Images of cellular ultrastructure of benthic foraminifera from Arctic seeps

Abstract

Dissociation of methane hydrates due to ocean warming releases methane, a powerful greenhouse gas, to the atmosphere. Dissociation of gas hydrates may have led to rapid and dramatic environmental changes in the past. Thus, understanding the impact of those events requires information about their timing and magnitudes. While the foraminiferal fossil record provides a powerful tool to understand past environmental conditions, seep-endemic foraminifera are unknown, which limits evaluation of seep-specific information. However, geographically widespread benthic foraminifera do inhabit seep sites, as documented widely in the literature, and may provide information useful to the understanding of past methane releases. In an effort to better understand how benthic foraminifera inhabit this chemosynthesis-based ecosystem, and if they faithfully record the methane emissions, we conducted a multipronged analysis of foraminifera associated with a gas hydrate emission site in the Arctic. Our goal was to simultaneously assess, in single representative calcareous benthic foraminiferal individuals, the cell biology, test stable carbon isotope ratio, and carbonate microstructure (e.g., wall thickness, survey for authigenic overgrowths), from samples collected south of Svalbard, or on Vestnesa Ridge, west of Svalbard). Serially, each specimen was scanned with microCT (computerized tomography) to assess test characteristics, then the test dissolved by acidification while capturing gas to measure stable carbon isotope ratio via continuous-flow mass spectrometry, and finally the remaining soft parts embedded and examined for cell ultrastructure with a Transmission Electron Microscope (TEM). TEM). Data from isotopic analyses, microCT scans and TEM imaging are presented here.