Spatial-temporal development of paleo-pockmarks on the Chatham Rise from 3D imaging with subbottom profiler data

Seafloor depressions, sometimes known as pockmarks, are commonly observed features on the ocean floor. Their shape and size can range from small, circular indentations (10s m) up to large, often irregularly shaped depressions (several kms in diameter). The origin of pockmarks is often attributed to focused fluid or gas seepage at the seafloor, but their formation mechanisms (e.g., gas/fluid composition, timing, physical processes) remain ambiguous in many cases. On the Chatham Rise, offshore New Zealand’s South Island, seafloor depressions cover an area >50,000 km², and appear to be bathymetrically controlled. For this region, it has been hypothesized that episodic release of geological CO₂ resulted in the recurring formation of pockmarks at glacial terminations. Seismo-acoustic surveys allow the investigation of potential fluid-flow pathways and buried paleo-pockmarks. High-resolution imaging of shallow subsurface features can be conducted using hull-mounted, parametric subbottom profilers that are available on most larger research vessels. Higher frequencies (>1 kHz) and narrow acoustic beams provide very high vertical resolution (decimetre range) and small lateral footprints capable of resolving smaller structures than using conventional seismic. A recent voyage in 2020 acquired an extensive grid of densely spaced (~25 m) 2D subbottom profiles over a dense pockmark field on the Chatham Rise.

Here we present a novel approach to create a comprehensive pseudo-3D cube from high-resolution 2D echosounder profiles using a recently developed processing workflow. Based on this generated cube, we perform a preliminary analysis of seafloor pockmarks and paleo-pockmarks in the shallow subsurface up to 150 m below the seafloor. Our analysis includes insights into the recurrence of pockmark formation at different geological times and an assessment of morphological changes and varying spatial locations over time. Additionally, we investigate a potential polygonal fault network beneath the lowermost layer of paleo-pockmarks that might channel upward fluid migration in the area.