Sea ice attached to the Antarctic Penninsula’s Larsen B embayment shattered and disintegrated sometime between January 16 and the 21st. The vast expanse of sea ice had formed in 2011 when it fastened itself to the coastline after the Larsen B ice shelf collapsed. Once the sea ice crumbled, it took a large chunk of the Scar Inlet ice shelf with it.
Nasa’s Moderate Resolution Imaging Spectroradiometer, a key instrument on the Terra and Aqua satellites, detected the phenomenon in the photos above.
Scientists are still investigating the reason for the breakup, but the early clearing of seasonal sea ice along the Antarctic Peninsula suggests that the austral summer has been warm and wet. Scientist Rajashree Tri Datta of University of Colorado, Boulder, noted that foehn winds, influenced by a large atmospheric river, helped destabilize the ice pack. The phenomenon is apparent in this animation composed with images from NOAA’s GEOS-16 satellite.
The breakup is the latest in a series of notable events in the Larsen B embayment over the past 20 years. Prior to 2002, glacial ice on the Antarctic Peninsula flowed toward the sea and fed into a vast floating ice shelf known as Larsen B. The shelf helped buttress inland tributary glaciers, pushing back against them and slowing their seaward flow. But in early 2002, the shelf abruptly fractured. With 3,250 square kilometers (1,250 square miles) of ice suddenly gone, glaciers thinned and flowed more quickly into the open water.
Following the collapse of Larsen B, landfast sea ice grew atop the seawater each winter and melted away entirely in most summers. But the sea ice that started to grow in late March 2011 stuck around. “It was the first time since the early 2002 shelf collapse that the Larsen B embayment was seen to freeze up and stay frozen through multiple austral summers,” said Christopher Shuman, a NASA/UMBC glaciologist. The sea ice retreated slightly at its edges during summers, and its surface occasionally became coated with blue meltwater, but the ice persisted until this January.
Satellite images of the often-cloudy region show the breakup occurred between January 19-21, 2022. Sea ice splintered and floated away from the coast, along with icebergs from the fronts of Crane Glacier and its neighbors to the north and south. Shuman thinks strong outflows of ice from the Flank and Leppard tributary glaciers likely widened a rift that led the Scar Inlet Ice Shelf—the southern remnant of the Larsen B Ice Shelf—to shed several large icebergs.
Compared to a massive ice shelf (like the original Larsen B), sea ice adjacent to land is less effective at holding back the seaward flow of glaciers, but it still plays a role. This summer’s breakup of the sea ice in the embayment is important because—unlike the meltwater from an ice shelf, icebergs, and sea ice (already floating)—the meltwater from a glacier adds to the ocean’s volume and contributes directly to sea level rise. With the sea ice now gone, “the likelihood is that backstress will be reduced on all glaciers in the Larsen B Embayment and that additional inland ice losses will be coming soon,” Shuman said.
Foehn winds are dry, warm, downslope winds described by wiki as “a rain shadow wind that results from the subsequent adiabatic warming of air that has dropped most of its moisture on windward slopes. Due to the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than equivalent elevations on the windward slopes.”
With the loss of the sea ice, the small glaciers on the NE region of the peninsula no longer have any buttressing to hold back the small glaciers in the area from emptying in the sea. Glaciers at Larsen A shelf have already vanished and drained into the sea, they are known as ghost glaciers. According to Nasa, these glaciers at Larsen B will also dump their land ice into the Weddel Sea.
Both Larsen A and B disintegrated over the past 30 years, they were 12,000 years old. Larsen C has begun to show signs of collapse, while Larsen D recently calved a large piece of its ice shelf. The Antarctic peninsula is the fastest-warming area on the continent.
Warm moist weather that was once unheard of on the peninsula melted and destabilized Larsen B bay. The crisis is here.
Yale e360 provides context on the melting of the Larsen ice shelves:
The Larsen Ice Shelf, formed over the course of more than 12,000 years and 750 feet thick in places, is located on the northeastern side of the Antarctic Peninsula on the Weddell Sea — the once-completely frozen body of water where Ernest Shackleton and the men of the Endurance expedition were trapped in sea ice in 1914 and 1915. The Antarctic Peninsula has been steadily warming in recent decades, causing the Larsen A Ice Shelf to collapse in 1995 and the 1,250-square-mile Larsen B — a shelf floating atop the Weddell Sea — to collapse in early 2002.
The Larsen B embayment was a portion of the defunct ice shelf that refroze in 2011 and was attached to the Scar Inlet Ice Shelf. Last month, the embayment broke apart, taking with it a portion of the Scar Inlet Ice Shelf. The combined Larsen ice shelves — A, B, C, and D — once extended along the 1,000-mile length of the eastern Antarctic Peninsula. Since 1995, however, the Larsen Ice Shelf has shrunk from 33,000 square miles to 26,000 square miles.
This image is before the sea ice formed in the embayment in 2011 after the collapse of the Larsen B ice shelf. The last buttressing effect is gone, the bay likely looks like this image today.
