https://phys.org/news/2018-06-antarctic-winter-solstice-icy-plunge.html

Casey station leader Rebecca Jeffcoat said midwinter day—the shortest of the year—was the most anticipated occasion on the Antarctic calendar and has been celebrated from the time of the early explorers.

"Swimming in Antarctica's below freezing waters is something of a mad tradition, but our hardy expeditioners look forward to it, with 21 of the 26 people on station brave enough to take an icy dip this year," she said.