Fig. 5: The harbor porpoise pits model.
From: Millions of seafloor pits, not pockmarks, induced by vertebrates in the North Sea
Schematic sketch of seafloor pits and pit-scours evolution through biological and oceanographic eroding agents both coming from above the seabed. We suggest the following model for the formation of the pits and pit-scours. Phase 1: Harbor porpoise acoustically search for buried fish (sandeel) using their sonar on a flat seafloor. Phase 2: Bottom grubbing similar to the one observed for dolphins and gray whales, resulting in decimeter to meter large pits with a distinct morphology. Phase 3: The pits act as nucleation points for bottom currents to initiate scouring and formation of pit-scours, erosion and sediment transport, which subsequently leads to the commingling of individual pit-scours, resulting in larger structures on the seafloor (Fig. 4). Phase 4: Episodic but severe storms predominantly in winter completely level out the structures over time and eventually form a flat seafloor, setting the start point for phase 1, thus closing the evolution cycle.
