Changing Sea Ice

Each year, sea ice covers a vast area of the Southern Ocean surrounding Antarctica. 

Sea ice varies seasonally. In the middle of winter it can cover an area the size of Antarctica itself.

Sea ice is a crucial component of our planet’s climate system, and one that is highly vulnerable to climate change and variability.

Antarctic sea ice is also a critical habitat for marine life, including penguins and seals.

Antarctic sea ice is changing.

On the Antarctic Peninsula, penguin populations are migrating to the south as warmer temperatures and changing sea ice conditions push their habitats poleward.

Today, sea ice trends around Antarctica are somewhat erratic and unpredictable, and the future of sea ice in Antarctica is uncertain.

SEA ICE

A story of change

Researchers have been recording Antarctica’s sea ice cover and seasonal patterns of advance, retreat and duration by satellite since 1978. 

While sea ice cover in the Arctic is in clear decline, the trends in Antarctica are less apparent. Since 1978, sea ice extent and behavior has varied dramatically between sectors. Over the past decade, Antarctic sea ice cover has become much more unpredictable overall, prompting researchers to take a closer look at why. 

5 sectors antarctic sea map_NASA Earth Observatory map
Photo credit: NASA Earth Observatory map by Joshua Stevens

Five sectors of change

CHANGING SEA ICE

At its winter maximum, Antarctic sea ice covers an area of around 11 million square miles (18 million sq.km): almost twice the size of the United States of America, and larger than Antarctica itself. 

Sea ice covers such a vast area of the Southern Ocean around Antarctica that it spans multiple oceanic and atmospheric zones. For this reason, scientists typically divide the sea ice area into five sectors to explore the nature and drivers of sea ice change and variability. These sectors are: the Weddell Sea; Bellingshausen and Amundsen Sea; Ross Sea; West Pacific Ocean and Indian Ocean sectors. 

Between 1978 and 2014 scientists were surprised to find that although temperatures were rising globally and Arctic sea ice was in steep decline, Antarctic sea ice was gradually increasing across four of the five sectors (all but the Amundsen/Bellingshausen Sea sector). 

Arctic Antarctic anomaly trend_National Snow and Ice Data Center
Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder.

Arctic and Antarctic sea ice cover

UNPREDICTABLE SEA ICE

In 2014, when Arctic sea ice cover was trending to dramatic lows, Antarctica experienced record high sea ice cover. Two years later, in 2016, it plummeted and by 2017 it had hit a record low. The pace of this change eclipsed any change in the Arctic. Within only three years, 35 years of gradual gains had been lost. Researchers are still investigating the causes of this extremely rapid decline.

antarctic sea ice extent_graph from NSIDC
Image adapted from National Snow and Ice Data Center’s Charctic.

Antarctic Peninsula Sea Ice Decline

UNPREDICTABLE SEA ICE

While much of Antarctica experienced an increase in sea ice cover before 2014, followed by a rapid decline, the Amundsen/Bellingshausen Sea sector told a very different story. 

Sea ice here was in steady decline throughout. Upper ocean temperatures in the Bellingshausen Sea, west of the Antarctic Peninsula, have increased by over 2°F (1°C) since 1955. On the west Antarctic Peninsula between 1978 and 2014, the winter sea ice duration declined by almost 100 days. However, between 2017 and 2019 it increased slightly, illustrating the unpredictability and seasonal variability of Antarctic sea ice. 

Adelie leaping on ice
Adelie leaping on ice

What’s driving the changes?

CHANGING SEA ICE

The relationship between sea ice, ocean temperatures and the atmosphere in Antarctica is complex. In some parts of Antarctica, including the Amundsen/Bellingshausen Sea region, warm ocean currents driven by the climate crisis are thought to be the primary cause of sea ice decline. However across the continent more broadly, Antarctic sea ice dynamics are being affected by many factors including warming oceans, local winds, cloud cover, meltwater from ice shelves, the ozone hole, and variable climate patterns such as the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode.

Researchers are continuing to monitor Antarctica’s changing sea ice, building upon existing data, carrying out research on the complex interactive processes involved, and working on improving the performance of climate models to better predict the changes to come. A big unknown at this stage is the thickness distributions of Antarctic sea ice and its snow cover – and whether or not these are changing.  The hope is that this information will emerge from a new suite of satellite altimeter missions.

CHANGING SEA ICE

What are the impacts?

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