@christiaanJ
I have seen marker dye deployed from a liferaft during a maritime exercise. The distance that it could be seen from the air was amazing - long before the raft itself was seen. The size and profile of the raft was not too dissimilar to the floating debris from an aircraft.
I'm suggesting that the dye capsule would be secured within the airframe, so that the marker train originates from the seabed location rather than from the floating debris.