After a year spent drifting across the top of the world, frozen in sea ice, a German research ship returned home Monday, ending the largest Arctic science expedition in history, one aimed at better understanding a region that is rapidly changing as the world warms.

The ship, the Polarstern, docked at its home port of Bremerhaven nearly 13 months after it left Norway. In October, it became deliberately frozen into the ice north of Siberia, about 350 miles from the North Pole, and drifted north and west for thousands of miles, leaving the little remaining ice for good late last month between Greenland and Norway.

The expedition, with a rotating contingent of about 100 scientists, technicians and crew, encountered nosy polar bears, fierce storms that damaged equipment, changing ice conditions and, most critically, the coronavirus pandemic that scrambled logistics. There were also accusations of sexual discrimination and harassment aboard a Russian support ship that accompanied the Polarstern for the first month.

But the leaders of the $150 million project, known as Mosaic and organized by the Alfred Wegener Institute in Germany with participants from 19 other countries, noted it as a success. They said the information collected about the ocean, ice, clouds, storms and ecosystems of the Arctic would prove invaluable in helping scientists understand the region, which is warming faster than any other part of the planet.

“It’s a historic milestone for Arctic research,” said Markus Rex, an atmospheric scientist at the institute and the expedition leader. “We come back with a pool of data and samples that will change Arctic research for a long time.”

The region’s sea ice has been steadily shrinking in recent decades, and summer ice coverage this year was the second lowest since satellite measurements began in 1979. Warming has also caused sharp declines in older, thicker ice.

Matthew Shupe, an atmospheric scientist at the University of Colorado who was aboard the Polarstern last fall and again over the summer, said working on the ice was a challenge. “We were embedded right in the middle of climate change,” he said.

Shupe, who was a co-coordinator of the expedition, said the ice floe that the ship had been frozen into for most of the year broke up July 31 in spectacular fashion. For two days, he and his colleagues had watched as the floe kept shrinking, its southward edge melting and drawing closer and closer to the ship. “We were getting a little nervous,” he said.

So July 30, they removed the last remaining equipment from the ice. “And then we woke up the next morning and our ice floe was in a thousand pieces,” he said.

Shupe’s second tour on the Polarstern began in June, when he arrived with a group to replace the scientists and technicians who had been on board since late February. The swap had been scheduled to take place in April, but the pandemic intervened.

Because of restrictions on travel and the need to quarantine participants in order to keep the expedition free of the virus, a planned transfer by aircraft was scrapped. Instead, in late May, the Polarstern left its ice floe to rendezvous with two smaller ships carrying Shupe and others off the Norwegian archipelago of Svalbard. The Polarstern then headed back to the ice.

Abandoning the floe for nearly a month affected some of the research, the expedition’s leaders said at the time. But many autonomous instruments kept collecting data during the ship’s absence.

Carin Ashjian, a biological oceanographer at the Woods Hole Oceanographic Institution in Massachusetts, was among those on board two months longer than planned. As the days dragged on, she said, morale suffered. “The world outside was going through this immense upheaval,” she said. “Everyone on the ship had different situations back home.”

Jennifer Hutchings, a sea ice researcher at Oregon State University aboard at the same time, said she had learned from previous work that “you always have contingency plans.”