Suppressed Basal Melting in Eastern Thwaites Glacier Grounding Zone: Implications for Sea Level Rise
Suppressed Basal Melting in Eastern Thwaites Glacier Grounding Zone: Implications for Sea Level Rise
Thwaites Glacier is a significant contributor to sea-level rise, as it is one of the fastest-changing ice-ocean systems in Antarctica. Its catchment area includes much of the ice sheet that is grounded below sea level, making it susceptible to rapid and irreversible ice loss that could significantly increase global sea levels. However, the extent and rate of ice loss are set by unknown ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat.
Recent observations from a hot-water-drilled access hole reveal that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, the ice-ocean boundary layer actively restricts the vertical mixing of heat towards the ice base, resulting in strongly suppressed basal melting. These findings suggest that the current model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier.
Marine-based ice sheets like Thwaites Glacier are particularly sensitive to warming climates, and their fate is dynamically linked to the fate of the floating ice shelves at their seaward margin. These ice shelves buttress the ice sheet and control the flow of grounded ice into the ocean. Over recent decades, elevated ocean-driven basal melting has triggered rapid thinning of many West Antarctic ice shelves, reducing the strength of ice-shelf buttressing and increasing the rate of ice-shelf mass loss.
Thwaites Glacier is especially susceptible to marine ice-sheet instabilities due to its grounding on a retrograde bed that deepens inland. Its grounding line has retreated 14 km inland since the late 1990s, and in some regions, is retreating by up to 1.2 km per year at present. The poorly understood ocean conditions and basal melt rate in the constantly evolving grounding-zone region make it difficult to predict the rate and extent of ice loss from Thwaites Glacier and whether it will proceed irreversibly.
These findings have significant implications for sea-level projections, as a rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates. A complete collapse of Thwaites Glacier within centuries could contribute 65 cm to the global sea level, and the full destabilization of the main glaciers in the Amundsen Sea sector would contribute 3 m to the global sea level over thousands of years. Therefore, it is crucial to continue monitoring the grounding-zone region of Thwaites Glacier and to better understand the complex interactions between ice, ocean, and atmosphere.