Nutrients in anoxic oceans – Trace metals in modern and ancient environments

ended

The global oceanic oxygen content has decreased by more than 2% since 1960 and is projected to drop further in the near future. This decline could drastically impact ocean nutrient cycles and marine life, but the exact progression of ocean anoxia and its impacts are hard to predict. Earth's history is punctuated by intervals of widespread ocean anoxia that manifest themselves in the sedimentary record as specific intervals of enhanced organic-carbon burial. These intervals last for 10,000-100,000s years, are marked by perturbations to global climate and biogeochemical cycles, represent major environmental disturbances, and are often associated with mass extinctions. The study of such past climate disturbances can improve projections of future ocean anoxia and environmental change by providing better constraints on the model boundary conditions. However, this requires the detailed reconstruction of past environmental parameters based on the sedimentary record. This project aims to develop and apply new ways of using geochemical tracers for past ocean environments. The focus is on the role of trace metals in anoxic waters and their impact on marine life and biogeochemical cycles. Trace metals are essential to life and are taken up in phytoplankton cells but are also reactive towards dissolved sulphide. Though such processes leave diagnostic geochemical imprints on the isotope composition of the marine sedimentary record, their interpretation is often complicated as a result of this dual sensitivity. This research project will establish new methods to distinguish between these two controls. These methods will then be applied to samples from a variety of modern environments to establish a thorough understanding of trace metal cycling in anoxic waters. Combined with biogeochemical modelling, these new methods will then be used to reconstruct the interplay between global warming and biogeochemical cycles during an interval of widespread anoxia in the Cretaceous.