Biomineralization of marine calcifiers

30 µm cross section of a coral (Photo: Gernot Nehrke)

The validation of paleo proxies, one of the focal points of our section BioGeoSciences, requires detailed investigation of the biomineralization and geochemistry of the proxy archives. These proxy archives, e.g. shells of foraminifera and coral skeletons, represent biominerals which are complex composites of organic and inorganic components. To be able to identify the physiological processes leading to the formation of these fascinating materials a detailed investigation of their structures is needed. In our lab we have specialized in these investigations using several highly advanced methods. The main instrument used is a confocal Raman microscope that allows for a chemical and structural characterization of a sample with a spatial resolution of up to 250 nm. The optimal sample preparation for the structural investigations e.g. preparation of polished cross sections is done in our sample preparation lab. For investigations at higher than 250 nm resolution we use two atomic force microscopes (AFM) that allow for a resolution of upt to a few nm. The bulk properties, e.g. the organic content of a biomineral are determined by thermogravimetric analysis (TGA).

The combination of these methods reveal that most biogenic carbonates investigated so far (foraminifera, shells of snails and molluscs and corrals) are built up of small crystallites (aragonite or calcite) surrounded by a thin organic envelop. These smallest growth entities form larger structural units in which the growth entities have random crystallographic orientation or have a common crystallographic orientation, which gives the impression that they are "inorganic" single crystals.

To better understand the role of organic molecules and mineral nucleation (growth), e.g. which properties determine the polymorph formed (e.g. aragonite or calcite), we use controlled calcium carbonate nucleation experiments performed in the fluid cell of an AFM which allows to investigate the interaction between crystal surfaces and organic molecules under controlled physic-chemical conditions.

If you are interested into one of the above described research areas or methods please feel free to contact me.