A diver from San Jose who was stationed in Antarctica drowned while swimming under the polar icecap, the New Zealand Press Assn. reported. The news agency said the victim, Mark T. Macmillan, 22, died while diving about 50 miles west of the U.S. scientific research base at McMurdo Sound on Ross Island. Macmillan, a certified diver, was a research assistant at the base. Quoting a statement from the U.S. National Science Foundation in Christchurch, the news agency said Macmillan was flown by helicopter to McMurdo Sound, where he was declared dead on arrival. The statement gave no further details. The United States maintains three permanent bases in Antarctica for scientific research.