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C:P ratios through the Ireviken (Silurian) Biogeochemical Event from the Altajme Core, Gotland, Sweden

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

morgan lyn havens

Authors:

Havens, Morgan¹, Hill, Talia², McNally, Anna³, Peate, David⁴, Cramer, Bradley⁵

(1) University of Iowa, Iowa City, USA, (2) University of Iowa, Iowa City, USA, (3) University of Iowa, Iowa City, USA, (4) University of Iowa, Iowa City, USA, (5) University of Iowa, Iowa City, USA,

Abstract:

The Ireviken Biogeochemical Event (IBE) occurred across the Llandovery-Wenlock boundary (~432 Ma) during the Silurian Period. This event includes perturbations to the global carbon cycle, the nitrogen cycle, the sulfur cycle, and many other major and trace-element cycles as well. Graptolites, conodonts, trilobites, and other taxa were affected by this extinction event, which began coincident with the positive carbon isotope excursion. The IBE has been identified as an Oceanic Anoxic Event (OAE) that resulted from an expansion of reducing environments in marine settings. However, the precise cause of the IBE remains difficult to identify.

The well-preserved Altajme Core from Gotland, Sweden, allows for a critical analysis better understanding of the role of changes in productivity and nutrient cycling through this event, and it is now the most highly resolved record of the IBE ever produced. Here, we investigated the organic carbon to phosphorus molar ratio (C_org: P_total) within the core through the IBE. There is a substantial increase in the C_org: P_totalratio during the IBE that begins at the same time as the Ireviken Extinction Event and coincides with the positive carbon isotope excursion through the remainder of the IBE. This parallel between the positive carbon isotope excursion and the C :P ratio is consistent with a low oxygen reducing environment, as the phosphorus is remobilized into the water while matter is buried. Together, these data support the interpretation of the IBE as an oceanic anoxic event during the Silurian.