Building Biominerals: finding the tools that shape biogenic calcite and its signatures

In paleoclimatological studies, where the climate and Earth's surface environment are reconstructed throughout the geological past, information is often obtained from signals in fossil shells, corals and other biologically formed minerals (biominerals). These signals, or proxies, are for example trace metal concentrations or isotope ratios measured in fossils, that tell us what sea surface temperature the organism experienced during the building of its shell, or how much nutrients were available; even how much polar ice was present can be reconstructed. However, reliable application of these proxies to reconstruct past environments and climate requires sound knowledge of the processes that lead to the recording of these proxies by biominerals

The first step in the uptake of trace metals by minerals occurs at the surface of those minerals and crucial in this step is the structure of that surface. Some trace metals prefer to attach to very "open" sites, while others prefer more "closed" sites. This preference for particular surface sites is one of the many factors that can affect the signal ultimately interpreted as a proxy. Organisms are highly capable of controlling the shape of the biominerals they build. By controlling this shape, they control the structure of the surface through which trace metals incorporate.

We know that organic compounds such as amino acids are used by organisms as tools to shape their biominerals. In order to understand the effects these organic compounds have on the growing biomineral surface, and on the process of recording proxies during biomineral growth, I will conduct both experimental and theoretical research.

The experimental line of research focuses on determining the interaction between amino acids and selected trace metals during mimicked calcite biomineralisation. Among others, I will grow calcite crystals in the presence of amino acids and trace metals. The results will quantify the extent to which biological regulation of crystal morphology may explain variations in trace metal signatures of biogenic calcites.

The theoretical line of research focuses on understanding the mechanisms behind the interactions observed experimentally. Atomic-scale simulation techniques developed for calcite within the host institute are the ideal tool to obtain detailed insight into the interaction of the calcite surface with trace metals and organic molecules. Previous geochemical models I developed for calcite will be used to bridge the macroscopic, microscopic and atomic-scale results. Ultimately, all results will be merged with current physiological biomineralisation concepts into a state-of-the-art biomineralisation model.

The outcome of my ambitious research project bridges between molecular level surface chemistry and macroscale geochemical modelling, validated at all stages by experimental data. Specific applications of the project are in the fields of biomineralisation and paleoclimatology.

The results of this project will be important for understanding the underlying mechanisms for a variety of processes, including carbon mineral sequestration, currently one of the most viable routes to lower atmospheric CO2 levels and the uptake of contaminants by the host rock of carbonaceous subsoils, aquifers and linings of waste repositories. The beneficiaries of this project range from (i) the general public, (ii) environmental protection agencies in the UK and abroad, and (iii) the Government and public sector, to potentially (iv) a variety of industries, as well as (v) academic colleagues, as outlined in the Academic Beneficiaries section.

(i) General Public
We are all aware of the threat from the potentially disastrous effects of climate change, such as rising sea levels and extreme weather conditions. Improved methods for the reduction of atmospheric CO2 levels will therefore benefit all humans as well as the natural environment.
In addition, any progress made in understanding immobilisation of contaminants by calcite, limestone and calcareous materials also benefits us all, whether by providing new routes to regenerate contaminated land to make it suitable for housing or for leisure/recreational purposes.
(ii) Environmental Protection Agencies
Detailed understanding of tailored mineral growth and trace metal uptake will aid in improving various remediation methods such as in situ precipitation of solids to form reactive barriers against ground water contaminant transport, and improving CO2 sequestration methods.
(iii) Government and public sector
In addition to improved carbon mineral sequestration routes to lower atmospheric CO2 levels, reliable (paleo)climate models for the quantitative prediction of future climate change are clearly of prime importance to policy makers and legislators. Reliable paleoclimate modelling and reconstruction depends up valid indicators of the past climate and environment, which in their turn rely on sound knowledge of the processes that lead to the formation of these indicators. In this sense, the proposed research is fundamental both in approach and application. Moreover, the prediction of the effects of Ocean Acidification on the production and stability of marine calcium carbonate minerals requires, among others, more realistic, pH dependent, simulations of the calcite surface, which will be facilitated tools provided in this project.
(iv) Industries
In particular manufacturers of tailored (nano)crystals may gain from understanding the morphological effect of combined application of trace elements and surface-active amino acids.
.