Surface gas hydrates and seep features in the Krishna Godavari Basin, Bay of Bengal

Abstract

Abstract The Krishna-Godavari (K-G) Basin along the eastern continental margin of India is characterized by active methane seepage and documented subsurface gas hydrate accumulations; however, constraints on gas hydrate occurring at or near the seafloor remain limited. Here, we present high-resolution acoustic and visual observations from an autonomous underwater vehicle (AUV) documenting localized near-seafloor gas hydrate exposure within an asymmetric mound-pockmark complex at ~ 1750 m water depth. Co-registered multibeam bathymetry, High-resolution Interferometric Synthetic Aperture Sonar (HISAS) backscatter, sub-bottom profiles (SBP), RMS amplitude analysis, and optical imagery reveal a white crystalline layer (~ 0.65 m thick) exposed at the sediment-water interface beneath a thin carbonate-cemented crust. Elevated backscatter intensity and enhanced RMS amplitudes coincide with this exposure, while shallow acoustic blanking and fracture-like discontinuities indicate underlying gas-charged sediments and focused methane migration pathways. Phase stability analysis confirms that the present bottom-water pressure-temperature conditions support hydrate stability at or near the seafloor. The integrated observations are consistent with hydrate mound-pockmark system formed through episodic methane flux, shallow hydrate crystallization, localized uplift, partial sealing, and subsequent collapse. These results provide new constraints on near-seafloor gas hydrate occurrence in the K-G Basin and demonstrate the value of high-resolution AUV surveys for resolving small-scale, structurally controlled hydrate systems.