** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its society members.
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Research
Biogeosciences
202409202409
Natural 14C abundances and stable isotopes suggest discrete uptake routes for carbon and nitrogen in cold seep animals
Hidetaka Nomaki, Shigeaki Kojima, Yosuke Miyairi, Yusuke Yokoyama, Chong ChenHidetaka Nomaki, Shigeaki Kojima, Yosuke Miyairi, Yusuke Yokoyama, Chong Chen
Nutrition, Stable carbon and nitrogen isotope ratios, Hydrocarbon seep, Chemosynthetic community, Chemosynthesis, Radiocarbon
Natural-abundance radiocarbon (Δ14C) of animals collected from cold seep sites around Japan. The gray bars indicate the estimated range of Δ14C values of bottom water dissolved inorganic carbon. More depleted Δ14C values of animals compared to that of the bottom water indicate higher contribution of seepage fluid-derived inorganic carbon to chemoautotrophic carbon production by symbiotic microbes.
Quantitative estimates of carbon sources for symbiotic chemoautotrophic microbes of cold seep animals, based on natural radiocarbon abundances. The dependences on seep-derived inorganic carbon vary greatly among different animals and habitats. The symbionts of these seep-endemic animals generally utilize dissolved inorganic carbon in the bottom water and the contribution from seep fluid is limited. Left to right: Abyssogena phaseoliformis （Japan Trench), Akebiconcha kawamurai（Kuroshima Knoll）, Lamellibrachia columna （Nankai Trough）.
Cold seeps, where geofluids containing methane and other hydrocarbons originating from the subseafloor seeps through the sediment surface, play important roles in the elemental and energy flux between sediment and seawater. These seep sites often harbor communities of endemic animals supported by chemolithoautotrophic bacteria, either through symbiosis or feeding. Despite these animal communities being intensively studied since their discovery in the 1980’s, the contribution of carbon from seep fluid to symbiotic microbes and subsequently host animals remains unclear. Here, we used natural-abundance radiocarbon to discern carbon sources: the ambient bottom water or the seeping geofluid. The 14C concentrations were measured for vesicomyid clams, a parasitic calamyzine polychaete, and a siboglinid tubeworm species from four different cold seep sites around Japan. We found most vesicomyid clams exhibiting 14C concentrations slightly lower than that of the ambient bottom water, suggesting up to 9% of C for chemolithoautotrophy originates from geofluid DIC. The different extent of fluid contribution across species may be explained by different routes to incorporate DIC and/or different DIC concentrations in the geofluid at each seep site. Stable nitrogen isotopic compositions further suggested N incorporation from geofluids in these clams, where the burrowing depth may be a key factor in determining their δ15N values. The siboglinid tubeworm showed a clear dependency for geofluid DIC, with a contribution of > 40%. Our results demonstrate the effectiveness of 14C analyses for elucidating the nutritional ecology of cold seep animals and their symbionts, as was previously shown for hydrothermal vent ecosystems.
