CO₂ flux from Javanese mud volcanism

Studying the quantity and origin of CO₂ emitted by back-arc mud volcanoes is critical to correctly model fluid-dynamical, thermodynamical, and geochemical processes that drive their activity and to constrain their role in the global geochemical carbon cycle. We measured CO₂ fluxes of the Bledug Kuwu mud volcano on the Kendeng Fold and thrust belt in the back arc of Central Java, Indonesia, using scanning remote sensing absorption spectroscopy. The data show that the expelled gas is rich in CO₂ with a volume fraction of at least 16 vol %. A lower limit CO₂ flux of 1.4 kg s^-1 (117 t d^-1) was determined, in line with the CO₂ flux from the Javanese mud volcano LUSI. Extrapolating these results to mud volcanism from the whole of Java suggests an order of magnitude total CO₂ flux of 3 kt d^-1, comparable with the expected back-arc efflux of magmatic CO₂. After discussing geochemical, geological, and geophysical evidence we conclude that the source of CO₂ observed at Bledug Kuwu is likely a mixture of thermogenic, biogenic, and magmatic CO₂, with faulting controlling potential pathways for magmatic fluids. This study further demonstrates the merit of man-portable active remote sensing instruments for probing natural gas releases, enabling bottom-up quantification of CO₂ fluxes.