The calcium carbonate shells of planktic foraminifera provide our most valuable geochemical archive of climate and ocean conditions spanning the last 100 million years, and play an important role in the ocean carbon cycle. These shells are preserved in marine sediments as calcite, the stable polymorph of calcium carbonate. The shells of live-collected planktic foraminifera are found to comprise metastable calcium carbonate polymorph vaterite, implying a non-classical crystallisation pathway involving metastable phases that transform ultimately to calcite. Current understanding of how planktic foraminifer shells record climate, and how they will fare in a future high-CO2 world is based on classical, inorganic, ion-by-ion growth and dissolution of calcite. This paradigm needs to change to non-classical crystallisation model involving formation and transformation of metastable calcium carbonate phases, with ramifications for shell geochemistry and solubility of the foraminiferal calcite in the ocean.
Steve Eggins is a geochemist with interests in elemental and isotopic proxy incorporation in marine calcifiers and the reliability of environmental reconstruction, and biogeochemistry more broadly. He undertook a PhD in experimental petrology and igneous geochemistry at the university of Tasmania, before coming to ANU where he developed ICPMS methods and laser ablation sampling technology to address problems in solid Earth geochemistry before moving into environmental geochemistry. He is currently Professor in the Biogeochemistry group and director of the RSES. He has growing interest in the enhancement of carbon fluxes in natural systems to effect the drawdown of CO2 from the atmosphere to alleviate the impacts of greenhouse gas warming.