“Surely” can mean “with full success” to some users. Clearly and with certainty tend to mean something greater than others.

EDIT: I hadn’t seen that the words were made links. If you said dolphins were definitely attempting to help them, you were saying that there was no doubt whatsoever

that the dolphins were there to help them. Surely could perhaps give off the same meaning? If I put it beside definitely I tend to believe that the message is trying to be conveyed as they were successful in their attempt to help the life guards. I bet you know if I want a very strict name and not absolutely. When you replace surely with “successfully” (which might sound weird) you can get a different meaning. Some of the words that were used in the text definitely are ambiguous which can be found in

other meanings of surely, as well. (Things like that etc.)