Influence of methane seepage on isotopic signatures in living deep-sea benthic foraminifera, 79° N

Fossil benthic foraminifera are used to trace past methane release linked to climate change. However, it is still debated whether isotopic signatures of living foraminifera from methane-charged sediments reflect incorporation of methane-derived carbon. A deeper understanding of isotopic signatures of living benthic foraminifera from methane-rich environments will help to improve reconstructions of methane release in the past and better predict the impact of future climate warming on methane seepage. Here, we present isotopic signatures (delta C-13 and delta O-18) of foraminiferal calcite together with biogeochemical data from Arctic seep environments from c. 1200 m water depth, Vestnesa Ridge, 79 degrees N, Fram Strait. Lowest delta C-13 values were recorded in shells of Melonis barleeanus, - 5.2 parts per thousand in live specimens and - 6.5 parts per thousand in empty shells, from sediments dominated by aerobic (MOx) and anaerobic oxidation of methane (AOM), respectively. Our data indicate that foraminifera actively incorporate methane-derived carbon when living in sediments with moderate seepage activity, while in sediments with high seepage activity the poisonous sulfidic environment leads to death of the foraminifera and an overgrowth of their empty shells by methane-derived authigenic carbonates. We propose that the incorporation of methane-derived carbon in living foraminifera occurs via feeding on methanotrophic bacteria and/or incorporation of ambient dissolved inorganic carbon.

Automated summary

This study investigates the isotopic signatures of benthic foraminifera in Arctic seep environments and finds that living foraminifera actively incorporate methane-derived carbon in sediments with moderate seepage activity. However, in sediments with high seepage activity, foraminifera die and their empty shells are covered by methane-derived authigenic carbonates. The researchers propose that the incorporation of methane-derived carbon in living foraminifera occurs through feeding on methanotrophic bacteria and/or incorporation of ambient dissolved inorganic carbon.