The Use of Foraminiferal Geochemistry to Investigate Methane Seepage at the Svyatogor Ridge, Arctic Ocean

Methane is a greenhouse gas contributing to contemporaneous global warming, and seepage is one of the ways through which it migrates from the deep sedimentary basins, all the way up to the hydro- and atmosphere. The study of methane seepage is still young as scientists are yet to discover most seep sites as well as seep associated biological species. A record of past methane seepage can be derived from the δ 13C stored in the foraminiferal tests and in the seafloor sediments via precipitation of carbonate minerals by microbial oxidation of methane. In this study, the stable isotopes of carbon and oxygen of the foraminiferal tests were used alongside sediment geochemistry and organic compounds of the sediment as proxies to investigate methane seepage at the Svyatogor Ridge, Arctic Ocean. Two lithological units were recognised from the gravity core (GC3), corresponding to different sedimentation patterns during the last deglaciation. 158 - 162 cm and 137 – 142 cm intervals of the gravity core were impacted by anaerobic oxidation of methane (AOM) processes based on the Ba/Ti peaks which represent barite fronts immediately above sulfate-methane transition zones (SMTZs). Also, the vertical shift in between the paleo-SMTZs shows an upward fluid flow. The paleo-SMTZs in the gravity core (GC3) formed later than 14.5 ca ka BP. The organic matter in the blade core (BlaC3) is highly depleted due to bacterial mat biomass which incorporated methane-derived carbon. The stable carbon and oxygen isotopes of the tests show that the foraminifera calcified under normal marine conditions and during the Younger Dryas post-Bølling period. The C/N (Carbon/Nitrogen) elemental ratios show a predominantly marine origin for the sedimentary organic matter with some mix of land-derived and marine-derived organic matter. The organic carbon concentration (%C) shows that the sediments are of low productivity. An interval rich in ice-rafted debris with bivalve shells associated with high C/N values was found at 120 to 140 cm interval in the gravity core, suggesting sedimentary inputs from nearby Svalbard margin. A foraminiferal δ 13C of -12.73 ‰ ~10 cm below this level indicates some secondary MDAC (Methane-derived authigenic carbonate) formation. It remains unclear whether the bivalves represent an ancient seep habitat or have been transported by icebergs from nearby Svalbard margin

Biogeochemical investigations of methane seepage at the ultraslow-spreading Arctic mid-ocean ridge: Svyatogor ridge, Fram Strait

The Arctic continental shelves are important reservoirs of methane stored in gas hydrates and deeper geological formations. However, little is known about methane dynamics in deeper oceanic settings such as mid-ocean ridges, mainly due to operational challenges related to their remoteness. This study investigates a recently discovered methane seepage environment at Svyatogor Ridge, a sediment-covered transform fault on the western flank of the Arctic mid-ocean ridge west of Svalbard. Svyatogor Ridge was previously hypothesized to host deep gas hydrates and active fluid flow systems, which is a unique combination for this setting and requires geochemical evidence. Based on sediment and foraminiferal geochemistry, we demonstrate that Svyatogor Ridge hosts a shallow methane cycle with anaerobic oxidation of microbial methane, sustaining chemosynthetic communities at the seafloor. Our geochemical datasets also suggest that methane fluxes were higher in the past than today and long-lasting, with episodes of intense methane oxidation recorded in pre-Holocene sediments. Methane seepage is still ongoing at this location, although no evidence exists that methane is reaching the sea surface. The results provide the first evidence of a methane seepage environment ever reported from the ultra-slow spreading Arctic mid-ocean ridge, thus calling for a reevaluation of the role of this type of ridge in the ocean methane cycle

The Use of Foraminiferal Geochemistry to Investigate Methane Seepage at the Svyatogor Ridge, Arctic Ocean

Methane is a greenhouse gas contributing to contemporaneous global warming, and seepage is one of the ways through which it migrates from the deep sedimentary basins, all the way up to the hydro- and atmosphere. The study of methane seepage is still young as scientists are yet to discover most seep sites as well as seep associated biological species. A record of past methane seepage can be derived from the δ 13C stored in the foraminiferal tests and in the seafloor sediments via precipitation of carbonate minerals by microbial oxidation of methane. In this study, the stable isotopes of carbon and oxygen of the foraminiferal tests were used alongside sediment geochemistry and organic compounds of the sediment as proxies to investigate methane seepage at the Svyatogor Ridge, Arctic Ocean. Two lithological units were recognised from the gravity core (GC3), corresponding to different sedimentation patterns during the last deglaciation. 158 - 162 cm and 137 – 142 cm intervals of the gravity core were impacted by anaerobic oxidation of methane (AOM) processes based on the Ba/Ti peaks which represent barite fronts immediately above sulfate-methane transition zones (SMTZs). Also, the vertical shift in between the paleo-SMTZs shows an upward fluid flow. The paleo-SMTZs in the gravity core (GC3) formed later than 14.5 ca ka BP. The organic matter in the blade core (BlaC3) is highly depleted due to bacterial mat biomass which incorporated methane-derived carbon. The stable carbon and oxygen isotopes of the tests show that the foraminifera calcified under normal marine conditions and during the Younger Dryas post-Bølling period. The C/N (Carbon/Nitrogen) elemental ratios show a predominantly marine origin for the sedimentary organic matter with some mix of land-derived and marine-derived organic matter. The organic carbon concentration (%C) shows that the sediments are of low productivity. An interval rich in ice-rafted debris with bivalve shells associated with high C/N values was found at 120 to 140 cm interval in the gravity core, suggesting sedimentary inputs from nearby Svalbard margin. A foraminiferal δ 13C of -12.73 ‰ ~10 cm below this level indicates some secondary MDAC (Methane-derived authigenic carbonate) formation. It remains unclear whether the bivalves represent an ancient seep habitat or have been transported by icebergs from nearby Svalbard margin