1. Sources and Flux of Dissolved Inorganic Carbon in the Hydrothermally Active Corner of a Backarc Basin (Southwestern Okinawa Trough)
- Author
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Lin, Yu‐Shih, Huang, Wei‐Jen, Lin, Li‐Hung, Lan, Tefang, Shao, Huan‐Jie, Su, Chih‐Chieh, Fu, Ke‐Hsien, Lee, Hsiao‐Fen, Huang, Chun‐Chieh, Wang, Bo‐Shian, Takahata, Naoto, Sano, Yuji, Chen, Song‐Chuen, Wang, Yunshuen, and Lee, I‐Huan
- Abstract
CO2released from subduction zones plays a vital role in the tectonic carbon cycle. However, the contribution of submarine backarc components to carbon emissions remains poorly understood compared to subaerial arc volcanos. This study utilized a combination of geochemical and hydrodynamic approaches to investigate the sources and flux of dissolved inorganic carbon (DIC) in the deep basin of the southwestern Okinawa Trough. Most deep‐water (depth ≥1,000 m) samples, even those retrieved from sites distant from active venting, exhibited mild geochemical anomalies of elevated 3He/4He ratios and higher DIC content than reference sites. Hydrodynamic observations using bottom‐mounted acoustic instruments in the deep basin revealed strong tidal currents and enhanced turbulent mixing. These findings suggest that active solute dispersal and mixing are responsible for the prevalence of mild geochemical anomalies in the basin. Mixing models indicated that hydrothermal vent fluids are the primary source of excess 3He and DIC above background levels in the deep basin, whereas both CO2and mineral acid in hydrothermal fluids cause excess acidity. Based on hydrodynamic and geochemical data, a box model estimated a hydrothermal DIC flux of 0.62 ± 1.40 × 1010mol y−1, equivalent to 40% of CO2emissions from persistently degassing volcanos in the Ryukyu Arc. Our results suggest that submarine carbon emissions are quantitatively important in subduction systems with subaqueous backarc components. The CO2released from subduction zones, where tectonic plates collide, is important for the Earth's carbon cycle. However, we know little about CO2released from submarine backarc basins compared to volcanoes on land. This study examined dissolved inorganic carbon (DIC) sources and quantities released into the deep basin of the southwestern Okinawa Trough. Even far from active hydrothermal vents, deep‐water samples had higher DIC levels than expected. Using instruments placed on the seabed, we discovered strong tidal currents and increased water mixing in the basin. These findings suggest that water movement and mixing contribute to the widespread occurrence of elevated DIC levels. Our calculations show that the primary source of the extra DIC in the deep basin is fluids released from hydrothermal vents, and both CO2and mineral acid cause excess acidity in the water. Based on our data, we estimate that hydrothermal vents release approximately 6 billion moles of DIC per year, equivalent to 40% of the CO2emissions from continuously active volcanoes in the Ryukyu Arc. These results demonstrate the potential significance of underwater carbon emissions in submerged backarc basins within subduction zones. Mild geochemical anomalies in 3He and dissolved inorganic carbon were widespread in the southwestern Okinawa Trough deep waterMixing models confirmed that hot vent fluids are the primary source of excess dissolved inorganic carbon in the deep waterThe carbon outgassing flux of the Ryukyu subduction system increases by at least 27% when the backarc contribution is considered Mild geochemical anomalies in 3He and dissolved inorganic carbon were widespread in the southwestern Okinawa Trough deep water Mixing models confirmed that hot vent fluids are the primary source of excess dissolved inorganic carbon in the deep water The carbon outgassing flux of the Ryukyu subduction system increases by at least 27% when the backarc contribution is considered
- Published
- 2024
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