Methane seepage is a key geological process influencing seafloor morphology, benthic ecosystems, and the marine methane budget, yet its spatial controls and short-term temporal behavior remain insufficiently constrained. This study presents a multi-platform investigation of methane seepage at two contrasting deep-marine settings in the Eastern Mediterranean: the Palmahim Disturbance (PD) along the Israeli continental margin (~1100 m water depth) and the Napoli Mud Volcano (NMV) in the Olimpi Mud Field (~1900 m depth).
At NMV, shipborne multibeam echosounder (MBES) surveys identified five active gas plumes, with maximum heights reaching 880 m above the seafloor. In contrast, a low-altitude AUV-mounted MBES survey at PD resolved 54 individual gas seeps using water-column imaging, with an additional five active seeps confirmed by ROV observations. All seepage at PD was strictly confined to rough, carbonate-rich, morphologically complex terrain, while smooth sedimentary areas showed no evidence of active emission. This clear spatial relationship demonstrates that seafloor roughness is a strong geomorphic indicator of active methane seepage and can be used to target high-probability seep areas in future surveys.
ROV video observations revealed pronounced short-term intermittency in bubble emission at all documented PD seeps. Active ebullition typically occurred during less than 50% of the observation period and varied substantially both within individual seeps and between neighboring seeps exposed to similar environmental conditions. These observations indicate that seep activity is highly heterogeneous on short timescales and that single-pass acoustic surveys are likely to underestimate both seep abundance and methane flux.
The results highlight the complementary strengths and limitations of shipborne MBES, AUV-based surveys, and ROV observations, and demonstrate that reliable characterization of methane seepage requires an integrated, multi-method approach. Importantly, this study provides new constraints on the geomorphic controls and temporal dynamics of methane seepage along the Israeli margin, with direct implications for regional seep mapping strategies and methane flux assessments.