Response of benthic foraminifera to methane emission in the Arctic Ocean: implications for interpretations of paleo-seepage environments

Abstract

Past methane seepage events are linked to climatic changes during the Quaternary and the Paleocene periods. As a large amount of natural gas is stored in Arctic sediments it is important to understand the fate of methane in modern environments, to better understand the potential impact of ongoing methane seepage on future climate. Fossil foraminifera are suggested as being reliable indicators of past methane seepage. Although information about the ecology and isotopic signature of modern foraminiferal remains one key to improve the interpretation of past records, this subject is still poorly studied. Ongoing methane seepage from subseafloor reservoirs is manifested by the presence of cold seep ecosystems, i.e., methane-dependent ecosystems. Cold seeps provide a good analogue for past methane-rich environments and offer an opportunity to investigate possible effects of methane on modern foraminiferal communities. We summarize results of distribution patterns and isotopic signatures (δ13C, δ18O) of benthic foraminifera in surface sediments from Arctic seep environments from Vestnesa Ridge, 79° N, Fram Strait, together with the downcore distribution of pore water biogeochemical data. The results indicate that foraminifera actively incorporate methane-derived carbon when living in sediments with moderate seepage activity, while in sediments with high seepage empty foraminiferal tests are overgrown by methane-derived authigenic carbonates. Additionally, the faunas changes according to the environmental successions of the cold seep stages 1, 2, 3, 4. Stage 5 has not been observed in our study area. Foraminifera thrive in sediments of stages 1, 3, and 4. In sediments of stage 2 with high seepage activity the toxic sulfidic environment cause reduction in the foraminiferal population. Results of these studies advance our understanding of the foraminiferal response to methane seepage events, but also facilitate their use in future studies of methane emissions