New Paper: Li in Calcite.
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In this paper we looked into how lithium (Li) is incorporated as a trace element in calcite, and how its incorporation and isotopic fractionation are affected by the conditions of precipitation. Specifically, we varied temperature, pH and dissolved inorganic carbon (DIC) concentration, and looked at how the partitioning and isotopic frationation of Li between the fluid and the solid.
We found that the partitioning of Li into calcite is significantly influenced by pH, while dissolved inorganic carbon (DIC) plays a smaller role. Both of these relationships are explained by an underlying control of mineral precipitation rate on Li incorporation - more Li is incorporated into the mineral at faster growth rates.
Surprisingly, we found that isotopic fractionation of Li did not follow any consistent trends across varying experimental conditions. This is quite different to past studies, which found some strong environmental controls on Li isotopic fractionation into calcite. It’s not completely clear why our results were so different to previous studies, but it could relate to different experimental conditions, such as the ionic strength of the solutions in which the precipitates were formed.
These findings have significant implications for the use of Li isotopes in marine carbonates as proxies for past environmental conditions. The lack of any significant environmental influence on Li isotopes is good news for those seeking to use Li isotopes in marine carbonates as a proxy for past seawater composition, but our understanding of Li incorporation and isotopic fractionation is still far from complete, and further research is needed to fully understand the processes involved.