Pine Island Glacier (PIG) is a large ice stream and the fastest melting glacier in Antarctica. It is responsible for about 13% of Antarctica's ice loss. The glacier flows west-northwest along the south side of the Hudson Mountains into Pine Island Bay, which is part of the Amundsen Sea. The area drained by Pine Island Glacier covers about 10% of the West Antarctic Ice Sheet. Satellite measurements show that the Pine Island Glacier Basin contributes more ice to the sea than any other ice drainage basin in the world. This contribution has increased because the glacier has sped up in recent years. In recent years, the glacier's flow has accelerated, and its grounding line has moved farther inland.
Since 2015, the breaking off of very large icebergs from Pine Island Glacier has happened about once each year. The largest iceberg, called Iceberg B-46, was initially 226 square kilometers (87 square miles) in size.
Pine Island Glacier is located in a very remote area, but scientists have studied it using radar, GPS, and seismic sensors. Most information about the glacier has come from aerial and satellite surveys.
Like the nearby Thwaites Glacier, Pine Island Glacier is a focus of proposed engineering projects aimed at reducing ice loss.
Location and setting
The Pine Island Glacier is part of the Antarctic ice sheet, which is the largest ice mass on Earth. This ice sheet holds enough water to raise global sea levels by 57 meters (187 feet). The ice sheet forms when snow falls on Antarctica and presses together under its own weight. Over time, the ice moves toward the edges of the continent. Most ice reaches the ocean through ice streams and outlet glaciers. The Antarctic ice sheet includes the large and stable East Antarctic Ice Sheet and the smaller, less stable West Antarctic Ice Sheet.
The West Antarctic Ice Sheet flows into the ocean through several large ice streams. Most of these streams lead to the Ross Ice Shelf or the Filchner-Ronne Ice Shelf. Pine Island and Thwaites Glaciers are two major ice streams in the West Antarctic Ice Sheet that do not flow into a large ice shelf. These glaciers are located in an area called the Amundsen Sea Embayment. A total area of 175,000 square kilometers (68,000 square miles), which is 10 percent of the West Antarctic Ice Sheet, drains into the ocean through Pine Island Glacier. This area is known as the Pine Island Glacier drainage basin.
The Pine Island Glacier is located in a southeast part of Pine Island Bay, which is part of the Amundsen Sea along the Walgreen Coast. To the northeast of the bay and glacier lies the Hudson Mountains, a volcanic region that includes both volcanoes above the ground and volcanoes under the ice.
The glacier was mapped by the United States Geological Survey (USGS) using surveys and air photos taken by the United States Navy (USN) between 1960 and 1966. It was named by the Advisory Committee on Antarctic Names (US-ACAN) in connection with Pine Island Bay.
Importance
The Pine Island and Thwaites glaciers are two of Antarctica's five largest ice streams. Scientists have found that these ice streams are moving faster in recent years. If they were to melt, global sea levels could rise by about 1.5 meters (59 inches). This could cause the West Antarctic Ice Sheet to become unstable and might also affect parts of the East Antarctic Ice Sheet. Pine Island Glacier is at risk of losing more ice because its base is below sea level and slopes downward toward the continent's interior. This means there is no natural barrier to stop the ice from retreating once it begins to move backward. Computer models show that once the glacier starts retreating, this process could continue for many centuries.
Between 1979 and 2017, Pine Island Glacier lost about 1,066 gigatonnes of ice. The rate of ice loss increased from 80 gigatonnes per year between 1979 and 1989 to 133 gigatonnes per year between 2009 and 2017. This means more ice is melting into the ocean than is being replaced by snowfall. The loss of ice from Pine Island Glacier alone accounts for 13% of all ice loss from Antarctica and caused global sea levels to rise by 0.34 millimeters from the 1970s to the 1990s. Computer models predict that Pine Island Glacier could contribute about 3 centimeters (1.2 inches) to sea level rise over the next 100 years.
In the 1940s, the glacier began retreating. At that time, its grounding line was on an underwater ridge about 47 kilometers (29 miles) downstream from its position in 2023. Of the total retreat, 31 kilometers (19 miles) occurred between 1992 and 2011.
As Pine Island Glacier retreats, it is moving faster and has produced more icebergs than usual. Some icebergs are as large as 226 square kilometers (87 square miles). The glacier's speed increased by 77% from 1974 to 2013, with half of this increase happening between 2003 and 2009. In 2020, the glacier's ice moved over 10 meters (33 feet) per day. GPS measurements showed that this increased speed was still strong nearly 200 kilometers (120 miles) inland. In 2007, ice moved 26% to 42% faster than in 1996.
As the glacier moves faster, it is also becoming thinner. The rate of thinning in the central part of the glacier increased four times between 1995 and 2006. At the current speed, the main part of the glacier could float above water within 100 years.
Observations
The first expedition to visit the ice stream was a United States over-snow traverse, which spent about a week near Pine Island Glacier (PIG) in January 1961. The team dug snow pits to measure snow accumulation and used seismic surveys to determine ice thickness. One scientist on this trip was Charles R. Bentley, who said, "we didn't know we were crossing a glacier at the time." At the time of the visit, PIG was about 50 km (31 mi) wide and looked the same as the surrounding ice from the ground. This expedition was called the "Ellsworth Highland Traverse."
A team from the British Antarctic Survey arrived at PIG on December 8, 2006, for the first of two field seasons. During the second season, they spent three months there from November 2007 to February 2008. Work on the glacier included radar measurements and seismic surveys.
In January 2008, a team led by Bob Bindschadler of NASA landed on the floating ice shelf of PIG for a reconnaissance mission to study the possibility of drilling through about 500 m (1,600 ft) of ice to place instruments below the glacier. It was determined that the small crevasse-free area was too difficult for further landings, so fieldwork was postponed. Instead, two GPS units and a weather station were placed as close to PIG as possible.
During the 2011–2012 field season, camp staff finally established the Main Camp just before New Year. The following week, Bindschadler and his team arrived. However, due to weather delays, helicopters could not reach the site in time, and the field season was canceled.
In 2013–2014, the British Antarctic Survey mapped 1,000 km (620 mi) of the ice sheet using ground-based radar. The expedition used a tractor-traverse, a group of vehicles and sledges, to transport scientists and equipment. Ice cores were collected during this trip, showing that the glacier began retreating in the 1940s.
The first ship to reach PIG’s ice shelf in Pine Island Bay was the USS/USCGC Glacier in 1985. This ship was an icebreaker operated by the U.S. Coast Guard. The mission, called Deep Freeze, had scientists on board who collected sediment samples from the ocean floor.
During the summer field season from January to February 2009, researchers aboard the U.S. Antarctic Program vessel Nathaniel B. Palmer reached the ice shelf. This was the second time the Palmer had successfully reached the glacier, the first being in 1994. Scientists from the U.S. and the UK used a robotic submarine called Autosub 3 to explore the glacier-carved channels on the continental shelf and the cavity below the ice shelf. Autosub 3, developed in the UK, completed six successful missions, traveling 500 km (310 mi) under the ice shelf. Autosub 3 can map the base of the ice shelf, the ocean floor, and collect water samples. Its success was notable because its earlier version, Autosub 2, was lost beneath the Fimbul Ice Shelf during its second mission.
In 2012, sea temperature measurements during a strong La Niña showed less melting due to cooler water temperatures. This study showed that ice shelf retreat is influenced by climate changes.
Because Pine Island Glacier is remote, most information about the glacier comes from airborne or satellite measurements.
During the 2004–2005 field season, a British Antarctic Survey Twin Otter aircraft with ice-penetrating radar completed an aerial survey of PIG and its surrounding ice sheet. The team flew 30 km grid patterns over PIG until January 18, mapping the sub-glacial terrain over an area of about 500,000 square kilometers (190,000 square miles).
Pine Island Glacier was a focus of NASA’s IceBridge aerial missions from 2009 to 2019. The IceBridge aircraft carried instruments like laser altimeters, radars, a gravimeter, and a magnetometer. In 2011, the IceBridge survey discovered a large crack in the ice sheet. The IceBridge mission was later replaced by the IceSat-2 satellite, which has tracked the glacier’s surface elevation every 91 days since 2019.
The extensive calving of Pine Island Glacier from 2015 onward was studied using the Terra MODIS instrument (through 2019) and satellites like Landsat 8 and Sentinel-1. Other satellites, such as TerraSAR-X, have been used to measure fractures in the glacier and ice sheet.
In January 2008, British Antarctic Survey scientists reported that a volcano erupted under the Antarctic ice sheet 2,200 years ago. This was the largest Antarctic eruption in the last 10,000 years. The volcano is located in the Hudson Mountains, near Pine Island Glacier. The eruption spread volcanic ash and tephra across the ice sheet, which was later buried by snow and ice. Scientists estimated the eruption’s date based on how deep the ash was buried, using dates from nearby ice cores. The presence of the volcano suggests that volcanic activity could affect the glacier’s movement. In 2018, researchers found a large volcanic heat source beneath Pine Island Glacier, about half the size of Iceland’s active Grimsvötn volcano. That same year, a study concluded that the bedrock beneath the West Antarctic Ice Sheet is rising faster than previously thought, which could help stabilize the ice sheet in the future.
Climate engineering
Pine Island Glacier and Thwaites Glacier can both greatly increase future sea level rise. Because of this, some scientists, including Michael J. Wolovick and John C. Moore, have proposed using climate engineering methods to stop warm ocean water from reaching the glaciers. Their first idea focused on Thwaites Glacier. They estimated that reinforcing it at its weakest points, without building large structures, would be one of the largest engineering projects ever attempted. However, they believe there is only a 30% chance this method would succeed.
In 2023, scientists proposed installing underwater curtains made of flexible material and anchored to the seafloor in the Amundsen Sea. These curtains would stop warm water from flowing toward the glaciers. This method could lower costs and last longer than rigid structures. The curtains would be placed about 600 meters (0.37 miles) below the ocean surface to avoid damage from drifting icebergs. Each curtain would be 80 kilometers (50 miles) long. Scientists believe this could help the Thwaites and Pine Island ice shelves return to a size they had about 100 years ago, which might stabilize the glaciers. However, this project would face challenges, such as the extreme conditions in Antarctica and the lack of enough specialized ships and underwater vehicles. The project would not require new technology, as similar methods are already used for laying pipelines at such depths.
Scientists estimated the project would take about 10 years to complete and cost between $40 billion and $80 billion initially. Annual maintenance would cost $1–2 billion. In comparison, a seawall to protect New York City could cost about the same as this project alone. The global cost of adapting to sea level rise caused by glacier collapse is estimated to reach $40 billion each year. Scientists also compared their idea to other climate engineering methods, such as stratospheric aerosol injection (SAI) or carbon dioxide removal (CDR). While these methods could address more aspects of climate change, their costs are much higher. SAI is estimated to cost between $7 billion and $70 billion annually, and CDR powerful enough to meet the Paris Agreement’s 1.5°C target is estimated to cost between $160 billion and $4,500 billion annually.