A PHase-Specific geochemical study of marine PRoductivity and nutrient cycling during the end-Permian mass extinction (PHoSPhoR)

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I want to study changes in marine productivity and nutrient availability that contributed to the end-Permian mass extinction. This event represents the most dramatic faunal turnover during the last 500 million years, followed by a prolonged 2-5 million-year period of marine ecosystem instability. The cause(s) of this event are still much debated. One open question concerns whether the event is associated with an ocean (almost) barren of life (a primary productivity collapse), or conversely, that the event represents a biodiversity crash amongst multi-cellular eukaryotes, but with otherwise generally high-marine productivity levels. (Elevated fluxes of nutrients stimulate organic matter production and result in expansion of oxygen depleted and hydrogen-sulphide enriched zones, caused by increased aerobic and anaerobic respiration.) I will test these competing hypotheses for the end-Permian biodiversity collapse through a highly novel geochemical study of key marine sedimentary archives. Taking this approach, a more comprehensive understanding of feedbacks between marine redox conditions, nutrient cycling and biogeochemical cycles will be achieved for this critical interval of Earth history. Central to this study will be a detailed evaluation of ocean redox conditions, using the most recently developed Fe speciation technique (which has only once previously been applied to any Permo-Triassic sections), in addition to utilising recent advances in our understanding of the differential behaviour of trace metals under different redox conditions. This will yield sensitive and robust proxy records for identifying a range of redox regimes (oxic, dysoxic, anoxic-sulphidic, or anoxic-ferruginous). These analyses will set the scene for the next geochemical phase, which will involve the highly novel application of phosphorus speciation techniques and barium concentrations to extract information about ancient nutrient fluxes (and recycling) and marine productivity. This is essential for two reasons: (1) Elemental analyses of bulk-rock (the standard technique) does not give an indication of bioavailable elemental fluxes or phases, but instead includes the detrital fraction, and (2) post-depositional (re)mobilization of these reactive elements under certain environmental conditions can only be achieved with phase specific techniques. I will improve on these studies by conducting geochemical analyses of specific sedimentary phases that are more likely to harbour a primary marine signal, which will be set firmly within the precise redox context of each sample. This will be combined with sulphur isotope analyses to provide further insight into controls on water column redox conditions.