Abstract
Studying the quantity and origin of CO(2) 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 CO(2) 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 CO(2) with a volume fraction of at least 16 vol %. A lower limit CO(2) flux of 1.4 kg s(-1) (117 t d(-1)) was determined, in line with the CO(2) flux from the Javanese mud volcano LUSI. Extrapolating these results to mud volcanism from the whole of Java suggests an order of magnitude total CO(2) flux of 3 kt d(-1), comparable with the expected back-arc efflux of magmatic CO(2). After discussing geochemical, geological, and geophysical evidence we conclude that the source of CO(2) observed at Bledug Kuwu is likely a mixture of thermogenic, biogenic, and magmatic CO(2), 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 CO(2) fluxes.