The Larsen Ice Shelf is a large ice shelf located in the northwest part of the Weddell Sea. It stretches along the east coast of the Antarctic Peninsula, from Cape Longing to the Smith Peninsula. The shelf is named after Captain Carl Anton Larsen, who was the leader of the Norwegian whaling ship Jason. During December 1893, he sailed as far south as 68°10' South along the ice front.

In more detail, the Larsen Ice Shelf consists of several sections that cover (or covered) different coastal areas. From north to south, these sections are called Larsen A (the smallest), Larsen B, and Larsen C (the largest) by scientists who study the region. Further south, there are also smaller sections named Larsen D, Larsen E, Larsen F, and Larsen G.

Scientists recently found ancient microfossils in the Larsen Ice Shelf. These fossils suggest that the shelf was once part of a large landmass connected to Antarctica. This discovery shows that the shelf has been moving and breaking apart for over 10 million years—much longer than previously believed. Since the mid-1990s, the ice shelf has been breaking apart. The collapse of Larsen B in 2002 was a major event. In July 2017, a large piece of the Larsen C shelf broke off, forming an iceberg called A-68.

The ice shelf originally covered an area of 85,000 km² (33,000 mi²). However, after parts of the shelf in the north broke apart and the iceberg A-68 separated, the shelf now covers an area of 67,000 km² (26,000 mi²).

Research

The collapse of Larsen B revealed a thriving ecosystem 800 meters (2,600 feet) below the sea. This ecosystem uses chemicals for energy. The discovery happened by accident. Scientists from the U.S. Antarctic Program were studying sediment layers in the north-western Weddell Sea, inside a deep glacial trough about 1,000,000 square kilometers (390,000 square miles) in size, which is twice the size of Texas or France. Scientists think methane and hydrogen sulfide from cold seeps provide the energy that supports the ecosystem. Before the ice shelf broke apart, the area was protected from debris and sediment. After the breakup, sediment began to build up on white microbial mats. Clams were seen gathered around vents in the area.

The former Larsen A region, which was located farthest north and just outside the Antarctic Circle, had previously broken up during the current warm period and reformed about 4,000 years ago. In contrast, the former Larsen B had remained stable for at least 10,000 years. The ice on the shelf is replaced more quickly than the long-term ice, and the oldest ice on the current shelf is only about 200 years old. After the collapse of Larsen B, the speed of Crane Glacier increased three times, likely because the ice shelf no longer provided support. Data collected in 2007 by an international team using satellite radar suggests that the overall ice-sheet mass balance in Antarctica is becoming more negative.

Breakup

The Larsen ice shelf events were unusual compared to past events. Usually, ice shelves lose mass when icebergs break off and when ice melts on the top and bottom. In 2005, The Independent linked these events to rising temperatures in the Antarctic Peninsula, which increased by about 0.5°C (0.9°F) each decade since the late 1940s. A 2006 study in Journal of Climate found that the peninsula near Faraday station warmed by 2.94°C (5.3°F) from 1951 to 2004, faster than the rest of Antarctica and the global average. This warming is caused by human activities that increase global temperatures and strengthen winds around Antarctica.

The Larsen A ice shelf broke apart in January 1995. It was located near the Prince Gustav Ice Shelf, stretching from Cape Longing to Robertson Island, and merged with Larsen B at Seal Nunataks. It remained stable for many years, covering about 4,000 km (1,500 mi) from 1961 until the 1980s, when large icebergs broke off, leading to its collapse. Scientists believe this event was closely tied to climate change. The way Larsen A broke up, with 2,000 km of ice turning into small icebergs, was a first-of-its-kind observation.

Between January 31, 2002, and March 2002, the Larsen B sector partially collapsed. About 3,250 km (1,250 mi) of ice, 220 m (720 ft) thick, broke apart. This area was similar in size to the U.S. state of Rhode Island. A 2015 study predicted that the remaining Larsen B ice shelf would disintegrate by 2020, based on observations of glaciers thinning and moving faster.

Larsen B was stable for at least 10,000 years, covering the entire Holocene period since the last ice age. In contrast, Larsen A was not present for much of that time and reformed about 4,000 years ago.

Despite its age, Larsen B was in trouble when it collapsed. Warm ocean currents eroded the bottom of the shelf, making it a "hotspot of global warming." It broke apart quickly over three weeks or less. Meltwater from the surface, which collected in ponds and flowed into cracks, acted like wedges to split the shelf. Other factors included warmer ocean temperatures and thinning ice on the peninsula.

In the austral winter of 2011, a large area of sea ice formed over the embayment where Larsen B once stood. This ice pack lasted until January 2022, when it suddenly broke apart, taking a piece of the Scar Inlet Ice Shelf the size of Philadelphia with it, according to NASA scientists.

As of July 2017, Larsen C was the fourth largest ice shelf in Antarctica, covering about 44,200 km (17,100 mi). Satellite data showed that between 1992 and 2001, the Larsen Ice Shelf thinned by up to 0.27 ± 0.11 meters per year. A 2004 report suggested that continued warming could cause Larsen C to break apart within the next decade.

The process of Larsen C breaking off began in mid-2016. By November 2016, a rift 110 km (68 mi) long and 500 m (1,600 ft) deep was visible. By December 2016, the rift had grown to the point where only 20 km (12 mi) of ice remained unbroken, making calving in 2017 certain. Scientists predicted that 9–12% of the ice shelf, or 6,000 km (2,300 mi), would break off—an area larger than Delaware or twice the size of Luxembourg. The iceberg was expected to be 350 m (1,150 ft) thick and one of the largest ever recorded.

On May 1, 2017, scientists noted a new crack 15 km (9 mi) long branching off the main rift. By late May, the rift had grown 18 km (11 mi), leaving less than 13 km (8 mi) of ice to hold the shelf together. Researchers predicted the iceberg would break away soon. The remaining part of the ice shelf would be less stable and could disintegrate like Larsen B did in 2002.

In June 2017, the part of Larsen C that would become an iceberg moved at 10 meters (33 ft) per day, the fastest speed ever recorded on the shelf. By July 12, 2017, a 5,800 km (2,200 mi) section of Larsen C had broken off, forming the iceberg A-68. It weighs over a trillion tons and is more than 200 m (700 ft) thick.

A new crack appeared in July 2017, extending north from where A-68 broke off. Scientists warned this could increase the risk of further instability. However, the departure of A-68 did not immediately affect global sea levels. Glaciers behind the ice shelf may now flow faster, and if all the ice currently held back by Larsen C entered the ocean, sea levels could rise by 10 cm (4 in).

The Larsen D Ice Shelf is located between the Smith Peninsula in the south and Gipps Ice Rise. It is generally stable, having expanded over the past 50 years, unlike other nearby ice shelves that have shrunk. Recent surveys measured it at 22,600 km. Fast ice along its front makes it difficult to distinguish between sea ice and shelf ice.