Ikaite: A palaeoenvironmental proxy
Lead Research Organisation:
Science and Technology Facilities Council
Department Name: Photon Science
Abstract
In order to predict the consequences of global warming, it is essential to understand the climate response in terms of temperature and ice volume (hence sea level) to atmospheric carbon dioxide. The geological record of past climatic fluctuations has the power to reveal the natural interplay between these three Earth system parameters. One of the great challenges in paleoceanography since its inception, has been to reconstruct an independent record of oceanic temperature, or sea level throughout the Pleistocene ice ages in order to obtain an idea of the sensitivity and phasing of two crucial climate components: ice volume and temperature, during the glacial cycles. Foraminiferal d18O, the traditional proxy, is influenced by a combination of both ice volume and temperature so lack of constraint on seawater d18O prevents complete and quantitative interpretation of any marine carbonate d18O record. We have hypothesised that ikaite (CaCO3.6H2O), a metastable hydrated form of calcium carbonate which precipitates in organic rich sediments, captures the isotopic composition of ambient waters as hydration waters within the crystal (Rickaby et al., 20061), and offers a promising method of probing directly the d18Osw for periods other than the Last Glacial Maximum (LGM). We propose a multi-disciplinary approach to integrate mineralogical and biogeochemical laboratory experiments with field observations to characterise and understand the presence and climatic significance of ikaite and its isotopes within the natural environment. Our primary aims are to lay the foundations for, and apply this novel ikaite proxy to the reconstruction of d18Osw, hence ice volume, and extend application of the proxy to different timeslices and water masses.
Publications
Zhou X
(2015)
Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity
in The Journal of Geology
| Description | The results of this and other studies though provide provides some indication that ikaite formation and hence the presence of glendonites may not be a reliable indicator of cold temperatures. To counter these observations, De Lurio and Frakes (1999) have suggested that the Brooks et al., (1950) experiments may have been undertaken in solutions with a low partial pressure of CO2, (pCO2), which Mucci (1986) determined was more favourable for phosphate inhibition of calcite precipitation. They further argue that sediment pore waters would have much higher pCO2, which would not be so effective for phosphate inhibition. In our study ikaite precipitated from the pore water solutions (experiment 2) with an initial pCO2 of 654±108, 376±62, 673±111 and 315±52 for batches 1-4 respectively, which were still be associated with strong inhibition of anhydrous carbonate precipitation. Thus our study shows that sediments supporting anoxic organic matter diagenesis, underlying bottom waters with a maximum annual temperature of ~8 oC, would still be able to sustain continued precipitation of ikaite and hence provide an environment for preservation in the form of glendonites |
| Exploitation Route | Others can now assess environment of deposition implied by glendonites found in the geological record. |
| Sectors | Environment |