Dr. Turney, who is a professor of climate change at the University of New South Wales, said that if the Australian ship was unable to clear a path to free the Shokalskiy, the Xue Long, which has remained in the area, had a helicopter that could be used to ferry people to the Australis. The Australis would take them to Casey Station, a base operated by the Australian Antarctic Division, and from there they would take other ships home.

“We’ve warned everyone on board that that’s a possibility,” Dr. Turney said. All on board are well and morale is good, he said.

The expedition, with a multidisciplinary team of about 25 professors and graduate students and 20 tourists, set sail from Bluff, New Zealand, on Dec. 8 on what was to be a monthlong voyage. The expedition is retracing some of the travels, and replicating some of the studies, of the Australian geologist Douglas Mawson, who first explored East Antarctica from 1911-14.

The ship anchored at the edge of pack ice on Dec. 18, and Dr. Turney and others spent a day journeying about 45 miles across the ice to Mawson’s hut. The ship then headed east through open water. But as it began heading north, it “ran afoul of very strong winds” that pushed the loose ice in its way. “It pegged us in,” he said, and the frozen expanse quickly grew as more ice piled up. “At first we were just two nautical miles from getting to open water, and now it’s 20,” he said.

Even though it is summer in the Antarctic, waiting for the ice to break up on its own is not an option, Dr. Turney said, because of the risk that the ship could drift along with the ice and collide with one of several icebergs in the area, which are drifting independently of the pack ice.