Dark Matter
It is worth pointing out that the "grid" you can see is approx 1km in the North South direction and just 450 metres East West. Each sweep is just over 200 metres from the last.
It strikes me that this is too "fine" a grid for a pinger search - and rather more a sonar search. Each pass would have to sweep a 200 metre or so wide path, but I rather hope somone with undersea submerisble/sonar expertise might step forward.
Some side scan sonars can produce a image of the sea floor out to 100m on a side. The sonar is usually towed from a long cable with the tow body near the sea floor. The image should show any of the larger parts and structures of the aircraft. One drawback it doesn't image directly below the tow body so you have to make sure the images overlap.