“If I die, let it be known that I went down wearing Valentino.” Bo, a 51-year-old Texan wearing designer slides, is psyching herself into taking a swim in the iceberg-strewn waters off the Larsen Ice Shelf. Dance music is pumping in the ship’s mudroom and staff have set up a bar offering shots of whisky, vodka and tequila. Fifty or so guests are lining up to jump off the marina on the ship’s port side into the icy waters before scrambling back on deck.

Before they do, a rope is tied around each person’s waist should anyone need to be hauled back on board. Bo jumps in with her husband, Steve. Next is Nancy, a New Yorker who is celebrating her 83rd birthday that very day. She has a history of cardiac problems but, having signed the mandatory waiver, she receives the blessing of the ship’s doctor to dangle her legs into the water which, at minus 1.5 degrees, is quite fresh.