Apparently the North Pole icepack was completely melted at the end of the 19th century:

They pile in the Aurora, which of course will not survive the trip, and head up to the Pole to whup savages. On the way back:

But eventually they did forget, I take it. They simply can't recall all of their adventures. Shore, Frank, remember when we took that flying ship to th' pole? Begorrah! What was the name of that wonderous vehicle?

"For tbe life of me, I've no idea. Ask Pomp. He keeps track of these things."