A field campaign beneath the Thwaites Eastern Ice Shelf produced one of the closest views yet of the processes acting where Antarctic ice meets the ocean. The results, highlighted by the British Antarctic Survey, challenged the simple expectation that warmer ocean water should produce uniformly rapid melting across the entire underside of the ice shelf.
Researchers used hot-water drilling to create a borehole roughly 600 metres deep through the ice shelf. Oceanographic instruments were lowered through the opening to monitor water temperature, salinity and basal melt. The Icefin robotic vehicle was also deployed through the borehole, allowing the team to travel horizontally beneath the ice and inspect the grounding-zone environment.
Measurements showed that the ocean near the grounding line became warmer and saltier during the observation period, yet melt rates directly beneath relatively flat portions of the ice remained lower than many models had anticipated. A layer of fresher water produced by melting can sit immediately beneath the ice and reduce the transfer of ocean heat to the flat ice base.
The underwater imagery, however, revealed that this suppression was only part of the story. The underside of the ice shelf contained terraces and crevasses where surfaces were steep rather than horizontal. These features experienced much stronger melting. Warm water moving through cracks can transfer heat and salt to the ice walls, widening fractures and reshaping the underside of the shelf.
This creates an important structural concern. Ice shelves do not need to melt uniformly to lose stability. Concentrated melting in fractures and other weak zones can help enlarge existing damage, particularly when large rifts are already developing across a shelf. The observations therefore shift attention from the question of only how much ice is melting to where the melting is taking place and what geometry is being affected.
The work formed part of the International Thwaites Glacier Collaboration, a major United Kingdom–United States research programme created to improve understanding of Thwaites Glacier and its potential contribution to future sea-level rise. Field teams combined oceanography, hot-water drilling, robotics, radar and modelling to investigate a region that is extremely remote and logistically demanding.
Thwaites is especially important because a substantial part of the glacier rests on bedrock below sea level. As its grounding zone retreats, ocean water can gain access to new areas beneath the ice. The glacier’s future therefore depends on a network of linked processes: ocean heat, ice geometry, fractures, grounding-line migration and the stabilizing effect of the floating ice shelf.
The close-up observations demonstrate why direct field measurements remain essential. A model can estimate average melt, but the robot can reveal a steep terrace, a widening crevasse or a layer of cold fresh water that changes the local physics. Combining those scales is crucial for producing more reliable projections of how rapidly Thwaites may change in the decades and centuries ahead.