How brilliant of Shackleton to have noticed the fearless symmetry in the name of the subject and to have linked it so elegantly to the relevant year via the subject's habitual whereabouts. Solving it really blew my mind. When TheBear69 says that he has seen "this sort of thing before", he may be thinking of such as Mpobo and Corylus, barring others, but I don't think that it has been done with quite such verve before.
I have now located the double-gridded, single-clued puzzles to which I previously referred. The first was called "Twin-set" by Jac (Listener 1867); it attracted only one correct entry. The second was "Instant Foolery" by Peeper, in Crossword 179 (March 1993).
[I should like to say how much extra pleasure I get out of the Listener when, after having completed the puzzles, I tune in to see what others thought. The various comments often take me deeper into the puzzles than I might otherwise bother to go, since there are so many other things to do besides crosswords. Many thanks to all.]