Bree Morgan leads the Geochemistry branch of the Geocoastal Research Group at the University of Sydney. Her research program, at the intersection of chemical sedimentology, aqueous geochemistry and mineralogy, teases apart the biogeochemical signatures of coastal systems to understand how matter and energy cycles through the Earth’s surface, and how this delicate balance is impacted by humans. In this seminar Bree will discuss how biogeochemical signatures recorded in sediments tell us a story about Earth surface processes, environmental perturbations and past environmental conditions. She will discuss a current research project which aims to decipher the biogeochemical drivers for modern dolomite formation, a highly stable, safe and permanent mineral sink for atmospheric CO2. Modern dolomite is extremely scarce and the specific conditions for its formation are unresolved. However, it is found in some, but not all, of the ephemeral carbonate playa lakes in South Australia and British Columbia, Canada, despite extreme contrasts between geochemical, lithological, topographic and climatic conditions. The disproportionate paucity of dolomite in modern times comparative to its widespread abundance in the deep past is referred to as the ‘The Dolomite Problem’, one of the longest standing unresolved problems in the natural sciences. Thus, these lakes provide the ideal natural settings to unravel the underlying mechanisms driving this >200-year old mystery.