Radiocarbon content of carbon dioxide and methane in hydrothermal fluids of Okinawa Trough vents

Here we quantify radiocarbon (14C) content in CO2 and CH4 from hydrothermal fluids collected at 5 vent sites in the Okinawa Trough. These data provide preliminary insights on how different carbon sources and circulation processes contribute to vent fluids and take into consideration all potential contaminations during sample processing and analysis with accelerator mass spectrometer. For CO2, 14C-dead values observed in fluids of most sites (Hatoma, Hitoshi, Noho) demonstrate the complete removal of the inorganic carbon in the recharged seawater. Conversely, the significantly positive 14CO2 are detected in fluids from the Daiyon-Yonaguni site, which implies the persistence of the recharged seawater-derived inorganic carbon and/or a contribution from thermal degradation of sedimentary 14C-containing carbon during fluid upwelling. The CH4 in these fluids were predominantly 14C-dead or nearly 14C-dead, suggesting a source of deep-buried, 14C-dead sedimentary carbon. The methods outlined in our study exemplify a useful way of elucidating radiocarbon contents of geofluids, and provide future studies with a means to improve our understanding of carbon circulation between hydrosphere and lithosphere.