Speaker: Brad Cramer

Title: Nutrients, Eutrophy, Anoxia & Extinction | An Ancient Example of a Green Tide Event

Abstract: The Ireviken Biogeochemical Event was a Silurian Oceanic Anoxic Event that dramatically altered major- and trace-element nutrient cycling in the oceans and led to a biotic crisis known as the Ireviken Extinction Event. This event, first identified in the fossil record of conodonts, is also identified by a major perturbation to the global carbon cycle with carbonate carbon isotope values reaching +6 per mil in some locations. Whereas this event has been identified in more than two dozen locations around the globe, and is the most well-studied Silurian biogeochemical event, the precise cause(s) of the event initiation remain enigmatic.

Here, we present new records of nitrogen isotopes and lipid biomarkers from across the Ireviken Biogeochemical Event from samples from the Altajme Drill Core. The Altajme Core was drilled in Gotland, Sweden, and now is the most highly resolved record of any Paleozoic biogeochemical event. The lipid biomarker data demonstrate that a bloom of green algae coincided with the onset of the Ireviken Biogeochemical Event and began just prior to the expansion of reducing environments during the earliest part of the Sheinwoodian Epoch. The nitrogen isotope data support the lipid data and demonstrate a crash in nitrogen isotope values during the green algal bloom, which most likely represents a decrease in bioavailable nitrogen created by excess productivity. This sequence of events in the data demonstrate that the Ireviken Biogeochemical Event was a productivity-driven ‘green-tide event’ in the Silurian.

Speaker: Heather Sander

Title: From local surveys to global patterns: Integrating multicity wildlife monitoring for global insight