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MISU Research seminar | Martin Renoult

Reconstruction of past methane emissions in the Arctic Ocean using foraminiferal isotopes and sedimentary proxies

by Martin Renoult
PhD student at the Department of Meteorology (MISU)

Time: 7 February 2019, 14h15–14h45
Venue: Rossbysalen C609, Arrhenius Laboratory, 6th floor

Abstract
The influence of methane, a powerful greenhouse gas, on enhancing global warming is of great interest. A tremendous quantity of methane is trapped in the sediments of continental margins, which can be released in the water and in the atmosphere due to climate warming. Offshore western Svalbard, the Vestnesa Ridge (79°N – 1200 m water depth) is a sedimentary feature where past and present methane releases have been observed. This project aims at studying the controls of methane seepages at the Vestnesa Ridge. A multi-proxy approach is applied, based on the taxonomy and the chemistry of the shell of marine microorganisms called foraminifera, and also sedimentary and geochemical data. In particular, it is possible to identify carbonate overgrowths on the shells of foraminifera, which were induced by methane due to geochemical reactions. As methane also has a very specific geochemical signature, hypothesis on the variations of gas fluxes are made. This specific signature coincides with Quaternary climatic period, such as the Heinrich Event 1 and the Bølling-Allerød, raising the question of temperature or geological controls on methane fluxes variations, and suggesting a feedback of methane on the environment. However, the timings of these events remain highly speculative as methane might influence conventional dating methods (14C, magnetic susceptibility, δ18O correlations). Promising dating methods would be useful, such as the barely modified foraminiferal stratigraphy, U/Th dating and bivalve-rich layers.

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