Pockmarks are concave, crater-like depressions on seabeds that are caused by fluids (liquids and gasses) escaping and erupting through the seafloor.
Before the two researchers King and McLean used the side scan sonar, they had noticed 'notches' on echo sounder and shallow seismic records in the seafloor off Nova Scotia.
It was, therefore, not before they surveyed with the area-coverage system, Side scan sonar, that they realized the notches were in fact closed depressions (craters) and not curvilinear features.
In these cases, pockmarks have been interpreted as the morphological expression of gas or oil leakage from active hydrocarbon system or a deep overpressured petroleum reservoir.
Specifically, long-term deep fluid flow resulting in pockmarks is linked to undersea methane gas escape under pressure.