Suppose the world’s most heavily monitored glacier is going to melt at a rate models cannot keep pace with? The Thwaites Glacier, somberly referred to as the “Doomsday Glacier,” is drawing new high-priority interest from climate scientists and engineers equally, not only because of its enormous size extends almost 80 miles across West Antarctica because of the complex, speeding-up processes now laid bare by next-generation satellite monitoring.
Behind this scientific feat is the use of NASA’s ICESat-2 satellite, whose Advanced Topographic Laser Altimeter System (ATLAS) has transformed how scientists track the ice. In contrast to its elder brother, ICESat-2 fires off 10,000 laser pulses per second, recording measurements of height every 2.3 feet along its orbit path. Such precision is needed to measure the slight changes in the elevation of the ice surface, with a virtual continuous record of the migrating fractures and glacier topography. ICESat-2 can measure surface height to a precision of about one inch, ICESat-2 mission personnel state, a technological leap that opens up new directions in glaciological research.
The Penn State-led study, published in the Journal of Geophysical Research: Earth Surface, capitalizes on this high-resolution imagery to map and document the vertical cracks that encircle the Thwaites Ice Shelf. The researchers’ new two-step method modifying old algorithms produces high-level elevation maps and stunning cross-sections, not just indicating where cracks are appearing, but also how they’ve changed over time. No small accomplishment. “We know little about fractures, and their behavior is much more complex than conventional models suggest,” says Shujie Wang, assistant professor at Penn State and co-author of the study. “Conventional models depend largely on simplified models and scarce, hard-to-obtain field observations.”
The stakes are high. The eastern part of the Thwaites Ice Shelf is experiencing aggressive fracturing, while the west sector is fairly stable. Why this gap is occurring is yet to be determined, but science indicates a mixture of increased heat in the ocean, shifting currents, and decreased sea ice are probable culprits. The effect of the cracks extends beyond appearance. As fissures increase in length, they increase the flow of the glacier into the ocean, resulting in more fracturing a feedback process. “We’ve seen ice shelves break off, but we’ve never seen one grow back,” notes Richard Alley, a co-author of the study, underscoring the irreversible nature of these events.
Beneath the surface, the dynamics grow even more complex. Recent studies have shown that warm seawater is intruding beneath the glacier’s grounding zone, melting ice from below in ways not yet fully captured by existing models. The region where grounded ice meets the ocean the grounding zone is also of central concern. In this zone, even the slight warming of the ocean by a bit can initiate self-reinforcing melting, with new cavity development allowing additional influx of warm water. This, described as having “tipping-point-like” processes, can result in abrupt and dramatic changes to ice flow and stability. As British Antarctic Survey’s Alex Bradley puts it, “Ice sheets are extremely sensitive to melting in their grounding zones. What we discover is grounding zone melting has a ‘tipping point like’ response, where a very small change in ocean temperature can bring very enormous growth in grounding zone melting, which would lead to a very enormous change in flow of the ice above it”.
Implications for sea-level rise globally are staggering. Thwaites alone has as much ice as would lift sea levels by up to 11 feet if it collapsed entirely. While most dire estimates-now feared to be less probable this century, naturally-are those of the marine ice cliff instability (MICI) process, the threat of sudden, destabilizing retreat still exists. As recent high-resolution modeling illustrates, the most catastrophic, domino-like collapse predicted by older models is unlikely in the near term. Nevertheless, the ongoing loss of the glacier, pegged at 136 billion tons a year, continues to add hugely to rising seas, risks destabilizing nearby ice sheets and increasing the stakes.
The new fracture database, made up of more than 40 Antarctic ice shelves, will be a resource for models and studies in the future. “We hope that this can be used as a starting observational dataset on fractures for researchers who model and study Antarctic ice-shelf dynamics,” says graduate student at Penn State Zhengrui Huang. Releasing these data to the world enables the scientific community to make improved predictions, strengthen early warning systems, and inform adaptation efforts for vulnerable coastal societies.
Now the task is to input these detailed observations into the next generation of climate models models that must not only represent the physics of ice breaking and flowing, but the newly found feedbacks in grounding-zone melting. While the scientific community is struggling at breakneck pace to close the gap between observation and prediction, the story of Thwaites Glacier is both a warning and a testament to the power of technological innovation to reveal the mechanisms of the world’s most powerful natural systems.
