Reinhard Kozdon

Video compiled from 180 individual SEM images (shell rotates 2° between images)

The video above shows a planktic foraminifera, a marine microfossil used for paleoclimate reconstructions, recovered from 56 million years old sediments from ODP Site 865 located in the tropical Pacific Ocean. The blade-shaped postules producing from the shell were diagenetically formed after the shell was deposited at the sea floor (inorganic precipitation) and feature a different chemical and isotopic composition than the remaining shell that was formed biologically by the organism in much warmer waters close to the sea surface. Conventionally, the whole shell is analyzed, averaging the chemical and isotopic composition of the biogenic and diagenetic calcite. In certain scenarios, this can cause a sizable bias in the paleoclimate information deduced from the shell's chemistry. These diagenetic overprints, which are ubiquitous on fossil foraminiferal shells, are one of the main challenges in paleoceanography. To circumvent these challenges, my research group applies novel instrumental approaches to analyze carefully selected, minute domains (a few thousands of a millimeter) in fossil foraminfera shells. These domains, which are located within the chamber wall and are thus somehow 'shielded' from direct chemical interaction with pore waters in the sediment column, largely preserve their original isotopic and chemical composition and thus allow for the compilation of more robust paleoclimate records.