PHOSPHOROUS AND THE IREVIKEN BIOGEOCHEMICAL EVENT

At least seven major biogeochemical events have been identified within the Silurian Period, with the Ireviken Biogeochemical Event (IBE), occurring at the Llandovery-Wenlock boundary, being the most well-known and well-studied. Previous carbon and sulfur isotope data from the Altajme core, drilled in Gotland, Sweden, demonstrate that this major positive carbon isotope excursion was likely driven by an expansion in reducing marine environments and an increase in organic carbon burial. However, these carbon isotope excursions can also be linked to changes in primary productivity. Whereas phosphorous is a critical nutrient for primary productivity, and therefore a good indicator of any potential productivity events, there are currently no phosphorous data available from this event. To investigate the role of primary productivity in the IBE, samples were taken through this interval in the Altajme core for P extraction.

Phosphorous exists in different phases, and therefore the total P concentration in the sediment cannot be used by itself as an accurate measurement of bioavailable P in the water column through time. As a result, the SEDEX sequential extraction method was used to isolate five different sedimentary P reservoirs for quantification, including Fe-bound P, authigenic P, detrital P, and organic-bound P. The data from these samples provide important information about the timing and magnitude of changes in marine nutrient cycling during this global biogeochemical event.