The benthic foraminiferal δS records flux and timing of paleo methane emissions.

In modern environments, pore water geochemistry and modelling simulations allow the study of methane (CH) sources and sinks at any geographic location. However, reconstructing CH dynamics in geological records is challenging. Here, we show that the benthic foraminiferal δS can be used to reconstruct the flux (i.e., diffusive vs. advective) and timing of CH emissions in fossil records. We measured the δS of Cassidulina neoteretis specimens from selected samples collected at Vestnesa Ridge, a methane cold seep site in the Arctic Ocean. Our results show lower benthic foraminiferal δS values (∼20‰) in the sample characterized by seawater conditions, whereas higher values (∼25-27‰) were measured in deeper samples as a consequence of the presence of past sulphate-methane transition zones. The correlation between δS and the bulk benthic foraminiferal δC supports this interpretation, whereas the foraminiferal δO-δS correlation indicates CH advection at the studied site during the Early Holocene and the Younger-Dryas - post-Bølling. This study highlights the potential of the benthic foraminiferal δS as a novel tool to reconstruct the flux of CH emissions in geological records and to indirectly date fossil seeps.