Australia's Antarctic expeditioners have taken an icy plunge to mark the shortest day of the year, although some will have to wait until the end of the month to see the sun rise.
The traditional swim is part of their "Christmas celebrations" on the frozen continent where chefs prepare a winter feast and expeditioners exchange gifts.
There are about 90 expeditioners spending winter at Casey, Davis and Mawson research stations in Antarctica and on sub-Antarctic Macquarie Island.
At Mawson Station, Australia's most remote outpost, the sun is down all day, with the next sunrise due on June 29.
Expeditioners gathered at Horseshoe Harbour where an excavator cut through a metre of sea ice to create a sub-zero swimming pool.
"This is a tradition in the Antarctic calendar to celebrate the middle of winter and the return of the sun," Mawson Station leader Rebecca Jeffcoat said.
"It's madness, it's ridiculous, but it's what we do here in Antarctica.
"It was minus 19C on the ice with a wind speed of six knots, so altogether it was probably about minus 25C with the wind chill factor.
"It's an Antarctic rite of passage to take a midwinter swim and once is definitely enough."
The swims are conducted under medical supervision, with safety equipment and a warm towel close at hand.
Australian Antarctic Division director Kim Ellis thanked those spending a year away from their families and friends.
"Expeditioners ... they keep the lights on and our stations running," he said.
"Midwinter is a chance to reflect on some of the incredible accomplishments in the past year such as the delivery of Australia's new icebreaker RSV Nuyina."