Sea ice that slowed the flow of Antarctic glaciers breaks sharply in three days
In just three days in late January, a mass of ice the size of Philadelphia broke up from Larsen Bay-B on the Antarctic Peninsula and blew away, after lingering there for more than a decade. NASA satellites captured the breakup between January 19 and 21, and with it saw the calving of icebergs from Crane Glacier and its neighbors as sea ice no longer supported their fronts. Now more vulnerable to melting and acceleration in the ocean, the glaciers that fringe the Antarctic Peninsula could directly raise sea levels.
The Larsen Ice Shelf is located along the northeastern part of the Antarctic Peninsula in the Weddell Sea. It is divided into four regions which occupy distinct bays along the coastline, called Larsen A, B, C and D running from north to south, each of which has undergone its own changes in recent decades. The great mass of ice tray holds back the flow of many glaciers from steep mountains to the sea, where they contribute to sea level rise. Larsen-A was the first to disintegrate in 1995, followed by the abrupt partial collapse of Larsen- B in 2002. Larsen-C was Antarctica’s fourth-largest ice shelf in July 2017, when a giant iceberg, named A68, emerged from it. , drawing worldwide attention to the region. Being the southernmost, and therefore the least prone to warming, the only part considered relatively stable is Larsen-D.
The loss of 3,250 square kilometers of ice from the Larsen B Ice Shelf in 2002 was blamed on warmer ocean waters melting it from below, and the presence of meltwater on its surface , which also accelerated ice loss. With only a portion remaining after the collapse, this section was much less stable and vulnerable to further disintegration. It thinned, allowing the glaciers on the land side to flow faster. Sea ice formed in the newly opened area each winter, but it wasn’t until 2011 that the sea ice remained year-round and did not melt the following spring. Between 2011 and 2022, the glaciers stabilized somewhat as remnants of pack ice and sea ice that were permanent and attached, fast to land, blocked their path to the ocean. But this large expanse shattered in three days in January, captured by NASA Earth and Aqua satellites.
Stef Lhermitteprofessor at TU Delft, specializing in geosciences and remote sensing, explained to GlacierHub that “[it’s] difficult to say what actually caused the disintegration as the sea ice was already showing cracks before breaking. Others suggested warmer summer temperatures and foehn winds which carried warm, humid air into the region are partly responsible. The annual sea ice break-up also happened earlier than usual this year, which would also have helped to destabilize the ice. However, “these rapid breakups are often typical of fast ice, because fast ice is often a frozen collection of loose sea ice segments. Once it breaks, it quickly disintegrates,” Lhermitte added.
The recent ice break-up in Larsen Bay-B is significant because the large glaciers that were underpinned by ice are now exposed to the sea. Unlike sea ice and melting sea ice, glaciers s ‘add directly to sea level. Although sea ice frozen onshore is not as effective at holding back glacier flow as the original ice shelf that was once present in Larsen Bay- B, it has played a role in minimizing contributions to sea level rise from the Antarctic Peninsula over the past decade.
At the same time that scientists were witnessing the breakdown of Larsen-B, a new study was published which details the life cycle of the huge iceberg that calved from Larsen-C in 2017, A68. It was the sixth largest iceberg ever documented by satellite observations, comparable to the size of Delaware when it broke away from the pack ice. A68 ceased to exist after three and a half years, when it suffered rapid disintegration near the South Georgia Islands east of the southern tip of South America in January 2021.
Principal author of the study, Anne Braakmann-Folgmannwho researched A68, says concerns were raised when it calved because “it significantly reduced the remaining sea ice surface [and] Larsen-A and -B had already disintegrated. Iceberg calving is known to influence the stability of the mother ice shelf it leaves behind, but since 2017 what remains of Larsen-C has remained stable.
With warming temperatures and changing climate patterns, notable events along the Larsen Ice Shelf are expected to occur more frequently. Scientists are able to closely follow every section of the Larsen Ice Shelf, documenting ice shelf collapse, sea ice growth and the long survival of giant icebergs that threaten remote areas. As the warming continues, questions prevail over how long the Larsen-D portion will be stable. Its location closer to the South Pole has protected it from the impacts of climate change – until now. Reducing emissions is not only important for the ice of the Antarctic Peninsula, but also for the larger ice sheets of East and West Antarctica.