Hmm, then what happens to outdated cables? Do we pull them up, or do we just turn off a switch at the shore and leave the rest in the ocean? Do the cables contain any substance that might pollute the seabed as the casing degrades away?
Probably, but we dump orders of magnitude more crap (both in volume and in hazard) in the ocean every day.
Plus, the impact from burning the fuel it would take to have a ship pull up a cable would be thousands of times worse than anything the cable might do.
In certain cases, e.g., the cables AT&T laid between Hawaii and the mainland US, they were decommissioned from active service and then used to power a network of undersea sensors used for research by the University of Hawaii:
I can't imagine what materials they would be made of that would be particularly harmful. My sense is they're mostly constructed of things like rubber, plastics, other polymers, steel, copper, and of course a little glass fiber.
The APNG-2 cable (http://en.wikipedia.org/wiki/APNG-2_(cable_system) ) reused part of the PacRimWest cable. They literally pulled some of it up, respliced it and moved the end-point to Papua New Guinea.
Given the cost of such an operation, I don't think you can get some profit even if they were made of gold.
As time passes, most of the cable is buried deeper and deeper under debris that falls on the ocean floor. This means that you cannot just pull it up, you would have to dig to get it out.
