Antarctic Ice

The Antarctic Ice Sheet began as a series of small glaciers, much like the ones we see in high alpine regions today. It started to form between 34 and 35 million years ago. At that time, South America and Tasmania, which had been connected to the Antarctica landmass for millions of years, started drifting to the north. The Southern Ocean began to flow around Antarctica like a great oceanic moat. Global temperatures fell and Antarctica was plunged into what some describe as a ‘34 million year winter’. 

Antarctica and its ice sheet are often divided into three main sectors: the East Antarctic, West Antarctic, and the much smaller Antarctic Peninsula ice sheet. 

East and west are separated by the Transantarctic Mountains, which rise about 2.5 miles (4km) above sea level and extend more than 2,000 miles (3200km) along the Antarctic continent. 

The Antarctic Peninsula Ice Sheet blankets a narrow, rocky mountain range, which extends out from the main bulk of Antarctica like a finger pointing towards South America. 

Roughly one tenth of Antarctica’s ice is in the west. Flowing down from the Transantarctic Mountains, the West Antarctic Ice Sheet drains into the Bellingshausen, Weddell, Amundsen and Ross seas via a network of glaciers, ice streams and ice shelves. It holds enough ice to raise sea levels by 10 feet (3 meters) if it all melted. 

Ice is melting more quickly than new snow can replace it, and the rate of loss is increasing. 

Each year, the ice sheet is shrinking more rapidly.

There are approximately 300 ice shelves around Antarctica. Together they cover around three quarters of the Antarctic coastline – roughly the same area as the entire Greenland Ice Sheet. 

Ice shelves vary in size. Some of the larger ones are the size of small nations and over a hundred feet thick. The largest ice shelf on earth, the Ross Ice Shelf, is almost as large as France. It terminates in an ice cliff more than 370 miles (600 kilometers) long, towering up to 160 feet (150 meters) above the ocean.

While ice shelves float on the sea, they are not considered sea ice. They are floating extensions of the Antarctic Ice Sheet, and contain freshwater ice that comes from the continent. One important difference between the ice sheet and its floating ice shelves is that ice shelves don’t contribute to sea level rise when they melt. As they are floating, they have already displaced the same amount of water they contain – much like when you put an ice cube in a glass, and the water level goes up. However, ice shelves play an important role in slowing sea level rise by slowing the flow of the ice sheet itself.

Every year for the past 25 years, Antarctic ice shelves have been losing mass. 

Many are becoming thinner, smaller and more vulnerable to sudden collapse on a vast scale. 

This has resulted in the loss of massive ice shelves over the past several decades.

Unlike the Antarctic Ice Sheet and ice shelves, which formed over millennia, Antarctic sea ice forms over weeks, days or even hours. When sea temperatures drop below 28.4°F (-1.8°C)* sea water begins to freeze. Small crystals begin to form in the ocean, which gradually accumulate into slush, then ice. 

Exactly how the sea ice forms depends on the state of the sea. In a quiet, sheltered bay, sea ice may form as a surface slick, gradually becoming thicker and deeper. In stormy seas, ice crystals may form in both shallow and deep water, colliding and congealing into plates of sea ice over time. 

Antarctic sea ice is changing dramatically as the climate crisis continues to advance. Sea ice around Antarctica has become increasingly volatile, with record breaking lows reached twice between 2017 and 2022. In February 2023 the Bellingshausen Sea west of the Antarctic Peninsula was ice free for the first time in the satellite record.

More research is needed to understand the complex factors contributing to the rapid decline of Antarctic sea ice. However, its decline is an urgent reminder of the need to take action to reduce the impacts of the climate crisis.