Four dozen Antarctic ice shelves have shrunk by at least 30% since 1997, and 28 of them have lost most of their ice during that time, according to a new study examining these key “gatekeepers” between the frozen continent’s massive glaciers and the open sea. ocean.

According to the study, 68 of the continent’s 162 ice shelves shrank significantly between 1997 and 2021, while 29 grew, 62 remained unchanged and three showed mass loss, although this is not a significant trend as scientists say. Improvements.

The melted ice that usually covers larger glaciers then flows into the sea. Scientists worry that melting in Antarctica and Greenland caused by climate change will lead to a dangerous and significant rise in sea levels over decades and centuries.

“Knowing exactly how and how much ice is lost from these protective floating shelves is an important step in understanding how Antarctica evolved,” said University of Colorado ice scientist Ted Scambos, who was not involved in the study.

Scambos said the study makes clear that freshwater is melting into the Amundsen Sea (Antarctica’s key region for sea level rise), not only adding height to the ocean but also making it less dense and salty.

The biggest culprit, he said, was giant icebergs the size of Delaware that broke off in 1999, 2000 and 2002. The study also looks at the melting of ice in warm water. Ice shelves are floating extensions of glaciers that act “like sentinels” and prevent a large glacier from flowing more quickly into the water, according to the study’s lead author.

Antarctic ice shelves have lost approximately 8.3 trillion tons (7.5 trillion metric tons) of ice in 25 years, according to the study. This amounts to approximately 330 billion tons (300 billion metric tons) per year and is similar to previous studies.

But the total is not the real story, said study lead author Benjamin Davison, a glaciologist at the University of Leeds in the United Kingdom. In his opinion, the most important thing is the loss patterns on individual shelves. New research shows huge losses: Four glaciers on the peninsula and the western side of the continent lost more than a trillion tons.

“Some of them lost a lot of mass over time,” Davison said. “Vordi is hardly an ice sheet anymore.”

Davison found that the Wardi Ice Shelf, which holds four glaciers near the tip of the Antarctic Peninsula, collapsed heavily in 1989 but has lost 87% of its remaining mass since 1997. Neighboring Larsen A lost 73% and Larsen B lost 57%. Larsen C, the largest of the Larsen ice shelves, lost 1.8 billion tons (1.7 trillion metric tons) of ice, about one-eighth of its mass.

The biggest casualty was the Thwaites Ice Shelf, which held a glacier nicknamed Doomsday because it melted so quickly and was so large. Since 1997, the shelf has lost 70% of its mass (about 4.1 trillion tons (3.7 trillion metric tons)) to the Amundsen Sea.

Growing ice shelves are mostly on the eastern side of the continent, where air isolates the land from warmer waters, Davison said. Eastern ice shelves grew more slowly than western ice shelves. It’s difficult to attribute individual ice shelf loss directly to human-caused climate change, but depletion is expected to continue as the world warms, he said.