Melting Antarctic Ice: Tracing Changes in Pinning Points
Antarctica, the icy continent at the southernmost part of the Earth, is experiencing significant changes in its ice shelves. Scientists have recently discovered that the pinning points, which are bumps on the surface of the ice that anchor glaciers in place, have been shrinking over the past few decades. This finding highlights the acceleration of melting in Antarctica and the potential impact it will have on global sea-level rise.
The study, published in the journal Nature, focuses on the ice shelves that surround 75% of Antarctica’s coastline. These shelves are the floating fronts of glaciers that extend into the ocean. Many of them, particularly those in the western part of the continent, are being affected by warm water, causing them to thin. This is concerning because these ice shelves act as a crucial braking mechanism, slowing down the movement of ice from the continent.
In areas where the seafloor is shallow, such as underwater hills, the ice shelves can become trapped, preventing the glacier ice behind them from flowing freely. These trapped areas are known as pinning points and can be easily identified by satellites due to the bumps they create on the surface of the ice.
To understand how these pinning points have changed over time, researchers from the University of Edinburgh analyzed satellite images of Antarctica’s coastline. Dr. Bertie Miles compiled cloudless mosaics of the coastline using images from the American Landsat spacecraft series. The team then examined how the size of the pinning point bumps had changed during three periods: 1973-1989, 1990-2000, and 2000-2022.
The analysis revealed that in the initial period, only 15% of pinning points had reduced in size. However, this percentage increased to 25% in the 1990s and reached 37% in the most recent period. According to Dr. Miles, “As we go through the decadal snapshots, you see these bumps in general getting smaller and sometimes completely disappearing.” Once an ice shelf loses contact with a pinning point, it becomes challenging to regain contact, leading to an acceleration in ice flow and the retreat of the grounding line, where the glacier touches the seabed.
What makes this study unique is its approach to assessing ice shelf thinning. Traditionally, scientists use altimeters, specialized satellites that measure the height of the ice surface, to track changes in ice shelves. However, this technique only dates back to the early 1990s. By analyzing the proxy of ice bumps in the Landsat images, researchers were able to extend the record of thinning observations by two decades.
This extended history provided valuable insights into when and where ice loss began. Professor Rob Bingham from the University of Edinburgh explains, “The Landsat record shows you, for example, that those well-known, big glaciers in West Antarctica – Pine Island and Thwaites – were quite unusual in that there was change happening on them already in the 1970s.” In other areas, particularly around the Amundsen Sea where thinning is widespread today, significant changes did not occur until the 1990s.
The research has been commended by Professor Helen Fricker from the Scripps Institution of Oceanography in San Diego. She compares the role of floating shelves to flying buttresses in buildings, providing structural support to the ice sheet. Pinning points enhance this effect, and as contact is lost, the support weakens. By focusing on pinning points, this study has assessed the stability of Antarctica’s support system and identified where and how it is weakening.
The findings of this study have significant implications for our understanding of Antarctica’s melting ice and its contribution to global sea-level rise. As more pinning points shrink or disappear, the braking mechanism that slows down the flow of ice from the continent weakens. This could lead to accelerated ice loss and a subsequent increase in sea levels worldwide. Further research and monitoring of these pinning points are crucial to better predict and mitigate the impacts of melting Antarctic ice.