ice shelf

The end of a supergiant iceberg

November 16, 2023 By EarthWise Leave a Comment

In 2017, a supergiant iceberg known as A-68 calved from the Larsen C ice shelf in Antarctica. In 2020, it drifted close to South Georgia, a British island in the South Atlantic Ocean, and then began to break up. This iceberg was enormous – nearly the size of Delaware. When it started to break up, it released huge quantities of fresh, cold meltwater in a relatively small region.

Scientists from the British Antarctic Survey and the University of Sheffield have studied how the melting iceberg has affected the temperature and the salinity of the ocean surface in the area. They found that the water near the surface was 8 degrees Fahrenheit colder than normal and the water only had about two-thirds of its normal saltiness.

The effects from the melted iceberg eventually extended well beyond South Georgia as the colder, less-salty water was carried by ocean currents to form a long plume that stretched more than 600 miles across the South Atlantic. It also took several months to disappear.

The calving of this massive iceberg provided a unique opportunity for scientists to study the impact of iceberg melting on surface ocean conditions. A-68 was one of the largest and most studied of all icebergs. The study has shown that each individual melting giant iceberg can have widespread and long-lasting impacts on ocean conditions, which has consequences for the plant and animal life that lives there.

Climate change is likely to lead to more giant iceberg calving in the future. It is important to monitor these events to assess their future impacts on ocean circulation, biology, and even seafloor geology.

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Supergiant iceberg makes surrounding ocean surface colder and less salty

Photo, posted October 24, 2018, courtesy of Jefferson Beck / NASA via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Antarctic Ice Collapse | Earth Wise

March 2, 2022 By EarthWise Leave a Comment

In Antarctica, a huge chunk of the Larsen B Ice Shelf collapsed suddenly and spectacularly in January.

The Larsen Ice Shelf is located on the northeastern side of the Antarctic Peninsula on the Weddell Sea. It was formed over the course of more than 12,000 years. The Weddell Sea used to be a completely frozen body of water. The famous Ernest Shackleton expedition in 1915 was trapped in its ice. But the Antarctic Peninsula has been steadily warming in recent decades.

The Larsen A Ice shelf collapsed in 1995 and the 1,250-square-mile Larsen B Ice Shelf collapsed in 2002. After that event, a portion of the detached ice shelf refroze in 2011 and was attached to the Scar Inlet Ice Shelf. The refrozen ice was called the Larsen B embayment.

In January, the embayment broke apart, taking with it a portion of the Scar Inlet Ice Shelf. It disintegrated within a matter of days. The combined Larsen Ice Shelves – called A, B, C, and D – once extended along a 1000-mile stretch of the eastern Antarctic Peninsula. Since 1995, it has shrunk from 33,000 square miles to 26,000 square miles.

These ice shelves float on the ocean, so their loss does not actually increase global sea levels. However, the shelves act as dams that hold back glaciers located on the land behind them. The loss of Antarctic ice shelves dramatically increases the rate at which glaciers flow into the sea, and that does increase global sea levels.

Now that the sea ice from the Larsen B embayment is gone, it is likely that there will be additional inland ice losses from the newly exposed glaciers.

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Remnant of Antarctica’s Larsen B Ice Shelf Disintegrates

Photo, posted February 13, 2018, courtesy of NASA/Nathan Kurtz via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Threat From Thwaites | Earth Wise

January 20, 2022 By EarthWise Leave a Comment

The Thwaites Glacier in Antarctica is the widest glacier in the world. It is about 80 miles across and in places extends to a depth of about 2,600 to 3,900 feet. The glacier is roughly the size of Florida, and it currently contributes 4% of annual global sea level rise as it continues to retreat from a warming ocean.

The International Thwaites Glacier Collaboration is a team of nearly 100 scientists dedicated to studying the glacier. According to the scientists, Thwaites has doubled its outflow speed within the last 30 years. The glacier in its entirety holds enough water to raise global sea levels by over two feet, which would be catastrophic.

A third of the glacier flows more slowly than the rest because it is braced by a floating ice shelf that is held in place by an underwater mountain. The concern is that the brace of ice slowing the glacier may not last for long.

Beneath the surface, warmer ocean water is attacking the glacier from all angles. The water is melting the ice directly beneath the glacier causing it to lose its grip on the underwater mountain. Massive fractures have formed and are growing.

Warm water is also a threat for what is called the grounding zone, which is the area where the glacier lifts off the seabed. There are many possible scenarios under which there could be a major ice loss from the glacier. It is unclear how quickly it could occur. It might take decades, or it could be centuries. The threat is large enough and real enough that continued observation and research is essential.

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The Threat from Thwaites: The Retreat of Antarctica’s Riskiest Glacier

Photo, posted October 16, 2012, courtesy of J. Yungel / NASA Ice via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A Giant Breakaway Iceberg | Earth Wise

April 7, 2021 By EarthWise Leave a Comment

Scientists have been closely monitoring multiple cracks and chasms that have formed in the 500-foot-thick Brunt Ice Shelf in Antarctica over the past few years. In late 2019, a new crack was spotted in a portion of the shelf north of an area known as the McDonald Ice Rumples. The rift was monitored by satellite imaging and was seen by February as moving about 15 feet a day.

In the early hours of February 26th, the crack widened rapidly before finally breaking free from the rest of the floating ice shelf. News reports around the world have described the massive 500-square-mile iceberg by comparing it to the size of well-known cities: 1.5 times the size of greater Paris, 10 times the size of San Francisco, twice the size of Chicago, nearly the size of Greater London, and so on.

Antarctica is known for churning out some enormous bergs. The new iceberg, which has been named A-74, is huge, but doesn’t compare to the iceberg A-68 that calved from the Larson C Ice Shelf in 2017. That one was almost five times larger.

The calving of A-74 does not pose a threat to the presently unmanned British Antarctic Survey’s Halley VI Research Station, which was repositioned in 2017 to a more secure location after the ice shelf was deemed to be unsafe. The section where the station now sits is still holding on, but when it eventually breaks, it will likely create a berg nearly 700 square miles in size.

It remains to be seen what will become of the new iceberg. Most likely, it will eventually get caught up in the Weddell Gyre, a clockwise-rotating ocean flow in the Southern Ocean that covers an area more than half the size of the US.

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Breakup at Brunt

Photo, posted October 27, 2016, courtesy of NASA/Nathan Kurtz via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Rapid Antarctic Melting

June 28, 2019 By EarthWise 1 Comment

The Ross Ice Shelf in Antarctica is the world’s largest ice shelf, covering an area roughly the size of France. Scientists have spent several years building up a record of how the northwest sector of the enormous ice shelf interacts with the ocean beneath it. Their results show that the ice is melting much more rapidly than previously thought because of in-flowing warm water.

In general, the stability of ice shelves is thought to be mostly influenced by their exposure to warm deep ocean water. But the new research has found that surface water heated by the sun also plays a crucial role in melting ice shelves.

The interactions between ice and ocean water that occur hundreds of meters below the surface of ice shelves have a direct impact on long-term sea level. The Ross Ice Shelf stabilizes the West Antarctic ice sheet by blocking the ice that flows into it from some of the world’s largest glaciers.

When ice shelves collapse, the glaciers that feed them can speed up by a factor of two or three. None of the collapsing shelves in the past have come anywhere close to the size of the Ross Ice Shelf, which is more than 100 times bigger.

The new study by New Zealand’s National Institute of Water and Atmospheric Research showed that sun-heated surface water flowing into the cavity under the ice shelf near Ross Islands caused melt rates to nearly triple during the summer months. This indicates that the loss of sea ice resulting from climate change is likely to increase melt rates in the future. While the Ross Ice Shelf is still considered to be relatively stable, the new findings show that it may be more vulnerable than previously thought.

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