The benthic foraminiferal δ34S records fux and timing of paleo methane emissions

Abstract

In modern environments, pore water geochemistry and modelling simulations allow the study of methane (CH₄) sources and sinks at any geographic location. However, reconstructing CH₄ dynamics in geological records is challenging. Here, we show that the benthic foraminiferal δ³⁴S can be used to reconstruct the fux (i.e., difusive vs. advective) and timing of CH₄ emissions in fossil records. We measured the δ³⁴S of <i>Cassidulina neoteretis</i> specimens from selected samples collected at Vestnesa Ridge, a methane cold seep site in the Arctic Ocean. Our results show lower benthic foraminiferal δ³⁴S 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 δ³⁴S and the bulk benthic foraminiferal δ¹³C supports this interpretation, whereas the foraminiferal δ¹⁸O-δ³⁴S correlation indicates CH₄ advection at the studied site during the Early Holocene and the Younger-Dryas – post-Bølling. This study highlights the potential of the benthic foraminiferal δ³⁴S as a novel tool to reconstruct the fux of CH₄ emissions in geological records and to indirectly date fossil seeps.