ANTÁRTICA: Reconstructing the history of Larsen C Ice Shelf

 

For the first time, geological records have been used to reconstruct the history of Larsen C Ice Shelf in Antarctica.  The ice shelf is the largest remaining remnant of a much more extensive area of ice on the Antarctic Peninsula that began to break up during the 1990s (Larsen A), and saw a huge collapse in 2002 (Larsen B). This new reconstruction enables scientists to better understand if and when the remaining ice shelf could collapse in the future.

Larsen C Ice Shelf on the Antarctic Peninsula. Photo credit_Ali Rose

The vast Larsen Ice Shelf, twice the size of Wales, attracted global media attention, after a 5,800-square-kilometre iceberg weighing more than a trillion tonnes calved in 2017. Last month (April) it broke up completely, following a three year journey drifting from the Antarctic Peninsula to the sub-Antarctic island of South Georgia.

The Larsen C Ice Shelf calved the mighty A68 iceberg in 2017.

Over the past 25 years, several of the region’s ice shelves have collapsed, including the rapid disintegration of the Larsen B Ice Shelf in 2002. The sequential breakup of ice shelves along the eastern Antarctic Peninsula is linked to warmer atmospheric temperatures which have gradually moved southward over the past 50 years. At the same time, warm ocean currents have also increased, weakening the region’s ice shelves from below.

Using hot water drilling technology to penetrate through the 300 m-thick ice shelf, the team collected seabed sediment cores from beneath the Larsen C Ice Shelf in 2011. Data from these were combined with data from sediment cores recovered offshore a decade earlier, enabling the science team to reconstruct the first detailed history of the ice shelf. The authors conclude that despite modest retreat and advances of the ice shelf front there was no significant collapse during the past 10,000 years.

The team used hot water to drill through the Larsen C Ice Shelf. Photo credit_James Smith.

Lead author, marine geologist Dr James Smith from British Antarctic Survey, says:

“There is a huge international scientific effort underway to get a better understanding of what’s happening to Antarctica’s ice shelves.  If we can understand what happened in the past we will have a sense of what might happen in the future.  We can perhaps differentiate natural events that affect the ice shelves from environmental change related to human activity. This new study provides the final piece of the puzzle to the history of this largest remaining ice shelf on the eastern Peninsula.”

Lead author Dr James Smith with a sediment core retrieved from beneath 300 metres of ice on Larsen C Ice Shelf. Photo credit_Paul Anker.

The team suggest that persistence of Larsen C, as well as Larsen B, implies that these ice shelves were more resilient to past climate warming because they were thicker, or that the heat from the atmosphere and ocean did not penetrate this far south.

In this context, the collapse of Larsen B in 2002 provided the first clue that the extent of contemporary ice shelf break-ups was starting to push further south than at any time during the past 10,000 years.  Larsen C is also showing signs that it might be the next ice shelf in line to collapse.

“We now have a much clearer picture of the pattern and extent of ice shelf break-ups, both past and present. It starts in the north and progresses southward as the atmosphere and ocean warms. Should collapse of Larsen C happen, it would confirm that the magnitudes of ice loss along the eastern Antarctic Peninsula and underlying climate change are unprecedented during the past 10,000 years” says Smith.

History of Larsen C Ice Shelf reconstructed from sub-ice shelf and offshore sediments by Smith, J.A., Hillenbrand, C.-D., Subt, C., Rosenheim, B.E., Frederichs, T., Ehrmann, W., Anderson, T.J., Wacker. L., Makinson, K., Anker, P., Venables, E.J., Nicholls, K.W. (2021) is published in Geology https://doi.org/10.1130/G48503.1.

BAS