213-4 Tracing Methane Seepage Events and Hypoxia using Benthic Foraminiferal Assemblages from the Bering Sea (IODP Site U1339)

Session: Cushman Symposium: Microfossils of Extremophiles: Living in the Danger Zone

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Abstract:

The Bering Sea is a climatically sensitive marginal basin where glacial–interglacial cycles exert strong control over benthic ecosystems and carbon cycling. This study investigates ecological and geochemical responses of benthic foraminifera across glacial-interglacial conditions from ~230,000-500,000 years ago (Marine Isotope Stages 7–12) at IODP Site U1339 on the Umnak Plateau. We integrate quantitative faunal assemblage data with stable isotope (δ¹³C, δ¹⁸O) measurements from Elphidium batialis, Uvigerina spp., Globobulimina auriculata, and Nonionellina labradorica to reconstruct bottom-water conditions. Principal Coordinates Analysis (PCO) of benthic foraminiferal relative abundances reveals that the primary gradient in faunal composition reflects an environmental gradient from shallower, better oxygenated conditions to deeper, hypoxic environments, which are most prominent during the MIS 11 interglacial. The second PCO axis represents a gradient from enhanced organic matter flux at positive PCO Axis 2 values and more reducing environments at negative values. Glacial assemblages generally exhibit higher PCO Axis 2 scores and are characterized by Uvigerina peregrina, Chilostomella oolina, and Pullenia bulloides, indicating food-rich conditions are more common during glacial times.  We also observe extremely negative δ¹³C values (down to –12‰ in E. batialis), likely a result of methane-derived authigenic carbonate. These extreme values preferentially occur in samples with high PCO 2 Axis scores, coincident with food-rich settings indicated by the faunas. The association of food-rich assemblages with methane-derived isotopic signatures suggests the low δ¹³C values reflect conditions contemporaneous with the living foraminiferal assemblages and are not just post-depositional authigenic carbonates. Thus, these assemblages suggest methane seepage events occurred preferentially in glacial times in the Bering Sea and can provide a tool for testing the role of methane release from seafloor sediments in global climate.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9903

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