Biomineralisation is the formation of hard mineral structures by living organisms. This process is found throughout all taxonomic clades. Examples include teeth, bones, shells and coral. Common materials forming biominerals comprise opal (diatoms, sponges), calcium phosphate (vertebrates), and calcium carbonates (corals, mussels, foraminifera, coralline algae). The process of biomineralisation is biologically controlled, but in addition is also affected by environmental parameters such as temperature, salinity and ionic composition of the surrounding medium. Therefore biominerals can be used as archives of environmental change if biological and environmental effects on mineral formation can be untangled. Understanding the mechanisms controlling biomineralisation improves the development and application of proxy archives. Changes in climate and seawater composition (e.g. ocean acidification and ocean warming) due to anthropogenic impacts can affect biomineral formation. Improved knowledge of biomineralisation mechanisms will allow to better evaluate the challenges organisms with biominerals will face in the future ocean.

The research unit Marine Geosystems is particularly interested in the processing of ions in calcifying organisms. We focus on cation transport during calcification, specifically on element partitioning and isotope fractionation.

In order to shed some light on these processes we culture marine calcifiers under controlled conditions. We have cultured foraminifera, coralline algae, reef-building, warm water corals, Alcyonarian softcorals and serpulids at Geomar, Kiel, and in collaboration with the Earth Science Institute at the Hebrew University of Jerusalem (Prof. Jonathan Erez). We investigate the incorporation of isotopes and trace elements in the skeletons and shells in response to changing environmental conditions (e.g. temperature, salinity, pH).

To identify inorganic processes influencing the composition of the biominerals we compare the results to values measured on inorganically precipitated carbonates.

Inorganic precipitation experiments are carried out at the Institute of Applied Geosciences, Graz University of Technology by Prof. Martin Dietzel: Formation of Calcium Carbonate.

Biogenic carbonates, even when formed under similar environmental conditions often show a different elemental and isotopic composition compared to inorganic precipitates. These differences can be explained by the influence of biological processes on calcification. To investigate the role of biological tissue, we study ion fluxes across coral epidermis in cooperation with the Institute of Physiology, Christian-Albrecht University, Kiel (Prof. Markus Bleich) within the trilateral TRION project. The influence of future ocean conditions on the biomineralisation of marine calcifiers is investigated within the framework of the joint project BIOACID II. In this project we study the composition of calcifiers in benthocosms and natural environments.