From another source:
“The flight was scheduled as a part of the U.S. Air Force’s winter fly season, which transports researchers and necessary equipment to Antarctica before the summer research season begins in the region. The aircraft is one flight that is scheduled annually to fly between Christchurch and both the U.S. and New Zealand’s research bases in Antarctica.”
Years ago,while in New Zealand,I met a marine biologist who was on her way home after having spent the winter in Antarctica (it was November,springtime in the Southern Hemisphere).I think I recall her saying that nothing goes in or out during the winter.