An Australian astrophysicist died suddenly of undetermined causes Friday at the Amundsen-Scott South Pole Station, a research center operated by the National Science Foundation, and his body must remain there until the Southern winter ends in October. It was only the third death at the pole in nearly 35 years.

While the death of the astrophysicist, Rodney Marks, is not thought to be related to the harsh conditions at the pole, it is a reminder that scientists operating the growing number of experiments there must contend with a perilous isolation when medical emergencies arise.

Individuals at the pole during the southern winter are trapped by the severe weather, no matter how ill they might become. Last year, a doctor at the station, Jerri L. Nielsen, found a lump in her breast and treated herself until she could be flown out at winter's end.

Dr. Marks, who was 32, had complained of severe breathing difficulties and reported to the station's physician, said Adair Lane, an astronomer at the Smithsonian Astrophysical Observatory.