Scientists based in Antarctica welcomed the winter solstice by plunging into icy waters Thursday as part of a "mad tradition" heralding the return of brighter days after weeks of darkness. In temperatures of minus 7.6 degrees Fahrenheit, staff at Australia's Casey research station marked midwinter's day by cutting a small pool in the thick ice before stripping off and jumping in.

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.

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"Midwinter day is really important in Antarctica because it marks the halfway point of our year here on the ice and it means the sun will spend slightly longer in the sky each day."

The station posted a video to social media showing swimmers treading water in the square-shaped pool.

"It's cold," one swimmer said after a quick dip.

Celebrations took place at all three of Australia's Antarctic research stations and its sub-Antarctic Macquarie Island base, with feasting, an exchange of handmade gifts, and messages from home read out.

Jeffcoat, who is experiencing her first Antarctic winter, said the continent was extraordinary.

"The environment is spectacular and harsh, and we experience the most incredible range of conditions, from below freezing blizzards to auroras, or the midwinter twilight as the sun skims the horizon," she said.

"It is challenging being so far from family and friends, but we have built a really close knit community of friends on station that we'll likely have for the rest of our lives as we've shared this great experience together."

Australia has 75 researchers living and working on the frozen continent as part of the Australian Antarctic Program, with most of them on 12-month postings.