Abstract
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 (δ13C and δ18O) of foraminiferal calcite together with biogeochemical data from Arctic seep environments from c. 1200 m water depth, Vestnesa Ridge, 79° N, Fram Strait. Lowest δ13C values were recorded in shells of Melonis barleeanus, − 5.2‰ in live specimens and − 6.5‰ 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.
Highlights
One of the consequences of the ongoing climate warming is an increase in ocean temperature[1]
It has been hypothesized that benthic foraminifera are able to record past methane seepage events by incorporating the low δ13C values derived from methane into their shells, and that they have a high potential to record variations in past methane release from the seabed[11,12]
We suggest that the major factor controlling the δ13C in the foraminiferal tests of RB-stained M. barleeanus and C. neoteretis in the seep samples from the Siboglinidae field MUC 10 comes from microhabitat effects related to presence or absence of methane
Summary
One of the consequences of the ongoing climate warming is an increase in ocean temperature[1]. Previous paleo-studies from ‘Lomvi’ pockmark revealed chemosymbiotic fossil macrofaunal communities related to the different types of seep e nvironments[26] (and references therein), and studies of fossil foraminifera showed diagenetic alterations of their tests[12,18]. Biological investigations from this pockmark documented the presence of species-rich live macro- and megafaunas[27,28], carbonate o utcrops[12,29], and heterogeneous environmental conditions associated with methane release. Pore water chemistry was determined in MUC 10 and 12
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