Fig. 5: Photographs of representative seafloor features observed during the submersible Limiting Factor dive #123.

a An undulating seafloor in zone 2. Horizontal stratification (yellow arrows) of damaged mud exposed in front suggests that the mounds consist of deformed beds rather than debris. b A fissure ca. 2 m wide among undulating sea floors of cohesive mud beds in zone 2. Note that undulations on both sides do not match, suggesting that they postdated the fissure. c A typical slope in zone 3 consisting of mud block debris. d Angular mud blocks with jigsaw fractures (labeled as z) and hackle marks (hk). Note that beige white mud blocks are blanketed by darker-colored very recent mud. e Looking down the boundary between mud block debris in Zone 3 and a basal part of subvertical cliff in zone 4. Larger garbage plastic bag (labeled as g1) and a fish (f1) are approximated as 40 cm and 20–30 cm long, respectively. f Downward view of the middle parts of the cliff in zone 4. The same plastic bags (g1 and g2) as in photo e are still visible. The fish f1 chasing the ascending submersible is the same individual as that in photo (e). g Downward view from the top level of the cliff in zone 4. h Zone 5 flat seafloor just above the top of the zone 4 cliff. Rough surfaces with fractures in front grade into less deformed smoother mud flat beyond. Photos (a–c) and (h) are lateral views by forward camera. Photo (d) overlooks forward through a submersible window using a handy camera. Photos (e–g) are vertical views by downward camera (note that time stamps are erroneous).