To see the impossible sea

Using extremely precise measurements of the changing height of the oceans caused by the gravity field underneath it, measured by a host of satellites, researchers have produced a more accurate map of the ocean floor than ever before.  And while doing so, they discovered a lot of new landmarks (perhaps more accurately called seamarks) down there.

Seafloor features are revealed by the gravity field  (this article has references)

Here's the global image:

You gotta be impressed with the technology.