals precipitated from shallow pore waters might lock the d18O composition of the seawater and be used as a record of ice volume.