Fig. 2: High-resolution bathymetric data from the formerly reported pockmark field north of Heligoland.
From: Millions of seafloor pits, not pockmarks, induced by vertebrates in the North Sea
a Multibeam echosounder data visualized in an interpolated and equidistant space digital terrain model manner spanning a 500 by 500 m wide area. The 1 by 1 m lateral resolution data reveal approximately one dozen of circular depressions in each tile (0.02 km²). b Color-coded bathymetric soundings in a point cloud close-up, no interpolation applied (400 kHz). The horizontal resolution is 0.2 m and the vertical acoustic range resolution~0.01 m. Owing to the centimeter-scale resolution, enigmatic shapes emerged that do not resemble classic pockmark morphologies. c Depth profile across a characteristic depression, resolving two 0.1 m deep furrows separated by a 0.05 m high in the middle, and surrounded by 0.05 m high mounds. Such ultra-high vertical resolutions become only feasible at short sonar ranges with modern broadband multibeam echosounders coupled with sophisticated inertial measurement units as applied during our surveys.
